Chapter 11.4-11.6 From DNA to Proteins - PowerPoint PPT Presentation


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Chapter 11.4-11.6 From DNA to Proteins


Chapter 11.4-11.6 From DNA to Proteins College Prep Biology Mr. Martino Introduction Protein synthesis is the process of making proteins 2 stages: 1. – PowerPoint PPT presentation

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Title: Chapter 11.4-11.6 From DNA to Proteins

Chapter 11.4-11.6From DNA to Proteins
  • College Prep Biology
  • Mr. Martino

  • Protein synthesis is the process of making
  • 2 stages
  • 1. Transcription process of transferring the
    DNA gene onto an mRNA transcript
  • 2. Translation process of tRNA and rRNA
    assembling the amino acids in the proper sequence
    according to mRNA
  • Involves RNA

11.4 Transcription
  • 3 main classes of RNA
  • mRNA messenger RNA carries the instructions
    from DNA
  • tRNA transfer RNA delivers amino acids to
    ribosome to form protein
  • rRNA ribosomal RNA a major component of

More Transcription
  • RNA is similar yet different from DNA
  • Single stranded
  • 4 types of nucleotides (uracil substitutes for
    thymine pairing with adenine)
  • Ribose substitutes for deoxyribose
  • Different types of RNA
  • Found in nucleus (like DNA) but also in cytoplasm

Uracil is only found in RNA
Transcription again
  • Transcription is similar to replication but
    differs in 3 important ways
  • 1. Only a small section of DNA (gene) serves as
  • Promoter a base sequence on DNA that signals
    the beginning of a gene
  • 2. RNA polymerase attaches nucleotides instead
    of DNA polymerase
  • 3. Results in a single strand of RNA not
    double helix

  • 3 Phases of transcription
  • 1. Initiation when RNA polymerase attaches to
    the promotor DNA
  • 2. Elongation growing of the RNA strand
  • As it continues, RNA strand pulls away from DNA
    DNA rejoins
  • 3. Termination RNA reaches a specific sequence
    that codes for stop
  • Polymerase detaches from RNA and gene

(No Transcript)
  • Not all of the new mRNA is used
  • Introns base sequences that are removed before
  • Exons parts of the mRNA that gets translated
    into a protein

11.5 Genetic Code
  • Gobind Khorana and Marshall Nirenberg realized
    ribsomes read nucleotides 3 at a time
  • Codon set of 3 nucleotides amino acid
  • 64 codons code for 20 amino acids
  • AUG codes for methionine /start
  • 3 codons for stop
  • Several codons code for some amino acids
  • Codons are universal for all living organisms

Structure and Function of tRNA rRNA
  • tRNA (transfer RNA) carry amino acids
  • One end has anticodon while other carries a.a.
  • Anticodon nucleotide triplet that base pairs
    with codon
  • Specific for 1 amino acid
  • rRNA component of ribosomes

11.5 Translation
  • Translation has 3 stages initiation,
    elongation, and termination
  • 1. Initiation
  • Step 1 mRNA binds to small subunit initiator
    tRNA locates binds to start codon (AUG)
  • Step 2 large subunit binds to small one

  • 2. Elongation After initiation, A.A.s are
    added one by one
  • Step 1 Codon recognition
  • tRNA anticodon matches mRNA codon
  • Step 2 Peptide Bond Formation
  • A.A. separates from tRNA and attaches to
    polypeptide (P to A)
  • Step 3 Translocation
  • A site tRNA moves to P site

  • Termination stop codon on mRNA is reached
  • Triggers a release factor to bind to ribosome
  • Enzyme detaches mRNA and polypeptide
  • Many polypeptides then float freely in cytoplasm
    others enter rough ER before being sent to
    their ultimate destinations

11.6 Mutations
  • Gene mutations change in nucleotide sequence of
    DNA genes
  • Substitution one amino acid is substituted for
  • Ex. Sickle-cell anemia
  • Frame shift mutations change down-stream
  • Insertion an extra base is put into a gene
  • Deletion loss of a base
  • Transposable Elements (translocation) DNA
    segments that move spontaneously

Causes of Mutations
  • Many mutations occur spontaneously during
  • Small number of mistakes do sneak by proofreaders
  • Mutagen mutation causing agents in environment
  • UV light, gamma rays, X-rays
  • Carcinogen cancer causing agents disrupt base
  • Only spontaneous mutations of germ cells or
    gametes are passed on to offspring