+

8.2 DNA Structure8.3 DNA Replication

8.2 DNA StructureKEY CONCEPT

DNA carries the genetic information in an organism.DNA structure is the same in all organisms.

+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.

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 groupa deoxyribose sugara nitrogen-containing base

phosphate group

deoxyribose (sugar)

nitrogen-containingbase

+DNA is held together by two types of bonds.

1. The backbone is connected by covalent bonds.

hydrogen bond covalent bond

2. The bases are connected by hydrogen bonds.

• There are 4 types of nucleotides: thymine, adenine, cytosine, and guanine

• The nitrogen containing bases are the only difference in the four nucleotides.

+

TA

CG

Nucleotides always pair in the same way.

The base-pairing rules show how nucleotides always pair up in DNA.

• Because a pyrimidine (single ring) pairs with a purine (double ring), the helix has a uniform width.

– A pairs with T

– C pairs with G

+• 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

+Write the pairing strand:

ATC GTC ACG TCA GTA

TAG CAG TGC AGT CAT

+8.3 DNA ReplicationKEY CONCEPT

General Description: DNA replication copies the genetic information of a cell.

+Replication copies the genetic information.

A single strand of DNA serves as a template for a new strand.

The rules of base pairing directreplication.

DNA is replicated during theS (synthesis) stage of thecell cycle.

Each body cell gets acomplete set ofidentical DNA.

+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.

+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.

+3. DNA polymerase enzymes bond the

nucleotides together to form the double helix.

3. DNA polymerase

4. new strand 2. Nitrogen bases

1. Sugar Phosphate Backbone

+

• DNA replication is semi-conservative, meaning one original strand and one new strand.

1. original strand 2. new strand

3. Two molecules of DNA

4. Two new molecules of DNA are formed, each with an original strand and a newly formed strand.

+DNA Replication Animations

https://www.youtube.com/watch?v=dKubyIRiN84

http://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120076/bio23.swf::How%20Nucleotides%20are%20Added%20in%20DNA%20Replication

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There are many origins of replication in eukaryotic chromosomes.

• DNA replication starts at many points in eukaryotic chromosomes.

Replication is fast and accurate.

• DNA polymerases can find and correct errors.