Chapter 18.1 - Prokaryotic Gene Expression

Question 1

Regulation of gene expression (3)

Answer 1

1. All Cells of an individual have the same complement of genes
2. Different cells/tissues have different functions that require specific genes
3. Requirements change during development and cells must respond to changes in environmental conditions

Question 2

Regulation can occur at several levels of gene expression (3)

Answer 2

1. Chromatin packing (Transcription initiation)
2. RNA stability (processing, translation initiation, translation termination)
3. Protein modification (protein stability/activity)

Question 3

When are genes turned on

Answer 3

Only when the protein (or RNA) that they encode is needed

Question 4

Operons (Transcriptional Units)

Answer 4

• genes encoding proteins in a common pathway often clustered on chromosome in bacteria
• expressed from one promoter

Question 5

Mechanisms for Control of Transcription initiation (2)

Answer 5

1. Repressors

2. Activators

Question 6

Repressors

Answer 6

Prevent RNA polymerase from binding to promoter. Negatively regulate operon.

Question 7

Activators

Answer 7

Increase affinity of RNA polymerase for promoter. Positively regulate operons

Question 8

What affects the shape and DNA binding activity of regulatory proteins?

Answer 8

Small molecules such as compressors and inducers that are often products of pathways that they control

Question 9

Lactose catabolism by bacteria

Answer 9

When lactose is available bacterium needs to make proteins for transport and degradation of lactose

Question 10

Lactose (lac) operon

Answer 10

When lactose is available transport protein (permease) and beta-glactosidase are produced

Question 11

Inducible Operon-Lactose Operon

Answer 11

Usually off but can be turned on.

• lac repressor (lacl) at two points so that DNA forms a loop
• this prevents binding of the promoter by RNA polymerase