DNA

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DNA PROTEIN SYNTHESIS

• CHAPTERS 9 10

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Main Idea

• How are proteins made in our bodies?

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WHAT MAKES UP DNA?

• IT IS A MOLECULE COMPOSED OF CHEMICAL SUBUNITS
  CALLED NUCLEOTIDES

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NUCLEOTIDES

• ARE COMPOSED OF THREE SUBUNITS

• A PHOSPHATE GROUP

• A FIVE CARBON SUGAR

• A NITROGEN-CONTAINING BASE

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NITROGENOUS BASES

• THERE ARE FOUR NITROGENOUS BASES IN DNA

• ADENINE

• CYTOSINE

• THYMINE

• GUANINE

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• ADENINE AND GUANINE ARE PURINES
• THEY ARE MADE OF TWO RINGS OF NITROGEN AND CARBON
  ATOMS

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• THYMINE AND CYTOSINE ARE PYRIMIDINES
• THEY CONTAIN A SINGLE RING OF CARBON AND NITROGEN
  ATOMS

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• THE DNA HAS TWO MAIN SIDES
• THE SIDES ARE LIKE THE UPRIGHT PARTS OF A LADDER
• THE SIDES ARE MADE OF THE SUGAR AND THE PHOSPHATE
  GROUP (ACID)

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• THEY ALTERNATE ALONG THE SIDES
• THE RUNGS OF THE LADDER ARE MADE OF NITROGEN
  BASES
• THERE ARE WEAK HYDROGEN BONDS BETWEEN THE BASE
  PAIRS

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CHARGAFFS OBSERVATIONS

• THE AMOUNT OF ADENINE EQUALS THE AMOUNT OF
  THYMINE
• THE AMOUNT OF CYTOSINE EQUALS THE AMOUNT OF
  GUANINE
• THE AMOUNTS VARY AMONG ORGANISMS

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DNA MODEL

• WATSON CRICK USED THE INFORMATION FROM CHARGAFF
  AND THE PHOTOGRAPHS FROM WILKINS AND FRANKLIN AND
  THEIR KNOWLEDGE OF CHEMICAL BONDING TO COME UP
  WITH A MODEL

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BASE-PAIRING RULES

• A PURINE ALWAYS PAIRS WITH A PYRIMIDINE
• THE STRICTNESS OF BASE PAIRING RULES PRODUCES
  COMPLIMENTARY BASE PAIRS

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• ADENINE BONDS WITH THYMINE

• CYTOSINE BONDS WITH GUANINE

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• THE ARRANGEMENT OF NUCLEOTIDES IS WHAT MAKES US
  DIFFERENT

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• THE ORDER OF BASES MAKE UP THE GENETIC CODE
• A SINGLE HUMAN CELL CONTAINS 6.6 BILLION BASE
  PAIRS OF DNA
• THIS WOULD BE 600,000 PRINTED PAGES WITH 500
  WORDS EACH

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DNA REPLICATION

• DNA MUST MAKE AN IDENTICAL COPY OF ITSELF DURING
  REPLICATION

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• DNA HELICASES (ENZYME) BREAKS THE HYDROGEN BONDS
  BETWEEN THE NITROGEN BASES
• THE MOLECULE BEGINS TO UNWIND

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• ONCE STRANDS ARE SEPARATED, PROTEINS ATTACH TO
  EACH STRAND TO HOLD THEM APART
• AREAS WHERE THE DOUBLE HELIX SEPARATE ARE CALLED
  REPLICATION FORKS

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DNA POLYMERASE (ENZYME) SWEEPS ALONG BONDING NEW
NUCLEOTIDES TO EACH SIDE OF THE PARENT CHAIN
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• THE PROCESS CONTINUES UNTIL ALL DNA HAS BEEN
  COPIED
• TWO NEW IDENTICAL DNA MOLECULES ARE FORMED

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• DNA POLYMERASE PROOF-READS THE STRAND
• NUCLEOTIDES ARE ADDED AND INCORRECT ONES ARE
  CORRECTED

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REPLICATION RATE

• EACH CHROMOSOME IS REPLICATED IN 100 SECTIONS
  WITH 100,000 NUCLEOTIDES
• WITH MULTIPLE REPLICATION FORKS, THIS TAKES ABOUT
  8 HOURS IN A HUMAN

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RNA

• A NUCLEIC ACID FOUND IN THE NUCLEUS AND CYTOPLASM
• COMPOSED OF A SINGLE CHAIN OF NUCLEOTIDES
• CONTAINS RIBOSE

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• CONTAINS URACIL INSTEAD OF THYMINE

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TRANSCRIPTION

• THE INSTRUCTIONS FOR MAKING A PROTEIN ARE
  TRANSFERRED FROM A GENE TO AN RNA MOLECULE
• WE CALL THIS PROCESS TRANSCRIPTION

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• IT INVOLVES THE FORMATION OF RNA
• RNA POLYMERASE BONDS TO THE START SIGNAL OF DNA
• THE DOUBLE HELIX UNWINDS

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• RNA POLYMERASE ADDS AND LINKS COMPLEMENTARY
  NUCLEOTIDES TO THE DNA TEMPLATE WITH COVALENT
  BONDS
• RNA MATCHES UP UNTIL A STOP SIGNAL IS REACHED

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• THE SINGLE-STRANDED MOLECULE BREAKS AWAY FROM THE
  DNA CHAIN
• THE DOUBLE HELIX REFORMS

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• THE RNA FORMED IS CALLED MESSENGER RNA (mRNA)
• mRNA CODES FOR PROTEIN PRODUCTION
• THE mRNA LEAVES THE NUCLEUS AND GOES TO THE
  RIBOSOME

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• http//www.fed.cuhk.edu.hk/johnson/teaching/genet
  ics/animations/transcription.htm

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CODING FOR PROTEINS

• 3 BASES IN A ROW CODES FOR A PARTICULAR AMINO
  ACID (CODON)
• MORE THAN ONE SET OF CODES CAN REPRESENT AN AMINO
  ACID

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• THERE ARE STOP CODONS THAT DO NOT CODE FOR AN
  AMINO ACID
• THEY READ ONLY IN ONE DIRECTION
• THE CODE IS UNIVERSAL FROM ORGANISM TO ORGANISM

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• INTRONS ARE LONG SEGMENTS OF NUCLEOTIDES THAT
  HAVE NO CODING INFORMATION
• EXONS ARE THE PORTIONS OF THE GENES THAT ARE
  TRANSLATED INTO PROTEINS

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• AFTER TRANSCRIPTION, THE INTRONS ARE CUT OUT
• THE EXONS ARE STITCHED BACK TOGETHER AND
  TRANSLATED

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THE GENETIC CODE

• IN 1961 MARSHALL NIRENBERG DECIPHERED THE CODE
  FOR PHENYLALANINE
• VARIOUS SCIENTISTS DECIPHERED THE REST OF THE CODE

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TRANSLATION

• THE PROCESS BY WHICH THE INSTRUCTIONS ON THE RNA
  MOLECULE ARE READ AND AN AMINO ACID CHAIN
  (PROTEIN) IS PRODUCED

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• TRANSFER RNA (tRNA) TEMPORARILY CARRIES A
  SPECIFIC AMINO ACID
• PROTEINS ARE MADE OF CHAINS OF AMINO ACIDS

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• AN ANTICODON IS A THREE-NUCLEOTIDE SEQUENCE ON A
  tRNA THAT IS COMPLEMENTARY TO AN mRNA CODON
• RIBOSOMAL RNA MOLECULES AND PROTEINS MAKE UP
  RIBOSOMES

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• THE CYTOPLASM CONTAINS THOUSANDS OF RIBOSOMES
• EACH RIBOSOME TEMPORARILY HOLDS ONE mRNA AND TWO
  tRNA MOLECULES

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• STEP 1
• mRNA WITH THE START CODON AUG BINDS TO THE
  ANTICODON OF TRNA CONTAINING METHIONINE

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• STEP 2
• THE tRNA WITH THE COMPLEMENTARY ANTICODON BONDS
  TO THE NEXT CODON.

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• STEP 3
• ENZYMES FORM A PEPTIDE BOND BETWEEN THE
  ADJACENT AMINO ACIDS

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• STEP 4
• THE MOLECULES THEN MOVE AS A UNIT AND THE NEW
  CODON RECEIVES THE NEXT TRNA AND ITS AMINO ACID
• STEP 5
• THE AMINO ACID BONDS TO THE GROWING PROTEIN CHAIN

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• STEPS 2 THOUGH 5 CONTINUES UNTIL A STOP CODON
  IS REACHED

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MUTATIONS

• MUTATIONS ARE MISTAKES IN THE REPLICATION OF
  GENETIC MATERIAL
• DAUGHTER CELLS CONTAIN DIFFERENT MATERIAL FROM
  THAT OF ITS PARENT

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GENE REARRANGEMENTS

• CAUSED WHEN AN ENTIRE GENE IS MOVED TO A NEW
  LOCATION

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GENE ALTERATIONS

• USUALLY RESULT IN THE PLACEMENT OF THE WRONG
  AMINO ACID DURING PROTEIN ASSEMBLY

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• DELETION - A NUCLEOTIDE IS LEFT OUT ALTERING THE
  AMINO ACID SEQUENCE

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• INSERTION - AN EXTRA NUCLEOTIDE IS ADDED ALTERING
  THE AMINO ACID SEQUENCE

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• POINT MUTATION - ONE NUCLEOTIDE IS SUBSTITUTED
  FOR ANOTHER RESULTING IN ONE AMINO ACID CHANGE