Lecture 31 - an alternative view by Rodwan Halimi XD

Question 1

How can knowledge of heat stress assist humans?

Answer 1

Hsp levels can be used as an indicator of stress.

Therapeutic uses of this can be carried out. (induce heat shock response to fight certain problems)

Question 2

How can knowledge of heat stress assist humans?

Answer 2

Hsp levels can be used as an indicator of stress.

Therapeutic uses of this can be carried out. (induce heat shock response to fight certain problems)

Question 3

What are the types of DNA damage that can occure?

Answer 3

Single strand breaks can occur in response to ROS or to UV radiation. This is easily repairable due to availability of the other strand to use as a template.

Double strand breaks are more severe because if unrepaired they can kill cell and if misrepaired can result in chromosomal translocation.

Question 4

What are the types of DNA damage that can occure?

Answer 4

Single strand breaks can occur in response to ROS or to UV radiation. This is easily repairable due to availability of the other strand to use as a template.

Double strand breaks are more severe because if unrepaired they can kill cell and if misrepaired can result in chromosomal translocation.

Question 5

What is the response that the cell undergoes to repair double strand breaks in DNA?

Answer 5

1) Detects double-strand break.
2) Cellular functions are altered and to stop cell division until break is repaired. Cell is killed if damage is severe and not repairable.

Question 6

What are the types of responses that cells undergo in response to DNA double stranded damage?

Answer 6

Senescence (permanent cell cycle arrest)

DNA repair

Apoptosis

Tolerance

Checkpoints activation

Question 7

What is the point of the DNA damage response?

Answer 7

Maintains genomic stability

Ensures cell cycle arrest, DNA repair. and apoptosis/survival decision making.

Question 8

What are the players in the response to DNA double strand breaks?

Answer 8

Sensors: continuously survey chromatin for DNA damage.

Transducers: relay and amplify signal

Effectors: receive signal and repair in response to the signal. They arrest the cell cycle or cause death of the cell.

Question 9

What is the MRN1/MRE11 complex?

Answer 9

A nuclear protein complex sensor of DNA double strand breaks; it is composed of:

MRE11, RAD50, and NBS1 and it governs the activation of downstream kinase ATM in response to DNA breaks. ATM phosphorylates histone 2Ax.

This complex is recruited rapidly and is retained at break site if histone is phosphorylated as well as other proteins such as PARP1, and MDC1.

Question 10

What is ATM?

Answer 10

ATM is the kinase responsible for phosphorylation of histone 2Ax. It also phosphorylates various other protein substrates including Chk2.

The ATM is the gene mutated in the condition known as ataxia-telangiectasia. This is caused by a loss of kinase activity of ATM which results in ataxia.

*ATM is a nuclear protein. It has a kinase domain similar to that of the PI3 family of lipid kinases but it is not a lipid kinase

Question 11

What are some complications of Ataxia - telangiectasia?

Answer 11

immunodeficiency

Extreme sensitivity to ionizing radiation

high rate of malignancies

Question 12

How is ATM activated?

Answer 12

Activation requires double stranded DNA with blunt ends or short overhangs.

2nd phase of activaion requires MRN as a cofactor.

Question 13

What are the advantages to sequential activation of kinases?

Answer 13

Amplification of the signal

Diversification of the signal

Question 14

What is the function of Chk1/Chk2?

Answer 14

Chk1/Chk2 - nuclear protein kinase amplify DNA damage response.

Question 15

What are the domains present on Chk1/Chk2?

Answer 15

SCD: SQ/TQ cluster domain. SQ and TQ are motifs that can be phosphorylated by PI3K kinases and ATM/ATR

FHA

Kinase domain

NLS domain localises it to the nucleus

Question 16

During normal growth Chk2 is not active. How is it activated?

Answer 16

After DNA damage it needs to be phosphorylated at multiple sites for activation. Phosphorylation is done by the PI3K family and by ATM and ATR.

Question 17

What is the result of phosphorylation of the SCD domain of Chk2?

Answer 17

Phosphorylation of Chk2 at the SCD domain results in dimerisation of the protein and activation of kinase domain. After activation of the kinase domain the dimers dissociate and are active.

Question 18

What is the sequence of events that takes place in response to double stranded DNA damage?

Answer 18

1) MRN1/MRE11 detects dsDNA damage and activates ATM/ATR.
2) ATM/ATR are kinases that are similar to PI3K kinases and they activate Chk1/Chk2 by binding to their SCD domain.
3) Chk2 undergoes a conformational change and dimerises and then is activated.
4) Dimer separates and the individual monomers are active kinases which activate p53.
5) p53 is a transcription factor that can activate p21 transcription. (it is in low amounts due to Mdm2 activity.
6) p21 transcription results in p21 protein which inhibits cyclin-dependent protein kinases
7) cyclin-dependent protein kinases inhibit the cell cycle from continuing.

Question 19

What is the function of p53?

Answer 19

p53 is a transcription factor which drives transcription of target factors. p53 is phosphorylated by Chk2 and as a result it stabilises p53 preventing it from being degraded by mdm2.

Question 20

Why are normal cell levels of p53 low?

Answer 20

in a normal cell p53 levels are very low due to being destroyed by mdm2 via ubiquitination.

Question 21

What is the function of p53?

Answer 21

p53 activates transcription of p21 mRNA. p21 is translated and forms p21 protein which inhibits cyclin-dependent protein kinases and as a result cell cycle is arrested.

Question 22

What are some other problems that could result from DNA damage?

Answer 22

increased inflammation

Decreased regeneration

Impaired cellular metabolism

Suppression of endcrine function

growth retardation

insulin resistance and type 2 diabietes