31. REGULATION OF GENE EXPRESSION

Question 1

1. What do Prokaryotes and Eukaryotes change their gene expression according to?

Answer 1

• they change it according to their environmental
  changes

Question 2

2. What does gene expression regulate in multicellular eukaryotes?

Answer 2

-it regulates development
- it is responsible for the differences between different
types of cells
- this is known as cell specialisation

Question 3

3. What do RNA molecules do?

Answer 3

• they play a role in regulating the gene expression of
  the eukaryote

Question 4

4. What has natural selection favoured bacteria to produce?

Answer 4

• they produce only the products that they need

Question 5

5. In which 2 ways can Bacteria regulate their metabolic pathways?

Answer 5

1. REGULATION OF ENZYME ACTIVITY
   
   • this is done by feedback inhibition
2. REGULATION OF ENZYME PRODUCTION
   
   • this is done by gene expression
   • it is controlled by Operons

Question 6

6. What is an Operon?

Answer 6

• this is a prokaryotic DNA segment

Question 7

7. What do Operons consist of?

Answer 7

• the operator
• the promoter
• a group of functionally related genes

Question 8

8. What is an Operator?

Answer 8

• this is a segment of DNA
• it works as a regulatory on and off switch
• it controls the clustered functionally related genes
• it consists of a specific sequence

THIS SPECIFIC SEQUENCE IS FOUND:
- within a promoter of these genes

Question 9

9. What is a Repressor?

Answer 9

• this is a protein
• it switches off the Operon
• this prevents gene transcription

Question 10

10. How does the Repressor switch off the Operon?

Answer 10

• it does this by binding to the Operator
• it then blocks the RNA Polymerase binding

Question 11

11. What produces the Repressor?

Answer 11

• a separate regulatory gene
• a repressor can be in an active or inactive form
• this depends on the presence of other molecules

Question 12

12. What is a Co-Repressor?

Answer 12

• this is a molecule
• it co-operates with the repressor protein
• it helps it to switch off the Operon
  and to inactivate the Operon

Question 13

13. What is Negative Gene regulation?

Answer 13

• this is when the Operon is switched off
  by an ACTIVE form of the Repressor

Question 14

14. List 3 characteristics of Repressible Operons?

Answer 14

1. THEY ARE USUALLY ACTIVE
2. THEY USUALLY REGULATE
   
   • a gene expression of enzymes
     - these are involved in anabolic pathways
3. THEIR SYNTHESIS IS REPRESSED
   
   • it is repressed by high levels of the end product
   • this end product is known as the Co-repressor
   • this co-repressor activates the repressor

Question 15

15. Give an example of a Repressible Operon?

Answer 15

• the trp Operon

Question 16

16. List 3 characteristics of Inducible Operons?

Answer 16

1. THEY ARE USUALLY INACTIVE
2. THEY USUALLY REGULATE
   
   • a gene expression of enzymes
     - these are involved in catabolic pathways
3. THEIR SYNTHESIS IS INDUCED
   
   • it is induced by a chemical signal
   • this is known as the Inducer
   • this inducer activates the repressor

Question 17

17. Give an example of an Inducible Operon?

Answer 17

• Iac Operon

Question 18

18. What can synthesise the amino acid names Tryptophan?

Answer 18

• E coli

Question 19

19. What is the trp Operon?

Answer 19

• this operon contains genes of enzymes
• these enzymes are involved in the synthesis of
  Tryptophan

Question 20

20. When it comes to a Repressible Operon, what can be said about the state of Transcription?

Answer 20

• Transcription is normally on
• this transcription can be inhibited and repressed
• this is done with a small molecule of Tryptophan
• this tryptophan binds allosterically to the regulatory
  protein

Question 21

21. What happens when the Tryptophan is absent?

Answer 21

• the trp Operon is activated
• the repressor is inactive
• the repressor cannot bind to the operator
• the genes for the enzymes required for tryptophan are
  transcribed
• tryptophan production starts

Question 22

22. What happens when the Tryptophan is present?

Answer 22

• the trp Operon is inactivated
• the trp is a corepressor
• this means that it will bind to the trp repressor protein
• the repressor is activated
• the repressor binds to the Operator
• the trp operon is inactivated
• tryptophan production stops

Question 23

23. When is the repressor active?

Answer 23

• only in the presence of the corepressor Tryptophan

Question 24

24. What happens if Tryptophan levels are high?

Answer 24

• the trp Operon will be repressed
• it will be turned off