Chapter 9 DNA: THE Genetic Material

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Chapter 9DNA THE Genetic Material

• Section1
• Identifying the Genetic Material

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Transformation

• Frederick Griffith, a bacteriologist, prepared a
  vaccine against pneumonia
• Vaccine a substance that is prepared from
  killed or weakened disease-causing agents,
  including certain bacteria
• To protect the body against future infections by
  the disease-causing agent

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Griffiths Experiments

• Griffith worked with 2 strains of S. pneumoniae
• 1st strain had a smooth capsule that protected
  the bacterium from bodys defense systems (S)
• Virulent (full of poison) able to cause disease
• 2nd strain lacked capsule and didnt cause
  disease (R)
• Mice injected with (S) strain died mice injected
  with (R) strain lived

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• Griffith injected mice with dead S bacteria
  mice lived
• Griffith injected mice with heat-killed S
  bacteria-mice still lived
• Meaning the capsule was not involved with killing
  the mice
• He mixed harmless live R bacteria with the
  harmless heat-killed S bacteria-mice died
• Transformation- a change in genotype caused when
  cells take up foreign genetic material

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Averys Experiments

• Oswald Avery co-workers demonstrated that DNA
  is the material responsible for transformation
• Almost 100 years after Mendels experiments

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Viral Genes and DNA

• Many scientists remained skeptical
• Knew little about DNA, so they could not imagine
  how DNA could carry genetic information

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DNAs Role Revealed

• Alfred Hershey and Martha Chase performed an
  experiment that settled the controversy
• Viruses are composed of DNA or RNA surrounded by
  a protective protein coat
• Bacteriophage (phage) a virus that infects
  bacteria

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• Step 1 grew E. coli contained radioactive
  sulfur (35S) protein coat incorporated the sulfur
• Grew second batch E. coli with radioactive
  phosphorus (32P) would become part of the phages
  DNA
• Step 2 Labeled phages used to infect two separate
  batches of E. coli

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• Step 3 Used centrifuge tubes to separate the
  bacteria (heavy) from the viral parts (lighter)
• Concluded that the DNA of viruses is injected
  into the bacterial cells, while most of the viral
  proteins remain outside
• Experiments have shown that DNA is the molecule
  that stores genetic information in living cells

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The Structure of DNA Section 2

• Watson Crick determined that a DNA molecule is
  a double helix two strands twisted around each
  other
• Nucleotides the subunits that make up DNA
• 3 parts a phosphate group, a 5-carbon sugar, and
  a nitrogen-containing base

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• Deoxyribose sugar molecule from which DNA gets
  its full name, deoxyribonucleic acid
• Nitrogen base may be adenine, guanine, thymine,
  and cytosine
• Adenine (A) and guanine (G) are classified as
  purines two rings of carbon nitrogen atoms
• Thymine (T) and cytosine (C) are classified as
  pyrimidines single ring C N atoms

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Discovering DNAs Structure

• Chargaffs 1949 observations the amount of
  adenine always equaled the amount of thymine
  amount of guanine always equaled the amount of
  cytosine but amount varied between different
  organisms

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Wilkins Franklins Photographs

• X-ray diffraction to study the structures of
  molecules
• 1952 Wilkins Franklin developed high-quality
  X-ray diffraction photographs of strands of DNA
  which suggested that the DNA resembled a tightly
  coiled helix and was composed of two or three
  chains of nucleotides

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Watson Cricks DNA Model

• 1953 Watson Crick used the information from
  Chargaff, Wilkins, Franklin along with their
  knowledge of chemical bonding, to make the
  spiral staircase configuration of DNA

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Pairing Between Bases

• Watson Crick determined that a purine on one
  strand of DNA is always paired with a pyrimidine
  on the opposite strand
• Base-pairing rule cytosine pairs with guanine
  and adenine with thymine
• Complementary base pairs sequence of bases on
  strand determines the sequence of N bases on the
  other strand of DNA

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HOMEWORK

• Section 1 Review p. 193 3-6
• Section 2 Review p. 197 1-6

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The Replication of DNA section 3

• Watson Crick proposed that one DNA strand
  serves as a template, or pattern, on which the
  other strand is built
• DNA replication the process of making a copy of
  DNA, which occurs during the (S) phase of the
  cell cycle

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• Step 1 The double helix needs to unwind before
  replication can begin
• Accomplished by enzymes called DNA helicases
  which open the double helix by breaking the
  hydrogen bonds between the two strands

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• Additional proteins prevent the strands from
  assuming their double-helical shape
• Replication forks areas where the double helix
  separates
• Enzymes known as DNA polymerases add nucleotides
  to the exposed nitrogen bases, according to the
  base-pairing rules forming two double helixes

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• Step 3 The process continues until all of the DNA
  has been copied the polymerases are signaled to
  detach
• Nucleotide sequences are identical in the two DNA
  molecules
• Checking for errors DNA polymerases are
  important in proofreading the nucleotides can
  backtrack
• Errors in DNA replication about one error per 1
  billion nucleotides

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Rate of Replication

• Replication does not begin at one end end at
  the other
• Prokaryotes usually have two replication forks
• Eukaryotic cells length a problem 33 days if
  done with a single point
• Each human chromosome is replicated in about 100
  sections replicated in about 8 hours

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HOMEWORK

• Section 3 Review p. 200 1-5
• Performance Zone p. 202 1-4, 6-12
• STP p. 203 1-3

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How Proteins Are Made

• Chap. 10
• Section 1

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Decoding the Information in DNA

• Traits are determined by proteins that are built
  according to instruction coded in DNA
• Ribonucleic acid is also involved
• RNA differs from DNA 3 ways
• a single strand
• five-C sugar, ribose
• Uracil (U) instead of thymine (T)

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• A genes instructions for making a protein are
  coded in the sequence of nucleotides in the gene
• Transcription a process were the instructions
  for making a protein are transferred from a gene
  to an RNA molecule

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• Translation the protein synthesis that takes
  place at ribosomes that uses the codons in mRNA
  molecules to specify the sequence of amino acids
  to make protein
• Gene expression (protein synthesis) the process
  by which proteins are made based on the
  information encoded in DNA

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Transfer of information from DNA to RNA

• RNA polymerase, an enzyme that adds and links
  complementary RNA nucleotides during
  transcription, is required
• Step 1 RNA polymerase binds to the genes
  promoter-a specific sequence of DNA that acts as
  a start signal fro transcription

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• Step 2 - RNA polymerase unwinds and separates the
  2 strands of the double helix, exposing the DNA
  nucleotides
• Step 3 RNA polymerase adds then links
  complementary RNA nucleotides as it reads the
  gene transcription follows the base-pairing
  rules for DNA except that uracil pairs with
  adenine

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• The RNA polymerase eventually reaches a stop
  signal in the DNA
• RNA nucleotides are linked together with covalent
  bonds during transcription
• Behind the RNA polymerase, the DNA closes up
  reforming the double helix
• In transcription, new molecule is RNA and only
  part of one of DNA strands serves as a template

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• Transcription in prokaryotic cells occurs in the
  cytoplasm in eukaryotic cells, in the nucleus
• Many identical RNA are made simultaneously from a
  single gene
• Look at Figure 3 page 210

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The Genetic Code Three-Nucleotide Words

• Different types of RNA are made during
  transcription
• Messenger RNA (mRNA) carries the instructions for
  making a protein from agene and delivers it to
  the site of translation
• Translated from the language of RNA (nucleotide)
  to language of proteins (amino acid)

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• Codons - a series of three-nucleotide sequences
  on the mRNA Marshall Nirenberg, American,
  deciphered the first codon by making artificial
  mRNA that contained only the base uracil (U)
• mRNA was translated into a protein phenylalanine
  amino-acid subuntis

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• Genetic code the amino acids and start and
  stop signals that coded for by each of the
  possible 64 mRNA codons

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RNAS Roles in Translation

• Translation takes place in the cytoplasm
• Transfer RNA molecules and ribosomes help in the
  synthesis of proteins.
• Transfer RNA (tRNA) are single strands of RNA
  that temporarily carry a specific amino acid on
  one end an anticodon at the other
• Anticodon a three-nucleotide sequence on a tRNA
  that is complementary to an mRNA codon

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• Ribosomes are composed of both proteins
  ribosomal RNA (rRNA)
• Ribosomal RNA molecules are part of the structure
  of ribosomes
• Each ribosome temporarily holds one mRNA and 2
  tRNA molecules

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• Step 1 The mRNA and the tRNA carrying methionine
  bind together start codon AUG, signals the
  beginning of a protein chain
• Step 2 The tRNA carrying the amino acid
  specified by the codon in the A site arrives
• Step 3 A peptide bond forms between adjacent
  amino acids
• S 4 The tRNA in the P site detaches and leaves
  its amino acid behind

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• S 5 The tRNA in the A site moves to the P site.
  The tRNA carrying the amino acid specified by
  the codon in the A site arrives.
• S 6 T peptide bond is formed. The tRNA in the
  P site detaches and leaves its amino acid behind.
• S 7 The process is repeated until a stop codon
  is reached. The ribosome complex fails apart.
  The newly made protein is released.

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• Another ribosome can find the AUG codon on the
  same mRNA and begin making a second copy of the
  same protein
• The genetic code is the same in all organisms,
  but for a few exceptions

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mutations
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Homework

• Section 1 review p. 214 1-6
• Chapter review p. 222 1,2,6,7,8,12
• P. 223 STP 1-3