Transcription

Question 1

What is transcription?

Answer 1

Synthesis of RNA from DNA template

Question 2

What is transcription catalyzed by?

Answer 2

RNA polymerase

Question 3

How many subunits if RNA polymerase made of?

Answer 3

multiple (alpha, beta, beta prime, omega, sigma70)

Question 4

What does transcription require?

Answer 4

A template:

1. RNA strand synthesized is complimentary to the “template strand” of DNA
2. The other DNA strand has the same sequence of the RNA strand w/ exception of the thymine (which is replaced with Uracil)
3. Ribonucleoside Triphosphate (ATP, cTP, UTP, and GTP)

Question 5

What direction does transcription occur in?

Answer 5

5’ to 3’ direction

Question 6

What is base +1?

Answer 6

First base that gets initiated/incorporated, initiates mRNA strand

Question 7

What is upstream of transcriptional start site?

Answer 7

The promotor

Question 8

What is the the promotor?

Answer 8

Where RNA polymerase binds

Question 9

What recognizes the promotor?

Answer 9

alpha subunit to facilitate initiation

Question 10

What components of the promotor?

Answer 10

-10 sequence, “pribnow box”
-35 sequence
(both on coding strand)

Question 11

TATAAT

Answer 11

-10 Sequence, “pribnow box”

Question 12

TTGAcA

Answer 12

-35 sequence

Question 13

What happens after RNA polymerase binds to promotor?

Answer 13

1. 17 bp segment of DNA unwinds
2. Results in an open “promotor complex”
3. RNA synthesis proceeds in 5’ to 3’ direction

Question 14

RNA synthesis can start without a ________.

Answer 14

Primer

Question 15

In bacteria, most newly synthesized RNA have ___ or ____.

Answer 15

pppG, pppA (1st nucleotide still with phosphate attached)

Question 16

Name two methods that can terminate RNA synthesis

Answer 16

1. Formation of an RNA hairpin from the transcribed gc-rich stop signal. On the mRNA transcript, a sequence of 4 or more uracils follow the hairpin.
2. Rho (p) protein activity: Uses ATP to “catch up” to RNA polymerase complex and then dislodge it.

Question 17

What is the Lac Operon?

Answer 17

Model system to examine transcriptional regulation (when transcription is turned on and of)

Question 18

What are the three components of the Lac Operon?

Answer 18

x, y, z, i-gene

Question 19

What is X in the lac operon?

Answer 19

B-Galactosidase

Question 20

What is the purpose of B-Galactosidase?

Answer 20

Breaks the glycosidic linkage in lactose between galactose and glucose (disaccharide into two monosaccharides)

Question 21

What is Y in the lac operon?

Answer 21

Permease

Question 22

What is the purpose of Permease?

Answer 22

allows lactose into bacterial wall (B/c lactose is very polar, making it difficult to pass through on its own)

Question 23

What is Z in the lac operon?

Answer 23

Transacetylase

Question 24

What is the purpose of Transacetylase ?

Answer 24

1. Assists with the metabolism of sugars

2. Transfers acetyl groups

Question 25

What is the i-gene in the lac operon?

Answer 25

Responsible for synthesis of repressor protein

Question 26

What is the repressor protein responsible?

Answer 26

tells us when transcription is turned on/off

Question 27

How does the repressor protein turn transcription off?

Answer 27

When it binds downstream to the 3' end of the promotor (prevent RNA polymerase from binding to the promotor)

Question 28

What turns transcription back on?

Answer 28

1, 6-Allolactose (Variation of Lactose, which is usually a 1,4 linkage)

Question 29

How does 1, 6-Allolactose turn transcription on?

Answer 29

By binding to repressor protein to inhibit repressor protein from binding to promotor

Question 30

What is another way transcriptional regulation can occur in the lac operon?

Answer 30

Via glucose regulation

Question 31

______ prefer to utilize _________ before breaking down _________.

Answer 31

e. coli, glucose, lactose

Question 32

What binds to cyclic AMP to for cAMP-cap complexes?

Answer 32

catabolite activator protein

Question 33

What is the function of cAMP-cap complexes?

Answer 33

To help recruit RNA polymerase to the promotor?

Question 34

When glucose is _______, cAMP levels are low.

Answer 34

abundant

Question 35

When glucose levels are abundant, cAMP levels are ___.

Answer 35

low

Question 36

What happens when cAMP levels are low and there are few cAMP-cap complexes?

Answer 36

Lac operon has low levels of transcription

Question 37

When _____ is scarce, cAMP levels are high.

Answer 37

glucose

Question 38

When glucose is scarce, cAMP levels are ____.

Answer 38

high

Question 39

What happens when cAMP levels are high and there are many cAMP-cap complexes?

Answer 39

Lac operon has high levels of transcription