1. DNA - Chapter 12

2. DNA

3. Searching for the “Secret of Life”
What is the fundamental unit of all living things?
The Cell
Which cellular structure controls the cell and carries the heredity information?
The nucleus
What substance in the nucleus carries the code of life?
DNA

4. Griffith & Transformation
Fredrick Griffith - trying to learn how certain bacteria caused pneumonia.
Isolated two different strains of pneumonia bacteria from mice and grew them in his lab.

5. Griffith set up four types of experiments:
Experiment 1: Mice were injected with pneumonia causing bacteria – developed pneumonia and died.

6. Experiment 2: Mice were injected with harmless strain of bacteria – didn’t get sick.

7. Experiment 3: Griffith heated the disease-causing bacteria
Experiment 3: Griffith heated the disease-causing bacteria. Then injected the heat-killed bacteria into the mice. The mice survived.

8. Experiment 4: Griffith mixed his heat-killed, disease-causing bacteria with live, harmless bacteria . The injected mixture gave the mice pneumonia & they died.

9. Griffith concluded that the heat-killed bacteria passed their disease-causing ability to the harmless strain.
Griffith called this process transformation – The harmless strain had changed permanently into a disease-causing strain.

10. Hershey and Chase Transformation Experiment (1952)… What did it prove?
This experiment is predicated on the idea that DNA contains P and not S… and Protein contains S and not P
DNA of the virus and not the protein of the virus enters the bacteria and conducts the transformation of the bacteria into a viral factory

11. Phage
head
Tail
Tail fiber
DNA
100 nm
Bacterial
cell

12. Chromatin

13. DNA DNA – Deoxyribose Nucleic Acid Structure
DNA is made of repeating units called nucleotides.
Nucleotides have 3 parts:
A nitrogenous base
A 5-carbon sugar (deoxyribose)
A phosphate group

14. Fig 12-5 – nucleotide structure
To help students remember: If it has a ‘Y’ in the name it is a pyrimidine

15. The Four Nitrogenous Bases The Purines – 2 carbon rings
A molecule that contains nitrogen and has the chemical properties of a base.
Why are these called nitrogenous bases?

16. How are the pyrimidines different from the purines?
Four Nitrogenous Bases (cont)
The Pyrimidines – 1 carbon ring
The purines are double ring molecules, and the pyrimidines have single ring structure.
How are the pyrimidines different from the purines?

17. The Sugar
Deoxyribose
The Phosphate

18. What force holds the two strands together?
Double Helix
The shape of DNA is described as a double helix (a twisted ladder).
What force holds the two strands together?
Hydrogen bonds between the base pairs hold the strands together. 2 hydrogen bonds for A – T pairing, and 3 H-bonds for G – C bonding

19. Double Helix (cont)
A simple model of DNA
Draw this!!

20. A C G G T T A C A A T G A T G C C A A T G T T A C T
Principles of Base Pairing (Chargaff)
The opposing bases always pair the same:
Adenine (A) pairs with Thymine (T)
Guanine (G) pairs with Cytosine (C)
What would be the complimentary base sequence for the strand of DNA below?
A C G G T T A C A A T G A
Chargaff's Rules: The percentages of guanine [G] and cytosine [C] bases are almost = in any sample of DNA. The percentages of adenine [A] and thymine [T] bases are almost = in any sample of DNA. T G C C A A T G T T A C T

21. Chromosomes & DNA Replication
Chromosomes contain DNA and protein, tightly packed together to form chromatin.
Chromatin consists of DNA tightly coiled around proteins called histones.

22. Eukaryotic Chromosome Structure
Fig
Eukaryotic Chromosome Structure
Chromosome
Nucleosome
DNA double helix
Coils
Supercoils
Eukaryotic chromosomes contain DNA wrapped around proteins called histones. The strands of nucleosomes are tightly coiled and supercoiled to form chromosomes.
Histones

23. DNA Replication
Before a cell divides, it duplicates its DNA in a process called replication.
Replication ensures that each copied cell will have a complete set of DNA.
In replication the DNA separates into two strands. Each strand produces two new complementary strands by base pairing.

24. New Strand Original strand Nitrogen Bases Growth Growth
During DNA replication, the DNA molecule produces two new complementary strands. Each strand of the double helix of DNA serves as a template for the new strand.
Replication Fork
Replication Fork
DNA Polymerase

25. How Replication Occurs
DNA replication is carried out by enzymes that “unzip” a molecule of DNA.
Hydrogen bonds between base pairs are broken and the two strands of DNA unwind.
The principal enzyme involved in DNA replication is DNA polymerase.

26. DNA Replication

27. How does DNA control living things?
DNA codes for the amino acid sequence in proteins
Every three bases (called a codon) codes for one amino acid.
1. Examples:
TTT codes for phenylalanine
GAA codes for leucine
TGG codes for tryptophan

28. The first step in DNA replication is
producing two new strands.
separating the strands.
producing DNA polymerase.
correctly pairing bases.

29. A DNA molecule separates, and the sequence GCGAATTCG occurs in one strand. What is the base sequence on the other strand?
GCGAATTCG
CGCTTAAGC
TATCCGGAT
GATGGCCAG