(SEM II) THEORY EXAMINATION 2018-19 BIOCHEMISTRY

B.Pharm (Sem II) – Biochemistry

Detailed Explanation of Questions and Answers

Biochemistry is the study of chemical processes that occur within living organisms. It explains how biomolecules such as carbohydrates, lipids, proteins, and nucleic acids interact to support life. For pharmacy students, understanding these biochemical pathways is essential because many drugs act by influencing metabolic reactions and enzyme systems. 

Section A – Detailed Answers

Phospholipids

Phospholipids are complex lipids that form the structural basis of biological membranes. They consist of a glycerol backbone attached to two fatty acid chains and a phosphate group.

The fatty acid chains are hydrophobic, while the phosphate group is hydrophilic. Because of this dual nature, phospholipids form bilayer structures in cell membranes.

Examples include lecithin and cephalin.

Energy-Rich Compounds

Energy-rich compounds are molecules that store and release large amounts of energy when their chemical bonds are broken.

The most important energy-rich compound in the body is ATP (adenosine triphosphate). Other examples include phosphocreatine and acetyl coenzyme A.

These compounds provide energy required for cellular processes such as muscle contraction and biosynthesis.

Glycogenesis and Glycogenolysis

Glycogenesis is the process by which glucose molecules are converted into glycogen for storage in the liver and muscles.

Glycogenolysis is the process by which stored glycogen is broken down into glucose when the body requires energy.

These processes help maintain stable blood glucose levels.

Hormones Regulating Blood Glucose

Blood glucose levels are regulated by several hormones.

Insulin lowers blood glucose levels by promoting uptake of glucose into cells and stimulating glycogen synthesis.

Glucagon increases blood glucose levels by stimulating glycogen breakdown in the liver.

Other hormones such as cortisol and adrenaline also influence glucose metabolism.

Transamination

Transamination is a biochemical reaction in which the amino group from one amino acid is transferred to a keto acid to form another amino acid.

This reaction is catalyzed by enzymes called aminotransferases and requires the coenzyme pyridoxal phosphate derived from vitamin B6.

Transamination plays a key role in amino acid metabolism.

Allosteric Inhibition

Allosteric inhibition occurs when a regulatory molecule binds to a site on an enzyme other than the active site.

This binding causes a conformational change in the enzyme, reducing its activity.

Allosteric inhibition allows cells to regulate metabolic pathways efficiently.

Genetic Code

The genetic code is the system by which sequences of nucleotides in DNA are translated into proteins.

Each group of three nucleotides, known as a codon, specifies a particular amino acid.

For example, the codon AUG codes for methionine and also acts as the start codon during protein synthesis.

Synthesis of Serotonin (5-HT)

Serotonin, also known as 5-hydroxytryptamine, is synthesized from the amino acid tryptophan.

The first step involves hydroxylation of tryptophan to form 5-hydroxytryptophan.

This compound is then decarboxylated to form serotonin.

Serotonin functions as an important neurotransmitter involved in mood regulation and sleep.

Biological Role of Nucleic Acids

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

DNA contains the genetic blueprint of the cell, while RNA participates in protein synthesis.

These molecules play a fundamental role in heredity and cellular function.

Enthalpy and Entropy

Enthalpy represents the total heat energy contained in a system. It reflects the energy required or released during chemical reactions.

Entropy represents the degree of disorder or randomness in a system.

Both enthalpy and entropy determine whether biochemical reactions occur spontaneously.

Section B – Detailed Explanation

Gluconeogenesis

Gluconeogenesis is the metabolic pathway through which glucose is synthesized from non-carbohydrate sources such as lactate, glycerol, and amino acids.

This process occurs mainly in the liver and kidneys. It is essential during fasting when blood glucose levels need to be maintained.

The pathway involves several enzymatic reactions that bypass irreversible steps of glycolysis.

Michaelis-Menten Equation

The Michaelis-Menten equation describes the relationship between enzyme reaction rate and substrate concentration.

It explains how the reaction velocity increases with substrate concentration until it reaches a maximum rate known as Vmax.

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

This model is widely used to study enzyme kinetics.

DNA Replication

DNA replication is the process by which a cell duplicates its genetic material before cell division.

The double helix structure of DNA unwinds, and each strand serves as a template for synthesis of a new complementary strand.

The process involves enzymes such as DNA polymerase, helicase, and ligase.

DNA replication ensures that genetic information is accurately transmitted to daughter cells.

Section C – Detailed Explanation

Glycolysis (Embden-Meyerhof Pathway)

Glycolysis is the metabolic pathway that converts glucose into pyruvate.

This process occurs in the cytoplasm and involves ten enzymatic reactions.

During glycolysis, ATP and NADH are produced, which provide energy for cellular activities.

Ketone Bodies

Ketone bodies are produced in the liver during periods of carbohydrate deficiency or prolonged fasting.

The main ketone bodies are acetoacetate, beta-hydroxybutyrate, and acetone.

These molecules serve as alternative energy sources for tissues such as the brain and muscles.

Urea Cycle

The urea cycle is a metabolic pathway that converts toxic ammonia into urea.

This cycle occurs in the liver and helps maintain nitrogen balance in the body.

Urea produced in this cycle is excreted through the kidneys in urine.

Protein Biosynthesis

Protein biosynthesis is the process through which cells produce proteins based on genetic information stored in DNA.

The process involves transcription of DNA into mRNA followed by translation of mRNA into a sequence of amino acids.

This sequence forms a polypeptide chain that folds into a functional protein.

Enzyme Inhibition

Enzyme inhibition occurs when a molecule decreases the activity of an enzyme.

There are two main types: competitive inhibition and noncompetitive inhibition.

In competitive inhibition, the inhibitor competes with the substrate for the active site.

In noncompetitive inhibition, the inhibitor binds to a different site on the enzyme.

Synthesis of Dopamine, Noradrenaline, and Adrenaline

These neurotransmitters are synthesized from the amino acid tyrosine.

Tyrosine is first converted into DOPA, which is then converted into dopamine.

Dopamine can be further converted into noradrenaline and adrenaline.

These neurotransmitters regulate several physiological processes such as heart rate, blood pressure, and stress response.

Fatty Acid Synthesis

Fatty acid synthesis is the metabolic process through which fatty acids are produced from acetyl-CoA.

This process occurs in the cytoplasm and involves a series of enzymatic reactions.

Fatty acids produced through this pathway are used for energy storage and membrane formation.

Conclusion

Biochemistry provides a comprehensive understanding of metabolic pathways and molecular processes that sustain life. For pharmacy students, knowledge of biochemical reactions is essential because many drugs interact with enzymes, metabolic pathways, and molecular targets.

Understanding these pathways helps explain disease mechanisms and guides the development of effective therapies.