Protein Synthesis

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Protein Synthesis Gene Expression

• DNA provides the instructions for how to build
  proteins
• Each gene dictates how to build a single protein
  in prokaryotes
• The sequence of nucleotides (AGCT) in DNA
  dictates the order of amino acids that make up a
  protein

nucleotide sequence of His protein
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Protein Synthesis Gene Expression
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Protein Synthesis Gene Expression

• Protein Synthesis Gene Expression
• The process in which the instructions encoded by
  a gene are used to build a protein

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Protein Synthesis Gene Expression

• Transcription
• RNA polymerase makes an mRNA (messenger RNA)
  copy of a gene
• occurs in cytoplasm of prokaryotes, nucleus of
  eukaryotes
• Enables cell to make many copies of a gene so
  that a lotof protein can be made at onetime
• Enables eukaryotic cells tokeep DNA protected in
  the nucleus, only mRNA copiesof genes leave the
  nucleus

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Protein Synthesis Gene Expression

• Transcription Initiation
• RNA polymerase binds to a region on DNA known as
  the promoter, which signals the start of a gene
• Promoters are specific to genes
• RNA polymerase does not need a primer
• Transcription factors assemble at the promoter
  forming a transcription initiation complex
  activator proteins help stabilize the complex
  
• Gene expression can be regulated (turned on/off
  or up/down) by controlling the amount of each
  transcription factor

HONORS
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Protein Synthesis Gene Expression

• Transcription Elongation
• RNA polymerase unwinds the DNA and breaks the
  H-bonds between the bases of the two strands,
  separating them from one another
• Base pairing occurs between incoming RNA
  nucleotides and the DNA nucleotides of the gene
  (template)
• recall RNA uses uracil instead of thymine

AGTCAT
UCA
GUA
HONORS
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Protein Synthesis Gene Expression

• Transcription Elongation

The gene occurs on only one of the DNA strands
each strand possesses a separate set of genes
RNA polymerase slides down the template strand
connecting together RNA nucleotides
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Protein Synthesis Gene Expression

• Transcription Termination
• A region on DNA known as the terminator signals
  the stop of a gene
• RNA polymerase separates from the mRNA and the DNA

HONORS
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Protein Synthesis Gene Expression
HONORS

• Exons are coding regions provide
  instructionsfor one or more proteins)
• Introns are removed
• different combinations of exons form different
  mRNA resulting in multiple proteins from the same
  gene
• Humans have 30,000 genes but are capable of
  producing 100,000 proteins

• Alternative Splicing (eukaryotes only)

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Web Resources

• Transcription
• http//www.biostudio.com/d_20Transcription.htm
• http//www.youtube.com/watch?vWsofH466lqk
• http//www.dnalc.org/resources/3d/TranscriptionBas
  ic_withFX.html

• Alternative Splicing
• http//www.youtube.com/watch?vFVuAwBGw_pQfeature
  related

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Protein Synthesis Gene Expression

• Translation
• mRNA is used by ribosome to build polypeptides
  (Ribosomes attach to the mRNA and use its
  sequence of nucleotides to determine the order of
  amino acids in the polypeptide)
• occurs in cytoplasm of prokaryotes and eukaryotes
• some polypeptides feed directly into rough ER in
  eukaryotes where they are modified and folded
  into the final protein

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Protein Synthesis

• TranslationInitiation
• Start codon signals where the gene begins (at 5
  end of mRNA)

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3
AUGGACAUUGAACCG
start codon
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Protein Synthesis Gene Expression

• TranslationInitiation
• Start codon signals where the gene begins (at 5
  end of mRNA)
• Ribosome binding site on the mRNA binds to a
  small ribosomal subunit
• Then this complex binds to a large ribosomal
  subunit forming the complete ribosome

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Protein Synthesis Gene Expression

• TranslationScanning
• The ribosome moves in 5 to 3 direction
  reading the mRNA and assembling amino acids
  into the correct polypeptide

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Protein Synthesis Gene Expression

• TranslationScanning
• Every three mRNA nucleotides (codon) specify an
  amino acid

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Protein Synthesis Gene Expression

• TranslationScanning
• Each tRNA carries a specific amino acid
• tRNA have an anticodon region that specifically
  binds to its codon

anticodon
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Protein Synthesis

• TranslationTermination
• Ribosome disengages from the mRNA when it
  encounters a stop codon

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Web Resources

• Translation
• Eukaryotic http//www.youtube.com/watch?v5bLEDd
  -PSTQfeaturerelated
• Prokaryotic http//www.biostudio.com/d_20Protei
  n20Synthesis20Prokaryotic.htm
• http//www.biostudio.com/d_20Peptide20Bond20For
  mation.htm
• http//www.johnkyrk.com/DNAtranslation.html
• http//www.dnalc.org/resources/3d/TranslationBasic
  _withFX0.html
• http//www.dnalc.org/resources/3d/TranslationAdvan
  ced.html

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Protein Synthesis Gene Expression

• Post-Translational Modifications
• Polypeptide is modified in the rough ER this
  might include cutting out sections and/or cut a
  section from one part of the polypeptide and
  moving it to another part
• Chaperone proteins help to fold the polypeptide
  into its final tertiary shape. Now it is called a
  protein.

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Protein Synthesis Gene Expression
Rough Endoplasmic Reticulum (ER)

• Folded membrane that forms compartments where
  newly synthesized proteins are processed (cut,
  joined, folded into their final shape)
• Ribosomes bind to rough ER when they start to
  synthesize proteins that are intended to be
  exported from the cell the proteins enter the
  ER directly from the ribosome

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Protein Synthesis Gene Expression
Golgi Apparatus

• Folded membranes form compartments that each
  contain different enzymes which selectively
  modify the contents depending on where they are
  destined to end up
• Processes and packages macromolecules produced
  by the cell (e.g. proteins and lipids) sent
  out as excretory vesicles labeled for their
  destination

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Protein Synthesis Gene Expression
Translation

• Multiple RNA polymerases can engage a gene at one
  time
• Multiple ribosomes can engage a single mRNA at
  one time

Transcription
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Protein Synthesis Gene Expression

• Eukaryotes transcription occurs in the nucleus
  and translation occurs in the cytoplasm
• Prokaryotes Transcription and translation occur
  simultaneously in the cytoplasm

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Protein Synthesis Gene Expression

• There are three main types of RNA
• mRNA (messenger RNA) - RNA copy of a gene used
  as a template for protein synthesis
• rRNA (ribosomal RNA) - part of structure of
  ribosomes
• tRNA (transfer RNA)- amino acid carrier that
  matches to mRNA codon

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Practice Question
Translate the following mRNA sequence AGCUACCAUACG
CACCCGAGUUCUUCAAGC
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Practice Question
Translate the following mRNA sequence AGCUACCAUACG
CACCCGAGUUCUUCAAGC
Serine Tyrosine Histidine Threonine
Histidine Proline Serine Serine Serine -
Serine
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Practice Question
Translate the following mRNA sequence AGCUACCAUACG
CACCCGAGUUCUUCAAGC
Serine Tyrosine Histidine Threonine
Histidine Proline Serine Serine Serine -
Serine
Ser Tyr His Thr His Pro Ser Ser
Ser - Ser
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Practice Question
Translate the following mRNA sequence AGCUACCAUACG
CACCCGAGUUCUUCAAGC
Serine Tyrosine Histidine Threonine
Histidine Proline Serine Serine Serine -
Serine
Ser Tyr His Thr His Pro Ser Ser
Ser - Ser
S Y H T H P S S S - S
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Protein Synthesis Gene Expression

• Protein Synthesis Gene Expression
• Process in which a gene is used to build a
  protein resulting in the presence of a particular
  phenotype (physical characteristic)
• Phenotypic variation among organisms is due to
  genotypic variation
  (differences in the sequence of their DNA
  bases)
• Differences exist between species and within a
  species
• Different genes (genomes) ? different proteins
  (proteomes)
• Different versions of the same gene alleles
• Differences in gene expression epigenetics

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Web Resources
Insulin Example of Protein Synthesis http//www.bi
otopics.co.uk/as/insulinproteinstructure.html
Hemoglobin Example of Protein Synthesis http//www
.biotopics.co.uk/as/insulinproteinstructure.html
Collagen Example of Protein Synthesis http//www.b
iotopics.co.uk/JmolApplet/collagen.html