Protein Synthesis: Detailed Overview

Key Components

• Replication, Transcription and Translation

  • Require direction from 5' to 3' direction.

• RNA and mRNA

  • New RNA nucleotides are added to the 3' end.
  • In translation, ribosomes move from 5' to 3'.

Genes and Their Role

• Genes

  • Segments of DNA coding for proteins.

• Promoter

  • Binding site for RNA polymerase or transcription factors.
  • Does not get transcribed; an example of non-coding regions.

Types of Non-coding Base Sequences

• tRNA and rRNA

  • Important but not polypeptides.

• Promoters and Telomeres

  • Structural DNA, non-coding.

• Introns and Exons

  • Introns are edited out post-transcription.
  • Exons are spliced together to form mature mRNA.

Transcription and Translation Process

• Prokaryotic vs Eukaryotic Cells

  • Prokaryotes: Transcription and translation occur simultaneously.
  • Eukaryotes: Compartmentalization allows post-transcriptional modification.

• Post-transcriptional Modifications

  • Introns are removed; exons are spliced.
  • 5' cap and poly-A tail are added to form mature mRNA.
  • Allows for alternative splicing and protein diversity from the same gene.

Translation Details

• tRNA Activation

  • Requires tRNA activating enzyme and ATP.
  • Amino acids attach to tRNA's 3' end.

• Ribosome Function

  • Small ribosome subunit finds start codon (AUG) on mRNA.
  • Large subunit attaches, beginning translation (initiation phase).

Post-translation Modifications

• Protein Maturation

  • Polypeptides fold into functional proteins.
  • May involve removal of amino acids and formation of disulfide bonds (as in insulin).

• Protein Life Cycle

  • Proteins have short lifespan and are recycled.
  • Proteasomes break proteins into amino acids for reuse.

Key Enzymes and Assistance

• Enzymes

  • RNA polymerase initiates transcription.
  • tRNA activating enzyme for amino acid attachment.
  • Proteasomes for protein breakdown.

• Energy Requirement

  • ATP needed for enzyme activities and protein synthesis/recycling.