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1 DNA - Chapter 12. 2 DNA 3 Searching for the “Secret of Life” 1.What is the fundamental unit of all living things? The Cell 2.Which cellular structure.

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Presentation on theme: "1 DNA - Chapter 12. 2 DNA 3 Searching for the “Secret of Life” 1.What is the fundamental unit of all living things? The Cell 2.Which cellular structure."— Presentation transcript:

1 1 DNA - Chapter 12

2 2 DNA

3 3 Searching for the “Secret of Life” 1.What is the fundamental unit of all living things? The Cell 2.Which cellular structure controls the cell and carries the heredity information? The nucleus 3.What substance in the nucleus carries the code of life? DNA

4 I.Griffith & Transformation A.Fredrick Griffith - trying to learn how certain bacteria caused pneumonia. B.Isolated two different strains of pneumonia bacteria from mice and grew them in his lab. 4

5 C.Griffith set up four types of experiments: 1.Experiment 1: Mice were injected with pneumonia causing bacteria – developed pneumonia and died. 5

6 2.Experiment 2: Mice were injected with harmless strain of bacteria – didn’t get sick. 6

7 3.Experiment 3: Griffith heated the disease- causing bacteria. Then injected the heat-killed bacteria into the mice. The mice survived. 7

8 4.Experiment 4: Griffith mixed his heat-killed, disease-causing bacteria with live, harmless bacteria. The injected mixture gave the mice pneumonia & they died. 8

9 D.Griffith concluded that the heat- killed bacteria passed their disease- causing ability to the harmless strain. E.Griffith called this process transformation – The harmless strain had changed permanently into a disease-causing strain. 9

10 Hershey and Chase Transformation Experiment (1952)… What did it prove? DNA of the virus and not the protein of the virus enters the bacteria and conducts the transformation of the bacteria into a viral factory This experiment is predicated on the idea that DNA contains P and not S… and Protein contains S and not P

11 Bacterial cell Phage head Tail Tail fiber DNA 100 nm

12 12 Chromatin

13 13 DNA I.DNA – Deoxyribose Nucleic Acid A.Structure 1.DNA is made of repeating units called nucleotides. 2.Nucleotides have 3 parts: a.A nitrogenous base b.A 5-carbon sugar (deoxyribose) c.A phosphate group

14 14 Fig 12-5 – nucleotide structure

15 15 B.The Four Nitrogenous Bases 1.The Purines – 2 carbon rings Why are these called nitrogenous bases?

16 16 B.Four Nitrogenous Bases (cont) 2.The Pyrimidines – 1 carbon ring How are the pyrimidines different from the purines?

17 17 C.The Sugar D.The Phosphate Deoxyribose

18 18 II.Double Helix A.The shape of DNA is described as a double helix (a twisted ladder). What force holds the two strands together?

19 19 II.Double Helix (cont) B.A simple model of DNA Draw this!!

20 20 III.Principles of Base Pairing (Chargaff) A.The opposing bases always pair the same:  Adenine (A) pairs with Thymine (T)  Guanine (G) pairs with Cytosine (C) What would be the complimentary base sequence for the strand of DNA below? A C G G T T A C A A T G A TGC C AAT G T TAC T

21 21 IV.Chromosomes & DNA Replication A.Chromosomes contain DNA and protein, tightly packed together to form chromatin. 1.Chromatin consists of DNA tightly coiled around proteins called histones.

22 22 Eukaryotic Chromosome Structure Chromosome Supercoils Nucleosome DNA double helix Histones Coils Fig

23 23 B.DNA Replication 1.Before a cell divides, it duplicates its DNA in a process called replication. 2.Replication ensures that each copied cell will have a complete set of DNA. 3.In replication the DNA separates into two strands. Each strand produces two new complementary strands by base pairing.

24 24 Nitrogen Bases Replication Fork DNA Polymerase Replication Fork Original strand New Strand Growth

25 25 C.How Replication Occurs 1.DNA replication is carried out by enzymes that “unzip” a molecule of DNA. 2.Hydrogen bonds between base pairs are broken and the two strands of DNA unwind. 3.The principal enzyme involved in DNA replication is DNA polymerase.

26 26 DNA Replication

27 27 V.How does DNA control living things? A.DNA codes for the amino acid sequence in proteins B.Every three bases (called a codon) codes for one amino acid. 1. Examples: TTT codes for phenylalanine GAA codes for leucine TGG codes for tryptophan

28 28 The first step in DNA replication is a.producing two new strands. b.separating the strands. c.producing DNA polymerase. d.correctly pairing bases.

29 29 A DNA molecule separates, and the sequence GCGAATTCG occurs in one strand. What is the base sequence on the other strand? a.GCGAATTCG b.CGCTTAAGC c.TATCCGGAT d.GATGGCCAG


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