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Chapter 12 Gene Expression

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Chapter 12 Gene Expression Unlocking the secrets of DNA – PowerPoint PPT presentation

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Title: Chapter 12 Gene Expression


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Chapter 12Gene Expression
  • Unlocking the secrets of DNA

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DNA is difficult to understand, even for the cell.
  • The nucleotide sequence of DNA is the blueprint
    for building proteins, but the ribosomes
    responsible for making proteins cannot read DNA.

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Ribonucleic Acid
  • 1) Messenger RNA
  • Single strand, complimentary copy of DNA created
    in nucleus contains triplet codons
  • 2) Transfer RNA
  • Cloverleaf-shaped strand that picks up amino
    acids and delivers them to the ribosome contains
    triplet anti-codons
  • 3) Ribosomal RNA
  • Makes up ribosomes joins amino acids together to
    create a growing protein chain

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RNA vs DNA
  • RNA is single instead of double strand
  • RNA has different sugar (ribose)
  • RNA has uracil which takes the place of thymine
  • RNA moves out of nucleus controls protein
    synthesis

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Transcription the production of RNA from the DNA
code
Adenine (DNA and RNA) Cystosine (DNA and
RNA) Guanine(DNA and RNA) Thymine (DNA
only) Uracil (RNA only)
RNApolymerase
DNA
RNA
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Protein Synthesis
  • 1. Transcription
  • Occurs in nucleus
  • DNA makes a complimentary copy in the form of
    M-RNA in a process similar to replication
  • M-RNA moves out of nucleus and to ribosomes in
    the cytoplasm

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Transcription
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Benefits of transcription
  • Transcribed copies of the DNA (in the form of
    RNA) are used instead of the original DNA.
  • In eukaryotes, DNA in the cytoplasm is degraded
    but RNA is not.

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How does transcription work?
  • DNA double helix must be separated at the
    hydrogen bonds between nitrogen bases.
  • Only one DNA strand is read by RNA polymerase.
  • RNA polymerase constructs an RNA polymer.

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Building RNA polymer
  • DNA ? (codes for) RNA
  • A ? U
  • T ? A
  • C ? G
  • G ? C

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Click on image to play video.
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What happens to the RNA once it is created?
  • In prokaryotes, the RNA is immediately
    translated.
  • In eukaryotes, the RNA is processed.
  • Introns removed
  • Exons joined together

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RNA processing
  • Introns (segments of useless genes) are removed,
    leaving on exons (expressed genes).

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  • 2. Translation
  • Occurs in cytoplasm
  • T-RNA delivers amino acids to ribosomes joins
    complimentary anti-codons, putting amino acids in
    proper order
  • R-RNA forms peptide bonds to join amino acids
    into a protein molecule
  • (T-RNA returns to pick up new amino acids)

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Translation
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Translation
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Ribosomes use this decoding scheme to determine
how to build the appropriate protein.
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How does the decoding work?
  • RNA AUGCGAGGGAGAUUAUAGGAC
  • Ribosomes read AUG CGA GGG AGA UUA UAG
    GAC.
  • Each 3 nucleotide word is called a codon.

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Try to decode AUG CGA GGG AGA UUA UAG GAC.
  • Met Arg Gly Arg Leu - stop

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What happens to MetArgGlyArgLeustop?
  • The ribosomes create an amino acid polymer that
    is folded into a protein.
  • The original DNA code, transcribed to RNA,
    instructs the cell to make a protein for a
    specific function.

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Click on image to play video.
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What happens if there is a mutation in the
original DNA?
  • Point mutations change of one nucleotide
    sequence
  • This may or may not affect the amino acid
    sequence, depending upon where the mutation
    occurs in the DNA sequence.

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Gene mutations
  • Point mutations
  • Change one nucleotide or just a few nucleotides
    in a gene
  • Examples sickle cell anemia cystic fibrosis
  • Frame-shift mutations
  • The reading pattern is displaced and shifts
    into new positions
  • Examples duchenne Muscular Dystrophy

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Frame shift mutations
  • The cat and the rat ran far.
  • The ca and the rat ran far.
  • The caa ndt her atr anf ar.

t
r
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Click on image to play video.
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Mutations
  • Disadvantages
  • Abnormal, even lethal genes can be passed on to
    offspring
  • Advantages
  • New, stronger genes can be passed on to offspring

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Chromosomal mutations
A B C D E F G H
  • Deletion
  • Insertion
  • Inversion
  • Translocation

A B C D E G H
A B C D J E F G H
A B C D E G F H
A B C D E F
G H W X Y Z
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  • DNA 5 A T G C C T G A A T G A 3
  • 3 T A C G G A C T T A C T 5 coding
    strand
  • mRNA A UG C C U G A A U G A codons
  • tRNA U A C G G A C U U A C U anti
    codons
  • amino
  • acids Met Pro Glu stop
  • protein

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The Central Dogma theory of Biology
(DNA RNA protein cell
functions)
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Animation of translation
  • Click to automatically start animation.

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Nucleus
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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tRNA
tRNA
Single Messenger RNA Strand
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tRNA
tRNA
Single Messenger RNA Strand
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tRNA
tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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tRNA
Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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Single Messenger RNA Strand
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tRNA
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Protein Synthesis overview
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Transcription DNA codes for RNA
  • RNA polymerase
  • A ? U
  • T ? A
  • C ? G
  • G ? C

108
mRNA processing
  • The RNA polymer made messenger RNA (mRNA)
  • DNA has junk genes. These are called introns
    (useless pieces of RNA made as a result of
    useless DNA).
  • Introns are cut (spliced).
  • Exons are remaining RNA nucleotides carrying the
    actual DNA code.
  • Exons are translated.

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Translation RNA to amino acids
  • Ribosomes read codons.
  • AUG start codon
  • tRNA with anticodons have amino acids attached.

111
Translation
Ribosomes read until the codon that indicates
STOP.
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Amino acid chain
  • The amino acid chain made in translation is then
    folded.
  • Folded proteins enzymes, pigments, etc.
  • Proteins made phenotype
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