1. DNA Replication & Chromosomes
Notes - DNA Replication & Chromosomes (Chapter 12-2)
DNA Replication & Chromosomes
Chapter 12-2

2. The structure of DNA explains how DNA can be replicated
Each strand of the double helix has the information necessary to construct the other side
Complimentary base-pairing (A-T, C-G)

3. DNA Replication – What is it?
DNA Replication – process where DNA is copied
Takes place before cell divides to ensure that each new cell has a complete set of DNA
In eukaryotic cells, replication takes place during the S phase of Interphase

4. DNA Replication – How is DNA copied?
DNA replication is a 3-step process:
“Unzipping” – hydrogen bonds between base pairs are broken & molecule separates into 2 strands
New complementary strands are produced using base-pair rules
EX. A strand with the bases TACGTT produces the complementary strand ATGCAA
Two identical DNA molecules are formed
After replication, each DNA molecule has one original strand and one new strand

5. DNA Replication

6. DNA Replication – 3D Animation

7. DNA Replication – Differences between eukaryotic & prokaryotic cells
In prokaryotic cells, replication begins at a single point and proceeds away from that point in both directions until two identical DNA molecules are formed
In eukaryotic cells, replication begins simultaneously at hundreds of places and proceeds in both directions

8. Enzymes are necessary for replication
Helicase – “unzips” DNA molecules by breaking bonds between base pairs
DNA Polymerase – bonds complementary nucleotides together creating new DNA strands

9. DNA & Chromosomes
DNA in a cell is organized into structures called chromosomes
Prokaryotic organisms (bacteria) have one large, circular DNA molecule in the cytoplasm
Eukaryotic organisms have a number of chromosomes that are located in the nucleus
Eukaryotes have more DNA than prokaryotes (~50X)
Chromosome number differs from species to species (Humans = 46, Fruit fly = 8, Dog = 78, etc.)

10. DNA Length DNA is a long molecule
The E. coli bacteria chromosome is over 4 million base pairs long (~1.6 mm)
A human cell contains about 1000X as many base pairs as a bacteria cell ( > 1 m of DNA)
DNA must be highly folded to fit into a cell

11. DNA Length

12. Chromosome Structure
Eukaryotic DNA is wound into coiled structures of DNA and protein called chromosomes
DNA strands are wound around histone proteins forming nucleosomes
Nucleosomes pack together in coils forming a thick fiber called chromatin
Chromatin is coiled further forming supercoils
Supercoils are wound into chromosomes

13. DNA Packaging