1. DNA

3. Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms & some viruses.
The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints or a recipe, since it contains instructions needed to construct other components of cells, such as proteins & RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.

4. DNA Genes are made of DNA = deoxyribonucleic acid
How could DNA code for everything genes do?
Genes had to carry information from one generation to the next
Genes had to put that information to work by determining the inheritable characteristics of organisms
Genes had to be easily copied, because it is replicated every time the cell divides

5. DNA’s Structure A long molecule made of units called nucleotides
Each nucleotide is made of 3 basic parts:
A 5-carbon sugar called deoxyribose
A phosphate group
A nitrogenous base (There are 4 kinds…)
A (Adenine) T (Thymine)
G (Guanine) C (Cytosine)
Purines Pyrimidines

6. A Single DNA Nucleotide
Phosphate
Group
Deoxyribose
Sugar
Nitrogenous
Base

7. DNA Structure Phosphate Group Deoxyribose Sugar Nitrogenous Base
Weak Hydrogen Bonds

8. Figure 12–7 Structure of DNA
Section 12-1
Nucleotide
Hydrogen bonds
Sugar-phosphate backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
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9. The Chargaff “rule”
It was discovered that the percentages of guanines (G) and cytosines (C) are almost equal and the percentages of adenines (A) and thymines (T) are almost equal
Erwin Chargaff came up with a “rule” that guanine (G) pairs with cytosine (C) and adenine (A) pairs with thymine (T) (DNA Base Pairing)

10. Let’s pair up DNA! What would pair up with ATCG?
TAGC
What would pair up with ATTAGC?
TAATCG
What would pair up with ATACGGTC?
TATGCCAG

11. The Double Helix
Rosaline Franklin’s x-ray showed that two DNA strands are twisted around each other.
James Watson and Francis Crick used Franklin’s x-ray to make a model of DNA.
Watson and Crick’s model of DNA was a double helix, in which two strands were wound around each other.
Watson and Crick also discovered that hydrogen bonding held the nitrogenous bases together.

12. The two strands of DNA unwind or “unzip” breaking the hydrogen bonds and separating. Then each strand becomes the guide or “template” for the making of a new strand.
A protein called an enzyme called DNA polymerase breaks the nitrogen base bonds and the two strands of DNA separate, polymerizes individual nucleotides to produce DNA and “proof reads” the new DNA.

13. STEP 1 Two original strands of DNA separates by unwinding
Replication fork
Two original strands of DNA separates by unwinding
This occurs through the action of an enzyme that breaks the hydrogen bonds between the strands
The two areas on either end where the DNA separates is the REPLICATION FORK

14. STEP 2
At the replication fork, DNA polymerase moves along the DNA Strands adding nucleotides
As DNA polymerase moves along two strands of DNA form

15. Step 3
DNA Polymerase continues until all the nucleotides have been added
Two new identical molecules of DNA are formed
Another enzyme connects all the pieces of DNA together

16. Proofreading
At the end of Replication, DNA polymerase goes through the DNA to make sure there are no errors
This prevents mistakes in the DNA sequences
Mutations- Change in the sequence of the DNA