Translation Flashcards
What is a ribosome?
A large macromolecular machine that synthesizes proteins by using the genetic information encoded in messenger RNA. Consists of subunits, each composed of ribosomal RNA and proteins.
What is a polyribosome?
A messenger RNA molecule that is being translated by two or more attached ribosomes (group of ribosomes)
What is transfer RNA (tRNA)?
An L-shaped RNA molecule that has an anticodon at one end and an amino acid attachment site at the other. Each tRNA carries a specific amino acid and binds to the corresponding codon in messenger RNA during translation.
What is an anticodon?
The sequence of three bases (a triplet) in a transfer RNA molecule that can bind to an mRNA codon with a complementary sequence.
What is aminoacyl-tRNA synthetase?
An enzyme that catalyzes the addition of a particular amino acid to its corresponding tRNA molecule.
What is aminoacyl tRNA?
A transfer RNA molecule that is covalently bound to an amino acid.
What is ribosomal RNA (rRNA)?
An RNA molecule that forms part of the ribosome.
What is the ribosome binding site?
In a bacterial mRNA molecule, the sequence just upstream of the start codon to which a ribosome binds to initiate translation.
What is an initiation factor?
Any of a class of proteins that assist ribosomes in binding to a messenger RNA molecule to begin translation.
What is translocation?
The movement of a ribosome down a messenger RNA during translation.
What is an elongation factor?
A class of proteins involved in the elongation phase of translation, assisting ribosomes in the synthesis of the growing peptide chain.
What is a release factor?
Any of a class of proteins that trigger termination of translation when a ribosome reaches a stop codon.
- Describe the relationship between a codon and an anticodon, using the terms “mRNA,” “tRNA,” “complementary base pairing,” and “antiparallel.”
A codon is a sequence of three nucleotides found on the mRNA (messenger RNA) strand that specifies a particular amino acid in the process of protein synthesis. Each codon is matched with a corresponding anticodon on the tRNA (transfer RNA). The anticodon is a sequence of three nucleotides that is complementary to the mRNA codon
Describe the relationship between a codon and an anticodon, using the terms “complementary base pairing,” and “antiparallel.”
The relationship between the codon and the anticodon is based on complementary base pairing(stabilized by H bonds), ensures that the tRNA with the appropriate anticodon will bind to the mRNA codon during translation, allowing the correct amino acid to be added to the growing polypeptide chain.
Additionally, the codon and anticodon strands are said to be antiparallel, meaning they align in opposite directions. The mRNA is read from 5’ to 3’, while the anticodon is aligned in the opposite direction, from 3’ to 5’. This alignment is crucial for proper base pairing and accurate translation.
- Explain why it is possible that although 61 different codons specify the 20 amino acids, there are only 40 different types of tRNAs.
The genetic code = redundant, 4 codons can code for 1 amino acid
Which of the properties of the genetic code best explains why wobble pairing is feasible?
It is conservative = 1st & 2nd nucleotide stays the same in the codon & the 3rd changes when redundant
Translation
is the process of synthesizing a protein from an mRNA template.
Initiation
The small ribosomal subunit binds to the mRNA near the start codon (AUG).
A tRNA carrying the amino acid methionine (Met) and the anticodon UAC pairs with the start codon.
The large ribosomal subunit attaches, forming the complete ribosome with three binding sites: A (aminoacyl), P (peptidyl), and E (exit). The start tRNA sits in the P site.
Elongation
A new tRNA carrying the next amino acid enters the A site, matching its anticodon to the next mRNA codon.
A peptide bond forms between the amino acid in the P site and the one in the A site, starting the growing polypeptide chain.
The ribosome shifts one codon forward, moving the empty tRNA to the E site, where it exits, and the tRNA with the peptide moves to the P site.
This process repeats, adding amino acids one by one to the chain
Termination
When the ribosome reaches a stop codon (UAA, UAG, or UGA), no tRNA matches it.
Instead, a release factor binds to the stop codon, triggering the release of the polypeptide chain from the ribosome.
The ribosomal subunits separate, and translation ends
Similarities of translation in prokaryotes & eukaryotes
Same three stages: Initiation, elongation, termination.
Ribosomes: Both use ribosomes to read mRNA and assemble amino acids into proteins.
tRNA and codons: Both use transfer RNA (tRNA) with anticodons matching mRNA codons to deliver amino acids.
Polypeptide formation: Both build polypeptide chains one amino acid at a time.
Differences of Prokaryotes & Eukaryotes translation (location & timing)
Prokaryotes: Cytoplasm (no nucleus), transcription & translation occur & same location simultaneously
Eukaryotes: Cytoplasm (after mRNA leaves the nucleus), translation only occurs after transcription is complete
Differences of Prokaryotes & Eukaryotes translation (mRNA modifications)
Eukaryotes: mRNA is modified (5’ cap, splicing, poly-A tail,) before leaving the nucleus.
Prokaryotes = no modifications
