1. 12-2 Chromosomes and DNA Replication

2. Single circular DNA molecule with all the cell’s genetic info
Prokaryotic Cells
No nucleus
DNA in the cytoplasm
Single circular DNA molecule with all the cell’s genetic info

3. Eukaryotic Cells 1000x the amount of DNA
DNA in the nucleus, form of chromosomes
Chromosome # varies from species to species
Human 2N cells = 46 chromosomes
Drosophila cells = 8

4. That’s like putting a 300 meter long rope into a backpack
DNA Length
E. coli have 4,639,221 base pairs and about 1.6 mm long all in one bacterium
That’s like putting a 300 meter long rope into a backpack

5. Chromosome Structure
Nucleus of a human cell contains > 1meter of DNA
Eukaryotic chromosomes contain DNA and protein tightly packed to form chromatin
Chromatin is DNA tightly coiled around histones to form a nucleosome
Nucleosomes fold huge lengths of DNA into the tiny spaces in the nucleus

7. Structure of DNA explains how it can be copied (replicated)
DNA Replication
Structure of DNA explains how it can be copied (replicated)
Complementary strands have all info needed to reconstruct other half by base pairing

8. DNA replication begins at a single point and proceeds
Prokaryotes
DNA replication begins at a single point and proceeds
(in two directions)

9. Eukaryotes
DNA replication occurs at hundreds of places
Proceeds in both directions until each chromosome is completely copied
Replication forks – points where separation and replication occur

10. Replication happens before a cell divides—copies its DNA
Two new complementary strands made following base pairing rules
Each strand is a template (model) for a new strand
TAGCAA

11. How Replication Occurs
Enzymes are very important
DNA helicase unzips the DNA
DNA polymerase joins individual nucleotides to produce a DNA molecule
DNA polymerase also proofreads each new DNA strand to ensure each molecule is a perfect copy of the original