Exam 3: Lect. 17

What is the ribosome made of?

composed of a LARGE AND SMALL SUBUNIT and small subunit, each of which is composed of rRNA AND MULTIPLE PROTEINS

What occupies the different tRNA binding sites?

The A SITE of the large ribosomal subunit is occupied by the AMINOACYL-tRNA; the P SITE contains PEPTIDYL-tRNA the E SITE is occupied by the OUTGOING tRNA

What elongation factors are used in translation? What do they use to work?

EF-Tu ESCORTS AMINOACYL-tRNA INTO A site and helps ensure the proper match to the codon, thereby contributing to proofreading; EF-G STIMULATES MOVEMENT OF RIBOSOME ALONG mRNA. Both elongation factors hydrolyze GTP in order to function

Why is a ribosome called a ribozyme?

The ribosome is called a ribozyme because it is an RNA that can act as a catalyst in biochemical reactions, similar to a protein enzyme (BECAUSE IT HAS ENZYMATIC ACTIVITY AND ACTS AS A CATALYST)

What part of the ribosome is responsible for catalyzing the peptidyl transferase reaction?

The LARGE SUBUNIT is responsible for the catalysis of the peptidyl transferase reaction, which forms the peptide bonds between the amino acids in the polypeptide chain

How does the stop codon cause translation to stop?

The stop codon uses molecular mimicry to stop translation, since the RELEASE FACTORS IS SHAPED LIKE tRNA. The release factor BINDS TO A SITE; since there is no tRNA that complementary base pairs with the stop codon, the polypeptide-tRNA link is hydrolyzed

What is meant by the terms poly- and monocistronic?

POLYCISTRONIC means that the mRNA ENCODES FOR MORE THAN ONE PROTEIN. monocistronic means the mRNA molecule only encodes for a single protein (eukaryoes are monocistronic, prokaryotes are polycistronic)

What is different about how eukaryotic ribosomes find the start codon versus the way a prokaryotic ribosomes find the start codon?

In prokaryotes, the small subunit of the ribosome complementary base pairs with one of several ribosome binding sites (ex: Shine-Dalgarno sequence) that are adjacent to the start codon; in contrast, several processes must occur for eukaryotic ribosomes to

What does eIF2 do? How does it work?

(eukaryotic initiation factor) eIF2 MEDIATES THE BINDING OF tRNAmet TO TO THE RIBOSOME. eIF2 is an aminoacyl-tRNA that binds to the small ribosomal subunit, without the complete ribosome being present. (It also binds directly to the P site.) After methion

What role does the 5' CAP play in translation initiation? What recognizes the CAP?

(go over a lot) The 5' cap is identified by the small subunit after it is bound to the initiation factors eIF4E and eIF4G(proteins). After that, the small subunit scans for the first start codon(AUG). After locating the first AUG in the mRNA molecule, the

When does the large subunit of the ribosome associate with the small subunit during translation?

(study circled slide) The large subunit binds to the small subunit after the initiation factors dissociate from the mRNA (which is after the first AUG is located)

True or false: mRNAs are translated once

FALSE mRNAs can be translated multiple times before they are degraded, especially in bacteria, where multiple ribosomes can bind to the ribosome binding sequences located throughout the whole mRNA molecule