From gene to protein

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From gene to protein
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Our plan

• Overview gene expression
• Walk through the process
• Review structure and function of DNA
• Transcription
• Translation
• Gene expression and mutations

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Overview
Gene expression- the process by which DNA directs
the synthesis of proteins
Transcription
Translation
mRNA
Protein
DNA
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Overview Cell as a city
DNA Blueprint for the city Nucleus City
Hall Nuclear envelope Fence around City Hall
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Overview Cell as a city
Transcription
Translation
mRNA
Protein
DNA

• The blueprint cannot leave City Hall
• Photocopies of the blueprint can be taken out
  into the city
• Architects and builders translate the blue print
  into the citys infrastructure

• The DNA remains in the nucleus
• Transcription generates mobile RNA transcripts
  using DNA as a template
• The RNA sequence can be translated into a protein

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Overview
Transcription
Translation
mRNA
Protein
DNA
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DNA
Genes- discrete units of hereditary information
consisting of a specific nucleotide sequence of
DNA
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Overview
Transcription
Translation
mRNA
Protein
DNA
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Transcription

• Transcription-DNA guides the production of RNA
• Takes place in three phases
• Initiation
• Elongation
• Termination

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Transcription

• Transcription-DNA guides the production of RNA
• Takes place in three phases
• Initiation
• Elongation
• Termination

• RNA polymerase binds to a promoter in the DNA
  (contains a signal sequence and at start point)
• The DNA is separated and unwound
• Transcription begins

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Transcription

• Transcription-DNA guides the production of RNA
• Takes place in three phases
• Initiation
• Elongation
• Termination

• RNA polymerase moves along the template strand
• Untwists the helix
• Adds complimentary RNA nucleotides to the 3 end
  of the chain

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Transcription

• Transcription-DNA guides the production of RNA
• Takes place in three phases
• Initiation
• Elongation
• Termination

• Transcription terminates after a special sequence
  is transcribed
• Termination sequence (proks-I.e. hairpins)
• Polyadenylation sequence (euks)
• The transcript is cut and released

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Transcription

• Eukaryotic cells modify RNA before it enters the
  cytoplasm
• Both ends of the transcript are processed
• Some sections are cleaved and those remaining are
  spliced together

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Transcription

• Eukaryotic cells modify RNA before it enters the
  cytoplasm
• Both ends of the transcript are processed
• Some sections are cleaved and those remaining are
  spliced together

• 5 end receives a 5 cap
• 3 end receives a poly-A tail

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Transcription

• Eukaryotic cells modify RNA before it enters the
  cytoplasm
• Both ends of the transcript are processed
• Some sections are cleaved and those remaining are
  spliced together

• Both
• Facilitate the export of the
• mRNA
• Protect mRNA from degradation
• Help ribosomes attach

• 5 end receives a 5 cap
• 3 end receives a poly-A tail

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Transcription

• Eukaryotic cells modify RNA before it enters the
  cytoplasm
• Both ends of the transcript are processed
• Some sections are cleaved and those remaining are
  spliced together

• Introns (non-coding regions) are cut
• Exons (coding regions) are spliced together

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Transcription
Question What would be the sequence of RNA
generated from the following DNA template
strand? DNA 3-A T C C G T-5
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Transcription
Question What would be the sequence of RNA
generated from the following DNA template
strand? DNA 3-A T C C G T-5 mRNA5-U A G G
C A-3
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Overview
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Translation

• Proteins are made from polypeptide polymers,
  which are made from amino acid monomers

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Translation

• Proteins are made from polypeptide polymers,
  which are made from amino acid monomers

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Translation

• Proteins are made from polypeptide polymers,
  which are made from amino acid monomers

How is the information in RNA transformed into an
amino acid?
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Translation-The genetic code

• Only four nucleotides in RNA and 20 amino acids
  (the genetic code is not like Chinese)
• More like English, different permutations of
  letters build meaningful words
• Only 16 two-letter combinations of nucleotides
  (42)
• 64 possibilities if three-nucleotide combinations
  code for an amino acid

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Translation-The genetic code

• Only four nucleotides in RNA and 20 amino acids
  (the genetic code is not like Chinese)
• More like English, different permutations of
  letters build meaningful words
• Only 16 two-letter combinations of nucleotides
  (42)
• 64 possibilities if three-nucleotide combinations
  code for an amino acid

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Translation-The genetic code

• Genetic instructions for a polypeptide are
  written in RNA as a series of non-overlapping
  three-nucleotide words (codons)

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Translation-The genetic code

• Genetic instructions for a polypeptide are
  written in RNA as a series of non-overlapping
  three-nucleotide words (codons)
• Ie. 5-AAG-3lysine

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Translation-The genetic code

• Genetic instructions for a polypeptide are
  written in RNA as a series of non-overlapping
  three-nucleotide words (codons)
• Ie. 5-AAG-3lysine
• 61 code for amino acids

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Translation-The genetic code

• Genetic instructions for a polypeptide are
  written in RNA as a series of non-overlapping
  three-nucleotide words (codons)
• Ie. 5-AAG-3lysine
• 61 code for amino acids
• 3 stop codons

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Translation-The genetic code

• Genetic instructions for a polypeptide are
  written in RNA as a series of non-overlapping
  three-nucleotide words (codons)
• Ie. 5-AAG-3lysine
• 61 code for amino acids
• 3 stop codons
• AUGMethionine or start

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Translation-The genetic code

• Genetic instructions for a polypeptide are
  written in RNA as a series of non-overlapping
  three-nucleotide words (codons)
• Ie. 5-AAG-3lysine
• 61 code for amino acids
• 3 stop codons
• AUGMethionine or start
• The code is redundant, but not ambiguous

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Translation-The genetic code

• Genetic instructions for a polypeptide are
  written in RNA as a series of non-overlapping
  three-nucleotide words (codons)
• Ie. 5-AAG-3lysine
• 61 code for amino acids
• 3 stop codons
• AUGMethionine or start
• The code is redundant, but not ambiguous
• This code is nearly universal

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Translation
Just as the architects and builders translate the
copied blueprints into the citys infrastructure,
tRNA translates mRNA codons into amino acids
3?
Amino acid attachment site
5?

• tRNA
• Consists of a single strand of RNA
• Anticodon on one end (can bind with an mRNA
  codon)
• Corresponding amino acid on upper portion

Hydrogen bonds
Anticodon
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Translation

• Three stages
• Initiation
• Elongation
• Termination

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Translation

• Initiation begins when mRNA binds to the small
  sub-unit of a ribosome

• Three stages
• Initiation
• Elongation
• Termination

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Translation

• Initiation begins when mRNA binds to the small
  sub-unit of a ribosome
• Charged tRNA binds to the start codon

• Three stages
• Initiation
• Elongation
• Termination

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Translation

• Initiation begins when mRNA binds to the small
  sub-unit of a ribosome
• Charged tRNA binds to the start codon
• Large ribosomal sub-unit binds
• Cluster is called the initiation complex

• Three stages
• Initiation
• Elongation
• Termination

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Translation

• Three stages
• Initiation
• Elongation
• Termination

• New tRNAs come in and bind at A site as their
  complimentary condon is made available

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Translation

• Three stages
• Initiation
• Elongation
• Termination

• New tRNAs come in and bind at A site as their
  complimentary condon is made available
• New amino acids is bonded to the growing chain

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Translation

• Three stages
• Initiation
• Elongation
• Termination

• New tRNAs come in and bind at A site as their
  complimentary condon is made available
• New amino acids is bonded to the growing chain
• Complex moves to free the A site

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Translation

• Three stages
• Initiation
• Elongation
• Termination

• New tRNAs come in and bind at A site as their
  complimentary condon is made available
• New amino acids is bonded to the growing chain
• Complex moves to free the A site
• tRNA that shifted to E site exits

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Translation

• Three stages
• Initiation
• Elongation
• Termination

• New tRNAs come in and bind at A site as their
  complimentary condon is made available
• New amino acids is bonded to the growing chain
• Complex moves to free the A site
• tRNA that shifted to E site exits
• New tRNA binds at the A site

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Translation

• Termination occurs when a ribosome encounters a
  stop codon
• Release factors bind
• mRNA and polypeptide are released

• Three stages
• Initiation
• Elongation
• Termination

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Transcription
Question What polypeptide sequence would be
generated from the following DNA template
strand? DNA 3-T T C A G T-5
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Transcription
Question What polypeptide sequence would be
generated from the following DNA template
strand? DNA 3-T T C A G T-5 RNA 5-A A G
U C A-3 Peptide sequence Lysine, serine
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Summary
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Point mutations

• Impacts of genetic mutation on gene expression
• Point mutations- change in a single base pair
• Base-pair substitution
• Silent-no change in polypeptide
• Missense (substituted amino acid)
• Nonsense (early stop codon)

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Point mutations

• Impacts of genetic mutation on gene expression
• Point mutations- change in a single base pair
• Insertion and deletion
• Addition or loss of base pairs
• Causes a frame shift

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You should understand

• The process of gene expression
• The impact of point mutations on gene expression