Lecture 12

Question 1

What is a Promoter?

Answer 1

A DNA sequence that directs/regulates transcription

Question 2

What is the Template Strand?

Answer 2

Strand of DNA that is used in transcription, it runs 3’ to 5’ away from promoter

Question 3

What is elongation?

Answer 3

Adding RNA nucleotides in a 5’ to 3’ direction

Question 4

What is RNA polymerase?

Answer 4

Initiates transcription at the +1 transcription factor

Question 5

What happens at termination?

Answer 5

RNA disassociates

Question 6

What is transcription?

Answer 6

DNA is transcribed into RNA

Question 7

What happens after transcription in Eukaryotes?

Answer 7

MeG and a poly-A-tail are added

Question 8

What is MeG? What does it do?

Answer 8

Methylated Guanine is added to the 5’ end of the RNA strand to prevent exonuclease from eating it

Question 9

What is a poly-A-tail? What does it do?

Answer 9

A poly-A-tail is about 200 adenines added to the 3’ end of the RNA to prevent exonuclease from eating it

Question 10

What is splicing?

Answer 10

Introns are removed from in-between exons with the enzyme spliceosome

Question 11

What are introns?

Answer 11

They are non-coding sequences

Question 12

What is a spliceosome?

Answer 12

A complex of snRNP’s which are protein/RNA complexes

Question 13

How does splicing work?

Answer 13

snRNP’s bind to the intron/exon boundary and loop out the intron. It is cut at 5’ end and attaches to a “branch point A”

Question 14

What is translation?

Answer 14

The genetic code carried by mRNA is translated into proteins

Question 15

What is tRNA?

Answer 15

Transfer RNA is has an a.a. binding region and an anticodon, it carries the correct a.a to the ribosomes

Question 16

What is Aminoacyl tRNA synthases?

Answer 16

It pairs the correct a.a to the tRNA based on the anticodon sequence

Question 17

What is a ribosome and what are the subunits of prokaryotic ribosomes?

Answer 17

A ribosome catalyzes peptide bonds and in prokaryotic ribosomes the large subunit is 50s and the small subunit it 30s

Question 18

What does the small subunit do?

Answer 18

Is used for recognition

Question 19

What is in the large subunit?

Answer 19

Approach site, Polymerization site and Exit site

Question 20

What happens in the large subunit?

Answer 20

The start codon (AUG) is positioned in the P site, the tRNA f-Met associates with the ribosomes so that it sits in the P site. The anticodon of the tRNA f-Met binds to the start codon of the mRNA

Question 21

What are the steps of the elongation phase?

Answer 21

Bind, Bond, Shift

Question 22

What happens during Bind?

Answer 22

A tRNA a.a. enters the A site and binds to the mRNA (anticodon to codon)

Question 23

What happens during Bond?

Answer 23

Peptide bonds form between tRNA f-Met and tRNA a.a. and the growing chain moves from the f-Met to the a.a. in the A site

Question 24

What happens during Shift?

Answer 24

The ribosome shifts down the ribosome towards the 3’ end in a one codon step. The first tRNA leaves through the exit site and the second tRNA is in the P site to continue the process

Question 25

What is termination phase?

Answer 25

When a STOP codon is encountered the ribosome stalls until release factor comes, the release factors release the a.a. chain which will go on to fold

Question 26

What are silent mutations?

Answer 26

A base pair is substituted but results in no change in the primary structure because of the redundancy of codons

Question 27

What are missense mutations?

Answer 27

A base pair is substituted but codes for a different amino acid

Question 28

What is a nonsense mutation?

Answer 28

A base pair is substituted and codes for a stop codon

Question 29

What is a frameshift mutation?

Answer 29

A base is added or deleted resulting in all a.a. after being affected