DNA

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DNA

• The Molecule of Life

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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

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What is DNA Made of?

• Deoxyribose sugar
• Phosphate
• Base
• Purine
• A, G
• Pyrimidine
• T, C

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What are the Structures of the Bases?

• Purines
• Adenine
• Guanine

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What are the structures of the bases?

• Pyrimidines
• Thymine
• Cytosine

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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)

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Nucleosides (examples)
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Nucleosides become Nucleotides

• Nucleosides form bonds with phosphate groups.
• Phosphate groups bind to the 5 C of the
  deoxyribose sugar.
• Nucleosides phosphate group NUCLEOTIDE

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A Nucleotide
A, G, C or T
Forms sugar Phosphate Backbone
What makes DNA Different from RNA?
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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

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Polynucleotide
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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

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Base pairing how it works

• Hydrogen Bonding between bases
• A-T Bonding
• 2 hydrogen bonds
• G-C Bonding
• 3 hydrogen bonds

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H-Bond Orientation

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

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Double Stranded DNA Complementary strands
(cont.)

• The bases pair COMPLEMENTARY to one another.

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Use

• This complementarity allows for DNA replication
  and transcription

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DNA

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

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DNA The Double Helix

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

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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.

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GENE

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

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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

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(No Transcript)
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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.

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DNA From Chromatin to Chromosome

• DNA supercoils around tiny proteins called
  HISTONES.
• The resulting strand with histones supercoils on
  itself.

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Size
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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

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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?

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Replication

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

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

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Transcription

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

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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?

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Transcription

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

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Translation

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

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Translation

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

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The Genetic Code
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Why is this important?

• Genetic Engineering
• Gene Splicing
• Mutations
• Cloning

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In Summary

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