1. Chromosomes & DNA Replication

2. I. DNA & Chromosomes
A. DNA is found in different ways depending on the type of cell you are looking at
1. In prokaryotic cells DNA is located in the cytoplasm in a single circular molecule known as a chromosome
2. In eukaryotic cells the DNA is located in the nucleus in the form of many chromosomes
B. DNA must be folded into at least 1/100 of its full length to fit in any type of prokaryotic cell

3. II. Chromosome Structure
A. In eukaryotic cells DNA has to be folded even further in order to do this chromosomes use the help of proteins.
1. Histones – proteins that have tightly wound DNA around them creating chromatin.
B. Together histones and DNA form a structure known as nucleosome, which gets further coiled into loops.
1. Only during mitosis are these fibers drawn together forming the tightly packed chromosomes. Which may help separate chromosomes during mitosis

4. III. DNA Replication
A. Each strand of the DNA double helix has the information to reconstruct the other half by base pairing.
1. Since each strand can be used to make the other the strand are said to be complimentary.
B. In prokaryotic cells replication occurs at one point and proceeds in 2 directions until the entire chromosome is replicated
C. In eukaryotic cells replication occurs in many points known as replication forks until each chromosome is completely copied

7. IV. Eukaryotic DNA Replication
A. DNA Replication – DNA molecule separates into 2 strands, then produces 2 new complimentary strands following the rules of base pairing. Each strand of the double helix serves as a template.
B. The 2 new DNA molecules each have one old strand and one new strand
C. In order for replication to occur DNA helicase “unzips” the DNA so that DNA polymerase can join the new nucleotides and proofreads to ensure correct base pairing