DNA

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DNA

• Deoxyribonucleic Acid
• the code of life

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Topics of Study

• DNA
• STRUCTURE
• REPLICATION
• TRANSCRIPTION
• TRANSLATION

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DNA

• Chemical basis of heredity
• In nucleus of eukaryotic cells
• In nucleoid region of prokaryotic cells
• Is a nucleic acid molecule

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DNA

• Large 2 stranded molecule
• Double helix shape
• NUCLEOTIDE building blocks
• 5-Carbon sugar molecule - deoxyribose
• Phosphate group
• Nitrogenous Base - 4 different types
• Tetranucleotide Theory
• Two halves joined with weak hydrogen bonds -
  double or triple

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DNA Double helix molecule
Nitrogenous Bases Cytosine always bonds to
Guanine Adenine always bonds to
Thymine Chargoffs Complementary Base Pairing
Rule A and G are purines T and C are pyrimidines
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DNA Constancy vs Diversity

• Constancy pairing of A-T and C-G is same for
  all species
• Diversity sequencing of A-T and C-G is
  different for each individual organism

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DNA Molecule of heredity

• Stores the necessary information to build and
  operate a cell
• Heredity information is coded in the sequence of
  nitrogenous bases in the molecule
• Sequence of nitrogenous bases forms a gene
• Gene has instructions for the synthesis of
  proteins (enzymes) in the cell
• Proteins (enzymes) produce the heritable
  characteristics of organism
• Genetic differences protein differences

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FORMS OF DNA

• Chromatin - DNA fragments
• Usual form of DNA in cell
• Chromosome - DNA strand
• Organized for cell division purposes
• Chromosomes composed of 1/2 DNA and
• 1/2 protein DNA wrapped around histone
• protein

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DNA Strands

• Have direction 5-------------------gt 3
• Double helix strands are anti-parallel
• 5-----------------
  --gt 3
• 3lt------------------- 5
• Strands are complementary to one another

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DNA History

• Meischer, 1869 - isolated white powder he called
  nuclein from nucleus of cells
• Levine, 1920s - chemical components of
• of sugar, phosphate, nitrogenous bases
• Hershey and Chase - DNA is genetic material in
  some viruses
• Chargoff, 1940s - complementary base pairing rule

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DNA History

• Mirsky - somatic cells have X amount of DNA
  gametes contain 1/2 X amount
• Pauling - suggested double helix shape
• Franklin and Wilkins - x-ray diffraction study of
  shape and size patterns with respect to location
  of components
• Watson and Crick, 1950s - first DNA model

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DNA Replication

• Process by which DNA makes a replica (copy) of
  itself

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PROCESSES INVOLVING DNA

• DNA can automatically self-copy its molecules in
  a process called REPLICATION
• REMEMBER C to G and A to T
• Replication must always preceed cell division so
  daughter cells will receive exact amount of DNA
• Replication occurs during S-stage of interphase

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DNA Replication

• DNA double helix unwinds and unzips (helicase)
• Nitrogenous bases separate at Hydrogen bonds
• Each half of DNA molecule serves as the pattern
  or template for the placement of nucleotides
  (DNA polymerase)
• Newly placed nucleotides form complementary side
  of new DNA
• Both DNA molecules the same

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DNA Replication

• Semiconservative Method of Replication
• Each double helix is half old / half new
• Proven by radioactive nitrogen
• Insures accuracy of base pairing - actually
  proofread by enzymes with less than 1 mistake
  in 1 billion nucleotides

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A SHORT STRING OF DNA to replicate
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DNA separates at Hydrogen Bonds
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Each half serves as template
Nucleotides made in the cell DNA building blocks
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Each half serves as template complementary
pairing matches building blocks to existing DNA
strand
Nucleotides made in the cell DNA building blocks
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Each half serves as template complementary
pairing matches building blocks to existing DNA
strand
2 Identical DNA Molecules exactly like the
original
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DNA Replication

• Produces 2 identical DNA molecules
• Each molecule has 1/2 of the original DNA
• the other 1/2 is newly synthesized
• SEMI-CONSERVATIVE REPLICATION
• Requires enzymes and ATP
• Rate 50 nucleotides per second in human cells

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Protein Synthesis

• Using the DNA genetic code to direct the
  synthesis of proteins
• Remember DNA expresses itself as protein
  differences

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Code of Genetic Information

• GENE is the code in DNA for a specific sequence
  of amino acids A PROTEIN
• Many genes found in DNA molecule
• Gene identified by
• INITIATOR (start) CODE (TAC)
• TERMINATOR CODE (ATT, ATC, ACT)
• DNA serves as template for the formation of a
  work horse molecule
• RNA (can move out of nucleus with copy of
  genetic code)

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RNA Molecule

• Single stranded molecule
• Ribose sugar
• Phosphate
• Uracil instead of Thymine, Uracil complementary
  to Adenine
• A - U and C - G

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3 Functional Kinds of RNA

• mRNA (encodes genetic message from DNA for
  protein)
• rRNA (forms 2/3 of ribosome along with 1/3
  protein)
• tRNA (transports amino acids to ribosomes for
  protein synthesis have anticodons)

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Genetic Code

• CODE DNA nucleotide triplet sequence
• Triplet CODON transcribed in mRNA (each triplet
  codes for an amino acid)
• ANTICODON triplet on tRNA complementary to mRNA
  (ensures correct placement of amino acid)

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Process of Interpreting the Genetic Code to
Protein

• TRANSCRIPTION occurs in nucleus
• mRNA synthesized using the DNA pattern
• TRANSLATION occurs at ribosomes
• mRNA directs the synthesis of protein
• Requires
• Ribosomes
• tRNA
• amino acids
• ATP

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TRANSCRIPTION

• Only 1 side of DNA used (sense strand)
• RNA polymerase only recognizes one of the
  directional DNA strands
• DNA serves as template for RNA nucleotide
  placement and formation
• Eukaryotes transcribe one gene at a time
• Eukaryotic genes have nonsense segments INTRONS
  that have to be removed from mRNA before use

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Use of transcribed mRNATRANSLATION (makes
protein)

• mRNA leaves nucleus thru nuclear pore
• 1st 2 mRNA triplets attach to ribosome
• tRNA transport amino acids to ribosomes
• tRNA with complementary bases (ANTICODONS) attach
  to mRNA
• Amino acids on other end of tRNA are bonded
  together by peptide bonds to make PROTEIN

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RNA Translation - 3 stages

• Initiation - mRNA binds to ribosome and initiator
  codon(AUG) begins process
• Chain Elongation - tRNAs transport and position
  amino acid in a protein chain according to mRNA
  triplet codons
• Termination - mRNA terminator codes stop
  translation

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Summary Process of Interpreting the Genetic
Code

• Genetic Code is TRANSCRIBED into mRNA molecule
• TRANSLATION of Genetic Code
• mRNA molecule attaches to RIBOSOME
• 2 codons at a time fit in ribosome
• tRNA transports amino acids
• (tRNA binds to mRNA in ribosome by complementary
  base pairing)
• Positions amino acids in correct sequence to make
  protein

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Mutations to Genetic Code

• Inheritable changes to DNAs code
• Caused by DNA mistakes or by a mutagen
• Rare event and usually harmful
• Helpful only if mutation increases an organisms
  ability to survive

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Mutations to Genetic Code

• Point Mutation - substitution in DNA nucleotides
  affects only 1 amino acid in a protein sequence
• Frame Shift Mutation - addition to or deletion
  from DNA nucleotides changes the entire sequence
  of amino acids beyond the mutated area