DNA, RNA,

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DNA, RNA, Protein Synthesis

• Ch.10

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(10-1) Discovery of DNA

• Griffith
• Transformation transfer of genetic material
  from 1 cell to another
• Avery
• Concluded DNA is responsible for transformation
  in bacteria
• Hershey-Chase
• Used bacteriophages to conclude that DNA is the
  hereditary molecule in viruses

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Griffith Avery
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Hershey-Chase
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(10-2) DNA

• Organic cmpd
• Made up of repeating subunits (nucleotides)
• 2 long chains

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Structure of DNA

• 3 parts
• Deoxyribose sugar molecule
• Phosphate group PO43-
• Nitrogen-containing base has N atom

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4 N-Containing Bases

• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Thymine (T)
• Purines 2 rings of C N atoms
• A G
• Pyrimidines 1 ring of C N atoms
• C T

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Double Helix

• Watson Crick (1953) suggested
• model
• Used Franklin Wilkins x-ray photograph

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Backbone

• Sugar phosphate covalently bonded
• Bases face center are perpendicular to backbone
• H-bonds hold strands together

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Complementary Base Pairing

• 2 rules
• C pairs w/ G
• A pairs w/ T
• Nucleotide sequence in 1 chain is complement of
  other chain

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(10-3) DNA Replication

• Replication fork area where chains separate
• Helicase enzyme that breaks H-bonds b/w bases
  causing chains to separate
• Each chain serves as a template for a new chain

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DNA Polymerase

• Enzyme that binds to separated strands of DNA
  assembles each strands complement
• Old ATTCCG
• New TAAGGC

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Accuracy Repair

• High accuracy
• Proofreading
• Repair enzymes
• Mutation change in nucleotide sequence
• DNA can also be damaged by chemicals UV light

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(10-4) RNA

• Ribonucleic acid
• 3 types m, t, r

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RNA Structure

• Repeating nucleotides
• Single-stranded
• Ribose sugar molecule
• Uracil replaces thymine
• U pairs w/ A

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Messenger (mRNA)

• Single, uncoiled chain
• Carries genetic info from DNA in nucleus to
  ribosomes in cytosol

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Transfer (tRNA)

• Single chain
• Nucleotides folded into hairpin shape
• Binds to specific amino acids (aa)

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Ribosomal (rRNA)

• Most abundant form
• Globular
• Make up ribosomes

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Transcription

• Genetic info is copied from DNA to mRNA
  (transcript)
• Occurs in nucleus
• Methylation regulation of gene expression can
  stop transcription
• Leads to cell specialization

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Steps of Transcription

1. RNA polymerase binds to promoter of a specific
   gene
2. Complementary copy of 1 strand made using RNA
   nucleotides (A w/ U, C w/ G)
3. Polymerase reaches termination signal
   transcription stops

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Genetic Code

• Correlation b/w nucleotide aas
• 20 different aa to make proteins (polypeptide)
• Used by most organisms to translate mRNA
  transcripts into proteins

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Codon

• 3 mRNA bases 1 codon
• Codes for proteins
• Start codon signal ribosome to start translating
  mRNA
• AUG
• Stop codon cause ribosome to stop translating
  mRNA
• UAA, UAG, UGA

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Translation (Protein Synthesis)

• Assembling proteins from info encoded in mRNA
• Anticodon tRNA segment complementary to mRNA
  codon

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Steps of Translation

1. Codon (mRNA) paired w/ anticodon (tRNA)
2. tRNA adds specific aa to the growing polypeptide
   chain

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Ribosomes

• Free in cytosol some attached to ER
• Binding sites for translation
• Holds mRNA transcript
• Holds tRNA

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Protein Assembly

• Ribosome attaches to start codon on mRNA
  transcript
• Pairs w/ tRNA anticodon
• Ribosomes move along mRNA
• Aa continue to attach as anticodons paired
• Ribosome reaches a
• stop codon
• mRNA is released
• protein is complete

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