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DNA

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DNA The Molecule of Life – PowerPoint PPT presentation

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Title: DNA


1
DNA
  • The Molecule of Life

2
What is DNA?
  • DeoxyriboNucleic Acid
  • Chargaffs Law
  • AT, GC
  • R. Franklin and M. Wilkins
  • Crystal X-ray
  • J Watson and F Crick
  • Model of DNA
  • Double stranded structure
  • Bases inside

3
What is DNA Made of?
  • Deoxyribose sugar
  • Phosphate
  • Base
  • Purine
  • A, G
  • Pyrimidine
  • T, C

4
What are the Structures of the Bases?
  • Purines
  • Adenine
  • Guanine

5
What are the structures of the bases?
  • Pyrimidines
  • Thymine
  • Cytosine

6
Assembly of the parts
  • Purines and pyrimidines form chemical bonds with
    deoxy-ribose (5-carbon) sugar. The carbon atoms
    on the sugar are designated 1', 2', 3', 4' and
    5'.
  • It is the 1' carbon of the sugar that becomes
    bonded to the nitrogen atom at position N1 of a
    pyrimidine or N9 of a purine. RNA contains
    ribose.
  • The resulting molecules are called nucleosides
    and can serve as elementary precursors for DNA
    (and RNA synthesis)

7
Nucleosides (examples)
8
Nucleosides become Nucleotides
  • Nucleosides form bonds with phosphate groups.
  • Phosphate groups bind to the 5 C of the
    deoxyribose sugar.
  • Nucleosides phosphate group NUCLEOTIDE

9
A Nucleotide
A, G, C or T
Forms sugar Phosphate Backbone
What makes DNA Different from RNA?
10
A Single Strand of Nucleotides
  • The nucleotides connect by a series of 5' to 3'
    phosphate-deoxyribose bonds.
  • Note the sequence of the bases in the next
    diagram.
  • Polynucleotide sequences are referenced in the 5'
    to 3' direction

11
Polynucleotide
12
Polynucleotide pairs are Complementary
  • One strand of DNA is arranged 5 to 3
  • The partner strand is arranged exactly 3 to 5.
  • Chargaffs law states A T and CG
  • The strands are held together by H-bonds between
    the bases

13
Base pairing how it works
  • Hydrogen Bonding between bases
  • A-T Bonding
  • 2 hydrogen bonds
  • G-C Bonding
  • 3 hydrogen bonds

14
H-Bond Orientation
  • H-bonds between OH and NH
  • Orientation in space
  • PAIRING of A with T,
  • PAIRING of G with C

15
Double Stranded DNA Complementary strands
(cont.)
  • The bases pair COMPLEMENTARY to one another.

16
Use
  • This complementarity allows for DNA replication
    and transcription

17
DNA
  • Two complementary strands of polynucleotides
  • Like a zipper but held together by H-bonds (which
    really are not bonds, but forces)

18
DNA The Double Helix
  • Like a ladder twisted about its axis
  • Each cell in our body contains 2 m worth of DNA.

19
The CODE
  • The specific base pairing and the sequence of the
    bases are significant.
  • We call the specific arrangement of bases the
    CODE
  • The sequences of code form the GENE for a
    specific trait. Genes are special sequences of
    hundreds to thousands of nucleotide base pairs
    that form templates for protein making
  • It codes for specific RNA bases for the making of
    specific proteins for the trait.

20
GENE
  • Exon regions that form the code for the trait
  • Intron regions that are part of the gene but are
    excised

21
Genes
  • Total number of genes is unknown, it estimated to
    be 30 000 to 120 000
  • Genes comprise only 3 of the chromosomethe rest
    is called junk DNAits code is meaningless junk

22
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23
What is important about base pairs?
  • Can predict sequence of one strand based on the
    sequence of the other because it is complementary
  • Replication and Transcription a single strand
    of DNA acts as a TEMPLATE for a new strand, or
    for making RNA.
  • Repair of damaged DNAthe template DNA allows for
    repairs.

24
DNA From Chromatin to Chromosome
  • DNA supercoils around tiny proteins called
    HISTONES.
  • The resulting strand with histones supercoils on
    itself.

25
Size
26
CHROMOSOMES
  • The supercoiled DNA further coils until it
    further supercoils as chromatin.
  • This is how 2 m of DNA can be packed into the
    nucleus of a single body cell.
  • At interphase of MITOSIS or MEIOSIS I, the DNA
    replicates itself. The chromatin become visible
    as double stranded DNA (DNA that has replicated).
  • Chromosomal Wrapping

27
Replication
  • Why?
  • When cells replicate, each new cell needs its
    own copy of DNA.
  • Where?
  • Nucleus in Eukaryotes.
  • Cytosol in Prokaryotes
  • When?
  • S phase of cell cycle
  • What?
  • Many proteins major is DNA Polymerase
  • How?

28
Replication
  • How?
  • 5?3 directionality
  • Starts with RNA primer
  • Leading Strand
  • Lagging Strand
  • Okasaki Fragments
  • Sequence determined by basepairing

29
  • Nova-Cracking the Code of Life
  • The Structure of DNA

30
Transcription
  • DNA ?RNA
  • What is the difference between DNA and RNA?
  • Ribose Sugar
  • Uracil not thymine

31
Transcription
  • Where?
  • Nucleus in Eukaryotes
  • Cytosol in Prokaryotes
  • What?
  • RNA Polymerase plus some minor proteins
  • When?
  • When RNA is needed
  • Why?
  • RNAs serve many important functions in cells
  • How?

32
Transcription
  • How?
  • 5?3 directionality
  • Usually only one strand
  • Uses Base-pairing
  • Same idea as with DNA replication
  • RNA Synthesis Animation

33
Translation
  • What?
  • RNA? Protein
  • Where?
  • Cytosol
  • When?
  • When proteins are need, after RNA is made
  • Why?
  • Proteins are vital for cells
  • How?

34
Translation
  • How?
  • Ribosomal Subunits
  • Small subunit
  • Large subunit
  • Codon
  • Triplet code used
  • tRNA, rRNA, mRNA
  • Translation Animation

35
The Genetic Code
36
Why is this important?
  • Genetic Engineering
  • Gene Splicing
  • Mutations
  • Cloning

37
In Summary
  • A nucleotide is made of three parts
  • A phosphate group
  • A five carbon sugar (deoxyribose)
  • And a nitrogen containing
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