1. 8.2 DNA Structure 8.3 DNA Replication

2. 8.2 DNA Structure
KEY CONCEPT DNA carries the genetic information in an organism.
DNA structure is the same in all organisms.

3. Watson and Crick determined the three-dimensional structure of DNA by building models.
Overall Shape:
They realized that DNA is a double helix that is made up of a sugar- phosphate backbone on the outside with bases on the inside.

5. DNA is composed of four types of nucleotides.
DNA is made up of a long chain of nucleotides.
Each nucleotide has three parts:
a phosphate group
a deoxyribose sugar
a nitrogen-containing base
phosphate group
deoxyribose (sugar)
nitrogen-containing
base

6. DNA is held together by two types of bonds.
1. The backbone is connected by covalent bonds.
2. The bases are connected by hydrogen bonds.
hydrogen bond
covalent bond

7. There are 4 types of nucleotides: thymine, adenine, cytosine, and guanine
The nitrogen containing bases are the only difference in the four nucleotides.

8. Nucleotides always pair in the same way.
The base-pairing rules show how nucleotides always pair up in DNA.
A pairs with T
C pairs with G
Because a pyrimidine (single ring) pairs with a purine (double ring), the helix has a uniform width. C G T A

9. Watson and Crick’s discovery built on the work of Rosalind Franklin and Erwin Chargaff.
Franklin’s x-ray images suggested that DNA was a double helix of even width.
Chargaff’s rules stated that A:T and C:G ALWAYS

10. Write the pairing strand:
ATC GTC ACG TCA GTA TAG CAG TGC AGT CAT

11. 8.3 DNA Replication
KEY CONCEPT General Description: DNA replication copies the genetic information of a cell.

12. Replication copies the genetic information.
A single strand of DNA serves as a template for a new strand.
The rules of base pairing direct replication.
DNA is replicated during the S (synthesis) stage of the cell cycle.
Each body cell gets a complete set of identical DNA.

13. Proteins carry out the process of replication.
DNA serves only as a template.
Enzymes and other proteins do the actual work of replication.
nucleotide
The DNA molecule unzips in both directions.

14. Process: How does DNA replication happen?
1. Enzymes unzip the double helix.
2. Free-floating nucleotides form hydrogen bonds with the template strand.
nucleotide
The DNA molecule unzips in both directions.

15. 3. DNA polymerase enzymes bond the nucleotides together to form the double helix.
1. Sugar Phosphate Backbone
3. DNA polymerase
4. new strand
2. Nitrogen bases

16. 4. Two new molecules of DNA are formed, each with an original strand and a newly formed strand.
DNA replication is semi-conservative, meaning one original strand and one new strand.
1. original strand
2. new strand
3. Two molecules of DNA

17. DNA Replication Animations
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18. Replication is fast and accurate.
DNA replication starts at many points in eukaryotic chromosomes.
There are many origins of replication in eukaryotic chromosomes.
DNA polymerases can find and correct errors.