DNAWhat is DNA?

Why is it important?Structure of DNADNA Replication

DNA Discoveries and Scientists

Why is DNA important (again)

What is DNA?• DNA- deoxyribonucleic acid• DNA contains the genetic

information that makes you, you… animals, animals and plants, plants…

• DNA is composed of:– Double helix– Phosphate group– 5 carbon sugar (deoxyribose)– Nitrogen containing base– Weak hydrogen bonds

Make up a Nucleotide

Why is DNA Important?• DNA is in all living things • It is found in the cytoplasm of

bacteria and in the nucleus of protists, fungi, plants, and animals.

The Structure of DNA• Nucleotides- subunits that make up

DNA– Phosphate group– 5 carbon sugar (deoxyribose)– Nitrogen containing base:

• Adenine Thymine (A – T)• Guanine Cytosine (G – C)

* Weak hydrogen bonds hold bases together

P

S

The Structure of DNA• Double helix- two strands of

nucleotides twisted around each other, like a winding staircase

• Complementary base pairs- the sequence of bases on one strand that determines the sequence of the other strand– Adenine Thymine – Cytosine Guanine

The Structure of DNA• So, if the sequence on one side is:

A

A

C

CG

G

AT

T

T

C

A Label:- Phosphate

(P)- 5 carbon

sugar(S)- Correct

base pairs(A, T, C, G)- Draw

hydrogen bonds

The Structure of DNA5’

5’3’

3’

The Structure of DNA*Note about bases:

– Pyrimidines- single ring of carbon• Tymine and Cytosine

– Purine- two rings of carbon• Adenine and Guanine

A purine must always bond with a pyrimidine!

DNA Replication• DNA Replication- the process of making

a copy of DNA• Why is this important?

– Cells need to copy their DNA for mitosis (growth, repair, and maintenance)

• Three steps:– Double helix unwinds and opens– DNA polymerases add nucleotides back– Polymerases detach once replication is

complete

DNA ReplicationStep 1:The double helix must unwind before

replication can begin.DNA helicases are enzymes that open

the double helix by breaking the hydrogen bonds that hold the complimentary bases together (think of a zipper)

Replication goes from 5’ to 3’

DNA ReplicationStep 1 con’t:Once separated, additional

proteins hold the strands apart.Where the double helix separates

is called a replication fork (because of it’s Y shape)

DNA ReplicationStep 2:At the replication fork enzymes called DNA

polymerases move along each of the DNA strands.

DNA polymerases add nucleotides to the exposed bases according to the base pair rules

DNA ReplicationStep 3:Step 2 continues until all

DNA has been copied and the polymerases detach

Produces 2 DNA molecules that are identical to each other and the original strand

DNA Discoveries and Scientists

• Alfred Hershey and Martha Chase- discovered that DNA stores genetic information in living cells

• James Watson and Francis Crick-

pieced together the structure of DNA

• Chargaff- noticed the rules for base pairing (Adenine- Thymine and Cytosine – Guanine)

Why is DNA important?• DNA is the basis of genetic material

and serves as the template for making proteins.

• Proteins make:– your eye color and hair color– antibodies in your blood– enzymes vital to your metabolism– skin and muscles

• Proteins make you, you!