A human cell has about 1000–2000 mtDNA molecules

A human egg has about 500,000 mtDNA molecules

A sperm has only about 100 mtDNA molecules

TLS Online TPP Program

#Id: 8926

#Unit 2. Cellular Organization

ATR activated by single-stranded DNA breaks.

TLS Online TPP Program

#Id: 8927

#Unit 2. Cellular Organization

ATM and DNA-PK are specifically activated by double-strand breaks

TLS Online TPP Program

#Id: 8928

#Unit 2. Cellular Organization

ATM and ATR, activate a triad of related protein kinases: Chk1, Chk2, and MK2

TLS Online TPP Program

#Id: 8929

#Unit 2. Cellular Organization

Chk1, Chk2, and MK2

cause cell cycle arrest by inhibiting Cdc25

stabilizing the transcription factor p53, which induces the transcription of CKI p21 

TLS Online TPP Program

#Id: 8930

#Unit 2. Cellular Organization

If the DNA damage is severe, p21 can cause the cells to senesce or p53 can induce apoptosis.

TLS Online TPP Program

#Id: 8931

#Unit 2. Cellular Organization

DNA-PK, ATM, and ATR phosphorylate a variant histone H2AX within the chromatin near the damage site & Phosphorylated H2AX acts as a landing pad for recruiting additional protein complexes that control DNA repair