1. DNA vs RNA DNA 1- Deoxyribose sugar
2- Adenine,Thymine, Cytosine, Guanine
3- Double-stranded, Long molecules
4. Inside the nucleus
RNA
1- Ribose sugar
2- Adenine, Uracyl, Cytosine, Guanine
3- Single stranded, shorter
4. Outside the nucleus

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Replication Facts
DNA has to be copied before a cell divides
DNA is copied during the S or synthesis phase of interphase
New cells will need identical DNA strands
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DNA Replication
Two strands open forming Replication Forks (Y-shaped region)
Replication
Fork
Parental DNA Molecule 3’ 5’
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4. Semiconservative Model of Replication
New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA
DNA Template
New DNA
Parental DNA
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DNA Replication
Prokaryotes (bacteria) have a single bubble
Eukaryotic chromosomes have MANY bubbles
Bubbles
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Question:
What would be the complementary DNA strand for the following DNA sequence?
DNA 5’-CGTATG-3’
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Answer:
DNA 5’-CGTATG-3’
DNA 3’-GCATAC-5’
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Question:
If there is 30% Adenine, how much Cytosine is present?
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Answer:
There would be 20% Cytosine
Adenine (30%) = Thymine (30%)
Guanine (20%) = Cytosine (20%)
Therefore, 60% A-T and 40% C-G
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DNA and Replication
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DNA Structure
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DNA
DNA is a polynucleotide,
made up of millions of subunits called nucleotides
Nucleotide made of:
1. Phosphate group
2. 5-carbon sugar
3. Nitrogenous base
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DNA Double Helix
Nitrogenous
Base (A,T,G or C)
“Rungs of ladder”
“Legs of ladder”
Phosphate &
Sugar Backbone
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14. Replication of Strands
Replication Fork
Point of Origin
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DNA Replication
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Proofreading New DNA
DNA polymerase initially makes about 1 in 10,000 base pairing errors
Enzymes proofread and correct these mistakes
The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors
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DNA Damage & Repair
Chemicals & ultraviolet radiation damage the DNA in our body cells
Cells must continuously repair DAMAGED DNA
Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA
DNA polymerase and DNA ligase replace and bond the new nucleotides together
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