1. What is DNA?
Although the environment influences how an organism develops, the genetic information that is held in the molecules of DNA ultimately determines an organism’s traits.
DNA achieves its control by determining the structure of proteins.
Within the structure of DNA is the information for life—the complete instructions for manufacturing all the proteins for an organism.

2. The structure of nucleotides
DNA is a polymer made of repeating subunits called nucleotides.(the monomer)
Nucleotides have three parts: a simple sugar, a phosphate group, and a nitrogenous base.
Nitrogenous base
Phosphate group
Sugar (deoxyribose)

3. The structure of nucleotides
in DNA there are four possible nucleotides, each containing one of these four bases.
The phosphate groups and deoxyribose molecules form the backbone of the chain, and the nitrogenous bases stick out like the teeth of a zipper.
The Bases Bind the two sides of the chain together with hydrogen bonds
Nitrogenous base (A, G, C, or T)
Phosphate group
Thymine (T)
Nucleotide
Sugar (deoxyribose)
DNA nucleotide
Sugar-phosphate backbone

4. The 4 Unique Nitrogenous Bases
2 Purines (larger):
Adenine (A)
Guanine (G)
2 Pyrimidines (smaller):
Cytosine (C)
Thymine (T)

5. Chargaff DNA composition: “Chargaff’s rules”
varies from species to species
all 4 bases not in equal quantity
bases present in characteristic ratio
Humans: A = 30.9%
T = 29.4%
G = 19.9%
C = 19.8%
A=T and C=G

6. Rosalind Franklin ( )
A chemist by training, Franklin had made original and essential contributions to the understanding of the structure of graphite and other carbon compounds even before her appointment to King's College. Unfortunately, her reputation did not precede her. James Watson's unflattering portrayal of Franklin in his account of the discovery of DNA's structure, entitled "The Double Helix," depicts Franklin as an underling of Maurice Wilkins, when in fact Wilkins and Franklin were peers in the Randall laboratory. And it was Franklin alone whom Randall had given the task of elucidating DNA's structure. The technique with which Rosalind Franklin set out to do this is called X-ray crystallography. With this technique, the locations of atoms in any crystal can be precisely mapped by looking at the image of the crystal under an X-ray beam. By the early 1950s, scientists were just learning how to use this technique to study biological molecules. Rosalind Franklin applied her chemist's expertise to the unwieldy DNA molecule. After complicated analysis, she discovered (and was the first to state) that the sugar-phosphate backbone of DNA lies on the outside of the molecule. She also elucidated the basic helical structure of the molecule.
After Randall presented Franklin's data and her unpublished conclusions at a routine seminar, her work was provided - without Randall's knowledge - to her competitors at Cambridge University, Watson and Crick. The scientists used her data and that of other scientists to build their ultimately correct and detailed description of DNA's structure in Franklin was not bitter, but pleased, and set out to publish a corroborating report of the Watson-Crick model. Her career was eventually cut short by illness. It is a tremendous shame that Franklin did not receive due credit for her essential role in this discovery, either during her lifetime or after her untimely death at age 37 due to cancer.

7. 1953 | 1962
Structure of DNA
James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin and Maurice Wilkens
Wilkins

8. Paired bases DNA structure Bases match together double helix
2 sides like a ladder
Bases match together
A pairs with T
C pairs with G

9. DNA is a double-stranded helix
Watson and Crick also proposed that DNA is shaped like a long zipper that is twisted into a coil like a spring.
Because DNA is composed of two strands twisted together, its shape is called double helix.

10. The structure of DNA Hydrogen bond Base pair
Partial chemical structure
Ribbon model
Computer model

11. The importance of nucleotide sequences
The sequence of nucleotides forms the unique genetic information of an organism. The closer the relationship is between two organisms, the more similar their DNA nucleotide sequences will be.
Scientists use nucleotide sequences to determine evolutionary relationships among organisms, to determine whether two people are related, and to identify bodies of crime victims.
Chromosome

12. DNA Packing Metaphase chromosome DNA double helix (2-nm diameter
Histones
“Beads on a string”
Nucleosome (10-nm diameter)
Tight helical fiber (30-nm diameter)
Supercoil (200-nm diameter)
700 nm
Metaphase chromosome

13. Nucleosomes “Beads on a string” 1st level of DNA packing
8 histone molecules
“Beads on a string”
1st level of DNA packing
histone proteins
8 protein molecules
positively charged amino acids
bind tightly to negatively charged DNA

14. Replication of DNA
Section objective:
Summarize DNA replication

15. Replication of DNA
Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes.
The DNA in the chromosomes is copied in a process called DNA replication.
Without DNA replication, new cells would have only half the DNA of their parents.
DNA is copied during interphase prior to mitosis and meiosis.
It is important that the new copies are exactly like the original molecules.

16. Replication of DNA DNA replication depends on specific base pairing
In DNA replication, the strands are separated by an enzyme
Enzymes then use each strand as a template to assemble the new strands
Nucleotides
Parental molecule of DNA
Both parental strands serve as templates
Two identical daughter molecules of DNA

17. Replication of DNA Semiconservative replication:
Parental strands of DNA separate, serve as templates and produce 2 molecules of DNA that have one strand of parental DNA and one strand of new DNA

18. Copying DNA
Matching bases allows DNA to be easily copied

19. DNA replication
DNA Helicase: enzyme responsible for uncoiling the double helix and unzipping the weak hydrogen bonds between the base pairs

20. DNA replication Enzyme DNA polymerase
adds new bases to the old strands
DNA bases in nucleus
DNA
polymerase

21. Leading strand- elongates as DNA unwinds
Lagging strand –elongates in opposite direction . Synthesized discontinuously into small segments called Okazaki fragments
DNA ligase (an enzyme)links these sections

22. New copies of DNA Get 2 exact copies of DNA to split between new cells
polymerase
DNA
polymerase