Gene Expression and Regulation Quiz

Gene Expression and Regulation

• Gene expression is the process by which information from a gene is used to synthesize a functional gene product, typically a protein.
• Gene regulation is the process of controlling the expression of genes.
• Gene regulation is crucial for responding to environmental changes, cell differentiation, and development.

mRNA Processing

• Pre-mRNA undergoes several processing steps to become mature mRNA:
  • 5' capping: A 7-methylguanosine cap is added to the 5' end for protection and ribosome binding.
  • 3' polyadenylation: A string of adenine nucleotides (poly(A) tail) is added to the 3' end for stability.
  • Splicing: Introns (non-coding regions) are removed, and exons (coding regions) are joined together.
• mRNA is then exported from the nucleus and transported to the cytoplasm.

Translation

• Translation is the process of protein synthesis.
• It involves decoding the mRNA sequence into a polypeptide chain.
• Ribosomes, tRNAs, and amino-acyl tRNAs are involved in the process.
• Ribosome has three binding sites (E, P, and A) where tRNAs bind during translation.

Translation Initiation (Prokaryotes)

• Initiation factors (IF1, IF2, IF3) bind to the 30S subunit.
• mRNA and initiator methionyl-tRNA (fMet-tRNA) bind to the complex.
• The 50S subunit joins to form a complete 70S ribosome.

Translation Initiation (Eukaryotes)

• Eukaryotic mRNAs have a 5' cap that's recognized by initiation factors to bind to 40S subunit.
• Small ribosomal subunit scans along the mRNA until it reaches the AUG codon.
• Methionyl tRNA is then attached to create the initiator complex.
• The large subunit joins to form a 80S ribosome complex.

Translation Elongation

• Aminoacyl-tRNA binds to the A site.
• Peptide bond formation between the amino acids on the tRNAs at the P and A sites.
• The ribosome translocates along the mRNA, shifting the tRNAs from the A and P sites to the E and P sites, respectively.
• The uncoupled tRNA is released from the E site.

Translation Termination

• A stop codon is reached on the mRNA.
• Release factors bind to the A site. -The polypeptide chain is released.
• Ribosome dissociates.

Components of translational process

• Amino-acyl tRNA: carries amino acids to the ribosome.
• Ribosome: translates mRNA into protein.
  • Ribosome large subunit and small subunit.
• mRNA: carries genetic information from DNA to ribosome
• GTP: an energy source.
• Protein factors: help facilitate various steps of translation.

tRNA Structure and Synthesis

• tRNAs are small RNA molecules with a cloverleaf shape.
• They have an anticodon that base-pairs with the mRNA codon.
• tRNAs are aminoacyl-tRNA-synthetase-specific.
• Transfer of an amino acid to tRNA is catalyzed by aminoacyl-tRNA synthetases.

Ribosome Structure

• Ribosomes are composed of rRNA and ribosomal proteins.
• Prokaryotes have 70S ribosomes (50S + 30S subunits).
• Eukaryotes have 80S ribosomes (60S + 40S subunits).
• The structure of rRNA is critical for its catalytic function (peptidyl transferase).

Control of Gene Expression

• Regulation at different levels (transcription, processing, translation).
• Prokaryotes use operons for transcription regulation.
• Eukaryotes use chromatin structure and transcription factors to regulate gene expression.
• Post-transcriptional control can also occur at different stages.

Online resources

• Useful links to supplementary websites and educational videos for further learning about the topic.