dna organization 6.5. chromosome structure the human genome consists of 23 pairs of chromosomes if...
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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”