CB7 & CB8 Regulation Of Gene Expression

Question 1

Explain the process of transcription (synthesis of RNA)

Answer 1

• Sigma factor within RNA polymerase recognises promoter region and DNA polymerase starts transcribing from a start site
• RNA polymerase forms phosphodiester bond between two nucleotides
• elongation of the transcript
• polymerase reaches a stop codon

Question 2

Define the term inducer

Answer 2

Something (e.g. Lactose) which binds to repressor

Question 3

Define the term operator

Answer 3

Part of DNA that repressor is bound to

Question 4

Define the term promoter

Answer 4

A DNA sequence upstream of the opera that helps the organism to regulate genes

Question 5

Define the term repressor

Answer 5

Protein which binds to DNA and stops it working

Question 6

Define the term polycistronic mRNA

Answer 6

Also called Operons
- mRNA corresponding to multiple genes whose expression is controlled by a single promoter

Question 7

Define the term sigma factor as they relate to the lac operon

Answer 7

Small piece of protein that binds to the polymerase & helps the polymerase find the promoter

Question 8

Describe the role of cyclic AMP & CAP in regulating the lac operon

Answer 8

Cyclic AMP binds to CAP (catabolite activating protein)
This complex aids RNA polymerase binding to promoter, allowing transcription of the lac operon

Question 9

Define the 3 types of RNA polymerase in eukaryotes

Answer 9

RNA polymerase l
- synthesises large ribosomal RNAs

RNA polymerase Il
- mRNA synthesis

RNA polymerase lll
- tRNA & small rRNA synthesis

Question 10

Describe the structure of a typical pol II gene

Answer 10

Eukaryotic genes vary greatly in size
Contain introns & exons

Question 11

Explain the processing of mRNA in eukaryotes

Answer 11

Transcript modified by:
• capping (addition of modified G to 5’ end)
• splicing (removal of introns)
• polyadenylation (addition of A to 3’ end)

Question 12

Define transcription factors

Answer 12

Modular proteins that bind to specific DNA sequences and regulate transcription

Question 13

Define enhancers

Answer 13

Short region of DNA that can be bound by proteins to increase the likelihood that transcription will occur

Question 14

Define DNA response elements

Answer 14

Short DNA sequences within a gene promoter/ enhancer region that are able to bind to specific transcription factors & regulate transcription of genes

Question 15

Describe how steroid hormone receptors, such as cortisol, influence transcription via hormone response elements

Answer 15

• Signalling molecule crosses plasma membrane & binds to nuclear receptor protein
• conformational change activates receptor protein
• activated receptor - hormone complex moves into nucleus
• activated receptor - hormone complex binds to hormone response element and influences transcription

Question 16

Describe the major overall difference between prokaryotes & eukaryotes in how they generally regulate the activity of metabolic pathways

Answer 16

Eukaryotic transcription:
- eukaryotes more complex
- regulate own environment
- most genes generate multiple different transcripts
- not all genes encode proteins