Question

Explain the "Lock and Key" mechanism of enzyme action or the Central Dogma of molecular biology.

Hint:

Two memory aids:

• Lock and Key = Enzyme specificity
• Central Dogma = DNA $\rightarrow$ RNA $\rightarrow$ Protein

Structure determines function in biology.

Answer 1

(A) Lock and Key Mechanism of Enzyme Action:
Concept: The lock and key model explains how enzymes interact specifically with substrates to catalyze biochemical reactions.
Explanation:

• Proposed by Emil Fischer.
• The enzyme has a specific active site.
• The substrate fits exactly into this active site like a key fits into a lock.

Steps:

• Substrate binds to enzyme's active site.
• Enzyme-substrate complex is formed.
• Reaction occurs and products are formed.
• Products are released; enzyme remains unchanged.

Key Features:

• High specificity
• Enzyme not consumed in reaction
• Explains substrate selectivity

(OR)
(B) Central Dogma of Molecular Biology:
Concept: The central dogma explains the flow of genetic information in living organisms.
Statement: \[ \text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein} \]
Steps:
1. Replication:

• DNA makes an identical copy of itself.
• Ensures genetic continuity.

2. Transcription:

• DNA is transcribed into messenger RNA (mRNA).
• Occurs in nucleus (eukaryotes).

3. Translation:

• mRNA is translated into protein at ribosomes.
• Amino acids are assembled into polypeptide chains.

Importance:

• Explains gene expression
• Basis of molecular genetics
• Foundation of biotechnology