Control of gene expression in prokaryotes Flashcards Preview

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Flashcards in Control of gene expression in prokaryotes Deck (25)
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1

Define the initiation rate

number of mRNA molecule whose synthesis is initiated per unit of time

2

What two factors impact the initiation rate

1. consensus sequences
2. Proteins that change the affinity of the RNA polymerase for the promoter

3

What are the two consensus sequences in the promoter region

1. TATAA
2. TTGACA

4

What are the two types of transcription control

Positive and negative control

5

Define positive control

Genes under positive control will only be expressed when an activator protein is present

6

Define Negative control

Genes under negative control are expressed unless a repressor protein is present to block their transcription

7

Define an inducer (in context of repressors)

A ligand that binds to a repressor protein, causing it to detach

8

Define a co-repressor

A ligand that is needed to help bind repressor to DNA

9

Define an inducer (in context of activators)

It binds the activator, allowing it to bind DNA and machinery

10

Define catabolic inhibition

The process by which genes coding for certain catabolic machinery is turned off when not needed.

11

What are the two main components of the lac operon?

1. cis-acting regulator elements
2. protein-coding structural genes

12

What are the four products of the lac operon?

LacI
Lac Z
Lac Y
LacA

13

Define the lac Z gene

codes for β-galactosidase, the enzyme that breaks the glycoside bond in
lactose

14

Define the lacY gene

codes for lactose permease, the protein that transports lactose in the cell

15

Define the lacA gene

Codes for sulfogalactoside transacetylase; this enzyme plays a role detoxification of
thiogalactosides that are also transported into the cell by the lacY gene product.

16

What type of control is the lactose repressor an example of?

Negative control:
- controlled by both a repressor and an activator

17

Define the repressor of the lactose operon

1. coded in the lacI gene
2. binds to the operator sequence, which overlaps with the start sequence, inhibiting it
3. Forms a tetramer

18

Define allolactose

1. Intermediate of lactose metabolism
2. binds to repressor protein, causing it to dissociate from the DNA

19

What kind of control is demonstrated in the activator of the lactose operon?

Positive control

20

What is the activator for the lactose operon?

CAP (catabolic activator protein)
-acts as a dimer, increases affinity of RNA pol. for promoter

21

cAMP must be present for CAP to bind DNA. What influences the relative presence of cAMP?

intracellular concentrations of glucose. As glucose conc. goes up, cAMP conc. goes down.

22

Status of operon when glucose and lactose present

Operon is off, because glucose inhibits cAMP, therby preventing the binding of CAP to DNA

23

Status of operon when only glucose present

repressor is bound, due to absence of allolactose. Therefore, operon is off

24

Status of operon when both lactose and glucose are absent

operon is off, lac repressor is still bound. However, CAP is bound as well, since absence of glucose allows presence of cAMP

25

Status of operon when only lactose present

CAP binds, allolactose removes repressor, operator is ON