Biochemistry Lecture 6 - Protein Synthesis

Question 1

What are the three stages of protein synthesis?

Answer 1

Initiation, elongation, termination

Question 2

What are the ribunucleoprotein particles that synthesize proteins called?

Answer 2

Ribosomes

Question 3

What are the eukaryotic rRNA sedimentation coefficients (small, large, total)?

Answer 3

60S, 40S, 80S for entire combined unit

Question 4

Which three small ribosomal RNA subunits associate with the large eukaryotic ribosomal subunit?

Answer 4

28S, 5.8S, 5S.

Question 5

Which small subunit associates with the small eukaryotic ribosomal subunit?

Answer 5

18S

Question 6

What is meant by redundancy of the genetic code?

Answer 6

More than one codon codes for an AA

Question 7

What two molecules initiate translation?

Answer 7

The special met-tRNA binds to the small 40S SUBUNIT first during initiation

Question 8

What is tRNA’s purpose in translation?

Answer 8

It acts as an adapter between the mRNA and the AAs.

Question 9

What is the tRNA folding pattern?

Answer 9

Cloverleaf

Question 10

How many bases comprise a tRNA and what kind of bases are they?

Answer 10

76-80 bases. The bases are “unusual.”

Question 11

What two purposes does linking the AA to the tRNA serve? Which end does the AA attach to?

Answer 11

1. It attaches the AA to the corresponding tRNA
2. It “energizes” the AA
   The AA is attached to the 3’ OH end of the tRNA

Question 12

What enzyme catalyzes the AA to AMP linkage?

Answer 12

Aminoacyl tRNA synthetases.

Question 13

What is the wobble hypothesis?

Answer 13

It is the idea that the third base of the anticodon is relaxed and can base pair with other atypical bases.

Question 14

Describe the initiation process of translation (including when enzymes come in and bone out).

Answer 14

The Met-tRNA complex binds to a protein eIF-2 and GTP forming a ternary complex (eIF2-GTP-mettRNA). This complex binds to the 40S subunit. Then more initiation proteins, notably eIF4F come in, and the 40S complex binds to mRNA. The 40S complex moves from 5’ to 3’ looking for the start codon. Once the start codon is found, eIF2 is released and the 60S subunit comes in.

Question 15

After the 40S complex with its associated proteins and tRNA find the start codon, what position is the met-tRNA in (P, S, or E)? What is the start codon?

Answer 15

Start codon is AUG. The met-tRNA is in the P site upon location of the start codon.

Question 16

On which end of the tRNA is the end that the peptide bonds are formed?

Answer 16

The 3’ OH end.

Question 17

What protein is required to place incoming aminoacyl-tRNAs on the ribosome? Does the step require energy?

Answer 17

EF1 (very abundant in eukaryotes!). GTP is hydrolyzed in this step.

Question 18

What protein is required for translocation? Does this step require energy?

Answer 18

EF2. This step hydrolyzes GTP.

Question 19

To which site is the nascent peptide chain transferred after peptide bond formation?

Answer 19

A site.

Question 20

What enzyme catalyzes peptide bond formation and where does it come from?

Answer 20

Peptidyl transferase is the enzyme and its a component of the 28S RNA.

Question 21

What are the three stop codons?

Answer 21

UAA, UAG, UGA

Question 22

What factors are involved in termination (stop recognition, and ester bond hydrolysis)?

Answer 22

Release factor (RF1 or RF2) recognize the stop codon and RF3 catalyzes hydrolysis of the ester bond.

Question 23

How close can polyribosomes be on a mRNA?

Answer 23

80 nts.

Question 24

What is another term for base substitution? What can it result in?

Answer 24

AKA point nt mutation. Can result in a missense mutation (single AA replacement).

Question 25

What is a nonsense mutation?

Answer 25

A nt mutation that results in the generation of a termination signal.

Question 26

What is a missense mutation?

Answer 26

A nt mutation that results in a single AA replacement.

Question 27

How can missense mutations affect splice sites?

Answer 27

They can generate cryptic splice sites.

Question 28

During periods of stress like AA starvation, what is one way a cell halts translation?

Answer 28

The cell will phosphorylate EIF2, which is the inactive state of the protein. This prohibits 40S-tRNA from combining.

Question 29

What is an IRES? What does it do?

Answer 29

Internal ribosome entry site. It is a viral component that recruits the pre-initiation complex to the start codon of viral RNA in a 5’ cap independent manner.

Question 30

Is protein synthesis important for learning and memory?

Answer 30

Protein synthesis is very important for learning and memory!