1

2 Chromosomes and DNA Chromosomes are made up of a chemical called DNA. They contain genes.

Genes Instructions to build proteins. –Examples: gene for hitchhiker’s thumb, widow’s peak, tongue-rolling… Humans have over 30,000 genes encoded in their genome. 3

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

6 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 m. The earth is 150 billion m or 93 million miles from the sun.

Packaging 7

8

9 The Shape of the Molecule DNA is a very long polymer. The basic shape is like a twisted ladder or zipper. This is called a double helix.

10 The Double Helix Molecule The DNA double helix has two strands twisted together. AVhhd-8

11 One Strand of DNA One strand of DNA is a polymer of nucleotide. nucleotide

12 Four DNA nucleotides Cytosine C Thymine T Adenine A Guanine G

13

14 Two Stranded DNA Remember, DNA has two strands that fit together something like a zipper. The teeth are the nitrogenous bases but why do they stick together?

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 with dotted lines

16 Hydrogen Bonds, Hydrogen Bonds, cont. When making hydrogen bonds, cytosine always pairs up with guanine Adenine always pairs up with thymine Adenine is bonded to thymine here C C C C N N N N N C C C C C N N O O C

17

18 Discovery of DNA Structure Erwin Chargaff showed the amounts of the four bases on DNA (A,T,C,G) In a body or somatic cell: A = 30.3% T = 30.3% G = 19.5% C = 19.9% Adapted from cmassengale

19 Chargaff’s Rule: Adenine and Thymine always join together A T Cytosine and Guanine always join together C G TA G C

Rosalind Franklin 20

21 Watson & Crick’s Model

22 EXIT SLIP! FUA6_Ucw3i4&feature=related

Hip Hip Hooray Blame it on the DNA 23

24 Nucleotides CC C O Phosphate O C C O -P O O O O O O O One deoxyribose together with its phosphate and base make a nucleotide. Nitrogenous base Deoxyribose

25 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

26 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

27 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

DNA Replication tion.htmlhttp:// tion.html 28