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DNA structure

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* Nucleotide Structure Three different components Phosphate group Nitrogen containing base (A,T,G,C,U) Five-carbon sugar (ribose or deoxyribose) Protein DNA Gene ... – PowerPoint PPT presentation

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Title: DNA structure


1
The Structure of DNA
2
DNA
  • DNA is often called the blueprint of life.
  • In simple terms, DNA contains the instructions
    for making proteins within the cell.

3
Why do we study DNA?
  • We study DNA for many reasons
  • its central importance to all life on Earth,
  • medical benefits such as cures for diseases,
  • better food crops.

4
A HISTORY OF DNA
  • Discovery of the DNA double helix
  • A. Frederick Griffith Discovers that a factor
    in diseased bacteria can transform harmless
    bacteria into deadly bacteria (1928)
  • B. Rosalind Franklin - X-ray photo of DNA.
  • (1952)
  • C. Watson and Crick - described the DNA
    molecule from Franklins X-ray.
  • (1953)

5
Rosalind Franklins photo
6
Watson and Crick with their famous model
7
Chromosomes and DNA
  • Our genes are on our chromosomes.
  • Chromosomes are made up of a chemical called DNA.

8
DNA Structure
  • DNA consists of two molecules that are arranged
    into a ladder-like structure called a Double
    Helix.
  • A molecule of DNA is made up of millions of tiny
    subunits called Nucleotides.
  • Each nucleotide consists of
  • Phosphate group
  • Pentose sugar
  • Nitrogenous base

9
One Strand of DNA
  • The backbone of the molecule is alternating
    phosphates and deoxyribose sugar
  • The teeth are nitrogenous bases.

phosphate
deoxyribose
bases
10
Nucleotides
Phosphate
Nitrogenous Base
Pentose Sugar
11
Nucleotides
  • The phosphate and sugar form the backbone of the
    DNA molecule, whereas the bases form the rungs.
  • There are four types of nitrogenous bases.

12
Nucleotides
13
Nucleotides
  • Each base will only bond with one other specific
    base.
  • Adenine (A)
  • Thymine (T)
  • Cytosine (C)
  • Guanine (G)

Form a base pair.
Form a base pair.
14
DNA Double Helix

15
DNA Structure
  • Because of this complementary base pairing, the
    order of the bases in one strand determines the
    order of the bases in the other strand.

16
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17
Two Kinds of Bases in DNA
N
  • Pyrimidines are single ring bases.
  • Purines are double ring bases.

C
N
C
C
O
C
N
18
Thymine and Cytosine are pyrimidines
  • Thymine and cytosine each have one ring of carbon
    and nitrogen atoms.

19
Adenine and Guanine are purines
  • Adenine and guanine each have two rings of carbon
    and nitrogen atoms.

20
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?

21
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

22
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

23
DNA Nucleotide

24
Chargraffs Rule
  • Adenine and Thymine always join together
  • A T
  • Cytosine and Guanine always join together
  • C G

25
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26
  • So if there is 30 Adenine, how much Cytosine
    will there be???
  • (Carefully calculate please.)

27
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28
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.

29
DNA Structure
  • To crack the genetic code found in DNA we need to
    look at the sequence of bases.
  • The bases are arranged in triplets called codons.
  • A G G - C T C - A A G - T C C - T A G
  • T C C - G A G - T T C - A G G - A T C

30
DNA Structure
  • A gene is a section of DNA that codes for a
    protein.
  • Each unique gene has a unique sequence of bases.
  • This unique sequence of bases will code for the
    production of a unique protein.
  • It is these proteins and combination of proteins
    that give us a unique phenotype.

31
  • 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)

32
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

33
ribose vs. deoxyribose
34
Nucleotide Structure
  • Three different components
  • Phosphate group
  • Nitrogen containing base (A,T,G,C,U)
  • Five-carbon sugar
  • (ribose or deoxyribose)

35
DNA
Gene
Protein
Trait
36
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