DNA Organization

6.5

Chromosome Structure

• the human genome consists of 23 pairs of chromosomes

• if all of the DNA was stretched out, it would measure 1.8 metres in length

• how does it fit into a typical human cell nucleus, 10 micrometres in diameter?

Hierarchical Organization

• DNA is coiled around a group of 8 stabilizing proteins called histones, forming nucleosomes

Chromosome Structure

• solenoid = a group of 6 nucleosomes coiled into chromatin fibres

• chromatin fibres fold into final chromatin structure through supercoiling.

Chromosome StructureSee animation: http://www.biostudio.com/c_%20education%20mac.htm

Prokaryotic DNA

• primary DNA is single circular chromosome

• supercoiling also in prokaryotes

• plasmids are other circular pieces of DNA that can be exchanged through conjugation

DNA Replication & Aging

6.6

Telomeres

Telomeres

• non-coding, repetitive sequences at the ends of chromosomes

• protect chromosomes from degradation, fusing to other chromosomes, assist in DNA repair

Telomere Shortening

• during replication, the 5’ primer on each strand is removed but not replaced with DNA

• telomeres shorten after each replication

• after many replications, telomeres will eventually disappear, allowing coding DNA to be damaged

Cell Senescence

• period in a cell’s lifespan when it loses the ability to divide & grow

• Hayflick limit = total number of times a normal cell can divide (about 50 in humans)

Dolly the Sheep

Telomerase

• enzyme that adds more DNA to shortening telomeres

• produced in germ line cells, stem cells, certain white blood cells

• cancer cells produce large quantity of telomerase

Anti-Aging

Dani Walker “Stop Aging Now TS-X Telomere Supplement”