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

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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.

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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