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DNA Structure and Replication

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Title: DNA Replication Author: Robert and Marsha Goodman Last modified by: Bow School District Created Date: 4/13/2010 2:54:35 PM Document presentation format – PowerPoint PPT presentation

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Title: DNA Structure and Replication


1
DNA Structure and Replication
2
DNA
  • Discovery of the DNA double helix
  • A. 1950s
  • B. Rosalind Franklin - X-ray photo of DNA.
  • C. Watson and Crick - described the DNA
    molecule from Franklins X-ray.

3
Rosalind Franklins photo
4
Watson and Crick with their famous model
5
DNA
  • Is a chemical compound
  • Is a molecule
  • Is a polymer made of many monomers (subunit of
    compound)

6
Deoxyribonucleic Acid (DNA)
  • Many nucleotides (the monomer of DNA) form a
    polymer (DNA molecule) in a DNA double helix
  • Nucleotide
  • 1. Phosphate group
  • 2. 5-carbon sugar
  • 3. Nitrogenous base

7
DNA Nucleotide

8
DNA Double Helix

9
DNA Double Helix

10
Nitrogenous Bases
  • PURINES
  • 1. Adenine (A)
  • 2. Guanine (G)
  • PYRIMIDINES
  • 3. Thymine (T)
  • 4. Cytosine (C)

11
BASE-PAIRINGS
  • Base of
  • Purines Pyrimidines Pairs H-Bonds
  • Adenine (A) Thymine (T) A T 2
  • Guanine (G) Cytosine (C) C G 3

12
BASE-PAIRINGS

13
Chargaffs Rule
  • Adenine must pair with Thymine
  • Guanine must pair with Cytosine
  • Their amounts in a given DNA molecule will be
    about the same.

14
  • So if there is 30 Adenine, how much Cytosine
    will there be???

15
  • Advantages of Double-Stranded Nature of DNA
  • Forms a stable structure
  • Hydrophobic (water repelling) bases stack on top
    of one another, away from solvent
  • Negatively charged phosphate backbone is on the
    outside accessible to solvent
  • Each strand of DNA molecule serves as the
    template
  • For a new strand of DNA (replication)
  • For an RNA molecule (transcription)

16
DNA is Coiled Around Histone Proteins
  • DNA wraps around nuclear proteins called Histones
  • Entire complex is a Nucleosome

17
The structure of DNA
18
Nucleic Acids
  • DNA and RNA are nucleic acids
  • Comprised of
  • A 5-carbon sugar (deoxyribose or ribose)
  • Nucleotides
  • DNA has two strands bonded together
  • RNA has one strand ONLY
  • C, H, N, O, P atoms

19
Nucleotide Structure
  • Three different components
  • Phosphate group
  • Nitrogen containing base (A,T,G,C,U)
  • Five-carbon sugar
  • (ribose or deoxyribose)

20
Synthesis Phase (S phase)
  • S phase in interphase of the cell cycle.
  • Nucleus of eukaryotes

21
DNA is Self-Replicating
  • Before Cells divide
  • Enzymes break bonds between bases
  • Complementary strands separate
  • Complementary bases are added to strands
  • Copy of DNA results

22
Replication Mechanisms
  • Replication begins at various points
  • Proceeds in both directions

23
DNA Replication
  • Origins of replication
  • 1. Replication Forks hundreds of Y-shaped
    regions of replicating DNA molecules where new
    strands are growing.

24
DNA Replication
  • Origins of replication
  • 2. Replication Bubbles
  • a. Hundreds of replicating bubbles
    (Eukaryotes).
  • b. Single replication fork (bacteria).

25
DNA Replication
  • Enzymes (nearly 100 special proteins) are
    needed in replication!!
  • 1) catalyze the unwinding and separation
    (breaking H-Bonds) of parental double helix.
  • 2) catalyze attachment and help keep the
    separated strands apart while replication occurs

26
DNA Replication
  • 3) relieves stress on the DNA molecule and
    keeps it straight

27
DNA Replication
  • 4) catalyze attachment of the first
    nucleotides in replication
  • 5) catalyze continued addition of
    nucleotides
  • 6) proofread the completed sequence for
    accurate base-pairing
  • 7) repair the incorrect sequences

28
DNA Replication
  • Synthesis of the new DNA Strands
  • 1. DNA Polymerase with a RNA primer in place,
    DNA Polymerase (enzyme) catalyze the synthesis
    of a new DNA strand in the 5 to 3 direction.

29
Remember!!!!

30
Remember!!!!!

31
DNA Replication
  • Semiconservative Model
  • the two strands of the parental DNA separate
  • each functions as a template for synthesis of a
    new complementary strand.

32
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33
Question
  • What would be the complementary DNA strand for
    the following DNA sequence, what would be the
    mRNA sequence?
  • DNA 5-GCGTATG-3

34
Answer
  • DNA 5-GCGTATG-3
  • DNA 3-CGCATAC-5
  • mRNA 5-GCGUAUG-3
  • tRNA anti-codon CGCAUAC

35
Gene
  • The unit of heredity
  • Is a sequence of nucleotides
  • Codes for amino acid sequences THAT will become
    PROTEINS

36
Mutations
  • Change can occur in DNA
  • Point mutation or gene mutation
  • Change in genetic message
  • Chromosome mutation

37
Extraction
Each human cell has enough DNA to code for all
the traits in the human body. If the DNA in one
cell was stretched out, how long would it be?
Answer over 2 meters
A human body has approximately 75 trillion cells.
If the distance to the sun is 150 X 109 meters,
how many round trips could your DNA make?
Answer 500 trips
38
Extraction
DNA from kiwi fruit
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