Telomeres

Telomeres

ends of chromosomes protect ends, maintain length

repeated sequence TTGGGG or TTAGGG or similar

How to visualize telomeres

FISH Flourecence In Situ Hybridization

FISH

southern blot but directly in chromosome

The end replication problem

RNA primer on 5’ end of an Okazaki fragment cannot add DNA into gap so ends get shorter

Telomerase

maintains telomere length equilibrium

uses internal RNA template to add telomere repeats

extends 3’ end and then adds from there to 5’ end in small segments

Telomere elongation process

templated extension

alignment region NOT copied just places 3 prime end in right place

Template region in green is what is extended

mutation in alignment region will NOT change sequence of repeats

Short telomeres lead or lack of telomerase leads to:

loss of tissue renewal

cell death

cell senescence - DNA damage checkpoint cause arrest at G1 or G2 phase

block cancer

DNA damage response leads to?

activation of kinase signaling cascade that causes arrest and repair or death

Double strand break (DSB) recruits?

MRN

and ATM (DNA damage induces kinase)

H2AX histone variant of H2A is phosphorylated and recruits other proteins like 53BP1

Way to visualize DNA damage

Flourescence microscopy to see Co-localization

aka Indirect immunofluorescence using 2 antibodies

where H2AX and 53BP1 overlap there is prob DNA damage

or combine Telomere FISH with 53BP1 staining to see overlap

Long telomeres lead to

cancer

telomerase is important in cells that divide a lot such as

stem cells

blood cell hematopoiesis

Long read nanopore sequencing

to determine length of telomeres

each chromosome has a unique telomere length