DNAdeoxyribonucleic acid

DNA Discovery

DNA is a polymer (nucleic acid)Made up of nucleotides (monomers):

phosphate

deoxyribose sugar

nitrogen base

adenine - thymine

guanine - cytosine

repeating nucleotidesbases are either purines (adenine, guanine) or pyrimidines (thymine, cytosine)

What is the difference?

What do 5’ and 3’ mean?

Antiparallel strands

hydrogen interactions join nitrogen bases

advantages of structure?

Why are the number of interactions different?

DNA Structure

DNA Replication

Process of DNA making an exact copy

Semi-conservative process

occurs at replication origin/replication fork

eukaryotic cells have several that fuse

Replication Process1. DNA uncoils due to helicase

2. H-bonds between bases break

3.Single Stranded Binding Proteins keep strands from rebinding

4.Topoisomerase prevents twisted ends from breaking

5. Primase adds RNA primer to DNA; gives starting point

6. Old strand serves as template for new strand

7. DNA polymerase III adds free nucleotides to complement, forms new strand

Figure 16.13

Topoisomerase

Primase

RNA primer

Helicase

Single-strand binding proteins

5ʹ3ʹ

5ʹ

5ʹ3ʹ

3ʹ

PROBLEM!!DNA polymerase adds nucleotides only to 3’ end

New strand forms 5’ to 3’--> leading strand

Other original strand gets nucleotides added in fragments --> lagging strand

Fragments are called Okazaki fragments

This strand moves away from replication fork

Solution!!

DNA ligase connects Okazaki fragments making continuous strand

Review

• DNA Replication

Telomeres-TTAGGG repeated 100-1000 times -contain no genes -can be extended by telomerase

Importance?

Figure 16.21

1 µm• Telomeres