L6- Protein Synthesis Flashcards Preview

Biochemistry Exam 1 > L6- Protein Synthesis > Flashcards

Flashcards in L6- Protein Synthesis Deck (36):
1

What subunits make up a eukaryotic ribosome?

60S and 40S.

2

What is the sedimentation coefficient of eukaryotic ribosomes?

80S.

3

Where are ribosomes usually found in the cell?

In the cytoplasm or attached to the endoplasmic reticulum.

4

What is the fate of proteins synthesized by ribosomes on the endoplasmic reticulum?

They are either exported from the cell or become part of the cellular membrane.

5

What is a codon?

A trinucleotide sequence of mRNA that determines which amino acid is added to a nascent protein during translation.

6

What is the sequence of the start codon?

AUG.

7

The start codon codes for which amino acid?

Methionine.

8

What are the sequences of the stop codons?

UAA, UAG, and UGA.

9

In which direction does a ribosome read RNA?

From 5' to 3' (the same direction as nucleic acid synthesis by DNA and RNA polymerases).

10

What is a peptide bond?

A covalent bond between an amino group of one molecule and the carboxyl group of another. Peptide bonds are formed between amino acids during protein synthesis.

11

What is the Wobble Hypothesis?

There are fewer tRNAs than codons. It was proposed that the 3’ end of the codon allows for a more relaxed bonding with the 5’ base of the anticodon. The potential for non-Watson-Crick base pairing at this position allows a single tRNA to pair with several different codons.

12

What class of enzymes activate and attach amino acids to their respective tRNAs?

Aminoacyl tRNA synthetases.

13

What are the three sites on ribosomes that interact with tRNAs during elongation of a peptide?

A, P and E sites.

14

What is the purpose of elongation factors?

Elongation factors (EF) position amino acyl-tRNAs on the ribosome and promote RNA translocation.

15

What is monocistronic mRNA?

mRNA that will code for only one polypeptide sequence. With very few exceptions, eukaryotic mRNA is monocistronic. Bacteria, on the other hand, frequently have polycistronic messages.

16

In bacteria, the region of the 3’ terminus of the 16S ribosomal RNA is complementary to the _______ (which sequence).

Shine-Dalgarno Sequence. This is the ribosome binding site on the mRNA. In eukaryotes the equivalent sequence is known as the Kozak sequence.

17

What is a missense mutation?

A single base substitution in which one amino acid replaces another.

18

What is a nonsense mutation?

A change in a codon that converts it to a stop codon, leading to premature termination of translation.

19

What is a frameshift mutation?

A mutation that causes the codons to be read out of frame, thereby leading to a misinterpretation of mRNA.

20

What is the sedimentation coefficient of bacterial ribosomes?

70S.

21

What is translation?

The process by which an mRNA template is used to synthesize a polypeptide chain.

22

Every tRNA has a ____ sequence at its 3' end.

CCA.

23

What kind of bond links the carboxyl group of an amino acid to the 3' CCA sequence of a tRNA molecule?

An ester bond.

24

What is an aminoacyl-tRNA?

A tRNA molecule bound to its corresponding amino acid.

25

What is an anticodon?

A tRNA trinucleotide sequence that is complementary, and therefore binds to, an mRNA codon.

26

What is the first tRNA binds to the small ribosomal subunit?

Met-tRNA (note that is binds regardless of whether or not there is a codon for methionine).

27

Which initiation factor is required for the initiator tRNA (Met-tRNA) to bind to the small ribosomal subunit in eukaryotes?

eIF2 (along with GTP).

28

To which binding site does the initiator tRNA (Met-tRNA) bind to on the ribosome?

It binds directly to the P site.

29

True or False. Interaction of the eIF2-GTP-Met-tRNA complex with the 40S ribosomal subunit must occur in the presence of mRNA.

False. It typically occurs in the absence of mRNA.

30

What is the function of eIF2 during translation?

It binds the 40S subunit to tRNA.

31

What happens to eIF2 when the anticodon of the initiator tRNA matches the AUG start codon?

GTP is hydrolyzed, allowing eIF2 to dissociate from the ribosome and the 60S subunit to bind to the 40S subunit.

32

Which elongation factor is required for tRNA to bind to the A site of the ribosome?

EF1.

33

Which elongation factor is required for translocation of tRNA from the A site to the P site of the ribosome?

EF2.

34

Which enzyme is thought to catalyze the nucleophilic attack on the carbonyl group of the peptidyl-tRNA by the amino group of the aminoacyl-tRNA? Where does this reaction occur on the ribosome?

The enzyme is peptidyl transferase and it occurs in the A site of the ribosome.

35

What is the function of the soluble protein called termination factor?

It promotes the cleavage of the polypeptide chain from the tRNA in the P site, releasing the mRNA from the ribosome.

36

What is the shape of a typical tRNA?

Cloverleaf.