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2 Chromosomes and DNA Our genes are on our chromosomes. Chromosomes are made up of a chemical called DNA.
3 DNA DNADNA is “the blueprint of life” DNA contains the instructions for making proteins within the cell.
4 What does DNA look like? Watson & Crick’s Model Double Helix Twisted Ladder
5 Made of nucleotides: 3 Components Sugar (deoxyribose) Phosphate Group Nitrogenous Base
6 The two sides of the ladder S S S P P S S S P P The sugar and phosphate make the sides of the ladder
7 The rungs are the bases
8 There are 4 bases A denine T hymine G uanine C ytosine A always pairs with T (sticks) C always pairs with G (curves)
9 A-T and C-G ATC T A G
10 Complimentary Base Pairing ATC Hydrogen bonds hold bases together T A G
11 DNA Why do we study DNA? medical reasons better food crops forensics
12 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.
13 Chargaff’s Rule Adenine ThymineAdenine must pair with Thymine GuanineCytosineGuanine must pair with Cytosine about the sameTheir amounts in a given DNA molecule will be about the same. G C TA
14 Question: Adenine CytosineIf there is 30% Adenine, how much Cytosine is present?
15 Question: When and where does DNA Replication take place?When and where does DNA Replication take place?
16 Synthesis Phase (S phase) S phase in interphase of the cell cycle. Nucleus of eukaryotes Mitosis -prophase -metaphase -anaphase -telophase G1G1 G2G2 S phase interphase DNA replication takes place in the S phase.
17 Replication DNA copies itself before division Steps: –Unwinds –Unzips –Copies using the old strands as templates Uses complementary base pairing Semiconservative: end up with one old strand and one new strand
18 DNA Replication DNA Replication Replication ForkshundredsY-shaped replicating DNA molecules Replication Forks: hundreds of Y-shaped regions of replicating DNA molecules where new strands are growing. ReplicationFork Parental DNA Molecule 3’ 5’ 3’ 5’
19 DNA Replication DNA Replication Replication Bubbles Replication Bubbles: Bubbles
20 DNA Replication Semiconservative Model:Semiconservative Model: Old strands serve as templates New molecules have one old, one new strand Parental DNA DNA Template New DNA
21 Question: What would be the complementary DNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’
22 Answer: DNA 5’-GCGTATG-3’ DNA 3’-CGCATAC-5’
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