Telomeres and Centromeres

BSCI 420 Lecture 7 Sept 24, ‘02

“Being paranoid is a problem only if people aren’t out to get you”

-Jim Lynch

Chromosomes, cont.

2. Telomeres are the structures at the ends of linear eukaryotic chromosomes.• They consist of a series of unique Dna sequences and specialized proteins that bind to them.• Telomerase adds a unique sequence on the ends of euk. Chromosomes.• Discovered in Tetrahymena macronucleus• T. cells have the sequence (TTGGG)n, humans (ATTGGG)n

• Structure:

5’ TTGGGGTTGGGGTTGGGG3” AAC GGGG

GG hairpin proteins T loop

T loop

Telomeres are needed at the ends of chromosomes for several reasons:

A. Telomeres prevent the chromosome ends from being ligated together. Consequence?B. Telomeres prevent the ends of chromosomes from being attacked by exonucleases.(Loop structure explains both of these)

C. Telomeres attach chromosomes to the NE lamina.

D. Telomeres begin pairing or synapsis of homologous chromosomes during meiosis

E. Telomeres can compensate for incomplete replication of linear chromosome ends.

Telomerase action

Telomerase

3. Centromeres