1. DNA Structure and Replication

2. DNA
RNA
Double stranded
Deoxyribose sugar
Adenine, guanine, cytosine, thymine
Holds the information to make proteins
Single stranded
Ribose sugar
Adenine, guanine, cytosine, uracil
Messenger, transfer, ribosomal

3. DNA Structure
Double strands of DNA are considered anti-parallel (arranged in opposite directions)
DNA strands are in different orientations—one side 5’ carbon is “up”, other side 3’ carbon is up

5. DNA Structure DNA double helix is very similar to a twisted ladder
The sides/backbone of the ladder are considered to made of a sugar phosphate complex
The “rungs” of the ladder are the nitrogenous bases
Backbone held together by covalent bonds
Rungs held together by hydrogen bonds

6. DNA Structure A, T, G, C can be separated into 2 groups PYRIMIDINES
Thymine
Cytosine
(Uracil in RNA)
Single ring
PURINES
Adenine
Guanine
Double ring, 2x size of the others
Thymine
Adenine

7. DNA Packaging Eukaryotic DNA condensed (prokaryotic DNA is “naked”)
Chromosomes are supercoiled, very tightly packed
Histones (proteins) help with this packaging
Amount of condensation is unbelievable: over 10,000x smaller when in the chromosome form

8. Amount of condensation is unbelievable: over 10,000x smaller when in the chromosome form
If you were to have a fully extended molecule of DNA that stretched to be 100 yds long…
A molecule that was 10,000x smaller than that would only measure .36 inches!

9. Beads on a string…
Nucleosomes: strands of DNA coiled around 8 histone proteins
DNA (--), histones (+) = attraction
Coiled DNA cannot be transcribed
Enzymes must uncoil DNA
This helps eukaryotes regulate transcription

11. Theories of DNA replication
Conservative
Original DNA double helix acts as a template for producing a new template
The original double helix is conserved
Geoff Brown, IB OCC Website 11

12. The original double helix is destroyed
Destructive
The original double helix is destroyed
Nucleotides from the original strands end up in all daughter strands
Geoff Brown, IB OCC Website 12

13. The original DNA strands are conserved, but...
Semi Conservative
The original DNA strands are conserved, but...
... the strands are separated and each daughter double helix inherits one original strand
Geoff Brown, IB OCC Website 13

14. DNA replication is semi conservative
The two original strands act as templates for the synthesis of two new strands
Free nucleotides pair with complementary bases A C T G
Template strand
Pairing of complementary bases preserves the sequence of bases when DNA replicates
Geoff Brown, IB OCC Website 14

15. - unwinds the double helix
The Details: A C T G
The enzyme Helicase:
- unwinds the double helix
- breaks the hydrogen bonds between complementary bases
- separates the two strands 15

16. A C T Helicase A C T A C T T A G T A G T A G
Free nucleotides pair up with complementary bases, and are held in place, by hydrogen bonding 16

17. A C T T A G A A C T A C T T G T A G T A G T A G A C T T A G
DNA Polymerase creates two new strands of DNA by creating covalent bond between adjacent nucleotides 17

18. Leading strand A C T A C T T A G A C T T A G T A G T A G
1) An RNA primer allows for the addition of RNA nucleotides that match exposed point of DNA after helicase splits the two strands A C T A C T
2) DNA polymerase III adds DNA nucleotides 5’ >> 3” T A G A C T T A G T A G T A G
3) DNA polymerase I removes RNA primer, replaces it with DNA nucleotides 18

19. Lagging strand Not continuous, slower, hence lagging strand
New nucleotides added in fragments, then later chemical bonded to form a full strand
Additional enzyme needed to complete this process
DNA ligase

20. Lagging strand A C T T A G A C T A C T T G A T A G T A G
1) An RNA primer allows for the addition of RNA nucleotides that match exposed point of DNA after helicase splits the two stands
2) DNA polymerase III adds DNA nucleotides 5’ >> 3”, but in small chunks called Okazaki fragments
3) DNA polymerase I removes RNA primer, replaces it with DNA nucleotides
4) DNA ligase bonds fragments together
Modified from Geoff Brown, IB OCC Website 20

21. DNA Replication-enzymes
PROTEINS
ROLE
Helicase
Unwinds the double helix at replication forks
Primase
Synthesizes RNA primer
DNA polymerase III
Synthesizes new strand by adding nucleotides onto the primer (5’ to 3’)
DNA Polymerase I
Removes the primer and replaces it with DNA
DNA ligase
Joins the ends of DNA segments and Okazaki fragments

22. DNA Replication Replication is insanely fast—up to 4,000 bp per second
VERY few mistakes, but they do happen-all repaired by specific enzymes
The same enzymes are responsible for repairing damaged DNA as a result of chemical damage or exposure to high energy waves (radiation)