Post on 11-Jun-2020
transcript
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
Telomeres-TTAGGG repeated 100-1000 times -contain no genes -can be extended by telomerase
Importance?