Controlling Gene Expression 19.2

Question 1

WhT are the 4 levels of transcription

Answer 1

1) transcriptional control - turning genes on/off
2) post transcriptional - editing RNA
3) translational - turning translation on/off
4) post translational - editing protein

Question 2

How do we turn genes on and off

Answer 2

Alter conditions to allow RNA polymerase to bind to the gene that we want to be transcribed,

Question 3

How do eukaryotes turn genes on and off

Answer 3

Histone modification for chromatic remodelling - We know that DNA associates with proteins called histones to be compact to form chromatin. In this form it is heterochromatin. This is involved in cell division

Question 4

What is the need to change heterochromatin to Euchromatin?

Answer 4

RNA polymerase cannot access the gene and no transcription can occur so it gets changed in a reversible reaction to euchromatin to allow for transcription. Here the dna is loosely wounded and the rna polymerase has access to the gene and bind to allow transcription

Question 5

How change heterochromatin to euchromatin

Answer 5

One way is through acetylation - adding acetyl group to the histones

Phosphorylation - add phosphate group to it.

Both decrease the overall positive charge of the histones so dna less inclined to be stuck to histones

Question 6

How to reverse euchromatin to heterochromatin and why

Answer 6

Maybe for stuff like cell division

Methylation - add methyl group. Increases hydrophobic nature of histones making dna more inclined to wrap around histones

Question 7

What is lac operon

Answer 7

The transcriptional level of control in prokaryotes.

Question 8

What is an operon

Answer 8

A group of genes controlled by the same regulatory mechanism and expressed at the same time.

Question 9

What are structural genes

Answer 9

Proteins not involved in DNA regulation. In lac operon there is lac z, lac y and lac a.

This will make
- beta galactosidase
- lactose permease
- lactose transacetylase

These three enzymes metabolise lactose

Question 10

What are regulatory genes

Answer 10

Lac I

This codes for proteins that are involved in dna regulation. LAC I will code for the repressor protein of the transcription of lac z y a

Question 11

What is the operator

Answer 11

DNA sequence right next to the promoter where the repressor protein binds

Question 12

What is the promoter rn

Answer 12

Sequence next to operator - where rna polymerase will bind

Question 13

What is the process when we have glucose available for prokaryotes to metabolise in respiration for energy?

Answer 13

1) LAC I gene expressed to make repressor protein, which binds to operator

2) due to its shape it blocks rna polymerase from binding to promoter and prevents transcription

Question 14

What happens when prokaryote has to metabolise lactose

Answer 14

Lactose binds to repressor protein, causing a conformational change, changing its shape, and the repressor is released from the operator

This allows rna polymerase to bind to promoter allowing the transcription of the three structural genes

cAMP receptor protein binds with cAMP. This complex binds to rna polymerase and regulates the transcription of the structural genes. The whole thing then moves across to transcribe 🛫

These enzymes metabolise lactose used to release energy

Question 15

What does the presence of glucose do after lactose hella

Answer 15

Presence of glucose cause lactose to release from repressor, causing conformational change, allowing repressor to bind and rna cannot transcribe. Glucose also decreases cAMP conc in cell which also down regulates transcription