Translation quiz #1 Flashcards
Translation quiz #1
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What are the main steps of translation in eukaryotic cells, and what roles do the ribosomal subunits play during this process?
Translation in eukaryotic cells begins with the small ribosomal subunit and initiator tRNA binding to the 5' end of mRNA, scanning for the start codon (AUG). Once found, the large subunit joins to form a complete ribosome. During elongation, tRNAs bring amino acids to the ribosome, which are added to the growing polypeptide chain as the ribosome moves along the mRNA. The large subunit catalyzes peptide bond formation, while the small subunit ensures correct tRNA-mRNA pairing. Translation ends when a stop codon is reached, and release factors help release the new protein and dissociate the ribosome. How does translation initiation differ between prokaryotic and eukaryotic cells?
In eukaryotic cells, translation initiation requires the ribosome to bind to the 5' cap of the mRNA and scan for the start codon. In prokaryotic cells, mRNAs lack a 5' cap; instead, the ribosome binds to a specific sequence called the Shine-Dalgarno sequence near the start codon. Additionally, prokaryotic ribosomes are smaller and are targeted by certain antibiotics that do not affect eukaryotic ribosomes. What are the three main sites on the ribosome involved in translation, and what is the function of each site?
The A site is where tRNA recognizes the codon, the P site is where the amino acid is added to the polypeptide chain, and the E site is where the tRNA exits the ribosome. During translation initiation in eukaryotes, what is the role of the small ribosomal subunit and the initiator tRNA?
The small ribosomal subunit binds to the initiator tRNA and then to the 5' end of the mRNA, scanning for the start codon (AUG) before the large subunit joins. How does the ribosome move along the mRNA during elongation, and what happens to the tRNAs?
The ribosome moves three nucleotides (one codon) at a time along the mRNA, with tRNAs entering at the A site, moving to the P site, and exiting at the E site. What is the function of elongation factors like EF-2 during translation?
Elongation factors such as EF-2 assist the ribosome in moving along the mRNA and help tRNAs bind to the mRNA, often using energy from GTP hydrolysis. How is translation terminated, and what role do release factors play?
Translation ends when a stop codon is reached; release factors hydrolyze a water molecule to release the new protein and dissociate the ribosome from the mRNA. What is the main difference in translation initiation between prokaryotic and eukaryotic cells?
Eukaryotic ribosomes bind to the 5' cap of mRNA and scan for the start codon, while prokaryotic ribosomes bind to the Shine-Dalgarno sequence near the start codon. Why are prokaryotic ribosomes targeted by certain antibiotics but not eukaryotic ribosomes?
Prokaryotic ribosomes are slightly smaller and structurally different from eukaryotic ribosomes, allowing some antibiotics to specifically inhibit prokaryotic translation. What are polyribosomes (polysomes), and how do they increase the efficiency of protein synthesis?
Polyribosomes are clusters of ribosomes translating a single mRNA simultaneously, allowing multiple copies of a protein to be made quickly from one mRNA transcript.
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