1. 12-2: Chromosomes and DNA Replication

2. Chromosomes DNA is found in structures called chromosomes
A chromosome has DNA plus proteins
Eukaryotic cells have rod-shaped chromosomes located in the nucleus.

3. Chromosome packing
Chromosomes are tightly packed into different levels
One level is called chromatin: DNA tightly coiled around proteins
histones: protein that DNA is tightly coiled around
Another level is the nucleosome:
Complex made of DNA and a histone molecule
beadlike

4. Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones

5. DNA Replication DNA must be copied so a cell can divide
Takes place in S phase of cell cycle
Called replication
The double helix structure of DNA allows for replication
Two sided
Complementary base pairs

6. Duplicating DNA A portion of the DNA opens into two strands
two new complimentary strands are produced using old DNA strands as templates
In eukaryotes, it proceeds in both directions at hundreds of places (replication forks)

7. How Replication Occurs
A series of enzymes unzips and unwinds the DNA
DNA polymerase:
enzyme that attaches complimentary nucleotides of DNA
proofreads the new strands
Another enzymes seals up the DNA strands