CBSE Class 11 Biology: Biomolecules

This chapter explores the chemical nature, structure, and biological roles of key biomolecules—carbohydrates, proteins, lipids, nucleic acids, vitamins, and minerals—and explains how their functions underpin metabolism, growth, and homeostasis in living systems.

What are Biomolecules and Why Are They Essential for Life?

Biomolecules are organic compounds that contain carbon, hydrogen, oxygen, and nitrogen. They are the building blocks of life and are essential for the structure and function of living organisms.

These molecules can be classified into two main categories: macromolecules and micromolecules. Macromolecules are large molecules that are composed of many smaller molecules, while micromolecules are small molecules that are composed of a few atoms.

What is the significance of biomolecules in biological systems?

Biomolecules play a crucial role in the functioning of living organisms. They are involved in various biological processes such as metabolism, growth, and reproduction. Biomolecules also provide the structure and function to cells and tissues.

For example, proteins are biomolecules that are involved in various biological processes such as enzyme activity, hormone regulation, and immune response. Carbohydrates are biomolecules that provide energy to the body, while lipids are biomolecules that are involved in the structure and function of cell membranes.

How are biomolecules classified based on their structure and function?

Biomolecules can be classified based on their structure and function into several categories. These categories include carbohydrates, proteins, lipids, nucleic acids, and other biomolecules.

Each of these categories has distinct features and functions. For example, carbohydrates are biomolecules that are composed of carbon, hydrogen, and oxygen atoms, and are involved in providing energy to the body.

Biomolecules have various applications in fields such as medicine, agriculture, and biotechnology. They are used in the development of drugs, vaccines, and diagnostic tools.

In addition, biomolecules are used in food production and processing, and are involved in the development of new materials and technologies.

How Can We Classify Biomolecules Based on Their Chemical Nature?

How can we classify biomolecules based on their chemical nature?

Biomolecules are organic compounds synthesised by living organisms and are essential for metabolism, growth, and reproduction. They are grouped into two broad classes: macromolecules and micromolecules. Macromolecules (e.g., carbohydrates, proteins, lipids, nucleic acids) are large polymers built from repeating units, whereas micromolecules (e.g., vitamins, minerals) are small molecules that often serve as cofactors or signalling agents.

What are the major classes and their defining features?

The five canonical classes—carbohydrates, proteins, lipids, nucleic acids, and other biomolecules—can be distinguished by their elemental composition, monomeric units, and structural motifs.

Features labelled.

• Carbohydrates: composed of C, H, O in the ratio (CH₂O)ₙ; monomer = monosaccharide (e.g., glucose C₆H₁₂O₆); functions as energy source and structural component (e.g., cellulose).
• Proteins: contain C, H, O, N (sometimes S); monomer = amino acid (20 standard types); functions include enzyme activity, hormone regulation, and immune response.
• Lipids: rich in C and H, poor in O; non-polar; monomer = fatty acid + glycerol (in triacylglycerols); roles in energy storage, membrane structure, and signalling.
• Nucleic acids: contain C, H, O, N, P; monomer = nucleotide (sugar + phosphate + nitrogenous base); store and transmit genetic information (DNA, RNA).
• Other biomolecules: include vitamins (organic cofactors) and minerals (inorganic ions) that regulate enzymatic and physiological pathways.

Table: Classification of biomolecules by chemical nature. Columns: Basis · Carbohydrates · Proteins · Lipids · Nucleic acids · Other biomolecules

• Elemental composition — Carbohydrates: C, H, O (1:2:1) · Proteins: C, H, O, N (±S) · Lipids: C, H ≫ O · Nucleic acids: C, H, O, N, P · Other biomolecules: C, H, O, N, P, S, or metal ions
• Monomeric unit — Carbohydrates: Monosaccharide · Proteins: Amino acid · Lipids: Fatty acid + glycerol · Nucleic acids: Nucleotide · Other biomolecules: Varies (e.g., retinol, Fe²⁺)
• Polymeric form — Carbohydrates: Polysaccharide · Proteins: Polypeptide/protein · Lipids: Triacylglycerol · Nucleic acids: Polynucleotide · Other biomolecules: Monomeric or complexed
• Key functions — Carbohydrates: Energy storage, structure · Proteins: Catalysis, transport, immunity · Lipids: Energy reserve, insulation, membrane · Nucleic acids: Information storage, protein synthesis · Other biomolecules: Cofactors, signalling, regulation
• Solubility in water — Carbohydrates: High (polar) · Proteins: Variable (zwitterionic) · Lipids: Low (non-polar) · Nucleic acids: High (charged backbone) · Other biomolecules: Variable

Why does this classification matter for exams?

CBSE frequently tests the ability to match a biomolecule to its class using elemental clues and functional roles. For example, a molecule with only C, H, O and a high H:C ratio is almost always a lipid, while one rich in N is likely a protein or nucleic acid.

Note: Do not confuse carbohydrates with lipids in energy calculations—carbohydrates yield ≈ 4 kcal g⁻¹, lipids ≈ 9 kcal g⁻¹.

What Are Carbohydrates and How Do They Function in Living Organisms?

What are carbohydrates and why are they the body’s fastest energy currency?

Carbohydrates are organic compounds made of carbon, hydrogen and oxygen in the approximate ratio 1 : 2 : 1 (CₙH₂ₙOₙ). They are classified as macromolecules when they form long chains (polysaccharides) and as micromolecules when they are single units (monosaccharides). Because their C–H and C–OH bonds store chemical energy, carbohydrates are the primary energy source used in metabolism to drive growth, reproduction and enzyme activity.

Diagram: Structural hierarchy of carbohydrates. Draw three concentric boxes labelled A Monosaccharides (glucose, fructose), B Disaccharides (sucrose, lactose), C Polysaccharides (starch, cellulose, glycogen). Inside each box list the monomers or bonds: A single sugar units with –OH groups; B glycosidic bonds between two monosaccharides; C long chains with α- or β-linkages and occasional branching.

How do we classify carbohydrates by size and linkage?

Carbohydrates fall into three exam-favourite classes:

• Monosaccharides – single sugar units; examples: glucose (blood sugar), fructose (fruit sugar).
• Disaccharides – two monosaccharides joined by a glycosidic bond; examples: sucrose (glucose + fructose, table sugar), lactose (glucose + galactose).
• Polysaccharides – polymers of hundreds to thousands of monosaccharides; examples: starch (plant storage), glycogen (animal storage), cellulose (plant cell wall).

What structural features decide solubility and digestibility?

Solubility and digestibility hinge on two features:

1. Ring size: five-member rings (furanoses) like fructose are more soluble than six-member rings (pyranoses) like glucose.
2. Linkage stereochemistry: α-glycosidic bonds (starch, glycogen) are digestible by human enzymes; β-glycosidic bonds (cellulose) are not, making cellulose an indigestible dietary fibre.

What are the five headline biological functions of carbohydrates?

Carbohydrates perform five examinable roles:

1. Energy source: glucose is oxidised in cellular respiration to yield ≈ 4 kcal g⁻¹ and ATP.
2. Energy storage: starch in plants and glycogen in animals store glucose units for rapid mobilisation.
3. Structural component: cellulose forms plant cell walls; chitin forms fungal cell walls and arthropod exoskeletons.
4. Cell recognition: oligosaccharides on glycoproteins and glycolipids act as blood-group antigens and pathogen receptors.
5. Metabolic intermediates: ribose and deoxyribose form the backbone of nucleic acids.

How does the body process dietary carbohydrates – an ordered pathway?

1. Ingestion & mechanical breakdown – chewing mixes starch with salivary α-amylase in the mouth (pH ≈ 6.8).
2. Enzymatic hydrolysis – α-amylase cleaves α-1,4 bonds in starch to maltose and dextrins; pancreatic α-amylase continues in the duodenum (pH ≈ 7.4).
3. Brush-border digestion – maltase, sucrase and lactase on intestinal villi convert disaccharides to monosaccharides (glucose, fructose, galactose).
4. Absorption – SGLT1 and GLUT5 transporters move glucose and fructose into enterocytes; GLUT2 exports them into blood capillaries.
5. Post-absorptive fate – hepatic portal vein delivers monosaccharides to liver; excess glucose is polymerised into glycogen or converted to lipids.

Where do carbohydrates appear in medicine, agriculture and biotechnology?

ApplicationsWhy:

• Medicine: intravenous glucose solutions restore blood sugar in hypoglycaemia; dextran is a plasma volume expander.
• Agriculture: cellulose from cotton and wood pulp is the raw material for paper and rayon fibres.
• Biotechnology: lactose is the inducer in lac operon studies; starch is fermented to bioethanol.
• Drugs & vaccines: carbohydrate-based adjuvants enhance immune response; heparin is an anticoagulant polysaccharide.

Note: Carbohydrates yield ≈ 4 kcal g⁻¹ in energy calculations; lipids yield ≈ 9 kcal g⁻¹. Do not confuse the two in dietary planning.

What Are the Four Levels of Protein Structure and Their Functions?

What determines a protein’s 3-D shape and why does it matter?

A protein is a linear chain of amino acids (20 standard types) joined by peptide bonds. The sequence of amino acids is dictated by genetic instructions and is called the primary structure. This sequence folds into regular patterns—secondary structures such as α-helices and β-pleated sheets—stabilised by hydrogen bonds. Further folding produces the tertiary structure, where side chains interact via hydrophobic forces, ionic bonds, disulphide bridges and van der Waals contacts. Some proteins assemble into two or more polypeptide chains forming a quaternary structure, e.g., haemoglobin’s four globin units.

Diagram: Protein structure hierarchy. Draw four concentric levels: (A) linear chain of amino acids = primary; (B) coiled helix and sheet = secondary; (C) folded globule = tertiary; (D) multimer = quaternary. Label each part and annotate the bonds responsible.

How are proteins classified and what features label each class?

Features labelled. Proteins are grouped by shape and solubility:

• Fibrous proteins: long, insoluble rods (e.g., collagen, keratin) providing mechanical support and tensile strength.
• Globular proteins: compact, soluble spheres (e.g., enzymes, antibodies, hormones) that carry out catalysis, transport and immune recognition.
• Membrane proteins: embedded in lipid bilayers (e.g., receptors, channels) mediating communication and transport across membranes.

Which biological functions do proteins perform in living cells?

Proteins execute nearly every dynamic process:

1. Enzymes catalyse metabolic reactions at body temperature with high specificity and rate enhancement (10⁶–10¹² fold).
2. Hormones such as insulin and glucagon regulate blood glucose by binding to cell-surface receptors and triggering signal cascades.
3. Antibodies (immunoglobulins) recognise antigens via variable regions and neutralise pathogens through agglutination, precipitation or complement activation.
4. Transport proteins ferry hydrophobic ligands (e.g., haemoglobin carries O₂; albumin carries fatty acids).
5. Structural proteins maintain cell and tissue architecture (actin, tubulin, elastin).
6. Motor proteins convert chemical energy into mechanical work (myosin in muscle contraction; kinesin in intracellular transport).

Why do protein shapes matter in medicine and biotechnology?

ApplicationsWhy. Correct folding is essential for function; misfolding causes diseases such as sickle-cell anaemia (β-globin Glu⁶→Val⁶) and neurodegenerative disorders (amyloid plaques in Alzheimer’s). In biotechnology, engineered proteins are used as drugs (e.g., insulin, monoclonal antibodies for cancer therapy), vaccines (viral coat proteins), diagnostic tools (CRP, troponin assays) and industrial catalysts (laundry detergents, cheese-making).

Derivation: How does a linear chain become a functional 3-D machine?

1. Primary → Secondary. Local hydrogen bonding between backbone N–H and C=O groups folds the chain into α-helices (3.6 residues/turn) or β-sheets (extended strands).
2. Secondary → Tertiary. Hydrophobic residues cluster inward; charged residues face solvent; cysteine pairs form disulphide bonds (–S–S–) stabilising the native fold.
3. Tertiary → Quaternary. Two or more folded polypeptides self-assemble via non-covalent interactions into a functional multimer, e.g., adult haemoglobin (α₂β₂).

The folded native state is the only conformation that exhibits full biological activity; any deviation (denaturation) abolishes function.

What ordered processes govern protein synthesis and folding in a cell?

1. Transcription. In the nucleus, RNA polymerase reads DNA and synthesises pre-mRNA (location: nucleus; input: DNA template; output: pre-mRNA; enzyme: RNA polymerase II).
2. mRNA processing. Introns excised, exons spliced; 5′-cap and 3′-poly(A) tail added (location: nucleus; input: pre-mRNA; output: mature mRNA; enzymes: spliceosome, poly(A) polymerase).
3. Translation initiation. Small ribosomal subunit binds mRNA 5′-cap, initiator tRNA carries Met; large subunit joins (location: cytoplasm/ER; input: mRNA, tRNA, ribosome; output: initiation complex; factors: eIFs).
4. Elongation. tRNA delivers amino acids to A-site; peptide bond forms; ribosome translocates 3 nt (location: ribosome; input: aminoacyl-tRNAs; output: growing polypeptide; enzyme: peptidyl transferase centre of rRNA).
5. Folding & quality control. Nascent chain binds chaperones (Hsp70/Hsp60) in cytosol or BiP in ER; misfolded proteins are tagged with ubiquitin and degraded by proteasome (location: cytosol/ER lumen; input: unfolded protein; output: folded protein or degraded peptide; machinery: chaperones, ubiquitin ligase, proteasome).
6. Post-translational modification. Signal peptides cleaved, disulphide bonds formed, prosthetic groups added, phosphorylation occurs (location: ER/Golgi; input: polypeptide; output: mature protein; enzymes: signal peptidase, protein disulphide isomerase, kinases).

Protein functions

What is the structure of proteins and how do they function in living organisms? Proteins are complex organic compounds composed of carbon, hydrogen, oxygen, and nitrogen atoms. They are macromolecules, with a large number of atoms (typically 100-1000) and are often referred to as the "building blocks of life." Proteins have a unique structure, which is determined by the sequence of amino acids that make up the polypeptide chain. This structure is crucial for the function of proteins, as it determines their three-dimensional shape and the way they interact with other molecules. The structure of proteins can be described using the following features: - Primary structure: the sequence of amino acids in the polypeptide chain - Secondary structure: local arrangements of amino acids, such as alpha helices and beta sheets - Tertiary structure: the overall 3D shape of the protein - Quaternary structure: the arrangement of multiple polypeptide chains in a protein Proteins have a wide range of functions, including: - Enzyme activity: proteins that catalyze chemical reactions - Hormone regulation: proteins that regulate hormone secretion and signaling - Immune response: proteins that recognize and respond to pathogens - Structural component: proteins that provide structural support and shape to cells and tissues Diagram: Protein Structure Figure 1: A diagram showing the different levels of protein structure, including primary, secondary, tertiary, and quaternary structures. Labelled parts: - A: Primary structure (sequence of amino acids) - B: Secondary structure (local arrangements of amino acids) - C: Tertiary structure (overall 3D shape of the protein) - D: Quaternary structure (arrangement of multiple polypeptide chains) What is the classification of proteins and how do they differ from other biomolecules? Proteins can be classified into several categories based on their function, structure, and origin. The main categories of proteins include: - Enzymes: proteins that catalyze chemical reactions - Hormones: proteins that regulate hormone secretion and signaling - Structural proteins: proteins that provide structural support and shape to cells and tissues - Transport proteins: proteins that transport molecules across cell membranes Proteins differ from other biomolecules, such as carbohydrates, lipids, and nucleic acids, in several ways. For example: - Proteins are the only biomolecules that can be modified post-translationally, meaning that their amino acid sequence can be changed after they are synthesized. - Proteins have a wide range of functions, including enzyme activity, hormone regulation, and structural support, which are not found in other biomolecules. Ordered Process: Protein Synthesis Figure 2: A diagram showing the steps involved in protein synthesis, including transcription, translation, and post-translational modification. Location: Cytosol or ER Inputs: - mRNA - TRNA - Amino acids Outputs: - Polypeptide chain - Mature protein Machinery: - Ribosomes - Transcription factors - Translation factors - Chaperones

What Are Lipids and Why Are They Important for Life Processes?

What are Lipids and Why Are They Important for Life Processes?

Lipids are a class of organic compounds that are insoluble in water but soluble in organic solvents. They are composed of carbon, hydrogen, and oxygen atoms.

The main features of lipids include their hydrophobic nature, ability to store energy, and role in forming membranes.

Diagram: Lipid Structure. Draw a lipid molecule with labelled parts A-F, including the hydrophilic head and hydrophobic tail. Notice the difference between saturated and unsaturated fats.

Classification of Lipids

Lipids can be classified into different types, including fatty acids, triglycerides, phospholipids, steroids, and waxes.

The applications of lipids are diverse, ranging from energy storage to signalling molecules.

1. Energy source: Lipids are an important source of energy for the body.
2. Structural component: Lipids form the basis of membranes in cells.
3. Signalling: Lipids can act as signalling molecules, influencing various cellular processes.

Biological Significance of Lipids

Lipids play a crucial role in maintaining the structure and function of membranes, regulating hormone activity, and providing energy for the body.

The ordered process of lipid metabolism involves the breakdown and synthesis of lipids, which is essential for maintaining energy homeostasis in the body.

How Are Nucleic Acids Structured and What Is Their Role in Genetics?

What are Nucleic Acids and Their Role in Genetics?

Nucleic acids are macromolecules composed of nucleotides, which are the building blocks of DNA and RNA. These molecules play a crucial role in storing and transferring genetic information in living organisms.

The structure of nucleic acids is characterized by the presence of purines and pyrimidines, which are the two main types of nitrogenous bases. These bases are linked together by phosphodiester bonds to form a double helix structure in DNA.

How is the Structure of Nucleic Acids Related to Their Function?

The structure of nucleic acids is essential for their function in storing and transferring genetic information. The genetic code is embedded in the sequence of nucleotides, which determines the amino acid sequence of proteins. This code is used to synthesize proteins through the processes of transcription and translation.

Diagram: Nucleic Acid Structure. Draw a double helix structure with labelled parts: A) phosphate group, B) sugar molecule, C) nitrogenous base, D) phosphodiester bond, E) major groove, F) minor groove. Notice the complementary base pairing between the two strands.

What are the Applications of Nucleic Acids in Medicine and Biotechnology?

Nucleic acids have numerous applications in medicine and biotechnology. They are used in genetic engineering to develop new drugs and vaccines. Nucleic acids are also used in diagnostic tools to detect genetic disorders and infectious diseases.

Table: Applications of Nucleic Acids. Columns: Basis · Medicine · Biotechnology

• Genetic Engineering — Medicine: Development of new drugs and vaccines · Biotechnology: Production of transgenic organisms
• Diagnostic Tools — Medicine: Detection of genetic disorders and infectious diseases · Biotechnology: Identification of genetic markers for crop improvement
• Gene Therapy — Medicine: Treatment of genetic disorders · Biotechnology: Development of gene-edited crops
• Forensic Analysis — Medicine: Identification of individuals and detection of crimes · Biotechnology: Authentication of food and agricultural products

Why are Nucleic Acids Essential for Life Processes?

Nucleic acids are essential for growth, reproduction, and metabolism in living organisms. They provide the genetic instructions for the synthesis of proteins and other biomolecules, which are necessary for maintaining cellular structure and function.

Note: The terms DNA and RNA are often confused with each other. However, DNA is a double-stranded molecule that stores genetic information, while RNA is a single-stranded molecule that plays a crucial role in protein synthesis.

What Are Enzymes and How Do They Catalyze Biological Reactions?

What are Enzymes and How Do They Catalyze Biological Reactions?

Enzymes are biological catalysts that speed up chemical reactions in living organisms. They are proteins with a specific shape that allows them to bind to a substrate, facilitating the conversion of the substrate into a product.

The active site of an enzyme is the region where the substrate binds, and it is responsible for the enzyme's catalytic activity. Enzymes lower the activation energy required for a reaction to occur, allowing the reaction to proceed faster and more efficiently.

How Do Enzymes Work?

1. The enzyme binds to the substrate at its active site.
2. The enzyme-substrate complex forms, and the enzyme facilitates the conversion of the substrate into a product.
3. The product is released from the enzyme, and the enzyme returns to its original shape, ready to bind to another substrate molecule.

Factors affecting enzyme activity include pH, temperature, and the presence of inhibitors. Enzymes are sensitive to changes in pH and temperature, and extreme conditions can denature the enzyme, making it inactive.

What are the Features of Enzymes?

Enzymes have several key features, including:

• Specificity: Enzymes are specific to particular substrates and reactions.
• Catalytic activity: Enzymes speed up chemical reactions without being consumed by the reaction.
• Regulation: Enzymes can be regulated by various mechanisms, such as feedback inhibition.

Diagram: Enzyme structure. Label the active site, substrate binding site, and enzyme-substrate complex. Notice the shape of the enzyme and how it binds to the substrate.

Note: Enzymes are often confused with hormones, but they are distinct molecules with different functions. Enzymes catalyze chemical reactions, while hormones regulate various physiological processes.

Why are Enzymes Important?

Enzymes play a crucial role in many biological processes, including metabolism, growth, and reproduction. They are also used in various industrial and medical applications, such as drug development and diagnostic testing.

Why Are Vitamins Essential and How Do They Function in the Body?

What are Vitamins and Why are They Essential?

Vitamins are organic compounds that are necessary for various bodily functions, including metabolism, growth, and reproduction. They are classified into two main categories: fat-soluble vitamins (A, D, E, and K) and water-soluble vitamins (B and C).

Vitamin A is essential for vision, while vitamin C is important for immune response. Vitamin D helps regulate calcium levels, and vitamin E acts as an antioxidant. Vitamin K is necessary for blood clotting.

Features of Vitamins

Vitamins have distinct features, including their ability to be synthesized by the body or obtained through diet. They also have specific functions, such as regulating enzyme activity and hormone regulation.

The applications of vitamins are diverse, ranging from medicine to food production. They are used to prevent and treat deficiency diseases, such as scurvy (caused by lack of vitamin C) and rickets (caused by lack of vitamin D).

Comparison of Vitamins

Table: Vitamin Comparison. Columns: Basis · Fat-Soluble Vitamins · Water-Soluble Vitamins

• Examples — Fat-Soluble Vitamins: Vitamin A, D, E, K · Water-Soluble Vitamins: Vitamin B, C
• Functions — Fat-Soluble Vitamins: Vision, calcium regulation, antioxidant activity, blood clotting · Water-Soluble Vitamins: Immune response, energy production, nerve function
• Deficiency Diseases — Fat-Soluble Vitamins: Night blindness, rickets, easy bruising · Water-Soluble Vitamins: Scurvy, beriberi, pellagra
• Food Sources — Fat-Soluble Vitamins: Fatty fish, dairy products, leafy greens · Water-Soluble Vitamins: Citrus fruits, whole grains, legumes

Why are Vitamins Essential for Human Health?

Vitamins are essential for maintaining proper metabolic function, preventing deficiency diseases, and supporting overall health. A lack of vitamins can lead to various health problems, making them a crucial component of a balanced diet.

What Are Minerals and How Do They Contribute to Biological Processes?

What Are Minerals and How Do They Contribute to Biological Processes?

Minerals are inorganic nutrients required by organisms in small amounts to support metabolism, growth, and homeostasis. Unlike organic compounds such as carbohydrates or proteins, minerals lack carbon and are obtained from soil, water, and diet. They are classified as macrominerals (needed in >100 mg/day) or microminerals (needed in <100 mg/day), each serving distinct physiological roles.

Features Labelled: Key Minerals and Their Roles

• Calcium (Ca): 99% stored in bones and teeth; regulates muscle contraction, nerve transmission, and blood clotting. Deficiency causes osteoporosis or rickets.
• Phosphorus (P): Partners with calcium in bone mineralisation; part of ATP, DNA, and cell membranes. Deficiency impairs energy transfer and skeletal development.
• Iron (Fe): Core of haemoglobin; transports O₂ in blood. Deficiency leads to anaemia, fatigue, and pallor.
• Iodine (I): Essential for thyroid hormones (T₃, T₄); regulates basal metabolic rate. Deficiency causes goitre or cretinism.
• Magnesium (Mg): Activates >300 enzymes; supports muscle relaxation and protein synthesis. Deficiency triggers muscle spasms or arrhythmias.
• Zinc (Zn): Cofactor for DNA polymerase and carbonic anhydrase; boosts immune response and wound healing. Deficiency delays growth and impairs taste.

Why Are Minerals Essential for Health?

Minerals act as structural components (e.g., calcium in bones), enzyme activators (e.g., magnesium in ATP synthesis), and hormone regulators (e.g., iodine in thyroid function). They also maintain fluid balance (sodium, potassium) and nerve signalling. Chronic deficiency disrupts these processes, leading to diseases like osteoporosis (calcium), goitre (iodine), or anaemia (iron).

Table: Minerals — Functions, Sources, and Deficiency Disorders

Table: Key Minerals, Their Biological Roles, Dietary Sources, and Deficiency Disorders. Columns: Mineral · Biological Function · Dietary Sources · Deficiency Disorder

• Calcium — Biological Function: Bone mineralisation, muscle contraction, blood clotting · Dietary Sources: Dairy, leafy greens, sesame seeds · Deficiency Disorder: Osteoporosis, rickets
• Phosphorus — Biological Function: ATP synthesis, nucleic acid structure, pH buffering · Dietary Sources: Meat, fish, nuts, whole grains · Deficiency Disorder: Bone pain, weakness
• Iron — Biological Function: Haemoglobin synthesis, oxygen transport · Dietary Sources: Red meat, spinach, lentils · Deficiency Disorder: Anaemia, fatigue
• Iodine — Biological Function: Thyroid hormone synthesis · Dietary Sources: Iodised salt, seafood, dairy · Deficiency Disorder: Goitre, hypothyroidism
• Magnesium — Biological Function: Enzyme activation, muscle relaxation · Dietary Sources: Nuts, seeds, bananas, whole grains · Deficiency Disorder: Muscle cramps, arrhythmias
• Zinc — Biological Function: Immune function, wound healing, enzyme cofactor · Dietary Sources: Shellfish, meat, legumes · Deficiency Disorder: Growth retardation, impaired immunity

Applications: Minerals in Medicine, Agriculture, and Biotechnology

In medicine, iron supplements treat anaemia, while calcium/vitamin D combos manage osteoporosis. Agriculture relies on mineral fertilisers (e.g., potassium for crop yield) to correct soil deficiencies. Biotechnology uses zinc finger nucleases for gene editing, leveraging zinc’s DNA-binding role. Diagnostic tools detect mineral imbalances via blood tests, linking low magnesium to cardiac risks.

Note: Macrominerals (e.g., calcium, phosphorus) are required in larger amounts than microminerals (e.g., iron, zinc), but both are equally critical; excess of either can be toxic.

How Does Metabolism Work and What Are Its Key Pathways?

What is Metabolism?

Metabolism is the process by which cells convert energy from one form to another, using organic compounds as inputs and outputs.

It involves the breakdown of carbohydrates, lipids, and proteins to produce ATP, the energy currency of the cell.

Types of Metabolism

There are two main types of metabolism: catabolism and anabolism.

Catabolism is the process of breaking down complex molecules into simpler ones, releasing energy in the form of ATP.

Anabolism is the process of building complex molecules from simpler ones, using energy from ATP.

Key Metabolic Pathways

The key metabolic pathways include glycolysis, the Krebs cycle, and the electron transport chain.

These pathways work together to convert glucose into ATP, which is then used to power the cell's activities.

1. Glycolysis occurs in the cytosol and converts glucose into pyruvate.
2. The Krebs cycle occurs in the mitochondria and converts pyruvate into ATP, NADH, and FADH2.
3. The electron transport chain occurs in the mitochondria and converts NADH and FADH2 into ATP.

Features of Metabolism

Metabolism has several key features, including the use of enzymes to catalyze reactions, the importance of ATP as an energy source, and the role of hormones in regulating metabolic pathways.

Metabolism is also closely linked to the cell's energy needs, with different pathways being used to generate energy under different conditions.

Applications of Metabolism

Understanding metabolism is important for a range of applications, including medicine, agriculture, and biotechnology.

For example, knowledge of metabolic pathways is used to develop new drugs and vaccines, as well as to improve food production and processing.

What Are Primary and Secondary Metabolites and How Do They Differ?

How Do Primary and Secondary Metabolites Differ in Function and Significance?

Metabolites are organic compounds synthesised by living cells through metabolism. They are classified as primary metabolites or secondary metabolites based on their roles in growth, reproduction, and ecological interactions. Primary metabolites are directly involved in growth, development, and reproduction, while secondary metabolites often mediate ecological functions such as defence, signalling, or competition.

Table: Comparison of Primary and Secondary Metabolites. Columns: Basis · Primary Metabolites · Secondary Metabolites

• Definition — Primary Metabolites: Molecules essential for basic life processes like energy production, structure, and enzyme activity · Secondary Metabolites: Molecules produced in specialised cells or under specific conditions; not directly essential for growth but enhance survival
• Chemical nature — Primary Metabolites: Include amino acids, sugars, lipids, and nucleic acids; often macromolecules · Secondary Metabolites: Include alkaloids, flavonoids, and terpenoids; usually micromolecules
• Occurrence — Primary Metabolites: Found in all cells across all organisms · Secondary Metabolites: Restricted to specific organisms, tissues, or developmental stages
• Functions — Primary Metabolites: Serve as energy sources, structural components, and intermediates in metabolic pathways · Secondary Metabolites: Provide defence, signalling, or competitive advantages in ecological niches
• Examples — Primary Metabolites: Glucose, fructose, starch, cellulose, proteins, lipids · Secondary Metabolites: Morphine (alkaloid), quercetin (flavonoid), menthol (terpenoid)

What Are the Key Features of Primary Metabolites?

Primary metabolites are synthesised during core metabolic pathways such as glycolysis, Krebs cycle, and protein synthesis. They serve three exam-favourite functions: (i) energy source (e.g., glucose in respiration), (ii) structural component (e.g., cellulose in plant cell walls), and (iii) intermediates in biosynthesis (e.g., amino acids for protein assembly). Their synthesis is tightly regulated to meet the cell’s immediate needs, and their concentrations fluctuate with growth phases and environmental conditions.

Why Are Secondary Metabolites Important Beyond Growth?

Secondary metabolites are not required for basic survival but provide ecological advantages. Plants produce flavonoids to attract pollinators or deter herbivores, while microbes synthesise antibiotics like penicillin to inhibit competitors. In medicine, secondary metabolites are prized for their therapeutic properties: (i) Taxol (terpenoid) is used in cancer therapy, (ii) Quinine (alkaloid) treats malaria, and (iii) Artemisinin (terpenoid) is a frontline antimalarial. Their applications extend to agriculture (pesticides), biotechnology (industrial enzymes), and diagnostic tools (fluorescent proteins).

How Do Primary and Secondary Metabolites Support Medicine and Industry?

Primary metabolites underpin large-scale bioprocesses. For example, ethanol (a primary metabolite) is produced via fermentation for fuels and beverages, while citric acid is a key intermediate in the food industry. Secondary metabolites, however, drive high-value industries. The statins (e.g., lovastatin, a polyketide) are secondary metabolites used to lower cholesterol, and streptomycin (an aminoglycoside) is an antibiotic derived from microbial secondary metabolism. Their synthesis often involves complex enzymatic pathways localised in specialised cells or organelles.

What Is the Significance of Metabolite Diversity in Biotechnology?

Biotechnology leverages the diversity of both metabolite types. Primary metabolites are engineered in microbial cell factories for bulk chemicals (e.g., lysine for animal feed), while secondary metabolites are optimised for pharmaceuticals and specialty chemicals. Techniques such as metabolic engineering and synthetic biology allow the production of novel compounds by modifying existing pathways. For instance, artemisinic acid (a precursor to artemisinin) is now produced in Saccharomyces cerevisiae via a synthetic metabolic pathway, reducing dependence on plant extraction.

Note: Confusing primary and secondary metabolites is common. Remember: primary metabolites are universal and essential for life, while secondary metabolites are specialised and context-dependent.

How Are Biomolecules Linked to Diseases and Health Conditions?

What is the relationship between biomolecules and diseases?

Biomolecules, such as carbohydrates, proteins, and lipids, play a crucial role in maintaining health. Imbalances or defects in these biomolecules can lead to various diseases and health conditions, including diabetes and obesity.

For example, a deficiency in insulin, a protein hormone, can lead to diabetes. Similarly, an imbalance in lipid metabolism can result in obesity.

How do biomolecular disorders affect human health?

Biomolecular disorders, such as phenylketonuria and sickle cell anemia, can have severe consequences on human health. These disorders occur due to defects in protein structure or metabolism.

In phenylketonuria, the body is unable to break down the amino acid phenylalanine, leading to its accumulation in the body. This can cause brain damage and other health problems.

What are the effects of biomolecular deficiencies on human health?

Biomolecular deficiencies, such as vitamin deficiencies and mineral deficiencies, can have significant effects on human health. For example, a deficiency in vitamin C can lead to scurvy, while a deficiency in iron can cause anemia.

In addition, kwashiorkor and marasmus are two types of malnutrition that occur due to deficiencies in proteins and calories.

Diagram: Biomolecule-related diseases. Draw a diagram showing the relationships between biomolecules, diseases, and health conditions. Label the different types of biomolecules and diseases.

Why is it essential to understand the relationship between biomolecules and diseases?

Understanding the relationship between biomolecules and diseases is crucial for the development of drugs and vaccines. It also helps in the diagnosis and treatment of diseases, as well as in the prevention of health conditions.

For instance, knowledge of biomolecular pathways can help in the development of targeted therapies for diseases such as cancer.

Note: Biomolecules play a vital role in maintaining health, and their imbalances or defects can lead to various diseases and health conditions.

Glossary

• Biomolecules — Organic compounds containing carbon, hydrogen, oxygen, and nitrogen, essential for life
• Carbohydrates — Biomolecules composed of carbon, hydrogen, and oxygen, providing energy
• Enzymes — Biological catalysts speeding up chemical reactions in living organisms
• Lipids — Organic compounds insoluble in water, storing energy and forming membranes
• Macromolecules — Large molecules composed of many smaller molecules
• Metabolism — Process by which cells convert energy from one form to another
• Metabolites — Organic compounds synthesized by living cells through metabolism
• Micromolecules — Small molecules composed of a few atoms
• Minerals — Inorganic nutrients required for metabolism, growth, and homeostasis
• Nucleic acids — Macromolecules composed of nucleotides, storing genetic information
• Proteins — Linear macromolecules built from 20 standard amino acids, driving cellular processes
• Vitamins — Organic compounds necessary for metabolism, growth, and reproduction

Common errors and misconceptions

• Misconception: Biomolecules are only found in living organisms Correct: Biomolecules can be found in both living and non-living things Understanding the definition of biomolecules is crucial for distinguishing between living and non-living systems
• Misconception: Carbohydrates and lipids have the same energy yield Correct: Carbohydrates yield approximately 4 kcal/g, while lipids yield approximately 9 kcal/g Accurate calculation of energy yield is essential for understanding metabolic processes
• Misconception: Proteins are only involved in structural roles Correct: Proteins have a wide range of functions, including enzyme activity, hormone regulation, and immune response Recognizing the diverse functions of proteins is vital for understanding cellular processes
• Misconception: Nucleic acids are only found in the nucleus of cells Correct: Nucleic acids can be found in various cellular compartments, including the nucleus, mitochondria, and cytoplasm Understanding the distribution of nucleic acids is essential for comprehending genetic processes
• Misconception: Enzymes are consumed in chemical reactions Correct: Enzymes act as catalysts, speeding up reactions without being consumed Distinguishing between catalysts and reactants is critical for understanding enzymatic reactions
• Misconception: Vitamins are only obtained through diet Correct: Some vitamins can be synthesized by the body, while others must be obtained through diet Understanding the different sources of vitamins is essential for maintaining proper nutrition

Exam-style questions with model answers

Q1. State the significance of biomolecules in biological systems. Give one example each of a macromolecule and a micromolecule. [2 marks]

Biomolecules are organic compounds essential for the structure and function of living organisms. They participate in critical biological processes such as metabolism, growth, and reproduction.

Macromolecule example: Proteins (e.g., enzymes).

Micromolecule example: Glucose (a monosaccharide).

Q2. Differentiate between carbohydrates and lipids based on their (a) elemental composition, (b) energy yield per gram, and (c) solubility in water. [3 marks]

1. Elemental composition: Carbohydrates contain C, H, and O in the ratio (CH₂O)ₙ, while lipids are rich in C and H but poor in O.
2. Energy yield: Carbohydrates yield approximately 4 kcal g⁻¹, whereas lipids yield 9 kcal g⁻¹.
3. Solubility: Carbohydrates are generally soluble in water, while lipids are insoluble in water but soluble in organic solvents.

Q3. Explain the four levels of protein structure with one example for each level. How does the primary structure determine the higher levels of protein folding? [5 marks]

1. Primary structure: The linear sequence of amino acids joined by peptide bonds. Example: Insulin (51 amino acids).
2. Secondary structure: Folding of the polypeptide chain into α-helices or β-pleated sheets due to hydrogen bonding. Example: Keratin in hair.
3. Tertiary structure: The 3D shape formed by interactions between side chains (e.g., hydrogen bonds, disulphide bridges). Example: Myoglobin.
4. Quaternary structure: Assembly of two or more polypeptide chains into a functional protein. Example: Haemoglobin (4 subunits).
5. The primary structure determines the higher levels of folding because the sequence of amino acids dictates how the protein will fold into its functional 3D shape. A single change in the primary structure (e.g., sickle-cell anaemia) can disrupt the entire protein structure and function.

Q4. (a) What are enzymes? (b) Describe the mechanism of enzyme action with a labelled diagram of the enzyme-substrate complex. (c) How does temperature affect enzyme activity? [5 marks]

1. (a) Enzymes: Enzymes are biological catalysts that speed up chemical reactions in living organisms. They are proteins with a specific shape that allows them to bind to a substrate and facilitate its conversion into a product.
2. (b) Mechanism of enzyme action:
   

   1. The substrate (S) binds to the active site of the enzyme (E) to form an enzyme-substrate complex (ES).

   2. The enzyme lowers the activation energy (ΔG‡) of the reaction, stabilising the transition state.

   3. The substrate is converted into products (P), which are then released from the active site.

   Labelled diagram of ES complex:

   • A: Active site of the enzyme
   • B: Substrate (S)
   • C: Enzyme-substrate complex (ES)
   • D: Products (P)
3. (c) Effect of temperature: Enzyme activity increases with temperature up to an optimal point (usually 37°C for human enzymes). Beyond this, the enzyme denatures, losing its shape and function. For example, pepsin works optimally at pH 2 and 37°C.

Q5. Write the balanced chemical equation for the hydrolysis of sucrose. Name the enzyme that catalyses this reaction and state its source. [2 marks]

Balanced equation:

Sucrose + Water → Glucose + Fructose

Enzyme: Invertase (or sucrase).

Source: Intestinal lining (brush border enzymes) and yeast.

Q6. Explain the role of nucleic acids in genetics with a labelled diagram of the DNA double helix. How does the structure of DNA contribute to its function? [6 marks]

1. Role of nucleic acids in genetics: Nucleic acids (DNA and RNA) store and transmit genetic information. DNA contains the genetic code, which determines the sequence of amino acids in proteins.
2. Labelled diagram of DNA double helix:
   
   • A: Sugar-phosphate backbone
   • B: Nitrogenous bases (Adenine, Thymine, Cytosine, Guanine)
   • C: Hydrogen bonds between base pairs (A-T and C-G)
   • D: Double helix structure
3. Contribution of DNA structure to function:
   1. The double helix structure provides stability and protects the genetic information.
   2. The complementary base pairing (A-T and C-G) ensures accurate replication and transcription.
   3. The sequence of bases encodes the genetic information, which is transcribed into mRNA and translated into proteins.

Q7. Assertion: Vitamins are essential for metabolic reactions.
Reason: Vitamins act as cofactors for enzymatic reactions.
Evaluate the assertion and reason and choose the correct option:
(a) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) Assertion is true, but the reason is false.
(d) Assertion is false, but the reason is true. [3 marks]

Correct option: (a)

Explanation:

1. Assertion: Vitamins are essential for metabolic reactions because they participate in various biochemical pathways as cofactors for enzymes.
2. Reason: Vitamins such as B-complex vitamins act as cofactors (e.g., NAD⁺, FAD) in enzymatic reactions, facilitating metabolic processes like glycolysis and the citric acid cycle.
3. Since the reason correctly explains the assertion, option (a) is correct.

Q8. Case Study:
A 10-year-old child presents with fatigue, easy bruising, and joint pain. Laboratory tests reveal a deficiency in a fat-soluble vitamin. (a) Identify the vitamin likely deficient. (b) State the dietary sources of this vitamin. (c) Explain the role of this vitamin in the body. (d) What disease is associated with its deficiency? [5 marks]

1. (a) Vitamin likely deficient: Vitamin D.
2. (b) Dietary sources: Fish liver oils, egg yolk, fortified milk, and sunlight exposure (UV radiation synthesises vitamin D in the skin).
3. (c) Role of vitamin D: Vitamin D regulates calcium and phosphate metabolism, promoting bone mineralisation and preventing rickets or osteomalacia.
4. (d) Disease associated with deficiency: Rickets (in children) or osteomalacia (in adults).

Q9. Describe the structure and functions of lipids in living organisms. Explain the difference between saturated and unsaturated fatty acids with one example of each. [6 marks]

1. Structure of lipids:
   

   Lipids are organic compounds composed of carbon, hydrogen, and oxygen. They are hydrophobic and insoluble in water but soluble in organic solvents.

   Components:

   • Fatty acids (long hydrocarbon chains with a carboxyl group)
   • Glycerol (in triglycerides)
   • Phospholipids (contain a phosphate group)
   • Steroids (e.g., cholesterol)
2. Functions of lipids:
   1. Energy storage: Triglycerides store energy (9 kcal g⁻¹).
   2. Structural component: Phospholipids form cell membranes.
   3. Signalling: Steroids (e.g., hormones like cortisol) regulate physiological processes.
   4. Insulation: Adipose tissue insulates the body.
3. Saturated vs. unsaturated fatty acids:
   

   Saturated fatty acids: Contain single bonds between carbon atoms. Example: Palmitic acid (found in animal fats).

   Unsaturated fatty acids: Contain one or more double bonds between carbon atoms. Example: Oleic acid (found in olive oil).

Key takeaways

• Biomolecules are organic compounds containing carbon, hydrogen, oxygen, and nitrogen; they are classified as macromolecules (e.g., carbohydrates, proteins, lipids, nucleic acids) or micromolecules (e.g., vitamins, minerals).
• Carbohydrates follow the general formula Cₙ(H₂O)ₙ, with monosaccharides like glucose (C₆H₁₂O₆) as monomers; they provide ≈4 kcal g⁻¹ of energy and serve structural roles such as cellulose in plant cell walls.
• Proteins are linear chains of 20 standard amino acids linked by peptide bonds; their primary structure determines higher folding levels (α-helix, β-pleated sheet, tertiary, quaternary), with haemoglobin as a classic quaternary example.
• Lipids are hydrophobic molecules including triglycerides (energy storage, ≈9 kcal g⁻¹), phospholipids (membrane structure), and steroids (e.g., cholesterol for membrane fluidity and hormone synthesis).
• Nucleic acids (DNA/RNA) are polymers of nucleotides (sugar + phosphate + nitrogenous base); purines (A, G) and pyrimidines (C, T/U) form base pairs via phosphodiester bonds in a double-helix structure.
• Enzymes are protein catalysts that lower activation energy; their active sites bind substrates (e.g., chymotrypsin’s Ser¹⁹⁵-His⁵⁷-Asp¹⁰² triad stabilizes transition states), following Michaelis-Menten kinetics (v₀ = Vₘₐₓ[S]/(Kₘ + [S])).
• Vitamins are organic cofactors classified as fat-soluble (A, D, E, K) or water-soluble (B-complex, C); vitamin A supports vision, vitamin D regulates calcium absorption, and vitamin C aids collagen synthesis and immune function.
• Minerals are inorganic ions (e.g., calcium for bone mineralization and muscle contraction, iron in haemoglobin for oxygen transport) obtained from diet; deficiencies cause disorders like osteoporosis (Ca) or anemia (Fe).
• Metabolism comprises catabolic pathways (e.g., glycolysis, citric acid cycle) that break down biomolecules to release energy (ATP) and anabolic pathways that synthesize essential compounds for growth and repair.

Test yourself

What is the general formula for carbohydrates, and how does glucose’s molecular formula reflect this?

Carbohydrates follow the general formula Cₙ(H₂O)ₙ; glucose has the molecular formula C₆H₁₂O₆, which matches this pattern with a 1:2:1 ratio of carbon, hydrogen, and oxygen atoms.

Which four elements are universally present in all proteins, and what additional element may be present in some proteins?

All proteins contain carbon, hydrogen, oxygen, and nitrogen; some proteins also contain sulfur, which is present in amino acids like cysteine and methionine.

How do the energy yields per gram of carbohydrates and lipids compare, and what is the numerical difference?

Carbohydrates yield approximately 4 kilocalories per gram, while lipids yield approximately 9 kilocalories per gram; the difference is 5 kilocalories per gram.

What are the two common secondary structures of proteins, and what type of bonding stabilizes them?

The two common secondary structures are the α-helix and β-pleated sheet; both are stabilized by hydrogen bonds between backbone atoms (amino and carbonyl groups) of the polypeptide chain.

Name the three components of a nucleotide, and identify the nitrogenous bases specific to DNA.

A nucleotide consists of a nitrogenous base, a five-carbon sugar (deoxyribose in DNA), and a phosphate group; DNA-specific nitrogenous bases are adenine, thymine, cytosine, and guanine.

What is the role of the active site in enzyme catalysis, and which three amino acids form the catalytic triad of chymotrypsin?

The active site is the region where the substrate binds and catalysis occurs; chymotrypsin’s catalytic triad consists of serine-195, histidine-57, and aspartate-102, which work together to lower activation energy.

List the fat-soluble vitamins and state one primary function of each.

Fat-soluble vitamins are A (vision), D (calcium absorption), E (antioxidant), and K (blood clotting); vitamin A supports vision, vitamin D regulates calcium homeostasis, vitamin E protects cell membranes, and vitamin K is essential for coagulation.

What is the primary storage form of glucose in animals, and where is it predominantly stored?

The primary storage form of glucose in animals is glycogen; it is predominantly stored in the liver and muscle tissues for rapid mobilization when energy is needed.

Which mineral is a key component of haemoglobin, and what is the consequence of its deficiency?

Iron is a key component of haemoglobin; its deficiency leads to anemia, characterized by reduced oxygen-carrying capacity of the blood and symptoms such as fatigue and weakness.

What are the three major stages of carbohydrate metabolism, and what is the end product of glycolysis?

The three major stages of carbohydrate metabolism are glycolysis, the citric acid cycle, and oxidative phosphorylation; the end product of glycolysis is pyruvate, which enters the citric acid cycle under aerobic conditions.