Lecture 3 - Regulation of Gene Expression in Prokaryotes

Question 1

What is the central dogma of molecular biology?

Answer 1

DNA is transcribed into RNA, and RNA is translated into proteins.

Question 2

What are structural RNAs, and how do they differ from mRNAs?

Answer 2

Structural RNAs (e.g., tRNAs, rRNAs) are not translated into proteins but play functional roles in cellular processes.

Question 3

How are transcription and translation coupled in prokaryotes?

Answer 3

In prokaryotes, ribosomes begin translating mRNA while it is still being transcribed because there is no nuclear membrane.

Question 4

What are the key regions of a gene in transcription?

Answer 4

Promoter: Upstream region where RNA polymerase binds.

Terminator: Downstream region signalling RNA polymerase to stop transcription.

5’ UTR: Contains the ribosome binding site.

Question 5

What is an operon?

Answer 5

An operon is a cluster of genes transcribed together from a single promoter, producing polycistronic mRNA.

Question 6

What is the role of sigma factors in prokaryotic transcription?

Answer 6

Sigma factors guide RNA polymerase to specific promoters and determine which genes are transcribed.

Question 7

How is transcription terminated in prokaryotes?

Answer 7

Transcription ends when a hairpin structure followed by a stretch of uracils destabilizes the RNA-DNA hybrid, causing dissociation.

Question 8

Why do cells need different amounts of proteins?

Answer 8

Different proteins have specific roles and are required in varying quantities depending on cellular needs.

Question 9

How do strong and weak promoters affect transcription?

Answer 9

Strong promoters: RNA polymerase binds frequently, leading to high transcription.

Weak promoters: RNA polymerase binds less often, resulting in lower transcription.

Question 10

How can promoter strength be tested?

Answer 10

By fusing promoters to reporter genes like GFP or lacZ and measuring fluorescence or enzymatic activity.

Question 11

What are the four levels at which gene expression can be regulated?

Answer 11

Transcription, post-transcription, translation, and post-translation.

Question 12

What is the role of alternative sigma factors?

Answer 12

Alternative sigma factors enable RNA polymerase to recognize and transcribe specific sets of genes in response to environmental changes.

Question 13

What is a regulon?

Answer 13

A group of genes scattered across the genome that are co-regulated by the same sigma factor.

Question 14

How does negative regulation work in gene expression?

Answer 14

A repressor binds to the operator, blocking RNA polymerase from binding to the promoter, turning transcription off.

Question 15

How does positive regulation work in gene expression?

Answer 15

An activator binds near the promoter, helping RNA polymerase bind and initiate transcription.

Question 16

What is the lac operon?

Answer 16

A transcriptional unit in bacteria that contains genes (lacZ, lacY, lacA) needed for lactose metabolism.

Question 17

How does the lac repressor (LacI) regulate the lac operon?

Answer 17

LacI binds to the operator in the absence of lactose, preventing transcription.

Question 18

What is the role of CAP and cAMP in positive regulation of the lac operon?

Answer 18

cAMP binds to CAP, enabling it to bind near the promoter and enhance RNA polymerase binding when glucose is absent.

Question 19

What is allosteric regulation?

Answer 19

A regulatory molecule binds to a site other than the active site, causing a conformational change that affects protein function.

Question 20

What is the role of allolactose in the lac operon?

Answer 20

Allolactose binds to LacI, causing it to release from the operator and allowing transcription.

Question 21

What causes lactose intolerance?

Answer 21

Reduced expression of the LCT gene after infancy due to regulatory elements in the MCM6 gene.

Question 22

How do bacteria prioritize glucose over lactose for metabolism?

Answer 22

Glucose inhibits cAMP production, preventing CAP activation and reducing lac operon transcription.

Question 23

What is a partial diploid in bacteria?

Answer 23

A bacterial cell with two copies of certain genes, one on the chromosome and one on a plasmid.

Question 24

What are bacterial plasmids, and why are they important?

Answer 24

Plasmids are circular DNA molecules that carry genes for antibiotic resistance, toxin production, or metabolic functions.

Question 25

How is transcription different in prokaryotes and eukaryotes?

Answer 25

In prokaryotes, transcription and translation are coupled, while in eukaryotes, transcription occurs in the nucleus and translation in the cytoplasm.

Question 26

How is lactose commercially produced?

Answer 26

Using fungi like Kluyveromyces lactis or Aspergillus niger to enzymatically convert lactose into glucose and galactose.

Question 27

How can lactose production be increased in bacteria?

Answer 27

Mutate the CAP gene to no longer require cAMP and delete the LacI gene to remove repression.

Question 28

What is the significance of -10 (TATA box) and -35 sequences in promoters?

Answer 28

These sequences are recognized by sigma factors to initiate transcription.

Question 29

What is the relationship between glucose, cAMP, and CAP?

Answer 29

High glucose inhibits cAMP production, which prevents CAP from activating transcription.

Question 30

Why do cells regulate gene expression?

Answer 30

To conserve energy and resources by producing only the proteins needed for current conditions.