1. DNA DNA = DeoxyriboNucleic Acid
Short nucleic acid
A polymer that stores genetic information
Found in the chromosomes of all organisms
Controls production of proteins depending on sequence of nitrogen bases
Unit of structure = nucleotide

2. DNA Nucleotide – 3 parts A sugar – deoxyribose A phosphate group – PO4
A nitrogen base
Draw the Picture

3. Nitrogen Bases Nitrogen Bases – name source for the nucleotides
2 different types:
Purines – double ring
Adenine
Guanine
Pyrimidines – single ring
Cytosine
Thymine

4. Nitrogen Bases Purines Pyrimidines Phosphate group Deoxyribose Adenine
Guanine
Cytosine
Thymine
Phosphate group
Deoxyribose

5. DNA Structure
Double Helix (twisting ladder) – modeled by Watson & Crick 1953
Sides/backbone - alternating deoxyribose sugar & phosphate
“Rungs” - nitrogen bases held together by hydrogen bonds

7. Base Pairing Base Pairing
The complementary bases always pair a certain purine with a certain pyrimidine
Base
A = adenine
T = thymine
C = cytosine
G = guanine
Complementary Base
thymine
adenine
guanine
cytosine

8. Base Pairing Rule: A always pairs with T C always pairs with G
Hydrogen bonds
Nucleotide
Sugar-phosphate backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)

9. Chromosomes Eukaryotes Found in the nucleus
Prokaryotes
DNA is found in the cytoplasm
Single circular DNA molecules
DNA replication begins at a single point in the chromosome & proceeds in both directions until the chromosome is replicated
Eukaryotes
Found in the nucleus
Chromosome number varies between species
DNA replication occurs at hundreds of places called replication forks

10. Chromosomes How much DNA in a human nucleus? What is chromatin?
more than 1 meter
What is chromatin?
DNA tightly coiled around proteins called histones

11. Spirals /13/12
Bellwork
1. Using these words, please describe DNA Replication:
semi-conservative, unzips, Helicase, DNA Polymerase, A, G, T, C
double helix, hydrogen bonds.
2. When during the Cell Cycle does DNA replication take place?

12. Chromosomes How are chromosomes constructed?
DNA & histones form beadlike structures called nucleosomes
Nucleosomes pack with one another to form thick fibers
Fibers are shortened by a system of loops & coils

13. Replication

14. Replication – General Info
The exact copying of DNA
Replication occurs in both directions
DNA must be copied before cells divide  each daughter cell has a complete set of DNA
Original strands serve as templates for new strands

15. Replication – General Info
How it happens:
Helicase (enzyme) unwinds the DNA by breaking hydrogen bonds

16. Replication – General Info
DNA polymerase (enzyme) joins individual nucleotides to each separated strand, producing DNA molecule
DNA polymerase also proofreads each new DNA strand to make perfect copies

17. Replication – General Info
Results: 2 DNA molecules  each contains one original
strand & one new strand (semi-conservative)

19. Exit Ticket 1. Describe the base pairing rules.
Spirals /10/12
Exit Ticket
1. Describe the base pairing rules.
2. Compare and contrast purines and pyrimidines.
3. How do you think DNA replicates itself.
YouTube DNA Replication