Gene expression is the process through which the information in DNA is converted into a functional product, usually a protein. Not all genes are active at the same time. Depending on the cell’s needs, some genes are turned “on,” while others remain “off.” Understanding gene expression helps explain how cells grow, divide, differentiate, and respond to the environment.
Steps in Gene Expression
1. Transcription
Transcription is the first step in gene expression. During this process, the DNA sequence of a gene is copied into a molecule called messenger RNA (mRNA).
Key Steps in Transcription
- RNA polymerase binds to the promoter region
- DNA unwinds and exposes the template strand
- RNA polymerase adds complementary RNA nucleotides
- A complete mRNA strand is formed
The newly formed mRNA then leaves the nucleus and enters the cytoplasm.
2. RNA Processing
Before mRNA is used to make a protein, it undergoes several modifications:
- 5′ cap addition – protects mRNA and helps ribosome binding
- 3′ poly-A tail – increases mRNA stability
- Splicing – removes introns and joins exons
3. Translation
Translation is the process where mRNA is decoded to build a protein. It occurs on ribosomes present in the cytoplasm or attached to rough ER.
Main Components
- mRNA – provides the codon sequence
- tRNA – carries amino acids to the ribosome
- Ribosomes – read codons and join amino acids
Steps in Translation
- Ribosome binds to mRNA
- tRNA brings the correct amino acids
- Amino acids join to form a polypeptide chain
- Process continues until a stop codon is reached
The final product is a protein with a specific structure and function.
Gene Regulation
Gene expression must be controlled so that the right proteins are made at the right time.
Levels of Gene Regulation
- Transcriptional control: regulates when a gene is turned on
- Post-transcriptional control: mRNA processing and stability
- Translational control: regulates how efficiently mRNA is used
- Post-translational control: protein folding, modification, and activation
Factors That Influence Gene Expression
- Environmental factors: temperature, nutrients, chemicals
- Developmental stage: embryo vs. adult
- Cell type: nerve cells express different genes than muscle cells
- Hormones and signals: activate specific pathways
Importance of Gene Expression
- Controls cell structure and function
- Allows cells to respond to stress and environmental changes
- Essential for growth and development
- Explains differences between cell types
- Helps understand disorders caused by abnormal gene activity
Examples of Gene Expression in Daily Life
- Production of insulin in pancreatic cells
- Melanin formation in skin cells
- Antibody production in immune cells
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