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1 2 Chromosomes and DNA Our genes are on our chromosomes. Chromosomes are made up of a chemical called DNA.

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Presentation on theme: "1 2 Chromosomes and DNA Our genes are on our chromosomes. Chromosomes are made up of a chemical called DNA."— Presentation transcript:

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3 2 Chromosomes and DNA Our genes are on our chromosomes. Chromosomes are made up of a chemical called DNA.

4 3 DNA DNADNA is “the blueprint of life” DNA contains the instructions for making proteins within the cell.

5 4 What does DNA look like? Watson & Crick’s Model Double Helix Twisted Ladder

6 5 Made of nucleotides: 3 Components Sugar (deoxyribose) Phosphate Group Nitrogenous Base

7 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

8 7 The rungs are the bases

9 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)

10 9 A-T and C-G ATC T A G

11 10 Complimentary Base Pairing ATC Hydrogen bonds hold bases together T A G

12 11 DNA Why do we study DNA? medical reasons better food crops forensics

13 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 0.000000002 m. The earth is 150 billion m or 93 million miles from the sun.

14 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

15 14 Question: Adenine CytosineIf there is 30% Adenine, how much Cytosine is present?

16 15 Question: When and where does DNA Replication take place?When and where does DNA Replication take place?

17 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.

18 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

19 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’

20 19 DNA Replication DNA Replication Replication Bubbles Replication Bubbles: Bubbles

21 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

22 21 Question: What would be the complementary DNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’

23 22 Answer: DNA 5’-GCGTATG-3’ DNA 3’-CGCATAC-5’

24 23 You Try it! http://www.pbs.org/wgbh/aso/tryit/ dna/shockwave-nojs.htmlhttp://www.pbs.org/wgbh/aso/tryit/ dna/shockwave-nojs.html

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