B Pharmacy Sem 3: Pharmaceutical Biochemistry I

Table of Contents

Subject 4. Pharmaceutical Biochemistry I

1. Structure & Function of Biomolecules: Carbohydrates & Lipids
2. Enzymes: Kinetics, Mechanism & Inhibition
3. Metabolic Pathways: Glycolysis, TCA Cycle & Oxidative Phosphorylation
4. Lipid Metabolism & Its Regulation
5. Vitamins: Classification, Coenzyme Roles & Deficiency Disorders
6. Hormones: Biosynthesis, Mechanism of Action & Clinical Correlates explain unit 1 like above

Unit 1: Structure & Function of Biomolecules – Carbohydrates & Lipids

This unit examines the fundamental structures, physicochemical properties, biological roles, and pharmaceutical significance of carbohydrates and lipids as essential biomolecules.

1.1 Carbohydrates

1.1.1 Definition & General Formula

Polyhydroxy aldehydes or ketones, or compounds that yield such on hydrolysis.
General empirical formula: Cₙ(H₂O)ₙ.

1.1.2 Classification

Monosaccharides: Simplest units (triose to heptose).
Oligosaccharides: 2–10 monosaccharide units (e.g., disaccharides, trisaccharides).
Polysaccharides: >10 units; homopolysaccharides (starch, glycogen) and heteropolysaccharides (glycosaminoglycans).

1.1.3 Structural Features

Fischer vs. Haworth Projections to depict stereochemistry and ring closure (α/β anomers).
Glycosidic Linkages: O‑ or N‑glycosidic bonds between anomeric carbon and hydroxyl/amino group of another molecule.

1.1.4 Biological Functions

Energy Source & Storage: Glucose in blood; glycogen in liver/muscle; starch in plants.
Structural Role: Cellulose in plant cell walls; chitin in arthropod exoskeletons.
Cell Recognition & Signaling: Glycoproteins and glycolipids on cell membranes mediate immune responses and receptor binding.

1.1.5 Pharmaceutical Relevance

Excipient Use:
- Microcrystalline cellulose as tablet binder/filler.
- Lactose as diluent in capsules.
Drug Conjugates: Glycosylation improves solubility and targeted delivery (e.g., glycosylated prodrugs).
Analytical Considerations: Enzymatic assays (glucose oxidase) for blood‑glucose monitoring.

1.2 Lipids

1.2.1 Definition & Classes

Amphipathic or hydrophobic biomolecules soluble in organic solvents.
Simple Lipids: Fatty acids, triglycerides (triacylglycerols).
Complex Lipids: Phospholipids, glycolipids, sphingolipids.
Derived Lipids: Steroids (cholesterol), fat‑soluble vitamins (A, D, E, K).

1.2.2 Fatty Acids

Structure: Carboxylic acid head with long aliphatic chain; saturated vs. unsaturated (cis/trans).
Nomenclature: C:D Δ^position (e.g., 18:1 Δ^9 for oleic acid).

1.2.3 Glycerides & Phospholipids

Triacylglycerols: Three fatty acids esterified to glycerol; major energy reserve.
Phospholipids: Glycerol backbone, two fatty acids, and a phosphate‑linked head (e.g., phosphatidylcholine) forming bilayers.

1.2.4 Sterols & Derived Lipids

Cholesterol: Tetracyclic ring structure; membrane fluidity regulator and precursor for steroid hormones and bile acids.

1.2.5 Biological Functions

Energy Storage: Triglycerides in adipose tissue (9 kcal/g).
Membrane Structure: Phospholipid bilayers and cholesterol maintain integrity and fluidity.
Signaling Molecules: Eicosanoids (prostaglandins, leukotrienes) derived from arachidonic acid.
Insulation & Protection: Subcutaneous fat layer.

1.2.6 Pharmaceutical Relevance

Lipid‑Based Drug Delivery:
- Liposomes and solid‑lipid nanoparticles for encapsulating hydrophobic drugs.
- Self‑emulsifying drug delivery systems (SEDDS) to enhance oral bioavailability.
API Lipids: Essential fatty acids (omega‑3) in cardiovascular health supplements.
Excipient Lipids: Medium‑chain triglycerides in parenteral nutrition; lecithin as emulsifier.

1.3 Interrelationship & Metabolic Considerations

Glycolipid & Lipopolysaccharide Biosynthesis: Carbohydrate–lipid conjugates in cell membranes.
Energy Metabolism:
- Glycolysis provides glycerol backbone and acetyl‑CoA for fatty‑acid synthesis.
- β‑Oxidation of fatty acids generates acetyl‑CoA for TCA cycle.
Pharmacokinetic Impact: Lipophilicity (log P) influences absorption, distribution, and membrane permeability.

1.4 Key Points for Exams

Draw:
- α‑ and β‑D‑glucopyranose Haworth projections.
- Structure of a phosphatidylcholine molecule.
Explain:
- Role of glycosidic bonds in energy storage polysaccharides.
- How fatty‑acid unsaturation affects membrane fluidity.
List:
- Three pharmaceutical applications of carbohydrates and of lipids.
- Two analytical assays for carbohydrate and lipid quantification.
Describe:
- Mechanism by which liposomes enhance solubility of hydrophobic drugs.

Unit 2: Enzymes – Kinetics, Mechanism & Inhibition

This unit explores enzyme structure and function, the quantitative description of enzyme-catalyzed reactions, mechanistic pathways, and modes of inhibition critical for drug design and therapeutic modulation.

2.1 Enzyme Structure & Catalytic Mechanisms

2.1.1 Enzyme Classification (EC Numbers)

EC 1: Oxidoreductases
EC 2: Transferases
EC 3: Hydrolases
EC 4: Lyases
EC 5: Isomerases
EC 6: Ligases

2.1.2 Active Site & Substrate Binding

Active Site: Three-dimensional cleft of amino acids forming catalytic residues and binding pockets.
Binding Forces: Hydrogen bonds, ionic interactions, van der Waals, hydrophobic effects.
Induced Fit: Conformational change upon substrate binding enhances specificity and catalysis.

2.1.3 Catalytic Strategies

Acid–Base Catalysis: Transfer of protons via histidine or other residues.
Covalent Catalysis: Transient enzyme–substrate covalent intermediate (e.g., serine proteases).
Metal Ion Catalysis: Zn²⁺, Mg²⁺ stabilizing negative charges or activating water.
Proximity & Orientation: Bringing substrates into close, correct geometry.

2.2 Enzyme Kinetics

2.2.1 Michaelis–Menten Model

Equation:

$v = \frac{V_{\max}[S]}{K_m + [S]}$ $v = K ^{m} + [ S ] V ^{m a x} [ S ]$
where
•
$v$ $v$ = initial reaction velocity
•
$V_{\max}$ $V_{m a x}$ = maximum velocity
•
$K_m$ $K_{m}$ = Michaelis constant (substrate concentration at
$v = V_{\max}/2$ $v = V_{m a x} /2$ )
Assumptions: Steady-state,
$[S] \gg [E]$ $[S] ≫ [E]$ , negligible product inhibition.

2.2.2 Kinetic Parameters

$K_m$ $K_{m}$ : Reflects enzyme affinity for substrate (lower
$K_m$ $K_{m}$ = higher affinity).
$k_{cat}$ $k_{c a t}$ : Turnover number (molecules of substrate converted per enzyme per second).
Catalytic Efficiency:
$k_{cat}/K_m$ $k_{c a t} / K_{m}$ indicates enzyme proficiency under low
$[S]$ $[S]$ .

2.2.3 Lineweaver–Burk & Alternative Plots

Double-Reciprocal Plot:

$\frac{1}{v} = \frac{K_m}{V_{\max}}\frac{1}{[S]} + \frac{1}{V_{\max}}$ $v 1 = V ^{m a x} K ^{m} [ S ] 1 + V ^{m a x} 1$
Useful for determining
$K_m$ $K_{m}$ and
$V_{\max}$ $V_{m a x}$ .
Eadie–Hofstee and Hanes–Woolf plots offer fewer weighting errors.

2.3 Enzyme Inhibition

2.3.1 Reversible Inhibitors

Type	Mechanism	Kinetic Effect
Competitive	Inhibitor binds active site	Increases apparent $K_m$ $K_{m}$ , $V_{\max}$ $V_{m a x}$ unchanged
Noncompetitive	Inhibitor binds allosteric site equally to E or ES	Decreases $V_{\max}$ $V_{m a x}$ , $K_m$ $K_{m}$ unchanged
Uncompetitive	Inhibitor binds only ES complex	Both $K_m$ $K_{m}$ and $V_{\max}$ $V_{m a x}$ decrease proportionally
Mixed	Inhibitor binds E and ES with different affinities	$V_{\max}$ $V_{m a x}$ decreases; $K_m$ $K_{m}$ ↑ or ↓ depending on affinities

2.3.2 Irreversible Inhibitors (Suicide Substrates)

Form covalent bonds with active-site residues (e.g., fluorophosphonates with serine proteases).
Example: Aspirin acetylates serine in cyclooxygenase → permanent enzyme inactivation.

2.4 Mechanistic Enzymology in Drug Design

2.4.1 Transition State Analogues

Mimic high-energy transition state to bind enzyme tighter than substrate (e.g., statins inhibiting HMG-CoA reductase).

2.4.2 Allosteric Modulators

Bind sites distinct from active site to induce conformational changes (e.g., Gleevec® binding inactive kinase conformation).

2.4.3 Prodrug Activation

Utilization of endogenous enzymes (e.g., esterases converting enalapril to enalaprilat).

2.5 Pharmaceutical Applications & Examples

ACE Inhibitors: Competitive inhibition of angiotensin-converting enzyme to lower blood pressure.
Protease Inhibitors: HIV therapy (e.g., saquinavir binds HIV-1 protease active site).
Monoamine Oxidase Inhibitors (MAOIs): Irreversible inhibition of MAO for depression management.

2.6 Key Points for Exams

Define
$K_m$ $K_{m}$ ,
$V_{\max}$ $V_{m a x}$ , and
$k_{cat}$ $k_{c a t}$ , and explain their significance.
Draw and interpret a Lineweaver–Burk plot for competitive vs. noncompetitive inhibition.
Describe the catalytic triad mechanism of serine proteases.
Differentiate reversible from irreversible inhibitors, with one drug example each.
Explain how transition state analogues inform rational drug design.

Unit 3: Metabolic Pathways – Glycolysis, TCA Cycle & Oxidative Phosphorylation

This unit elucidates the central energy‑yielding pathways—glycolysis, the tricarboxylic acid (TCA) cycle, and oxidative phosphorylation—detailing each step, its cellular location, regulation, and pharmaceutical relevance.

3.1 Glycolysis

3.1.1 Overview & Cellular Location

Definition: Ten‑step anaerobic conversion of one glucose (6C) to two pyruvate (3C) molecules, producing ATP and NADH.
Location: Cytosol of all cells.

3.1.2 Key Steps & Energetics

Step	Enzyme	Substrate → Product	ATP/NADH Yield or Consumption
1	Hexokinase/Glucokinase	Glucose → Glucose‑6‑phosphate	–1 ATP
2	Phosphoglucose isomerase	G6P → Fructose‑6‑phosphate	–
3	Phosphofructokinase‑1 (PFK‑1)	F6P → Fructose‑1,6‑bisphosphate	–1 ATP
4	Aldolase	F1,6BP → Glyceraldehyde‑3‑P + DHAP	–
5	Triose phosphate isomerase	DHAP ↔ Glyceraldehyde‑3‑P	–
6	Glyceraldehyde‑3‑P dehydrogenase	G3P → 1,3‑Bisphosphoglycerate + NADH	+1 NADH
7	Phosphoglycerate kinase	1,3BPG → 3‑Phosphoglycerate + ATP	+1 ATP
8	Phosphoglycerate mutase	3PG → 2‑Phosphoglycerate	–
9	Enolase	2PG → Phosphoenolpyruvate	–
10	Pyruvate kinase	PEP → Pyruvate + ATP	+1 ATP

Net Yield per Glucose: 2 ATP (steps 7 & 10) and 2 NADH (step 6).
Regulatory Enzymes:
- Hexokinase/Glucokinase (step 1): inhibited by G6P (hexokinase) or regulated by insulin (glucokinase).
- PFK‑1 (step 3): allosteric ↑ by AMP, fructose‑2,6‑bisphosphate; ↓ by ATP, citrate.
- Pyruvate kinase (step 10): activated by F1,6BP; inhibited by ATP, alanine.

3.1.3 Fates of Pyruvate

Aerobic: Converted to acetyl‑CoA by pyruvate dehydrogenase (PDH) → enters TCA cycle.
Anaerobic: Reduced to lactate by lactate dehydrogenase (LDH), regenerating NAD⁺.
Other: Transamination to alanine; carboxylation to oxaloacetate by pyruvate carboxylase.

3.2 Tricarboxylic Acid (TCA) Cycle

3.2.1 Overview & Location

Definition: Eight‑step oxidation of acetyl‑CoA to CO₂ generating NADH, FADH₂, and GTP.
Location: Mitochondrial matrix.

3.2.2 Key Steps & Energetics

Step	Enzyme	Substrate → Product	NADH/FADH₂/GTP Yield
1	Citrate synthase	Acetyl‑CoA + Oxaloacetate → Citrate	–
2	Aconitase	Citrate ↔ Isocitrate	–
3	Isocitrate dehydrogenase (IDH)	Isocitrate → α‑Ketoglutarate + CO₂	+1 NADH
4	α‑Ketoglutarate dehydrogenase	α‑KG → Succinyl‑CoA + CO₂	+1 NADH
5	Succinyl‑CoA synthetase	Succinyl‑CoA → Succinate + GTP	+1 GTP
6	Succinate dehydrogenase	Succinate → Fumarate	+1 FADH₂
7	Fumarase	Fumarate → Malate	–
8	Malate dehydrogenase	Malate → Oxaloacetate + NADH	+1 NADH

Total Yield per Acetyl‑CoA: 3 NADH, 1 FADH₂, 1 GTP.
Regulatory Enzymes:
- Citrate synthase: inhibited by ATP, NADH, succinyl‑CoA.
- IDH: activated by ADP; inhibited by ATP, NADH.
- α‑KG dehydrogenase: inhibited by ATP, NADH, succinyl‑CoA.

3.3 Oxidative Phosphorylation (Electron Transport Chain & ATP Synthase)

3.3.1 Overview & Location

Definition: Coupling of electron transfer from NADH/FADH₂ through complexes I–IV to proton pumping and ATP synthesis via Complex V.
Location: Inner mitochondrial membrane.

3.3.2 Electron Transport Chain (ETC)

Complex	Name	Electron Donor → Acceptor	Protons Pumped per 2 e⁻
I	NADH:Ubiquinone oxidoreductase	NADH → Q	4
II	Succinate dehydrogenase	FADH₂ → Q	0
III	Ubiquinol:Cytochrome c oxidoreductase	QH₂ → Cyt c₁	4
IV	Cytochrome c oxidase	Cyt c → O₂ → H₂O	2

Ubiquinone (Q): Mobile carrier between I/II and III.
Cytochrome c: Mobile carrier between III and IV.

3.3.3 Proton Gradient & Chemiosmotic Theory

Proton pumping creates electrochemical gradient (∆p) across inner membrane.
∆pH + ∆ψ drives protons back into matrix.

3.3.4 ATP Synthase (Complex V)

F₀ subunit: Proton channel in membrane.
F₁ subunit: Catalytic unit that synthesizes ATP from ADP + Pi.
Stoichiometry: ~3 H⁺ per ATP; total ≈ 2.5 ATP per NADH, 1.5 ATP per FADH₂.

3.4 Integration & Regulation of Pathways

PDH Complex Regulation:
- Activated by pyruvate, NAD⁺, ADP, Ca²⁺.
- Inhibited by acetyl‑CoA, NADH, ATP, phosphorylation by PDH kinase.
Substrate Availability: ADP/ATP ratio and NADH/NAD⁺ ratio modulate PFK‑1, IDH, ATP synthase.
Interpathway Links:
- Anaplerotic Reactions: Pyruvate carboxylase refills oxaloacetate.
- Biosynthetic Withdrawals: Citrate → fatty‑acid synthesis; α‑KG → amino‑acid synthesis.

3.5 Pharmaceutical Relevance

Metabolic Disorders:
- Pyruvate dehydrogenase deficiency: Lactic acidosis, neurological deficits.
- Mitochondrial myopathies: ETC complex mutations → reduced ATP production.
Drug Targets:
- Metformin: Inhibits complex I, activates AMPK, reduces hepatic gluconeogenesis.
- Statins: Indirectly affect TCA substrate availability by lowering acetyl‑CoA from cholesterol synthesis.
Biomarkers: Elevated lactate and pyruvate ratios indicate mitochondrial dysfunction.

3.6 Key Points for Exams

Trace the flow of carbons and electrons from glucose to CO₂ through glycolysis and TCA.
List the number of ATP/NADH/FADH₂ yielded per glucose molecule.
Describe how the proton gradient drives ATP synthesis and calculate ATP per NADH.
Explain the allosteric regulation of PFK‑1 and IDH in response to cellular energy status.
Relate a clinical example of a metabolic enzyme defect to its biochemical consequence.

Unit 4: Lipid Metabolism & Its Regulation

This unit examines the pathways of lipid synthesis, degradation, and interconversion, the key regulatory checkpoints, hormonal control, and the pharmaceutical interventions that target lipid‑metabolic disorders.

4.1 Fatty Acid Biosynthesis

4.1.1 Location & Overview

Occurs in the cytosol of liver, adipose, lactating mammary gland.
Precursor: Acetyl‑CoA from mitochondrial citrate shuttle.

4.1.2 Key Enzymes & Steps

Step	Enzyme	Reaction
Carboxylation	Acetyl‑CoA carboxylase (ACC)	Acetyl‑CoA + CO₂ + ATP → Malonyl‑CoA + ADP + Pi
Chain Elongation (repeated)	Fatty acid synthase (FAS) complex	Malonyl‑CoA + Acyl‑Carrier → Extended Acyl‑ACP + CO₂
Termination	Thioesterase	Release of palmitate (C16:0) from ACP

ACC Regulation:
- Allosteric: ↑ by citrate; ↓ by long‑chain acyl‑CoA.
- Covalent: Phosphorylation by AMP‑activated protein kinase (AMPK) inactivates; dephosphorylation by insulin‑stimulated phosphatase activates.

4.2 Fatty Acid β‑Oxidation

4.2.1 Location & Overview

Occurs in mitochondrial matrix; very‑long‑chain in peroxisomes initially.
Generates NADH, FADH₂ and acetyl‑CoA per two‑carbon cycle.

4.2.2 Key Steps & Enzymes

Step	Enzyme	Reaction
Activation	Acyl‑CoA synthetase	FA + CoA + ATP → Acyl‑CoA + AMP + PPi
Transport	Carnitine acyltransferase I & II	Carnitine shuttle imports Acyl‑CoA into matrix
Oxidation	Acyl‑CoA dehydrogenase	Acyl‑CoA → trans‑Δ²‑enoyl‑CoA + FADH₂
Hydration & Oxidation	Enoyl‑CoA hydratase & H‑CoA DH	→ 3‑Hydroxyacyl‑CoA → 3‑Ketoacyl‑CoA + NADH
Thiolysis	β‑Ketothiolase	3‑Ketoacyl‑CoA + CoA → Acetyl‑CoA + shortened Acyl‑CoA

Regulation: Malonyl‑CoA inhibits CPT‑I to prevent futile cycling with biosynthesis.

4.3 Ketogenesis & Ketone Utilization

4.3.1 Ketone Body Formation

In liver mitochondria when acetyl‑CoA > TCA capacity (fasting, diabetes).
Steps: 2 Acetyl‑CoA → Acetoacetyl‑CoA → HMG‑CoA → Acetoacetate → β‑Hydroxybutyrate or acetone.

4.3.2 Peripheral Utilization

Extrahepatic tissues reconvert β‑hydroxybutyrate → Acetoacetate → 2 Acetyl‑CoA for TCA.

4.4 Cholesterol Metabolism & Lipoprotein Transport

4.4.1 Biosynthesis

Rate‑Limiting Step: HMG‑CoA reductase (ER membrane) converts HMG‑CoA → Mevalonate.
Regulation:
- SREBP‑mediated transcriptional control (↑ by low cholesterol).
- Phosphorylation by AMPK ↓ activity; dephosphorylation by insulin ↑.
- Feedback: Cholesterol and downstream sterols promote reductase degradation.

4.4.2 Lipoprotein Assembly & Function

Lipoprotein Class	Origin	Function
Chylomicrons	Intestine	Dietary TG transport to adipose and muscle
VLDL	Liver	Endogenous TG transport
LDL	VLDL remnant	Cholesterol delivery to peripheral tissues
HDL	Liver & intestine	Reverse cholesterol transport to liver

4.4.3 Reverse Cholesterol Transport

HDL acquires free cholesterol via ABCA1; esterified by LCAT; returns to liver via SR‑B1 receptor.

4.5 Hormonal & Nutritional Regulation

Insulin:
- ↑ ACC and FAS expression & activity; promotes lipid synthesis.
- ↑ LPL activity in adipose; ↓ hormone‑sensitive lipase (HSL).
Glucagon/Epinephrine:
- ↑ HSL in adipose → lipolysis; ↓ ACC activity via AMPK.
AMPK: Cellular energy sensor; phosphorylates ACC and HMG‑CoA reductase, ↓ lipogenesis and cholesterol synthesis.

4.6 Pharmaceutical Interventions

Target	Drug Class	Mechanism
HMG‑CoA Reductase	Statins (e.g., Atorvastatin)	Competitive inhibition; ↓ cholesterol synthesis
PCSK9	Monoclonal antibodies (e.g., Alirocumab)	↑ LDL receptor recycling; ↓ LDL‑C
Bile Acid Sequestration	Resins (e.g., Cholestyramine)	Bind bile acids in gut; ↑ cholesterol catabolism
Fibrates (PPARα agonists)	Gemfibrozil, Fenofibrate	↑ LPL activity; ↓ VLDL synthesis
Niacin	Vitamin B₃	↓ hepatic VLDL secretion; ↑ HDL

4.7 Key Points for Exams

Outline the steps of fatty‑acid synthase and the control by ACC.
Describe the carnitine shuttle and its regulation in β‑oxidation.
Explain how HMG‑CoA reductase is regulated at transcriptional and post‑translational levels.
Compare the roles and composition of chylomicrons, VLDL, LDL, and HDL.
List two drugs for each lipid‑lowering strategy and their mechanism of action.

Unit 5: Vitamins – Classification, Coenzyme Roles & Deficiency Disorders

This unit examines the two major classes of vitamins—water‑soluble and fat‑soluble—their biochemical functions as coenzymes or cofactors, the clinical manifestations of their deficiencies, and their pharmaceutical applications.

5.1 Classification of Vitamins

Class	Vitamins
Water‑Soluble	B₁ (Thiamine), B₂ (Riboflavin), B₃ (Niacin), B₅ (Pantothenic acid), B₆ (Pyridoxine), B₇ (Biotin), B₉ (Folate), B₁₂ (Cobalamin), C (Ascorbic acid)
Fat‑Soluble	A (Retinol & provitamin β‑carotene), D (Calciferols), E (Tocopherols), K (Phylloquinone & menaquinones)

5.2 Water‑Soluble Vitamins

5.2.1 Vitamin B₁ (Thiamine)

Coenzyme Form: Thiamine pyrophosphate (TPP)
Function: Decarboxylation of α‑ketoacids (pyruvate dehydrogenase, α‑ketoglutarate dehydrogenase); transketolase in pentose phosphate pathway.
Deficiency:
- Beriberi: Wet (cardiac failure, edema), Dry (peripheral neuropathy).
- Wernicke–Korsakoff: Ataxia, ophthalmoplegia, memory loss (in alcoholics).

5.2.2 Vitamin B₂ (Riboflavin)

Coenzymes: Flavin mononucleotide (FMN), Flavin adenine dinucleotide (FAD)
Function: Electron transfer in redox reactions (complex I of ETC, fatty‑acid β‑oxidation, succinate dehydrogenase).
Deficiency: Cheilosis, angular stomatitis, glossitis, seborrheic dermatitis.

5.2.3 Vitamin B₃ (Niacin)

Coenzymes: NAD⁺, NADP⁺
Function: Hydride transfer in catabolic (NAD⁺) and anabolic (NADP⁺) pathways.
Deficiency: Pellagra—“3 Ds”: Dermatitis (photosensitive), Diarrhea, Dementia; if untreated → death.

5.2.4 Vitamin B₅ (Pantothenic Acid)

Coenzyme: Coenzyme A (CoA) and 4′‑phosphopantetheine in acyl‑carrier protein.
Function: Acyl transfer in fatty‑acid metabolism, TCA cycle (acetyl‑CoA), synthesis of cholesterol and steroids.
Deficiency: Rare; symptoms include fatigue, paresthesia, GI distress.

5.2.5 Vitamin B₆ (Pyridoxine)

Coenzyme: Pyridoxal phosphate (PLP)
Function: Amino‑acid metabolism (transamination, decarboxylations), neurotransmitter synthesis (GABA, serotonin).
Deficiency: Convulsions, hyperirritability, peripheral neuropathy, sideroblastic anemia.

5.2.6 Vitamin B₇ (Biotin)

Enzyme Prosthetic Group: Biotin–enzyme conjugates
Function: Carboxylation reactions (pyruvate carboxylase, acetyl‑CoA carboxylase, propionyl‑CoA carboxylase).
Deficiency: Dermatitis, alopecia, enteritis, often due to raw egg white (avidin).

5.2.7 Vitamin B₉ (Folate)

Coenzyme: Tetrahydrofolate (THF) derivatives
Function: One‑carbon transfers in nucleotide biosynthesis (purines, thymidylate) and amino‑acid metabolism.
Deficiency: Megaloblastic anemia, neural‑tube defects in fetus (spina bifida).

5.2.8 Vitamin B₁₂ (Cobalamin)

Coenzymes: Methylcobalamin, 5′‑deoxyadenosylcobalamin
Function: Homocysteine methylation to methionine; methylmalonyl‑CoA mutase in odd‑chain fatty‑acid catabolism.
Deficiency: Megaloblastic anemia, subacute combined degeneration of the spinal cord; pernicious anemia (intrinsic‑factor autoantibodies).

5.2.9 Vitamin C (Ascorbic Acid)

Function: Reducing agent for prolyl and lysyl hydroxylases in collagen synthesis; antioxidant; enhances Fe³⁺→Fe²⁺ reduction and iron absorption.
Deficiency: Scurvy—poor wound healing, bleeding gums, petechiae, impaired collagen formation.

5.3 Fat‑Soluble Vitamins

5.3.1 Vitamin A (Retinoids & Carotenoids)

Forms: Retinol, retinal, retinoic acid; provitamin β‑carotene.
Function: Visual cycle (11‑cis‑retinal in rhodopsin), gene regulation (retinoic acid receptor), epithelial differentiation.
Deficiency: Night blindness, xerophthalmia, keratinization of epithelium.
Toxicity: Hypervitaminosis A—headache, hepatic enlargement, teratogenic.

5.3.2 Vitamin D (Calciferols)

Forms: D₃ (cholecalciferol), D₂ (ergocalciferol); active form calcitriol (1,25‑(OH)₂D).
Function: ↑ Ca²⁺ and PO₄³⁻ absorption in gut, bone mineralization, gene regulation in calcium homeostasis.
Deficiency: Rickets in children, osteomalacia in adults.
Toxicity: Hypercalcemia → stones, metastatic calcification.

5.3.3 Vitamin E (Tocopherols & Tocotrienols)

Function: Lipid‑soluble antioxidant protecting membrane polyunsaturated fatty acids from peroxidation.
Deficiency: Hemolytic anemia, neurological deficits (spinocerebellar syndrome), due to malabsorption (e.g., cystic fibrosis).

5.3.4 Vitamin K (Phylloquinone & Menaquinones)

Function: γ‑Carboxylation of glutamate residues in clotting factors (II, VII, IX, X), osteocalcin activation.
Deficiency: Hemorrhagic disease (prolonged prothrombin time), particularly in newborns.
Drug Interaction: Warfarin antagonizes vitamin K recycling (vitamin K epoxide reductase).

5.4 Pharmaceutical Applications

Supplement Formulations:
- Multivitamin tablets/capsules with balanced B‑complex and fat‑soluble vitamins.
- Injectable vitamin B₁₂ (cyanocobalamin) for pernicious anemia.
- Oral vitamin D₃ and Ca²⁺ combinations for osteoporosis.
Therapeutic Use:
- Niacin (B₃) in high doses for dyslipidemia (↓ LDL, ↑ HDL).
- Folate (B₉) fortification to prevent neural‑tube defects.
Quality Control: HPLC assays for potency; stability testing under ICH conditions.

5.5 Key Points for Exams

Classify vitamins into water‑ and fat‑soluble groups with two examples each.
List the coenzyme form and one key reaction for vitamins B₁, B₂, B₆, and B₉.
Describe the clinical features of deficiencies of vitamins C, D, and K.
Explain the mechanism of warfarin action and its relationship to vitamin K.
Outline one pharmaceutical formulation for vitamin B₁₂ and its route of administration.

Unit 6: Hormones – Biosynthesis, Mechanism of Action & Clinical Correlates

This unit examines the major classes of hormones, their pathways of synthesis and secretion, molecular mechanisms of action, physiological roles, and their dysregulation in disease—with emphasis on pharmaceutical interventions.

6.1 Classification of Hormones

Class	Source	Solubility & Transport	Examples
Peptide/Protein	Anterior pituitary, pancreas, hypothalamus	Water‑soluble; circulate unbound	Insulin, glucagon, growth hormone (GH), oxytocin
Amino Acid–Derived	Thyroid gland, adrenal medulla	Lipid‑soluble (thyroid) or water‑soluble (catecholamines)	Thyroxine (T₄), epinephrine
Steroid	Adrenal cortex, gonads, placenta	Lipid‑soluble; require carrier proteins (e.g., albumin, SHBG)	Cortisol, aldosterone, estrogen, testosterone
Eicosanoids	Membrane phospholipids (local)	Autocrine/paracrine; short‑lived	Prostaglandins, leukotrienes

6.2 Biosynthesis & Secretion

6.2.1 Peptide Hormones

Gene Transcription → preprohormone → signal peptide removed → prohormone in rough ER → packaged into secretory granules → proteolytic processing to active hormone → exocytosis in response to stimulus (e.g., ↑ blood glucose → insulin release).

6.2.2 Amino Acid–Derived

Thyroid Hormones: Iodide uptake by thyroid follicular cells → oxidation (thyroid peroxidase) → iodination of tyrosyl residues in thyroglobulin → coupling to form T₃/T₄ → proteolysis and release.
Catecholamines: Tyrosine → L‑DOPA (tyrosine hydroxylase) → dopamine → norepinephrine → epinephrine (PNMT in adrenal medulla).

6.2.3 Steroid Hormones

Cholesterol precursor → side‑chain cleavage by CYP11A1 → pregnenolone → pathway branches:
- Glucocorticoids (cortisol): via 17α‑hydroxypregnenolone → 11‑deoxycortisol → cortisol.
- Mineralocorticoids (aldosterone): via progesterone → deoxycorticosterone → aldosterone.
- Androgens/Estrogens: via 17α‑hydroxyprogesterone → DHEA → androstenedione → testosterone → estradiol (aromatase).
Secretion: Diffuse across membrane; circulate bound to specific globulins (CBG, SHBG).

6.3 Mechanisms of Hormone Action

6.3.1 Peptide & Catecholamine Hormones

Cell‐Surface Receptors: Bind G‑protein–coupled receptors (GPCRs) or receptor tyrosine kinases (RTKs).
Second Messengers:
- cAMP (via adenylate cyclase) → PKA activation (e.g., glucagon receptor).
- IP₃/DAG (via PLC) → Ca²⁺ release and PKC activation (e.g., vasopressin V₁ receptor).
- Receptor‐Tyrosine Kinase: Insulin receptor auto‐phosphorylation → PI3K/Akt and MAPK cascades.

6.3.2 Steroid & Thyroid Hormones

Intracellular Receptors:
- Cytosolic/Nuclear: Ligand binding → receptor dimerization → translocation to nucleus → bind hormone‐response elements (HREs) → modulate gene transcription over hours to days.
Examples:
- Glucocorticoid receptor regulates anti‑inflammatory genes.
- Thyroid hormone receptor increases metabolic enzyme transcription.

6.3.3 Eicosanoids

Autocrine/Paracrine action via GPCRs (e.g., prostaglandin receptors) to modulate inflammation, vascular tone, platelet aggregation.

6.4 Clinical Correlates & Pharmaceutical Modulation

Hormone	Disorder	Clinical Features	Pharmacological Agents
Insulin	Diabetes mellitus (type 1 & 2)	Hyperglycemia, polyuria, ketoacidosis	Insulin analogs (e.g., lispro, glargine); insulin secretagogues (sulfonylureas)
Glucagon	Hypoglycemia management	↑ blood glucose	Glucagon emergency kits
Thyroxine (T₄)	Hypothyroidism	Fatigue, weight gain, cold intolerance	Levothyroxine
Antithyroid	Hyperthyroidism (Graves’)	Weight loss, heat intolerance, tachycardia	Methimazole, propylthiouracil
Cortisol	Cushing’s syndrome	Central obesity, hypertension, hyperglycemia	Ketoconazole (inhibits steroid synthesis), mifepristone (glucocorticoid receptor antagonist)
Mineralocorticoid	Addison’s disease	Hypotension, hyponatremia, hyperkalemia	Fludrocortisone replacement
Estrogen/Progesterone	Contraception, menopausal symptoms	Suppress ovulation, reduce vasomotor symptoms	Combined oral contraceptives, HRT formulations
Prostaglandin E₁	Erectile dysfunction	↑ penile blood flow	Alprostadil

6.5 Key Points for Exams

Outline the biosynthetic pathway from cholesterol to cortisol, identifying the rate‑limiting enzyme.
Compare second‑messenger systems for peptide vs. steroid hormones.
Describe the mechanism of action of insulin at its receptor and downstream effects on glucose uptake.
List three clinical uses of glucocorticoid antagonists or synthesis inhibitors.
Explain how thyroid hormones are activated (T₄ → T₃) in peripheral tissues and their genomic effects.

M	T	W	T	F	S	S
	1	2	3	4	5	6
7	8	9	10	11	12	13
14	15	16	17	18	19	20
21	22	23	24	25	26	27
28	29	30	31

B Pharmacy Sem 3: Pharmaceutical Biochemistry I

Subject 4. Pharmaceutical Biochemistry I

Unit 1: Structure & Function of Biomolecules – Carbohydrates & Lipids