Gene regulation

Question 1

How do stem cells become specialized cells?

Answer 1

Cell differentiation

A cell becomes specialized in structure and function by changes in gene expression

Question 2

How do different cell types specialize to perform their functions

Answer 2

Through selective gene expression

Certain genes are expressed while others are not

Question 3

Prokaryotes vs Eukaryotes (Gene regulation)

Answer 3

Prokaryotes:

• does not undergo post-transcriptional mRNA processing
• have operons
• codes for several proteins in one mRNA
• operator region present
• RNA do not have introns

Eukaryotes:

• undergoes post-transcriptional mRNA processing
• do not have operons
• codes for only one protein in one mRNA
• operator region absent
• RNA have exons and introns

Question 4

How do transcription factors work?

Answer 4

(Focus on an eukaryotic promoter)
Several transcription factors will assemble on the promoter
Transcription initiation complex forms
Termination and release of polymerase and complete RNA chain

Question 5

What is the function of transcription factors?

Answer 5

Proteins that will bind to the TATA box located in the promoter region
It recruits RNA polymerase to initiate transcription

Question 6

What is the function of a silencer?

Answer 6

Acts as an operator
DNA folds, bringing the silencer close to the promoter
Repressor binds to the silencer, gene is switched “off”

Question 7

What is the function of an enhancer?

Answer 7

Activator binds to the enhancer
Helps RNA polymerase to transcribe
Gene is switched “on”

Question 8

What is the function of an activator?

Answer 8

Binds to the gene at the enhancer

Increase rate of transcription

Question 9

What is the function of a repressor?

Answer 9

Binds to the gene at the silencer

Decrease the rate of transcription

Question 10

What is the function of a co-activator?

Answer 10

Integrate signals from activators

Question 11

What is DNA methylation?

Answer 11

Methylation of promoter by DNA methyltransferase make it unrecognizable by TF
Only the cytosine located neat to the guanine will be methylated

Question 12

What is Demethylation?

Answer 12

Demethylase will remove the methyl group that is binded to the cytosine
TF are able to bind to the promoter region
RNA polymerase binds to the promoter and initiates transcription

Question 13

How is DNA methylation inherited?

Answer 13

Methylated cytosine is maintained after DNA replication and passed down to daughter cells
Methylation pattern in daughter strand is the same as the parent strand

Question 14

What is histone acetylation?

Answer 14

The addition of acetyl group to lysine residues in histone tails will reduce the positive charge by histone acetyltransferase
Decrease the interaction of histones with the negatively charged DNA
Condensed chromatin is transformed into a more relaxed structure

Question 15

What is the function of histone deacetylase?

Answer 15

Remove the acetyl group from the histone
Histones would be able to interact with the negatively charged DNA
The relaxed chromatin structure will transform into a more condensed structure as DNA coils around the histones

Question 16

What are the functions of writer proteins, eraser proteins and reader proteins (apply to histone modifications)

Answer 16

writer proteins: enzymes that add histone modifications
reader proteins: enzyme that binds to histone modifications, alter gene activity and protein production
eraser proteins: enzyme that removes histone modifications

Question 17

What is histone methylation?

Answer 17

Depending on which amino acid is methylated, different reader proteins will be recruited to confer different epigenetic status

Question 18

Function of histone methyltransferase and histone demethylase?

Answer 18

Histone methyltransferase: add methyl groups to the amino acids

Histone demethylase: removes methyl group from the amino acids