(SEM II) THEORY EXAMINATION 2021-22 BIOCHEMISTRY

B.Pharm (Sem II) – Biochemistry

Detailed Explanation of Questions and Answers

Biochemistry studies the chemical reactions and molecular mechanisms that occur inside living cells. It explains how biological molecules such as carbohydrates, lipids, proteins, and nucleic acids interact to sustain life. In pharmacy education, biochemistry is essential because many diseases arise from biochemical abnormalities, and many drugs act by modifying biochemical pathways. 

Section A – Detailed Answers

Phospholipids

Phospholipids are a class of complex lipids that form the main structural component of biological membranes. They consist of a glycerol backbone attached to two fatty acid chains and a phosphate-containing head group.

The fatty acid chains are hydrophobic, meaning they repel water, while the phosphate group is hydrophilic and interacts with water. Because of this dual nature, phospholipids arrange themselves into a bilayer when placed in an aqueous environment.

Examples of phospholipids include lecithin and cephalin. These molecules are essential for maintaining cell membrane integrity and facilitating transport of substances across the membrane.

Essential and Non-Essential Amino Acids

Amino acids are organic compounds that serve as the building blocks of proteins. They contain both an amino group and a carboxyl group attached to a central carbon atom.

Essential amino acids are those that the human body cannot synthesize in sufficient amounts and must be obtained from dietary sources. Examples include leucine, lysine, and methionine.

Non-essential amino acids are those that the body can synthesize on its own from other metabolic intermediates. Examples include alanine, glycine, and glutamic acid.

Transamination

Transamination is a biochemical reaction in which the amino group from one amino acid is transferred to a keto acid to form a new amino acid. This reaction is catalyzed by enzymes known as aminotransferases.

For example, the amino group from alanine can be transferred to alpha-ketoglutarate to form glutamate and pyruvate.

Transamination plays an important role in amino acid metabolism and allows the body to synthesize non-essential amino acids.

Genetic Code

The genetic code is the system through which genetic information stored in DNA is translated into proteins. It consists of sequences of three nucleotides known as codons.

Each codon corresponds to a specific amino acid during protein synthesis. For example, the codon AUG codes for the amino acid methionine and also serves as the start codon for protein synthesis.

The genetic code is universal, meaning it is nearly the same in all living organisms.

Enthalpy and Entropy

Enthalpy refers to the total heat energy contained in a system. It represents the energy required to break chemical bonds or released during formation of bonds.

Entropy represents the degree of disorder or randomness in a system. Biological systems tend to move toward greater entropy while maintaining order through energy input.

Both enthalpy and entropy determine whether a biochemical reaction occurs spontaneously.

Diseases Associated with Glycogen Metabolism

Glycogen metabolism disorders occur due to defects in enzymes responsible for glycogen synthesis or breakdown.

One example is Von Gierke disease, which results from deficiency of glucose-6-phosphatase and leads to excessive glycogen accumulation in the liver.

Another example is McArdle disease, which results from deficiency of muscle glycogen phosphorylase and leads to muscle weakness during exercise.

Ketone Bodies and Ketoacidosis

Ketone bodies are molecules produced during the breakdown of fatty acids in the liver. The main ketone bodies include acetoacetate, beta-hydroxybutyrate, and acetone.

Under normal conditions, ketone bodies serve as an alternative energy source during fasting or prolonged exercise.

However, excessive production of ketone bodies may lead to ketoacidosis, a condition in which blood becomes acidic due to accumulation of ketone bodies. This condition commonly occurs in uncontrolled diabetes.

Apoenzyme and Holoenzyme

An apoenzyme is the protein portion of an enzyme that is inactive on its own. It requires the presence of a cofactor or coenzyme to become active.

When the apoenzyme combines with its cofactor, the complete and active enzyme complex is called a holoenzyme.

This interaction allows enzymes to perform their catalytic functions effectively.

Electron Transport Chain and ATP

The electron transport chain is a series of protein complexes located in the inner mitochondrial membrane. These complexes transfer electrons from NADH and FADH₂ to oxygen.

As electrons move through the chain, energy is released and used to pump protons across the mitochondrial membrane. This creates a proton gradient.

The enzyme ATP synthase uses this gradient to synthesize ATP, which serves as the main energy currency of the cell.

Biological Role of Nucleic Acids

Nucleic acids include DNA and RNA, which are responsible for storing and transmitting genetic information.

DNA contains the genetic blueprint of the cell and controls the synthesis of proteins.

RNA participates in protein synthesis by carrying genetic information from DNA to ribosomes and helping assemble amino acids into proteins.

Section B – Detailed Explanation

Enzyme Kinetics and Michaelis-Menten Equation

Enzyme kinetics studies the rate at which enzyme-catalyzed reactions occur. The Michaelis-Menten equation describes the relationship between reaction velocity and substrate concentration.

The equation explains how reaction rate increases as substrate concentration increases, eventually reaching a maximum velocity known as Vmax.

The Michaelis constant (Km) represents the substrate concentration at which the reaction rate is half of Vmax.

This model helps scientists understand enzyme efficiency and substrate affinity.

Ketone Body Formation

Ketone bodies are produced in the liver during periods of low carbohydrate availability. Fatty acids are converted into acetyl-CoA through beta-oxidation.

When excess acetyl-CoA accumulates, it is converted into ketone bodies through a series of enzymatic reactions.

These ketone bodies are transported to other tissues, where they are converted back into acetyl-CoA and used for energy production.

Section C – Detailed Explanation

Oxidative Phosphorylation

Oxidative phosphorylation is the final stage of cellular respiration. It occurs in the mitochondria and produces the majority of ATP in aerobic organisms.

Electrons from NADH and FADH₂ are transferred through the electron transport chain. The energy released during electron transfer drives proton pumping across the membrane.

The resulting proton gradient powers ATP synthesis through the enzyme ATP synthase.

β-Oxidation of Fatty Acids

Beta-oxidation is the metabolic pathway through which fatty acids are broken down to produce energy. This process occurs in the mitochondria.

During beta-oxidation, fatty acids are progressively shortened by removing two-carbon units in the form of acetyl-CoA.

Each cycle of beta-oxidation produces NADH and FADH₂, which enter the electron transport chain to generate ATP.

DNA and RNA Structure

DNA consists of two strands forming a double helix. Each strand contains nucleotides composed of a sugar, phosphate group, and nitrogenous base.

The bases adenine and thymine pair together, while cytosine pairs with guanine.

RNA differs from DNA in that it contains ribose sugar and uracil instead of thymine. RNA is usually single-stranded and participates in protein synthesis.

Conclusion

Biochemistry provides insight into the molecular processes that sustain life. Understanding metabolic pathways such as oxidative phosphorylation, β-oxidation, and the urea cycle helps pharmacy students understand how the body generates energy and maintains metabolic balance.

This knowledge also helps explain how diseases occur and how medications target specific biochemical pathways.