Lecture 7 Flashcards Preview

Genes: Organisation and Function > Lecture 7 > Flashcards

Flashcards in Lecture 7 Deck (26):
1

Tryptophan operon regulation in Bacillus subtilis:
(3)

- Alternate, mutually exclusive stem-and-loop structures in the mRNA lead to termination or anti-termination
- High tryptophan leads to TRAP forming (C&D) resulting in anti-termination
- antiTRAP protein binds to inactivate TRAP, regulated by uncharged tRNAtrp

2

Regulation of gene expression is mediated by
(4)

- Positive/negative
- DNA-binding/RNA binding
- Regulating transcription initiation/termination
- Most are regulated by an effector molecule having an allosteric effect on the conformation and activity of the protein

3

Riboswitches influence gene expression in eukaryotes (some in fungi and plants) by..
(4)

- Altering the structure in the mRNA through the binding of an effector molecule, influencing gene expression by..
- Transcription termination (attenuation)
- Translation initiation
- No regulatory protein involved

4

Alternative structures of riboswitches
(2)

- The normal confirmation does not result in transcription termination, but upon binding by an effector molecule
- A change in confirmation results in transcription termination

5

Riboswitch example:
(2)

- SAM is a small effector molecule that binds when there is enough in the cell.
- When not bound 2&3 bind, but when bound 1&2 pair and 3&4 pair and termination follows

6

Other riboswitches examples:
(6)

- Coenzyme B12
- Guanine
- Lysine
- Adenine
- Thyamine
- Flavin

7

Bacteriophage lambda:
(2)

- A simple model organism
- Temperate bacteriophage of E.coli
- Lysis or lysogeny are the binary outcomes based on regulatory events of genes

8

The Lambda life cycle:

- Infection of a cell
- 50kb linear genome circularises via cohesive sticky ends within the cell
- Either lytic growth (phage infects cell and replicates new phage, cell burst etc)
- OR lysogenic growth ohage

9

The Lambda lytic pathway:

- Phage infects cell
- 50kb genome circularises using sticky ends
- DNA replicates using host machinery
- Cells lyses and lambda infects new cells

10

The lambda lysogenic pathway

- Phage infects cell
- 50kb genome circularises using sticky ends
- DNA integrates into the cell chromosomes and lambda repressor is expressed
- Replicates with cell machinery until the repressor is turned off
- lysis follows

11

Induction

- The lysogen is induced into the lytic cycle
- Often occurs under host cell stress

12

Lambda genome parts:
(7)

- Cos sticky ends circularise
- Head protein genes
- Tail protein genes
- Lysis genes for breaking open the cell
- Integration and excision of E.coli
- DNA replication genes
- Regulatory functions

13

Phage lytic development involves:

- A cascade of gene expression from early to middle to late genes
- New phage RNAP, sigma factors, promoters and anti-termination factors are used to progress to the next stage of gene expression

14

Early genes:

- Phage genes are transcribed by host RNA polymerase

15

Middle genes:

- Early product causes transcription of middle genes

16

Late genes:

- Middle product allows transcription of late genes containing phage components

17

Early genes are divided into two groups: Immediate early genes encode:

- Are transcribed by host RNAP from PL and PR
- cro from PL = negative regulator
- N from PR= antiterminator, which allows transcripts to extend into delayed early genes

18

Early genes are divided into two groups: delayed early genes encode:

- Transcription initiates at PR and pQ
- cII/cIII = regulators, using 7 recombination genes and 2 replication genes
- Q = anti-terminator, allow transcripts to extend into late genes

19

Late genes:

- 10 head genes
- 11 tail genes
- 2 lysis genes

20

cIII

- maintains cII
- used in lysogeny

21

N

- anti-terminator
- Turns on delayed early genes
- used in lysogeny and lysis

22

cI

- lysogenic repressor
- lysogeny

23

cro

- negative regulator
- turns off repressor
- lysis

24

cII

- turns on repressor
- lysogeny

25

Q

- anti-terminator
- turns on late genes
- used in lysis

26

The promoters for the lytic cycle are

- PL
- Pr
- PR'