Module 10: V5 - V8

Question 1

What is an element?

Answer 1

a sequence of DNA

Question 2

What are transcription factors?

Answer 2

proteins that bind to elements on the DNA strand which either activate or repress transcription

Question 3

What is an operon?

Answer 3

a sequence of genes following the operator (found in bacteria)

Question 4

What is the purpose of the trp operon?

Answer 4

producing tryptophan amino acids

Question 5

How are individual proteins synthesised from the same strand of DNA?

Answer 5

multiple start and stop codons along the length of the DNA strand

Question 6

When is tryptophan synthesised in bacteria?

Answer 6

when there is no tryptophan present in the external environment

Question 7

What happens when tryptophan is found in the external environment?

Answer 7

binds to an inactive repressor, thereby activating it resulting in decreased gene expression and synthesis of tryptophan

Question 8

Is the repressor of the lac operon produced in the active or inactive state?

Answer 8

in the active state

Question 9

Is the lac operon active when there is lactose present or when there is no lactose present?

Answer 9

when lactose is present

Question 10

What happens to the lac operon when lactose is present?

Answer 10

allolactose binds to the repressor of the lac operon, thereby inactivating it resulting in transcription of the lac operon

Question 11

Which type of proteins does the lac operon produce?

Answer 11

permease which allows lactose to be transported into the bacterial cell and β-galactosidase which is used to break down lactose so that it can be used as an energy source

Question 12

What is tryptophan acting as in the trp operon?

Answer 12

a corepressor

Question 13

What is allolactose acting as in the lac operon?

Answer 13

an inducer

Question 14

Are the trp and lac operons examples of negative or positive regulation?

Answer 14

negative regulation

Question 15

What is the significance of the lac repressor?

Answer 15

a dimer binding to a palindrome sequence
binding results in the formation of a loop in the DNA which prevents the ability of RNA polymerase to transcribe the lac operon

Question 16

What is combinatorial control?

Answer 16

there are usually several important regulators of a single gene and messages are integrated for a single response
gene activation is synergistic

Question 17

What does combinatorial control allow E. coli to do when both glucose and lactose is present in the external environment?

Answer 17

allows bacteria to carry out the more efficient process of breaking down glucose so that it can be used as an energy source before breaking down lactose

Question 18

What is CAP?

Answer 18

a protein that is inactive unless bound to cyclic AMP and is able to bind to the lac operon
binds to a region where it activates the likelihood that RNA polymerase will transcribe

Question 19

When is there more cAMP in the cell?

Answer 19

when there is less glucose and therefore less ATP

Question 20

What happens to the lac operon when lactose and glucose is present?

Answer 20

since glucose is present this means that ATP is increased in the cell resulting in decreased cAMP and therefore inactivated CAP -> little lac mRNA synthesised even though the lac repressor is inactive (overridden)

Question 21

What happens to the lac operon when lactose is present and glucose is scarce?

Answer 21

since glucose is scarce this means that ATP is decreased in the cell resulting in increased cAMP and therefore activated CAP -> abundant mRNA synthesised

Question 22

What does regulation of gene expression allow cells to have?

Answer 22

different shapes and functions

Question 23

What are the major differences in regulation of transcription between prokaryotes and eukaryotes?

Answer 23

separation of transcription and translation, chromatin can block RNA polymerase access, ↓ basal transcription, majority of regulation is +ve not -ve, ↑ proteins involved in transcriptional regulation, ↑ transcription factors that control each genes

Question 24

What are the two aspects of chromatin regulation?

Answer 24

methylation of DNA and histones which causes nucleosomes to pack tightly together
histone acetylation which results in loose packing of nucleosomes

Question 25

What is a regulatory element?

Answer 25

the DNA sequence that transcription factors bind to
repressors (rare) bind to sequences called silencers
activators bind to sequences called enhancers or enhancer elements

Question 26

How does gene regulation occur?

Answer 26

activator protein binds the enhancer element -> histone modification / nucleosome remodelling complexes bind -> mediator (co-activator) binds and facilitates binding of the TBP -> other basal transcription factors and RNA pol II bind -> phosphorylation of the CTD of RNA pol II leads to transcription initiation