DNA, RNA

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DNA, RNA Protein Synthesis
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Griffiths Transformation Experiment

• 1928 Frederick Griffith is studying how certain
  strains of bacteria cause pneumonia and
  inadvertently makes a discovery about how genetic
  information is passed from organism to organism
• His Experiment
• Grow two slightly different strains (types) of
  bacteria
• One strain proven harmless and other deadly
• Laboratory mice are injected with these strains

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Griffiths Results
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What caused Griffiths results?

• The heat-killed strain passed on its
  disease-causing ability to the live harmless
  strain.
• In Griffiths words, one strain of bacteria was
  TRANSFORMED into another.
• It was later demonstrated by Oswald Avery and
  other scientists that the transforming factor was
  DNA (deoxyribonucleic acid)

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The Hershey-Chase Experiment

• Alfred Hershey Martha Chase studied viruses,
  which are non-living particles smaller than a
  cell that can infect living organisms.
• Bacteriophages specific group of viruses that
  infect bacteria.
• OBJECTIVE To determine which part of the virus
  (protein or DNA) enters a bacteria it is
  infecting.

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What did Hershey Chase do?

• If Hershey and Chase could determine which part
  of the virus entered an infected cell, they would
  learn whether genes were made of protein or DNA.
• To accomplish this, they grew viruses in cultures
  containing radioactive isotopes of phosphorus-32
  (32P) and sulfur-35 (35S).
• Some viruses had P-32 in their DNA, and others
  had S-25 in their protein coat.
• If S-35 is found in the bacteria, it would mean
  that viruses release their protein and if P-32 is
  found in the bacteria it would mean that viruses
  release their DNA.

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Recall Method of Bacteriophage Infection

• When a bacteriophage enters a bacterium, the
  virus attaches to the surface of the cell and
  injects its genetic information into it.
• The viral genes replicate to produce many new
  bacteriophages, which eventually destroy the
  bacterium.
• When the cell splits open, from viral overload,
  hundreds of new viruses burst out and can infect
  surrounding cells

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Hershey-Chase Results
So The genetic material in bacteriophages was
the DNA, (not the protein)!!!
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DNA Structure

• Made of monomers called nucleotides
• Nucleotide structure

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A nucleotide can have one of four bases

• Types of bases
• Adenine
• Guanine
• Cytosine
• Thymine

A G are bigger and are called purines C T are
smaller and are called pyrimidines
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Chargaffs Rule Rosalind Franklin

• Edwin Chargaff discovered that in almost any DNA
  sample, the G nearly equals the C and the A
  nearly equals the T
• Rosalind Franklin used x-ray diffraction to get
  information about the structure of DNA.
• She aimed an X-ray beam at concentrated DNA
  samples and recorded the scattering pattern of
  the X-rays on film.

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Watson Crick

• Using clues from Franklins X-ray pattern, shown
  to them by Maurice Wilkins, James Watson and
  Francis Crick built a 3-D model that explained
  how DNA carried information and could be copied.
• Watson, Crick Wilkins were awarded the 1962
  Nobel Prize in Physiology or Medicine for their
  work.

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Base-Pairing

• Watson Crick discovered that bonds can only
  form between certain base pairs, Adenine
  Thymine and Cytosine Guanine.
• The base-pairing rule means that purines only
  pair with pyrimidines, making the rungs equally
  spaced like a ladder.
• The nitrogenous bases are held together by
  hydrogen bonds.
• A T are held together by TWO hydrogen bonds
• C G are held together by THREE hydrogen bonds

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DNA is a double-helix or twisted ladder

• The backbone or sides of the DNA molecule are
  made up of alternating sugars and phosphates and
  the rungs are made up of interlocking nitrogen
  bases.
• The sugars and the phosphates are held together
  by covalent bonds and the nitrogen bases are held
  together by hydrogen bonds.

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Molecular Structure of DNA
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DNA Replication

• Before a cell can divide, its DNA must be
  replicated or copied in the S-phase of the cell
  cycle.
• In most prokaryotes, replication begins at a
  single point and continues in two directions.
• In eukaryotes, replication occurs in hundreds of
  places simultaneously and proceeds until
  complete.
• Sites of replication are called replication
  forks.

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How does the process occur?

• Helicase untwist DNA molecules.
• Restriction enzymes unzip the molecule.
• DNA polymerase brings in complementary base pairs
  for each strand
• Ligase glues together the nucleotides
• Process is semi-conservative.
• Each new strand of DNA consists of one original
  template strand and one newly made strand.
• This allows for proofreading, using the template
  strand as the master.

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Visual Summary of DNA replication
Animation
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Replication Bubbles
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The Central Dogma of Genetics

• Genes are coded DNA instructions for the
  construction of proteins.
• DNA is located in the nucleus, but proteins are
  made in ribosomes
• To avoid damage to the DNA molecules, they are
  first decoded into RNA which is sent to the
  ribosome to be the instructions for protein
  synthesis.

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DNA v. RNA
DNA RNA
Sugar is deoxyribose Double-stranded A, T, C G bases Sugar is ribose Single-stranded Uracil instead of thymine
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Three types of RNA

• mRNA (messenger) carries copies of instructions
  for assembling amino acids into proteins
• rRNA (ribosomal)
• makes up part of the ribosome
• tRNA (transfer) carries each AA
• needed to build the protein to the ribosome

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The Flow of Genetic Information

• Protein synthesis occurs in 2 steps
• transcription (DNA ? RNA) translation (RNA ?
  protein)

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Transcription

• RNA is produced when RNA polymerase copies a
  sequence of DNA into a complementary RNA strand.
• DNA TACGGACACATT
• RNA AUGCCUGUGUAA

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Translation

• Decoding of an mRNA message into a polypeptide
  chain (protein)
• mRNA molecules are read in three base segments
  called codons
• Each codon specifies a particular amino acid
• Some AA are specified by more than one codon.

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The Genetic Code
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RNA Processing (Editing)
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Additional Details of Transcription

• Initiation RNA polymerase attached to promoter
  sequence of DNA and RNA synthesis begins
• 2. Elongation RNA elongates and the
  synthesized RNA strand peels away from DNA
  template allowing the DNA strands to come back
  together in regions transcribed
• 3. Termination RNA polymerase reaches
  sequence of DNA bases called a terminator
  signaling the end of the gene and polymerase
  molecule detaches

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A Closer Look at tRNA
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A Closer Look at Ribsomes
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Steps of translation - Initiation

• After RNA is transcribed in the nucleus, it
  enters the cytoplasm and attaches to a small
  ribosomal subunit
• special initiator tRNA binds to the start codon
  bringing in the amino acid MET
• large ribosomal subunit binds to the small one
  creating a functional ribosome

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Steps of Translation - Elongation

• The anticodon of an incoming tRNA molecule with
  AA pairs with mRNA codon in A site
• AA detaches from tRNA in P site and peptide bond
  forms between it and the AA in the A site
• translocation P site tRNA leaves the ribosome
  and the A site complex (AA, tRNA anticodon and
  mRNA codon) shift s over to the P site
• Process continues until a STOP codon is reached

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Steps of Translation - Termination

• Stop codons UAA, UAG, and UGA do not code for
  amino acids
• These codons signal the end of translation
• The completed polypeptide is released from the
  last tRNA and exits the ribosome
• The ribosome splits into individual subunits

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Animation
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Mutations

• Mutations are changes in the genetic material
• Gene Mutations change in the nucleotide
  sequence within a single gene
• Chromosomal mutations change in an entire
  chromosome may involve loss or duplication of
  multiple genes
• Point mutations are gene mutations involving a
  change in one or a few nucleotides
• Substitution usually changes only one AA
• Frameshift addition or deletion of a nucleotide
  shifts the grouping of codons

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Causes Effects of Mutations

• Causes Mutagenesis can occur in many ways
• Spontaneous mutations occur during DNA
  replication or recombination
• Physical or chemical agents called mutagens may
  induce mutations (ex. High energy radiation from
  x-rays or UV light)
• Effects Can be harmful, beneficial or neither
• May cause of genetic disorders
• May be beneficial and lead to production of
  proteins with new or altered activities, which
  has an important role in the evolutionary process
  of natural selection
• Some mutations are silent and have no effect
  because the nucleotide change results in a new
  codon that codes for the same amino acid as the
  original codon

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Substitutions Mutations
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Frameshift Mutations
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4 Types of Chromosomal Mutations
Polyploidy extra set of chromosomes