1. The Double Helix

2. The Structure of DNA DNA is a nucleic acid (Deoxyribonucleic acid)
Nucleic acids are polymers (long chains) of nucleotides.

3. Nucleotides
3 Parts:
Phosphate group
5 carbon sugar
Nitrogenous base

4. DNA Nucleotides
In DNA, there are four types of nucleotides divided into two categories…
Purines: (Adenine & Guanine) two rings of carbon and nitrogen.
Pyrimidines: (Cytosine & Thymine) one ring of carbon and nitrogen.

5. Purines
Adenine Guanine

6. Pyrimidines
Cytosine Thymine

7. Chargaff’s Rule
Amount of nucleotides in a DNA sample follows a pattern
Adenine = Thymine
Cytosine = Guanine

8. Base Pairs
A & T / C & G

9. Chemical Bonds in the Double Helix
Backbone of helix
Covalent bonds alternating between phosphate groups and sugars
Nitrogenous Bases
Weak Hydrogen bonds between bases

11. An enzyme called helicase causes the molecule to untwist.

13. *
*The enzymes here are called DNA polymerases.

15. Accuracy and Repair… • 1 error in every 10,000 paired nucleotides
-change = mutation
• Proofreading and repair enzymes make error rate 1 per billion nucleotides
• DNA can also be damaged by carcinogens and U.V. light

16. DNA Replication

17. DNA Replication Cell Division (aka Mitosis!)
Once the DNA has replicated itself the cell is ready for:
Cell Division
(aka Mitosis!)

18. What is the ultimate purpose of DNA?
To make PROTEINS!
These proteins will tell the body how to act and look.

19. 2 steps to making proteins!
Transcription (making RNA from DNA code)
Translation (sending RNA to ribosomes)

20. But first a word from….RNA
Function: carries out genetic instructions contained in DNA
Structure: Similar to DNA except for the following:
-single strand
-ribose sugar
-uracil pairs with adenine

21. mRNA: The DNA decoding tool (“m” stands for messenger)

22. Transcription: Part of a DNA molecule is copied to mRNA
mRNA nucleotides pair with “unzipped” DNA

23. mRNA: The Journey
mRNA copies the DNA strand, leaves the nucleus and travels to the cytoplasm.
In the cytoplasm, mRNA attaches to a ribosome where the code is “translated”

24. The Genetic Code mRNA nucleotides are “read” in groups of three.
These groups are called Codons.
Each codon “translates”
into a specific type of
amino acid.
There are 20 amino acids
The order of the amino acids
Determines what the protein does

25. Translation Translation begins w/ the start codon AUG
An anticodon of tRNA
pairs with a specific
codon of mRNA.
tRNA adds an amino
acid to the forming
protein chain

26. Putting it all together

27. The Finished Product...
Translation is finished when the ribosome reaches a stop codon.
The sequence of the amino acids assembled at the ribosome determines the characteristics of the protein

29. A.A. chain
Protein Synthesis
mRNA
Ribosome