Regulation Of Transcription And Translation

Question 1

What’s a transcriptional factor

Answer 1

controls the transcription of target genes

Question 2

What do the transcriptional factors do

Answer 2

It has a site that binds to a specific base sequence of the dna in the nucleus

When it binds it causes the region of dna to begin the process of transcription

mRNA is produced and the info it carries is then translated into a polypeptide

Question 3

What happens to a transcriptional factor when the gene is not expressed

Answer 3

The site of the transcriptional factor that binds to dna is not active therefore it cannot cause transcription and protein synthesis

Question 4

Describe how the transcription of genes is controlled by transcription factors

Answer 4

Transcription factors moves from the cytoplasm to the nucleus

In the nucleus they bind to specific dna sites near the start of their target genes - the genes they control the expression of

They control expression by controlling the rate of transcription factors

Some transcription Factors, called activators, stimulate or increase the rate of transcription e.g. they help rna polymerase bindto the start of the target gene and activate transcription

Other transcription factors, called repressors, inhibit or decrease the rate of transcription e.g. they bind to the start of the target gene, preventing rna polymerase from binding, stopping transcription

Question 5

Describe how how oestrogen can activate the dna binding site causing it to change

Answer 5

Oestrogen (lipid soluble molecule) diffuses easily through the phospholipid portion of the cell membrane

Once inside the cytoplasm of cell, oestrogen binds with a site on a receptor molecule of the transcriptional factor. The shape of this site and the shape of the oestrogen molecule compliment one another

By binding with the site, the oestrogen changes shape of the dna binding site on the transcriptional factor, which can now bind to dna

The transcriptional factor can now enter the nucleus through a nuclear pore and bind to the specific base sequences on the dna

The combustion of the transcriptional factor with dna stimulates transcription of the gene that makes up the portion of dna

Question 6

What is RNAi

Answer 6

It’s where a small double stranded rna molecule that stop mRNA from target genes being translated into proteins

Question 7

Describe how RNAi works in plants

Answer 7

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 unwinds. A single strand then binds to the target mRNA. The base sequence of the siRNA is complimentary 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, which contains tools to degrade them
4. A similar process happens with miRNA in plants

Question 8

Describe miRNA in mammals

Answer 8

1. In mammals, the miRNA isn’t usually fully complimentary to the target mRNA. This makes it less specific than siRNA and so it maybtarget more than one mRNA molecule
2. Like siRNA, it associates with proteins and binds to target mRNA in the cytoplasm
3. Instead of the proteins associated with miRNA cutting mRNA into fragments, 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. When it’s stored, it can be returned and translated another time

Question 9

What is the role of transcriptional factors

Answer 9

THey stimulate transcription of a gene