Enabling Replicative Immortality W6

Question 1

How can telomer erosion cause cellular apoptosis and senescence

Answer 1

The hayflick limit

Cultured normal human cells have limited capacity to divide approx. 20-70 times

This cellular ageing is called senescence or ceased proliferation

Question 2

Telomers

Answer 2

are protective caps at the end of repetitive DNA at the end of chromosomes

consist of hexameric TTAGGG nucleotide repeats

Telomeres keep chromosomes from unravelling

Like the plastic caps that prevent fraying of shoelaces.

Question 3

Each time a cell divides …

Answer 3

the telomeres get shorter and shorter

Eventually the ends of the chromosomes become frayed

Question 4

Crisis point

Answer 4

triggered when the cell identifies that there are damaged bits of DNA

The result is either a kind of long-term sleep known as senescence, or death.

Question 5

Telomerase

Answer 5

a cellular reverse transcriptase that adds DNA sequences (TTAGGG) onto telomeres to prevent shortening

Detected in 85-90% of all malignant tumours

Question 6

When telomerase becomes critically shortened

Answer 6

Triggers a DNA damage singal where cells can die or become senescent

Tumour cells bypass this crisis by upregulating telomerase and avoiding cell cycle checkpoint genes