CHAPTER 10: DNA,RNA

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CHAPTER 10 DNA,RNA Protein Synthesis
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I. Discovery of DNA

• Scientist originally believed PROTEINS would be
  the molecules which contained hereditary
  information.
• Some scientists who did experiments that proved
  DNA had genetic information
• 1. Fredrick Griffith
• 2. Oswald Avery
• 3. Hershey Chase

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James Watson Francis Crick

• In 1953 DNA structure discovered
• Double Helix model.
• (2 chains of DNA)
• Showed how DNA could replicate.
• Relied on work of other scientists
• Rosalind Franklin Maurice Wilkins took X-ray
  photos of DNA structure
• ( Franklin died 1958 before Watson Crick
  received Nobel Prize. 1962.)

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II. DNA structure

• Double Helix shape is formed by base pairs
  attached to a sugar-phosphate backbone.
• -

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B. Parts of Nucleotides

• 1. 5 carbon sugar in DNA- deoxyribose
• (in RNA ribose)
• 2. phosphate group
• 3. nitrogenous bases ( there are 4 different
  ones)
• Adenine
• Guanine
• Cytosine
• Thymine
• (in RNA- no thymine- Uracil is the base)

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C. How Chemical Bonds hold DNA together

• Covalent bonds- between sugar phosphates of 2
  nucleotides
• Hydrogen bonds- between complementary nitrogenous
  bases

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D. Base Pairing Rules

• Adenine always bonds with Thymine (AT)
• Guanine always bonds with Cytosine (GC)
• Note 3 hydrogen bonds GC
• 2 Hydrogen bonds AT

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• Must have 1 purine (a 2 ring shape) plus 1
  pyriomidine (1 ring shape) in each pair or the
  would not fit inside ladder of DNA
• 2. Purines (A, G) double C ring
• 3. Pyrimidines (T, C) single C ring

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III. DNA Replication

• A. Is the process by which DNA is copied in a
  cell before a cell divides by mitosis, meiosis or
  binary fission.

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B. Steps in Replication

• 1. Helicase enzymes -separate hydrogen bonds in
  strands create replication fork
• 2. Attach- DNA polymerase enzyme -adds
  nucleotides
• 3. Release DNA polymerase enzyme now have 2
  identical DNA strands

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C. Errors

• DNA replication is very accurate.
• Errors occur 1 in 1 billion paired nucleotides.
• Proofreading enzyme checks for spelling
  errors.
• If a mistake does occur- new DNA is different
• Mutation- a change in the nucleotide sequence of
  a DNA molecule.
• Caused by chemicals, radiation,UV rays.
• Mutations can be favorable
• - or harmful. (example- cancer)

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IV Protein Synthesis

• Flow of Information (DNA RNA - Proteins)
• Before protein can be synthesized, the
  instructions in DNA must first be copied to
  another type of nucleic acid called messenger
  RNA.
• Then -a group of 3 nucleic acids codes for an
  amino acid it is built at the ribosomal RNA
  with help from the transfer RNA

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RNA differs from DNA in the following ways

• RNA is single stranded while DNA is double
  stranded.
• RNA has a sugar called ribose while DNA has a
  sugar called deoxyribose.
• RNA has the nitrogenous base uracil while DNA has
  the base thymine.

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• B. 3 types RNA
• 1. messenger RNA(mRNA)
• 2. transfer RNA (tRNA)
• 3. ribosomal RNA (rRNA)

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• Messenger RNA, or mRNA.
• carries the code for building a protein from the
• nucleus to the ribosomes in the cytoplasm. It
  acts
• as a messenger.
• Transfer RNA or tRNA.
• picks up specific amino acids in the cytoplasm
• brings them into position on ribosome where
• they are joined together in specific order to
• make a specific protein.
• Ribosomal RNA or rRNA
• place for protein synthesis

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C. Steps in Transcription-making RNA

• 1. RNA polymerase (enzyme) binds to promoter
  area on DNA
• 2. Nucleotides added joined by the enzyme (RNA
  polymerase)
• Termination signal- stop- RNA polymerase releases
  both DNA new RNA molecules

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D. Proteins

• Review of protein structure
• -recall that proteins are made of amino acids
  joined together with peptide bonds
• -there are 20 different amino acids, the order
  they are joined determines the structure
  function of the proteins.
• -proteins can be very large, complicated
  molecules

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mRNA codons for specific amino acids

• Each 3 nucleotide sequence (letters) in mRNA
  encodes for 1 specific amino acid, or a start
  or stop signal.
• Each 3 nucleotide group is called a codon.
• The genetic code- means the rules that relate how
  a particular sequence of nitrogenous bases
  corresponds to a particular amino acid.

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E. Steps in Translation

• Initiation- tRNA mRNA join together.
• (The codon is on the mRNA, the anticodon is on
  tRNA)
• The tRNA has an amino acid attached to it)
• Elongation- continued as ribosome moves the
  distance of 1 codon on mRNA
• Elongation is built with new tRNAs attaching each
  amino acid as it reads the codons on the mRNA.
• Termination- ribosome reaches stop codon on the
  mRNA
• Disassembly each piece is free.
• (see sequence page 208-209 in textbook)

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Remember

• Replication- copying DNA from DNA
• Transcription- making RNA from DNA
• Translation- making proteins