EXER 6: GENE REGULATION

Transcription and Translation – Gene Action

✓ Only if they need to produce gene products.

✓ Depends on the type of cell and developmental stage.

Central Dogma

• Control the timing, location, and amount of gene expression.

• Occurs in both prokaryotic and eukaryotic organisms.

• Helps conserve energy by producing proteins only when needed.

1. Cellular differentiation

2. Metabolic efficiency

3. Response to environment

4. Disease prevention

Gene Regulation: Importance (4)

Allows stem cells to develop into specialized cells.

Metabolic Efficiency

Prevents unnecessary energy expenditure.

Response to Environment

Enables organisms to adapt to changes.

Disease Prevention

Abnormal regulation can lead to diseases like cancer (oncogenes)

Prokaryotic

Organization:

• Genes often grouped into operons

Eukaryotic

Organization:

• Genes are individually regulated

Prokaryotic

Transcription & Translation

• Occur simultaneously in the cytoplasm

Eukaryotic

Transcription & Translation

• Transcription in nucleus; translation in cytoplasm

Prokaryotic

RNA processing:

• NONE, mRNA is directly translated after transcription

Eukaryotic

RNA processing:

• mRNA undergoes splicing (removal of introns), capping, and polyadenylation before translation.

Regulation

Regulation:

• Primarily at the transcriptional level using repressors and activators.

Regulation

Regulation:

• Multi-level: ex. post-transcriptional and post-translational.

1. Constitutive enzymes

2. Inducible enzymes

Two main types of enzymes based on their synthesis and expression:

Constitutive enzymes

produced constantly, regardless of environmental conditions.

Inducible enzymes

synthesized only when needed, in response to specific conditions or substrates.

Operon

• Functional unit of DNA that contains a cluster of genes regulated together.

• Allows coordinated expression of genes with related functions.

Regulatory gene

codes for a repressor protein that can bind to the operator to regulate the operon's activity.

Promoter

RNA polymerase binding site to initiate transcription.

Operator

Regulatory DNA sequence located near or within the promoter. Acts as binding site for a repressor proteinq

1. Regulatory gene

2. Promoter

3. Operator

4. Structural genes

5. Terminator

Components of an Operon (5)

Structural genes

Actual genes within the operon that encode proteins needed for a specific function.

Terminator

Signals the end of transcription

Lac Operon (Inducible System)

Found in E. coli, regulates lactose metabolism.

LacZ

Codes for β-galactosidase, which breaks down lactose into glucose and galactose + converts lactose into allolactose (inducer).

LacY

Codes for lactose permease, which transports lactose into the cell.

LacA

Codes for thiogalactoside transacetylase (function not well understood).

1. LacZ

2. LacY

3. LacA

Key genes in lac operon (3)

No lactose

__ → LacI repressor binds to the operator → No transcription.

Lactose is present

___ → binds to the repressor → inactivates repressor → transcription proceeds

1. β-Galactosidase

2. Lactose Permease

Lac operon products (2)

β-Galactosidase

Breaks down lactose into glucose and galactose.

Lactose Permease

Helps transport lactose into the cell.

Trp Operon (Repressible System)

Found in E. coli, regulates tryptophan biosynthesis.

Tryptophan

__ is an essential amino acid, which is needed for protein synthesis and other metabolic processes

1. trp E

2. trp D

3. trp C

4. trp B

5. trp A

Key genes in trp operon (5)

1. trp E

2. trp D

3. trp C

4. trp B

5. trp A

Encode enzymes for tryptophan synthesis

Anthranilate synthetase

encoded by trpE and trpD

Anthranilate synthetase

catalyzes the first two steps in the tryptophan pathway, converting chorismic acid into anthranilate

Indole-3-glycerol phosphate synthase

encoded by trpC

Indole-3-glycerol phosphate synthase

catalyzes the next two steps in the pathway, converting anthranilate into indole-3-glycerol phosphate.

Tryptophan synthase

catalyzes the final step, converting indole-3-glycerol phosphate and serine into tryptophan.

Tryptophan synthase

encoded by trpA and trpB

Trp operon products

Enzymes for tryptophan biosynthesis, ensuring amino acid availability

Low tryptophan

__ → operon is active to synthesize more tryptophan

High tryptophan

__ → it binds to the TrpR repressor → activating repressor → transcription is blocked

Differentiation

process by which cells specialize into distinct types.

1. Transcription factors

2. Epigenetic modifications

3. Non-coding RNAs

Regulatory Mechanisms of Differentiation (3)

Transcription factors

activate or repress specificmgenes to drive differentiation.

Epigenetic modifications

alter gene expression without changing DNA sequence.

Non-coding RNAs

play roles in post-transcriptional regulation.

Experimental Procedure to Monitor Gene Products

• Collecting samples at different developmental stages.

• Extracting proteins from cells.

• Using gel electrophoresis to separate proteins and detect expression levels of isozymes

Tissue-Specific LDH Patterns

Distinct metabolic profiles since DH5 dominates in skeletal muscle and retina (anaerobic metabolism), while LDH1 is prevalent in the heart and brain (aerobic metabolism)