Protein Synthesis in Medical Biology

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17 Questions

What is the function of the peptidyl (P) tRNA binding site in the ribosome during protein synthesis?

Binds peptidyl-tRNA (tRNA that is attached to growing oligopeptide)

In which direction does the ribosome read mRNA during protein synthesis?

5'->3' direction

What is the central dogma of molecular biology regarding protein synthesis?

One gene – one protein

Where does translation of mRNA begin in prokaryotes?

Before transcription has finished

During protein synthesis, what event causes termination?

Addition of a water molecule to the carboxyl terminus of the nascent polypeptide

What is the role of a release factor during termination of protein synthesis?

It promotes dissociation of the ribosomal complex

Which modification can occur during posttranslational processing of peptides?

Attachment of prosthetic groups

What happens to uncharged tRNA during protein synthesis?

It is translocated from the P site to the E site

What occurs when a stop codon occupies the A site during protein synthesis?

Promotion of ribosomal complex dissociation

What is responsible for transferring the growing polypeptide chain from tRNA in the P site to tRNA in the A site?

Peptidyl-transferase

What signals termination in protein synthesis?

Recognition of a stop codon by a release factor

During which stage of protein biosynthesis are peptide bonds formed between amino acids?

Elongation

Where does the activation of amino acids occur?

In the cytoplasm

In prokaryotes, which molecule forms part of the initiation complex for protein synthesis?

$30S$ ribosomal subunit

What is the role of eIF4F in eukaryotic initiation complex formation?

Binds to the 5' cap and associates with the poly(A) binding protein

What happens during termination in protein biosynthesis?

$70S$ ribosome dissociates from mRNA

What is the role of tRNA in protein biosynthesis?

Carrying amino acids to the ribosome

Study Notes

  • Transfer RNA (tRNA) forms attachments to individual amino acids and recognize the encoded sequences of mRNAs for correct insertion into elongating polypeptide chains.
  • Ribosomal RNA (rRNA) assembles with ribosomal proteins to form ribosomes, which engage mRNAs and create a catalytic domain for tRNAs to enter with their attached amino acids.
  • Protein biosynthesis occurs in five stages: 1) activation of amino acids, 2) initiation, 3) elongation, 4) termination, and 5) folding and posttranslational processing.
  • Activation of amino acids requires the carboxyl group to be activated for peptide bond formation and a link to the mRNA.
  • Activation of amino acids occurs off the ribosome through the action of aminoacyl tRNA synthetases, which attach amino acids to specific tRNAs.
  • Initiation is the process of starting protein synthesis and involves the formation of the initiation complex.
  • In prokaryotes, the initiation complex forms with the ribosome 30S unit, mRNA, and N-formyl methionyl-tRNA.
  • Eukaryotic initiation complex forms with elF1, elF2, elF3, eIF4, and eIF5.
  • Elongation is the stage in which peptide bonds are formed between amino acids.
  • Incoming aminoacyl-tRNAs bind to the ribosome's A site, and the ribosome translocates one codon towards the 3' end of the mRNA.
  • A peptide bond is formed between the amino acids bound by their tRNAs to the A and P sites on the ribosome.
  • The genetic code is redundant, meaning multiple codons can specify a single amino acid, but not ambiguous, as no codon specifies more than one amino acid.
  • The ribosome does not bind at the AUG start codon but upstream at the Shine-Dalgarno sequence.
  • In eukaryotic cells, mRNAs are bound to ribosomes as a complex with specific binding proteins.
  • Eukaryotic cells have at least nine initiation factors, including the eIF4F complex, which binds to the 5' cap and associates with the poly(A) binding protein.
  • Elongation in eukaryotic cells involves the binding of incoming aminoacyl-tRNAs at the ribosome's A site, formation of a peptide bond, and translocation of the ribosome.
  • During termination, a release factor binds to the ribosome, causing the ribosome to dissociate from the mRNA and release the completed polypeptide.
  • Posttranslational processing includes folding and modification of the polypeptide chain, often catalyzed by various enzymes.

Test your knowledge of protein synthesis in medical biology with this quiz. Explore the components of the ribosome, the site of protein synthesis, and the central dogma of one gene-one protein.

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