Intracellularly - Telomeres

Question 1

Telomere

Answer 1

This protects chromosomal ends from erosion over cell divsions and against interchromosomal fusion

Question 2

What happens when telomeres become too short?

Answer 2

Cell cycle arrest and apoptosis triggering

Question 3

What are telomeres improtant for?

Answer 3

Genomic integrity.

Question 4

What happens to telomeres every cell division?

Answer 4

They shorten, inducing instability of chromosomes

Question 5

How do cancer cells achieve immortality?

Answer 5

Bypass shortening through telomerase production through TERT expression.

Question 6

What causes increased hTERT expression in cancer cells?

Answer 6

Two mutations in the promoter region about 130BP upstream of TERT translation site.

Question 7

What are techniques used to induce cell death of cancer cells?

Answer 7

Antisense oligonucleotides
Immunotherapy
G-Quadruplex Stabilisers
Small Molecule Inhibitors

Question 8

Shelterin Complex

Answer 8

This regulates telomerase activity by binding telomeres and inducing t-loop formation.

Question 9

T Loop

Answer 9

A cap of 300 BP ssDNA stabilising telomere, preventing ends from being recognised as break points by DNA repair machinery.

Question 10

What sequence are telomeres rich in?

Answer 10

Tandem repeats of TTAGGG

Question 11

How long is the teloemre?

Answer 11

About 10-15KB long.

Question 12

What terminates the telomeres tandem repeats?

Answer 12

A 150-200 NT long overhang.

Question 13

What is the function of the telomere overhang?

Answer 13

Forms T-Loop by folding back onto the 3’ strand, invading the TTAGGG region.

Question 14

What are the components of the Shelterin Complex?

Answer 14

TRF1 and 2 heterodimer associated to POT/TPP1 heterodimer linked by TIN2.

Question 15

TRF1

Answer 15

Controls replication of telomeric DNA

Question 16

TRF2

Answer 16

Required for T-Loop formation and DDR supression and repression mediated by ATM preventing end-end chromosomsal fusion

Question 17

POT1

Answer 17

Associates TPP1 and ss 3’ overhang and represses recruitment of RPA

Question 18

TIN2

Answer 18

Links the POT1/TPP1 heterodimer to the TRF1/2 heterodimer, maintaing structural integrity.

Question 19

TERRA(Telomeric Repeat ContainingRNA)

Answer 19

A long, non-coding RNA essential for integrity, functioning in heterochromatin reguloation, teloemrase regulation and DDR

Question 20

How much is TL reduced per cell division?

Answer 20

About 50-150BP

Question 21

Replicative Senescences

Answer 21

This is where nonmalignant cells stop divding after about 50 cell divsions.

Question 22

M2 Crisis

Answer 22

When telomeres are so short they cannot form protective structures to protect chromosome ends.

Question 23

How do cancer cells bypass M1?

Answer 23

Expression of reactivating telomerase expression OR teloemrase independet ALT mechanisms.

Question 24

ALT mechanisms

Answer 24

A mechanism of which cancer cells use to bypass telomeric degradation.

Question 25

How many cells in a pool of M1 undergo M2?

Answer 25

1 in 5 million.

Question 26

What are the components of telomerase holoenzyme?

Answer 26

TERT (telomerase reverse transcription) hTERC (Human telomerase RNA component) NHP, NOP10, Dyskerin and GAR1.

Question 27

What is the general assembly process of Telomerase?

Answer 27

Translocation of hTERT to the nucleus with assembly with hTR then telomerase recruitment.

Question 28

What do NHP, NOP1, dyskerin and GAR1 do?

Answer 28

Associate with small, nucleoalr RNA important in pseudouridylation

Question 29

Pseudouridylation

Answer 29

The process of conversion of uridine to pseudouridine within RNA.

Question 30

TCAB1

Answer 30

Binds hTR sequecne to direct holoenzyme to Cajal Bodies of the nucleolus.

Question 31

What is the process of Telomerases function?

Answer 31

Diassociates TPP1 and POT1 interactions of shelterin by DAT domains then synthesis from 3' end.

Question 32

How does telomerase mediate TPP1 and POT1 diasscoation?

Answer 32

A DAT domain binds amino acid rich Tel patch of TPP1 and binds POT1 and TIN2.

Question 33

End Replication Problem

Answer 33

This proposes that linear DNA ends are not replicated completely during lagging strand DNA synthesis

Question 34

What happens to G-rich/C-rich strands in replication?

Answer 34

G-rich by leading strand synthesis and C-rich by lagging strand synthesis.

Question 35

Why is the lagging strand not completely replicated.

Answer 35

There is no room for okazaki fragment RNA primers to bind, resulting in an overhang and shortened telomere

Question 36

How does telomerase bypass End Replication Problem?

Answer 36

Increases leading strand to allow okazaki fragment RNA primer to be placed.

Question 37

What repair systems are DSB telomeres recognised by?

Answer 37

NHEJ Homologous recombination repair

Question 38

What is the first step in NHEJ and HRR?

Answer 38

MRN complex recognises DSB, activating ATM

Question 39

What does ATM do after being activated by MRN?

Answer 39

Phosphorylates DNA repair proteins activating them

Question 40

What is the major DSB pathway?

Answer 40

NHEJ?

Question 41

When might HRR be activated?

Answer 41

If NHEJ does not repair quick enough, ATM activates other two pathways by generation of SS 3' strand overhang.

Question 42

Why are cancer cells immortal?

Answer 42

Upregulation of catalytic subunit TERT of telomerase.