Cellular Control - Module 6

Question 1

What is the transcriptional control in prokaryotes? Describe it

Answer 1

Lac operon

1. A repressor protein is binded to the operator, blocking the promoter so RNA polymerase cannot bind
2. When lactose is present it binds to the repressor protein resulting in a conformational change so it detaches from the operator and moves away from the
3. RNA polymerase can now bind to the promoter and start transcribing the lac Z, Y, A genes that metabolise lactose

Question 2

What is the transcriptional change that occur in eukaryote? Describe it

Answer 2

Histone modification

Heterochromatin - when DNA tightly wraps itself around histones making the gene RNA polymerase wants to access very difficult

So, acetylation occurs causing the DNA to loosen forming euchromatin - RNA polymerase can now access the gene for transcription

To reverse this process methylation occurs, causing DNA to bind more tightly again

Question 3

What happens in the post transcriptional level of cellular control?

Answer 3

Modification of mRNA

This turns pre mRNA to mature mRNA

1. Introns are removed by splicing
2. Special nucleotide head is placed on 5’ end
3. Adenosine base cap is placed on the other end of the
4. Editing of the mRNA may occur to make different combinations so different proteins may be formed

The mRNA is now ready to be transported in the cytoplasm without degradation

Question 4

How does translational control occur in cells?

Answer 4

Translation controls involves switching translation on and off

1. Degrade mRNA in cytoplasm
2. Inhibitory factors proteins binding to mRNA
3. Initiation factors allowing mRNA to bind to ribosome e.g cAMP

Question 5

Describe post translational control in cells?

Answer 5

Post translational control is modification of the protein by;
1. Adding non-protein groups
2. Changing 3d tertiary structure
3. Modification by cAMP