cellb u8:gene expression

Question 1

What does “gene expression” mean?

Answer 1

It’s the process by which information from a gene is used to make RNA or protein.

Question 2

Why do cells control gene expression?

Answer 2

To produce only the proteins needed at the right time and place, saving energy and maintaining cell identity.

Question 3

What happens if a cell fails to regulate gene expression properly?

Answer 3

It can lead to disease, uncontrolled growth, or incorrect cell specialization.

Question 4

What is the most common and energy-efficient level of control?

Answer 4

transcriptional control.

Question 5

What is a transcription regulator?

Answer 5

A protein that binds to DNA sequences near genes to control transcription

Question 6

What are the two main types of transcription regulators?

Answer 6

Activators (turn genes on) and repressors (turn genes off).

Question 7

What DNA sequence do transcription regulators recognize and bind to?

Answer 7

The regulatory DNA sequence, often called a promoter or operator region.

Question 8

How do transcription regulators interact with DNA?

Answer 8

They fit into the major groove of the double helix and make specific contacts with the DNA bases.

Question 9

What do transcription regulators control in bacteria?

Answer 9

A: They turn groups of genes on or off in response to environmental changes, often as operons.

Question 10

What is an operon?

Answer 10

A cluster of genes controlled by a single promoter and operator, allowing coordinated expression.

Question 11

What is the lac operon used for in E. coli?

Answer 11

To control the breakdown of lactose — it turns on only when lactose is present and glucose is low.

Question 12

What does the lac repressor do?

Answer 12

It binds to the operator to block transcription when lactose is absent.

Question 13

What removes the lac repressor from the operator?

Answer 13

Allolactose (a lactose derivative) binds to the repressor, changing its shape so it detaches.

Question 14

What is the role of CAP (catabolite activator protein) in the lac operon?

Answer 14

It activates transcription when glucose levels are low by helping RNA polymerase bind to the promoter.

Question 15

In eukaryotes, where do transcription regulators bind?

Answer 15

to regulatory DNA sequences called enhancers, which can be far from the gene they control.

Question 16

How do activators and repressors affect transcription in eukaryotes?

Answer 16

They recruit coactivators or corepressors that modify chromatin and help or block RNA polymerase binding.

Question 17

What are chromatin-remodeling complexes?

Answer 17

Enzyme complexes that reposition or restructure nucleosomes to make DNA more or less accessible.

Question 18

What does histone acetylation do?

Answer 18

Adds acetyl groups to histones, loosening DNA–histone interactions and promoting transcription.

Question 19

What does histone deacetylation do?

Answer 19

Removes acetyl groups, tightening DNA–histone interactions and repressing transcription.

Question 20

What is an enhancer?

Answer 20

A regulatory DNA sequence that greatly increases transcription when bound by activators.

Question 21

What do mediator proteins do?

Answer 21

They act as a bridge between transcription regulators and RNA polymerase to coordinate transcription.

Question 22

How do eukaryotic transcription factors combine their effects?

Answer 22

Through combinatorial control — multiple regulators work together to fine-tune gene expression.

Question 23

what are “master transcription regulators”?

Answer 23

Special regulators that can activate whole groups of genes, defining a cell’s identity.

Question 24

What happens during cell memory in gene regulation?

Answer 24

Cells pass on patterns of gene expression to daughter cells during division, preserving cell identity.

Question 25

What are the three main ways cells maintain gene expression patterns after division?

Answer 25

Positive feedback loops (a regulator activates itself). Histone modification inheritance. DNA methylation inheritance.

Question 26

What is RNA interference (RNAi)?

Answer 26

A mechanism that uses small RNAs (siRNAs or miRNAs) to silence specific genes by degrading their mRNA or blocking translation

Question 27

What do microRNAs (miRNAs) do?

Answer 27

They base-pair with complementary mRNAs to prevent translation or trigger degradation.

Question 28

What do siRNAs do?

Answer 28

They come from double-stranded RNA and guide the degradation of matching mRNAs.

Question 29

What is the difference between miRNAs and siRNAs?

Answer 29

miRNAs come from the cell’s own genes; regulate many targets. siRNAs come from foreign or experimental dsRNA; silence specific targets.

Question 30

What is the main function of post-translational control?

Answer 30

Regulates protein activity by chemical modifications (e.g., phosphorylation, degradation).

Question 31

What is gene silencing by methylation used for in eukaryotes?

Answer 31

Turning off genes long-term, such as during development or X-chromosome inactivation.

Question 32

Why is gene expression control important for multicellular organisms?

Answer 32

It allows differentiation, different cells express different genes even though they share the same DNA.