Transcriptional regulation in prokaryotes

Question 1

How are “housekeeping genes” expressed

Answer 1

constitutively

Question 2

What type of gene expression is “switched on and off”

Answer 2

induced or repressed

Question 3

What processes are controlled by housekeeping genes

Answer 3

metabolism

Question 4

In prokaryotes, at what level does most transcription occur and why

Answer 4

transcription i.e. before the synthesis of mRNA
to conserve energy and resources

Question 5

What is a promoter

Answer 5

the sequence of DNA adjacent to the gene which determines where and in which direction RNA polymerase binds DNA

Question 6

Explain positive regulation

Answer 6

The gene is on unless the protein is present

Question 7

Explain negative regulation

Answer 7

The gene is off unless the protein stimulates transcription

Question 8

What do sigma factors do and where do they bind

Answer 8

A transcription factor which recruits RNA polymerase binds core promoter elements (-10 and -35 sequences)

Question 9

What dictates the rate of transcription of sigma factor-induced transcription

Answer 9

The variance of the signal sequences they bind
Strong promoters conform well to the consensus sequence and frequently initiate transcription

Question 10

Explain coordinated gene expression in prokaryotes

Answer 10

variants of sigma factors can bind multiple genes in response to the same stimuli

Question 11

Which saccharide is preferred for ATP synthesis

Answer 11

glucose

Question 12

When conditions dictate how is lactose used for ATP synthesis

Answer 12

split into two galactose and acetylated to metabolise it
takes 3 enzymes

Question 13

What is an inducer

Answer 13

a compound that induces protein synthesis making inducible proteins

Question 14

What are constitutive proteins

Answer 14

proteins made at a constant rate

Question 15

Explain the two methods of regulation of metabolic pathways

Answer 15

allosteric regulation of enzyme-catalyzed reactions - faster fine-tuning, higher energy requirements
regulation of gene expression (of enzymes) - slower with a lag time but conserves resources

Question 16

What is an operon

Answer 16

a cluster of genes with a single promoter that is transcribed together into a single mRNA, usually involved in the same processes

Question 17

What does an operon consist of

Answer 17

a promoter
two or more structural genes
an operator

Question 18

what is an operator

Answer 18

a short stretch of DNA between the promoter and structural genes of an operon that allows for regulatory protein binding

Question 19

Explain the three ways to control operon transcription

Answer 19

inducible operons - regulated by a repressor, default is off, turned on by a metabolic substrate eg lactose

repressible operons - regulated by a repressor, default is on, repressed when a corepressor binds its repressor

regulated by activator protein - default is off unless stimulated

Question 20

where is the repressor for the lac operon encoded and how is it transcribed

Answer 20

before the promoter
constitutively

Question 21

What is the role of lactose in the lac operon system

Answer 21

inducer
it changes the conformation of the repressor so it cannot bind DNA

Question 22

What is polycistronic mRNA

Answer 22

mRNA that encodes multiple proteins

Question 23

What type of pathway do inducible systems control and when are they turned on

Answer 23

catabolic
when substrate is available

Question 24

What type of pathway do repressible systems control and when are they turned on

Answer 24

anabolic pathways
on until product concentration becomes excessive

Question 25

What is CRP and what happens when it is bound

Answer 25

cAMP receptor protein
binds the promoter region and makes sigma factor/RNA polymerase binding more efficient

Question 26

When is CRP activity highest

Answer 26

when cAMP levels are low due to glucose and lactose being at high levels