Regulation of transcription and translation

Question 1

What do transcription factors do?

Answer 1

Control the transcription of target genes

Question 2

How do transcription factors work?

Answer 2

In eukaryotes transcription factors move from the cytoplasm to the nucleus. In the nucleus they bind to specific DNA sites near the start of their target genes. They control expression by controlling the rate of transcription.

Question 3

What are activators?

Answer 3

Transcription factors that stimulate or increase the rate of transcription

Question 4

What are repressors?

Answer 4

Transcription factors that inhibit or decrease the rate of transcription

Question 5

What can oestrogen do?

Answer 5

Initiate the transcription of target genes

Question 6

What is oestrogen?

Answer 6

A steroid hormone

Question 7

How can oestrogen affect transcription?

Answer 7

It binds to a transcription factor called an oestrogen receptor forming an oestrogen-oestrogen receptor complex. The complex moves from the cytoplasm into the nucleus where it binds to specific DNA sites near the start of the target gene. The complex can act as an activator of transcription.

Question 8

What can affect gene expression in eukaryotes?

Answer 8

RNA interference (RNAi)

Question 9

What is RNA interference?

Answer 9

RNAi is where small double stranded RNA molecules stop making mRNA from target genes being translated into proteins.
A similar process to RNAi can also occur in prokaryotes.

Question 10

Name the molecules that are involved in RNAi

Answer 10

Small interfering RNA (siRNA)
Micro RNA (miRNA)

Question 11

How does RNAi work in plants?

Answer 11

1. Once mRNA has been transcribed it leaves the nucleus for the cytoplasm.
2. In the cytoplasm double stranded siRNA associates with several proteins and unwind. A single strand binds to the target mRNA. The base sequence of the siRNA is complementary to the base sequence in sections of the target mRNA.
3. The proteins associated with the siRNA cut the mRNA into fragments so it can no longer be translated. The fragments then move into a processing body with contains ‘tools’ to degrade them.
4. A similar process happens with miRNA in plants.

Question 12

How does RNAi work in mammals?

Answer 12

1. In mammals the miRNA isn’t usually fully complementary to the target mRNA. This makes it less specific than siRNA and so it may target more than 1 mRNA molecule.
2. It associates with proteins and binds to target mRNA in the cytoplasm.
3. The miRNA protein complex physically blocks the translation of the target mRNA.
4. The mRNA is then moved into a processing body where it can either be stored or degraded