Control Of The Gene Expression

Question 1

What are transcription factors?

Answer 1

They are substances that can stimulate or inhibit the transcription of target genes by either assisting or preventing RNA polymerase from binding to the DNA.

Question 2

What are promoter regions?

Answer 2

These are base sequences before genes where transcription factors bind.

Question 3

How do promoter regions allow transcription factors to bind to the DNA?

Answer 3

They have binding sites that are complementary to specific transcription factors.

Question 4

THE CONTROL OF GENE EXPRESSION VIA EPIGENETICS

Question 5

What is epigenetics?

Answer 5

Heritable changes in the gene functions of eukaryotic cells due to changes in the environment. It does not involve changes to the DNA base sequence.

Question 6

What is methylation?

Answer 6

The addition of a methyl group to the carbon 5 of cytosine bases at the CpG sites.

Question 7

What is a CpG site?

Answer 7

It is a nucleotide with a cytosine base joined to a nucleotide with a guanine base by a phosphodiester bonds.

Question 9

Describe how a change methylation affect the trancrition of target genes?

Answer 9

1. Decreased methylation of the CpG sites stimulates the transcription of target genes by allowing the RNA polymerase to bind to the DNA.
2. Increased methylation of the CpG sites inhibits the transcription of target genes by preventing the RNA polymerase from binding to the DNA.

Question 10

What is acetylation?

Answer 10

The addition of an acetyl group to histones.

Question 11

How does a change in the acceleration of histones affect the transcription of target genes?

Answer 11

1. Increased acetylation of the histones causes the chromatin to become loosely packed. This allows the RNA polymerase and transcription factors to bind to the DNA and initiate transcription.
2. Decreased acetylation causes the chromatin to condense, so the transcription factors and RNA polymerase can’t bind to the DNA and initiate transcription.

Question 12

THE ROLE OF OESTROGEN IN THE TRANSCRIPTION OF GENES.

Question 13

How does oestrogen activate the transcription of genes?

Answer 13

1. The oestrogen binds to an oestrogen receptor in the nucleus to form an oestrogen-oestrogen receptor complex.
2. The oestrogen-oestrogen receptor complex binds to the promoter regions of the DNA and acts as a transcription factor.
3. It then activates the transcription of genes.

Question 14

RNA INTERFERENCE AND THE TRANSLATION OF GENES

Question 15

How do microRNA and small interfering RNA stop the translation of target genes?

Answer 15

1. The miRNA and siRNA are transcribed from DNA.
2. They then bind to a protein to form an RNA-induced silencing complex ( RISC)
3. They then can bind to mRNA with a completely base sequence.
4. This causes the mRNA to be hydrolysed by RNA hydrolase, so it is not able to bind to ribosomes. This is because ribosomes can’t bind to double-stranded RNA.
5. This prevents the mRNA from being translated, and the gene is silenced.

Question 17

How is miRNA produced and what does it mature into?

Answer 17

It is produced as pre-miRNA which is a single strand folded in half. It then matures into miRNA that is single-stranded

Question 18

What type of mRNA does miRNA inhibit?

Answer 18

It inhibits the translation of multiple mRNAs in mammals and plants.

Question 19

How is siRNA produced and what does it mature into?

Answer 19

It is produced as pre-siRNA that is double-stranded and matures into siRNA that is single-stranded.

Question 20

What type of mRNA does siRNA inhibit?

Answer 20

One specific mRNA.