LECTURE 20

Question 1

3 MAJOR Types OF RNA

Answer 1

1) tRNA (transfer RNA, used in translation)
2) rRNA (ribosomal RNA, part of ribosomes)
3) mRNA (messenger RNA, codes for proteins)

Question 2

Codons

Answer 2

A series of non overlapping three letter codes made of the 4 nucleotide bases

Question 3

As in DNA replication, RNA is synthesized in a

Answer 3

5’ —> 3’, antiparallel direction

Question 4

Codons are read in a

Answer 4

5’-3’ direction

Question 5

Redundancy in codons

Answer 5

Some amino acid are specified by more then one codon

Question 6

AUG has a dual function:

Answer 6

1) codes for methionine

2) START translation

Question 7

UAA, UGA, UAG

Answer 7

Don’t specify an amino acid, but STOPs translation

Question 8

Transcription is done by an enzyme called

Answer 8

RNA polymerase (RNA pol or RNAP)

Question 9

RNA pol

Answer 9

• adds nucleotides (5’—>3’)
• doesn’t need primer
• catalyzes phosphodiester bonds

Question 10

Bacteria and archaea have one RNA pol for all

Answer 10

Transcription

Question 11

Eukaryotes have 3 classes of RNA pol :

Answer 11

1) RNA pol l —> synthesized rRNA
2) RNA pol ll —> synthesizes mRNA
3) RNA pol lll —> synthesizes tRNA

Question 12

RNA pol initially binds to specific DNA sequence called a

Answer 12

Promoter

Question 13

Promoter

Answer 13

• upstream of transcription
• provides a target for other proteins to bind to, which then recruit RNA pol in the correct orientation
• directs the timing and frequency of initiation

Question 14

Initiation

Answer 14

The recruitment of RNA pol, unwinding DNA helix, and starting transcription

Question 15

Do RNA require primer to start synthesizing RNA

Answer 15

NO

Question 16

What’s the rate-limiting step in gene expression ?

Answer 16

Initiation

Question 17

Bacteria promoter sequence

Answer 17

• pribnow box (-10 Element) TATAAT
• -35 element
  TTGACA

Question 18

Eukaryote and archaea promoter sequence

Answer 18

Contains a TATA box (TATAAA), upstream of transcription start site

Question 19

RNA pol needs help to bind to the promoter sequence in bacteria

Answer 19

• protein called SIGMA binds directly to -10 and -35 elements
• one transcription begins, SIGMA dissociates

Question 20

RNA pol needs help to bind to the promoter sequence in eukaryotes

Answer 20

• non of the 3 classes of RNA pols can bind promoters on their own
• several proteins called general transcription factors (GTFs) bind to promoter site, helping recruiting RNA pol to promoter
• as transcription beings, some GTFs dissociate and are replaced by proteins required for elongation