3. DNA DNA. DNA is often called the blueprint of life. In simple terms, DNA contains the instructions for making proteins within the cell.

4. DNA Why do we study DNA? We study DNA for many reasons, e.g., its central importance to all life on Earth, medical benefits such as cures for diseases, better food crops.

5. DNA Structure DNA consists of two molecules that are arranged into a ladder-like structure called a Double Helix. A molecule of DNA is made up of millions of tiny subunits called Nucleotides. Each nucleotide consists of: 1. Phosphate group 2. Pentose sugar 3. Nitrogenous base

6. Nucleotides Phosphate Pentose Sugar Nitrogenous Base

7. Nucleotides The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”. There are four types of nitrogenous bases.

8. Nucleotides A Adenine T Thymine G Guanine C Cytosine

9. Two Kinds of Bases in DNA Pyrimidines are single ring bases. Pyrimidines are single ring bases. Purines are double ring bases. Purines are double ring bases. C C C C N N O N C C C C N N N N N C

10. Thymine and Cytosine are pyrimidines Thymine and cytosine each have one ring of carbon and nitrogen atoms. Thymine and cytosine each have one ring of carbon and nitrogen atoms. C C C C N N O N cytosine C C C C N N O O thymine C

11. Adenine and Guanine are purines Adenine and guanine each have two rings of carbon and nitrogen atoms. Adenine and guanine each have two rings of carbon and nitrogen atoms. C C C C N N N Adenine N N C C C C C N N O N Guanine N N C

12. Nucleotides Each base will only bond with one other specific base. Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Form a base pair.

13. DNA Structure Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.

14. G G A T T A A C T G C A T C

15. C C C C N N O N C C C C N N O N N N C Hydrogen Bonds The bases attract each other because of hydrogen bonds. Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA. (The bonds between cytosine and guanine are shown here.)

16. Hydrogen Bonds, Hydrogen Bonds, cont. When making hydrogen bonds, cytosine always pairs up with guanine, And adenine always pairs up with thymine. (Adenine and thymine are shown here.) C C C C N N N N N C C C C C N N O O C

17. AS Biology. Gnetic control of protein structure and function

18. DNA Structure To crack the genetic code found in DNA we need to look at the sequence of bases. The bases are arranged in triplets called codons. A G G - C T C - A A G - T C C - T A G T C C - G A G - T T C - A G G - A T C

19. A gene is a section of DNA that codes for a protein. Each unique gene has a unique sequence of bases. This unique sequence of bases will code for the production of a unique protein. It is these proteins and combination of proteins that give us a unique phenotype.

20. Protein DNA Gene Trait

21. Your Task Draw a flow chart to show how to get from:

22. Looking Ahead: Properties of DNA Property 1 - it must contain, in a stable form, information encoding the organism’s structure, function, development and reproduction Property 2 - it must replicate accurately so progeny cells have the same genetic makeup Property 3 - it must be capable of some variation (mutation) to permit evolution

23. Replication of DNA and Chromosomes Speed of DNA replication: 3,000 nucleotides/min in human 30,000 nucleotides/min in E.coli Accuracy of DNA replication: Very precise (1 error/1,000,000,000 nt)

24. More DNA by the numbers Each cell has about 2 m of DNA. The average human has 75 trillion cells. The average human has enough DNA to go from the earth to the sun more than 400 times. DNA has a diameter of only 0.000000002 m. The earth is 150 billion m or 93 million miles from the sun.