Protein synthesis - mRNA translation

What are the three main objectives of translation?

mRNA processing

What are the three main steps of protein synthesis?

Initiation

What modifications occur during mRNA processing?

5′ methyl‑G cap addition

What is the purpose of the 5′ cap?

Protects mRNA from degradation and helps ribosome binding.

What is the polyadenylation signal?

AAUAAA sequence near the 3′ end.

What is the purpose of the poly(A) tail?

Protects mRNA from degradation and regulates stability.

What removes introns?

The spliceosome.

What is alternative splicing?

Joining different combinations of exons to produce multiple protein variants from one gene.

Are eukaryotic mRNAs monocistronic or polycistronic?

Monocistronic.

Are prokaryotic mRNAs monocistronic or polycistronic?

Polycistronic.

What regulates translation and mRNA decay?

Sequence elements in the 5′ and 3′ untranslated regions (UTRs).

What is the Shine‑Dalgarno sequence?

A prokaryotic ribosome‑binding site in the 5′ UTR.

What is the role of mRNA?

Carries the genetic code for protein synthesis.

What is the role of tRNA?

Decodes mRNA codons and carries amino acids.

What is the role of rRNA?

Forms the catalytic core of the ribosome and links amino acids.

What are the three ribosomal tRNA binding sites?

A (acceptor)

What energy sources are required for translation?

ATP and GTP.

What is the genetic code?

A set of 64 codons encoding 20 amino acids and 3 stop signals.

What does “degenerate code” mean?

Multiple codons can encode the same amino acid.

What does “specific/unambiguous code” mean?

Each codon always specifies the same amino acid.

What does “universal code” mean?

The genetic code is nearly identical across organisms.

What does “non‑overlapping and comma‑less” mean?

Codons are read continuously in groups of three without gaps.

What is the start codon?

AUG (methionine).

What are the stop codons?

UAA

What is initiation?

Assembly of ribosomal subunits

What is the initiator tRNA in eukaryotes?

Met‑tRNAi.

What is the initiator tRNA in prokaryotes?

Formyl‑methionine tRNA (fMet).

What is elongation?

Sequential addition of amino acids to the growing polypeptide chain.

What enzyme forms peptide bonds?

Peptidyl transferase (28S rRNA).

What is translocation?

Ribosome movement by three nucleotides along the mRNA.

What is termination?

Release of the polypeptide when a stop codon enters the A site.

What is the eukaryotic release factor?

eRF.

What are polysomes?

Multiple ribosomes translating a single mRNA simultaneously.

Why is the prokaryotic ribosome a major antibiotic target?

Its structure differs from eukaryotic ribosomes

What do aminoacyl‑tRNA synthetases do?

Attach specific amino acids to their corresponding tRNAs.

How many aminoacyl‑tRNA synthetases exist?

20 (one per amino acid).

What is the wobble hypothesis?

Flexibility at the 5′ anticodon base allows one tRNA to recognize multiple codons.

How many tRNAs are typically needed?

About 30–40

What determines the reading frame?

The position of the start codon (AUG).

In what direction is mRNA read?

5′ to 3′.

In what direction is protein synthesized?

N‑terminus to C‑terminus.

What are post‑translational modifications?

Chemical changes to proteins after synthesis.

What is a signal peptide?

A sequence directing proteins to specific organelles or secretion pathways.

What forms disulfide bonds?

The ER

What is glycosylation?

Addition of sugars in the ER or Golgi.

What is lipidation?

Attachment of lipids to anchor proteins in membranes.

What is phosphorylation?

Addition of phosphate groups to regulate protein activity.

What is hydroxylation?

Modification of lysine and proline in collagen.

What are microRNAs (miRNAs)?

Small RNAs that repress translation or degrade mRNA.

How long are microRNAs?

21–22 nucleotides.

What is the effect of perfect miRNA base pairing?

mRNA degradation.

What is the effect of imperfect miRNA base pairing?

Translation repression.

Why are microRNAs important in medicine?

They regulate ~50% of genes and serve as biomarkers for disease.

What are siRNAs?

Synthetic RNA molecules that silence specific genes by perfect base pairing.

What do antibiotics targeting translation do?

Inhibit bacterial ribosomes without affecting eukaryotic ribosomes.

What drugs inhibit bacterial thymidine monophosphate synthesis?

Fluorocytosine and trimethoprim.

What drug inhibits HIV reverse transcription?

AZT (azidothymidine).

What drug inhibits bacterial RNA polymerase?

Rifampicin.

What cancer drugs inhibit DNA synthesis?

Fluorouridine

What cancer drug inhibits topoisomerase?

Etoposide.

What causes many cancers?

DNA damage from mutations