Protein Synthesis

Question 1

what is the central dogma of molecular biology?

Answer 1

DNA-RNA-Protein

Question 2

What is a UTR

Answer 2

Untranslated region near the beginning of the mRNA, they are exons.

Question 3

what does the 5’ UTR do?

Answer 3

determines the rate at which the protein is synthesized

Question 4

what does the 3’ UTR do?

Answer 4

affects the stability of the RNA. (how long it can stay in the cell without being degraded)

Question 5

How many possible codons are there?

Answer 5

64

Question 6

How many types of ribosome are there?

Answer 6

2
one is bound to the ER
one is free in the cytosol

Question 7

where in the ribosome does protein synthesis happen?

Answer 7

the cleft of the ribosome

Question 8

What are the Ribosomal subunits?

Answer 8

60S subunit and 40S subunit which combined make up 80S ribosome

Question 9

describe initiation

Answer 9

→ cap binding protein associates with the cap and the poly A binding protein associates with the poly A tail.

→initiation factors assemble on the small subunit and have GTP bound to it.

→a met-tRNA binds to the peptidyl binding site on the small ribosomal subunit.

→the small subunit binds to the 5’ cap of the mRNA and the ribosome moves along until it finds the AUG start codon which is next to a kozak sequence.

Question 10

what happens once the start codon is found?

Answer 10

→60S binds to 40S forming complete 80S ribosome.
→EIF2 hydrolyzes the GTP to form GDP and releases pyrophosphate.
→All EIFs are released from the ribosome.

Question 11

What do viruses do that prevent antiviral proteins from being made?

Answer 11

inactivate EIF3 and EIF4

Question 12

what is the enzyme that moves the amino acid in the P site to the A site?

Answer 12

peptidyl transferase

Question 13

describe elongation

Answer 13

→ tRNA with the next amino acid comes to the A site which involves elongation factor 1

→when the covalent bond forms between methionine and the next amino acid, peptidyl transferase moves the amino acid in the P site to the A site

→ the tRNA on the P site is now empty

→the tRNA in the A site has both amino acids attached to it.

→P site tRNA now moves to the E site so it can go and get recharged so a new tRNA can enter the A site.

Question 14

what is translocation and what does it require?

Answer 14

→tRNAs moving from the A & P sites to the P & E sites respectively.
→uses up one GTP
→ the enzyme translocase and EF2.

Question 15

what enzyme recharges tRNA?

Answer 15

→aminoacyl tRNA synthase

Question 16

what is produced when tRNA is recharged

Answer 16

→AMP and pyrophosphate

Question 17

what is a polysome?

Answer 17

→when multiple ribosomes are attached to one piece of RNA

Question 18

what is termination?

Answer 18

→ribosome reaches the stop codon the release factor recognizes it
→using GTP it hydrolyzes the bond holding tRNA to the peptide chain.

Question 19

how energetically expensive is initiation?

Answer 19

→GTP and nATP

Question 20

how energetically expensive is elongation?

Answer 20

→2 GTPs

Question 21

how energetically expensive is termination?

Answer 21

→1 GTP

Question 22

how energetically expensive is charging tRNA?

Answer 22

→1 ATP

Question 23

why do antibiotics work on bacteria?

Answer 23

they have different ribosomes than humans 70S so they can be targeted without damaging human ribosomes.

Question 24

What is the name of the eukaryotic initiation factor that binds to the 40S subunit at the beginning of initiation, and what is its purpose?

Answer 24

EIF3, and it’s there to prevent the association of the 40S subunit with the 60S subunit.

Question 25

What does translocase do?

Answer 25

It aids in the movement of met-tRNAis between sites in the ribosomal subunit.

Question 26

what is synonymous alteration in genes?

Answer 26

when a nucleotide changes in the chain, but the coding remains the same.

Question 27

what are the two subunits of a ribosome called, and what rRNA (and proteins) are they made up of?

Answer 27

→The ribosome is split into two subunits,

→smaller 40S subunit, and a larger 60S subunit.

→The 40S is made up of 18S rRNA (and 33 proteins), →60S is made up of 5S, 5.8S and 28S rRNA (and 49 proteins).

Question 28

what are the three sites in the ribosome called?

Answer 28

→Aminoacyl tRNA binding site
→ Peptide binding site
→ Exit
(APE)

Question 29

describe the three stages of protein synthesis

Answer 29

→INITIATION: assembly of the ribosome on mRNA together with the first initiator tRNA
→ aminoacyl tRNA (met-tRNAi)

→ELONGATION: charged tRNAs are delivered to the ribosome, and the amino acids are added one at a time, building the polypeptide

→TERMINATION: a stop codon is encountered, which signals the end of protein synthesis and the release of the polypeptide

Question 30

what is EIF3 and what is it for?

Answer 30

→ eukaryotic initiation factor

→prevent the association of the 40S subunit with the 60S subunit.

Question 31

what attaches to the met-tRNAi before it settles into one of the sites?

Answer 31

→EIF2 and GTP

Question 32

what is the 48S initiation complex?

Answer 32

→40S ribosomal subunit
→EIF3
→met-tRNAi
→EIF2 
→GTP

Question 33

what happens when a start codon is found?

Answer 33

→EIF3 dissociates
→GTP gets hydrolyzed along with it
→releasing energy that allows the 60S subunit to join the complex

Question 34

what are the components of a prokaryotic ribosome?

Answer 34

→70S ribosome
→50S and 30S subunits

→50S: 23S and 5S rRNA (31 proteins)
→30S: 16S (21 proteins)

Question 35

what are the components of a eukaryotic ribosome?

Answer 35

→80S ribosome
→60S and 40S subunits

→60S: 5S, 5.8S and 28S (49 proteins)
→40S: 18S (33 proteins)

Question 36

what does streptomycin do?

Answer 36

inhibits the initiation misreading of the genetic code