CGE: Regulation of Transcription and Translation

Question 1

Transription

Answer 1

When a gene is copied from DNA into messenger RNA.

Question 2

RNA polymerase

Answer 2

The enzyme responsible for synthesising mRNA from DNA

Question 3

When a gene is copied from DNA into messenger RNA.

Answer 3

Transcription

Question 4

The enzyme responsible for synthesising mRNA from DNA

Answer 4

RNA polymerase

Question 5

Why does the structure and function of a cell vary?

Answer 5

Although they all contain the same genes, different genes are expressed (transcribed and used to make a protein).

Question 6

The transcription of genes is controlled by what?

Answer 6

Protein molecules called transcription factors.

Question 7

Briefly describe how transcription factors work in eukaryotic cells:

Answer 7

1. TF move from cytoplasm to the nucleus.
2. Bind to specific DNA sites near start of target genes.
3. Control expression by controlling rate of transcription.

Question 8

What are the two main types of transcription factors?

Answer 8

Activators and repressors

Question 9

If a transcription factor is an activator, what does it do?

Answer 9

Stimulates or increases the rate of transcription.

Eg. help RNA polymerase bind to start of target gene and activate transcription.

Question 10

If a transcription factor is a repressor, what does it do?

Answer 10

Inhibits or decreases the rate of transcription.

Eg. they bind to the start of the target gene, preventing RNA polymerase from binding, stopping transcription.

Question 11

Other than transcription factors, what else can affect the expression of genes?

Answer 11

Other molecules in the cell, like oestrogen.

Question 12

How does oestrogen affect the expression of genes?

Answer 12

• Steroid hormone.
• Binds to a transcription factor called an oestrogen receptor - forms an oestrogen-oestrogen receptor complex.
• Complex moves from cytoplasm into nucleus and binds to specific DNA sites near the start of the target gene.
• Can act as an activator of transcription - helping RNA polymerase bind to start of target gene.

Question 13

Is oestrogen always an activator?

Answer 13

No - it is dependent on the type of cell and the target gene.

In some cells the oestrogen-oestrogen receptor complex can act as a repressor of transcription.

Question 14

Apart from transcription factors affecting transcription, what else can affect the gene expression in eukaryotes?

Answer 14

RNA Interference (RNAi) can inhibit the translation of mRNA.

Question 15

RNAi

Answer 15

A process where small, double stranded RNA molecules stop mRNA from target genes being translated into proteins.

Question 16

What are the molecules involved in RNAi?

Answer 16

siRNA (small interfering RNA)

miRNA (microRNA)

Question 17

RNAi molecules

Answer 17

Small lengths of non-coding RNA (don’t code for proteins)

Question 18

How does siRNA (and miRNA in plants) inhibit the translation of mRNA?

Answer 18

• Transcribed mRNA leaves the nucleus for the cytoplasm.
• In the cytoplasm, double-stranda siRNA associates with several proteins and unwinds.
• Single strand (and associated proteins) binds to target mRNA, as base sequences are complementary.
• Associated proteins cut mRNA into fragments - can no longer be translated.
• Fragments move into a processing body and are degraded.

Question 19

How does miRNA in mammals inhibit the translation of mRNA?

Answer 19

• miRNA isn’t fully complementary - less specific and may bind to more than one mRNA molecule.
• Associates with protiens and binds to target mRNA in cytoplasm.
• miRNA-protein complex physically blocks the translation of target mRNA.
• mRNA moved to processing body and is stored (can be returned and translated another time )or degraded.

Question 20

Where does siRNA and miRNA inhibit the translation of mRNA?

Answer 20

In the cytoplasm of a cell.