Genetics Lecture 5

Question 1

Name three features of the genetic code.

Answer 1

Triplet, continuous, and redundant.

Question 2

Is the genetic code universal?

Answer 2

Nearly.

Question 3

What is the start codon, and what does it code for?

Answer 3

AUG - modified methionine.

Question 4

Name the 3 stop codons, and what they code for.

Answer 4

UAA
UGA
UAG
They dont code for an amino acid.

Question 5

What structure is tRNA made of?

Answer 5

RNA forming 3 hairpin loops.

Question 6

Where is the anticodon found in tRNA?

Answer 6

Loop 2.

Question 7

There are 64 codons, but only 20 amino acids. How can this be? Name the theory name.

Answer 7

Base-pair wobble
First two codons will always be complimentary. The third anticodon is a special nucleotide allowing it to bind to more than one nucleotide.

Question 8

How many enzymes are there for tRNA? What is the enzymes name? What does it do, and where does it get its energy?

Answer 8

20 amino acyl tRNA synthetases - attaches a tRNA to its appropriate amino acid, using energy from ATP hydrolysis.

Question 9

What are the two prokaryotic ribosomal subunits? Which rRNA attaches to each?

Answer 9

Large 50S - 23S and 5S rRNA attaches

Small 30S - 16S rRNA attaches

Question 10

Where are ribosomes made in eukaryotes?

Answer 10

Nucleolus, exported to the cytosol.

Question 11

Which RNA is the most abundant?

Answer 11

rRNA.

Question 12

What are the three ribosomal sites?

Answer 12

A site - aminoacyl-tRNA site
P site - peptidyl binding site
E site - exit site

Question 13

What does translation initiation require?

Answer 13

GTP

Question 14

What aligns the ribosome with the initiation codon?

Answer 14

Shine-Dalgarno sequence.

Question 15

Which prokaryotic ribosomal subunit is the Shine-Dalgarno sequence complimentary to?

Answer 15

16S rRNA of the small 30S.

Question 16

Describe the steps of initiation of translation.

Answer 16

30S binds to the mRNA, with a GTP molecule. Initiator tRNA binds to the AUG sequence on mRNA.
50S hydrolyses GTP, binding it to 30S, forming 70S.
Initiator tRNA binds to the P site.

Question 17

After translation initiation is over, how are subsequent tRNAs brought to the 70S ribosome?

Answer 17

Elongation Factors Ts and Tu use GTP to do so.

Question 18

What is peptidyl transferase responsible for?

Answer 18

Breaks the bond between tRNA and the amino acid, and forms a peptide bond between two adjacent amino acids.

Question 19

How does the ribosome move forward, and what is this called?

Answer 19

Codon translocation

Done by elongation factor G, and uses GTP for energy.

Question 20

What does the E site typically hold?

Answer 20

An uncharged tRNA (no amino acid).

Question 21

In prokaryotes, what happens when the termination sequence is reached?

Answer 21

A release factor binds to the mRNA codon, causing the polypeptide and ribosomal units to release.
It has no amino acid.

Question 22

Can an mRNA be translated by many ribosomes at a time, or one by one?

Answer 22

By many.

Question 23

Can mRNA be translated as it is being transcribed by RNA polymerase?

Answer 23

Only in prokaryotes - poly-ribosomes.

Question 24

How are polypeptides needing post-translational modifications moved to the appropriate organelle (name it)?

Answer 24

They bind to signal recognition particles - SRPs.
They carry it to the ER and bind to an SRP receptor.
They are sorted within the cisternal space within the ER.

Question 25

Do prokaryotes and eukaryotes have the same RNA polymerases?

Answer 25

No.

Question 26

What are the ribosomal subunits of eukaryotes?

Answer 26

60S and 40S.