6 - protein synthesis and tracking
DESCRIPTION
TRANSCRIPT
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Outline for Today
I. Protein SynthesisA. Overview of Information Transfer
B. Transcription
C. Translation
II. Protein TraffickingA. What goes where and why care?
B. Ribosome role
C. Pathway of secreted protein
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Overview
Fig. 4.10
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Overview
What is a gene?
• Gene = sequence of nucleotides that codes for the synthesis of a piece of RNA
• (simplified version)
http://library.thinkquest.org/19037/genome.html
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RNA
• Ribonucleic acid• Types of RNA
– mRNA (messenger RNA)
– tRNA (transfer RNA)– rRNA (ribosomal RNA)
http://folding.stanford.edu/education/m.html
Overview
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mRNA
• Patterned from DNA in the nucleus
• Moves to the cytoplasm
• 10% of RNA is of this type
• 3 base sequence constitutes a codon http://www.alumni.ca/~mcgo4s0/t3/RNA.html
Overview
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tRNA
• Carries the amino acid from the cytoplasm to the ribosome
• Anticodon is a recognition area – Complimentary to the
codon of the mRNA
• Specific for an amino acid• 10% of the RNA is of this
type Fig. 4.8
Overview
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rRNA
• The RNA portion of ribosomes• 80% of RNA is of this type
Fig. 4.9
Overview
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Overview Protein Synthesis
Information transferfrom nucleus to cytoplasm
Culminates in protein formation
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Stages
• Two stages to protein synthesis– Transcription– Translation
3rd. Ed Fig. 4.6
Overview
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Stages
• Transcription– DNA to mRNA code
• Not all of the DNA is transcribed at once
– Language of the nucleotides
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/chem/nucleic/chpt15/transcription.gif
Overview
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Stages
• Translation– Translate the code
from “A, C, G, and U” to amino acid language
– Nucleic acid language to amino acid language
3rd. Ed Fig. 4.6
Overview
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Transcription
• DNA to mRNA– nucleus
• Stretch of DNA helix unwinds
• RNA polymerase• DNA rules of
complimentarity apply DNA RNA G C C G T A A U
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/chem/nucleic/chpt15/transcription.gif
Transcription
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Transcription
Separation of strands
Enzymes link nucleotides together based upon laws of complementarity
Russo, handout
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What are introns?(intervening regions)
• Consider the following
• inthebekweoitwoenasdfginninggodcreatedtheheavensdsjfaoiqwerjwqandtheearth
• inthebekweoitwoenasdfginninggodcreatedtheheavensdsjfa
oiqwerjwqandtheearth
• inthebeginninggodcreatedtheheavensandtheearth
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mRNA Processing
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/chem/nucleic/chpt15/intron.htm
Don’t confuse introns and exons (expressed regions).
Finished mRNA
Trans-Trans link
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Translation
Ribosome
Russo, handout
The Players!
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Overview
• mRNA leaves the nucleus and goes to the cytoplasm
• Is recognized by the ribosomal subunit
Translation
Russo, handout
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Overview
• Binding of subunits (amino acids) to get the polypeptide
Translation
Russo, handout
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Role of tRNA
• “transfers” or carries the amino acid from the cytoplasm to the ribosome
• Anti-codon– 3 nucleotide base
sequence– Complimentary to the
codon
http://www.alumni.ca/~mcgo4s0/t3/RNA.html
Translation
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Codon
• Triplet sequence on mRNA– 1 codon codes for 1
amino acid– Remember this was
coded from the DNA
Translation
Russo, handout
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Anticodon
• Triplet sequence on tRNA– 1 anticodon for a
specific amino acid
Translation
Russo, handout
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All RNA’s involved• rRNA makes up the ribosome• tRNA brings the amino acid to
the ribosome• mRNA carries the message
from the nucleus (DNA)
• The three types of RNA together carry out translation
http://www.cancerquest.org/index.cfm?page=45
Translation
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Let’s Watch a Video
https://paris.mcgraw-hill.com/sites/0073525693/student_view0/chapter4/how_translation_works.html
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Steps• Initiation
– tRNA with amino acid binds to ribosome subunit
– AUG is start codon• Therefore UAC is the anti-
codon– Other subunit comes in– Another tRNA comes in with
an aminio acid– Form the first peptide bond
– Ribosome shifts a distance of 1 codon
– How is the correct amino acid brought to the ribosome?
http://kvhs.nbed.nb.ca/gallant/biology/translation_initiation.jpg
Translation
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The genetic code
Campbell et al., Fig. 10.11
This lets you determine what amino acid is brought to the ribosome.
(read in mRNA)
Translation
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Steps
• Elongation– Ribosome moves
along the mRNA– Bond forms between 2
adjacent amino acids– Bond breaks between
amino acid and tRNA– Process keeps going
like a ticker tapehttp://www.science.siu.edu/microbiology/micr302/figure%207.25.JPG
Translation
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Elongation = lengthening of peptide chain
Translation
Russo, handout
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Steps
• Termination– The process stops
because the protein is complete
– Get one of the 3 stop codons• UAA• UAG• UGA
Campbell et al., Fig. 10.11
Translation
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Termination = addition of amino acids stops
Stop Codon =Codon for which there is nocomplementary anticodon
Translation
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Overview of the process
Campbell et al., Fig. 10.20
Translation
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Relationships
Fig. 4.10
Protein Synthesis
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Translation
Ribosome
= amino acid
mRNA message is “read” as triplet sequence of nucleotides: CODON
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Mutations
• Mutation is a change in the base of the DNA– At least one type of mutation
is this type– (There are others that involve
an addition or a deletion of a base
• Sickle cell disease is caused by one change in the DNA bases resulting in an improper amino acid in the hemoglobin
• A mistake at either transcription or translation can result in problems
Campbell et al., Fig. 10.21
Protein Synthesis
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Fig. 4.11
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What goes where• Way of determining
what protein goes where in the cell– Tay-Sachs disease the
proteins are supposed to go to the lysosome but they don’t
– Get fatty acids accumulations
http://medgen.genetics.utah.edu/photographs/pages/tay.htm
http://www.dynagene.com/education/tay.html
Protein Trafficking
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Ribosome location
– Free ribosomes• Protein will stay in the
cytoplasm or move to the nucleus or mitochondria
• Stays in the cell
– Anchored (to er)• Associated with the ER• Proteins destined for
the plasma membrane , the lysosome,or released from the cell (secretion)
Fig. 3.26b
Protein Trafficking
Fig. 3.26a
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Pathway• Initial sequence of amino
acids is a signal– Called the signal sequence
• Signal is recognized by a particle in the cytoplasm– Signal recognition particle
(SRP)
• SRP pulls the complex to the endoplasmic reticulum– Signal peptide goes into
the lumen of the ER
Protein Trafficking
Fig. 4.11
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Synthesis begins
RER
Initial sequence of amino acids is a
SIGNAL that directs protein to
the ER
“element” in cytoplasmrecognizes signal
and moveswhole complex to the
surface of the RER
Signal sequence istranslocated across
membrane of the ER to the inside
whole protein threadsinto the interior
of the ER
Protein Trafficking
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Protein Trafficking• Inside the ER the signal
sequence is cleaved• Can be altered in the ER
– Remove some aa’s, folding, stabilizing with S-S bridges, adding carbs, etc.
– Insulin starts out as 1 chain of 86 aa’s but ends up as 2 chains of 21 and 30 aa’s.
• Protein put into a bud of the ER that forms a transport vesicle
• Transport vesicle goes to the Golgi– Fuses with Golgi– Protein is liberated into the
Golgi
Protein Trafficking
Fig. 4.11
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Protein TraffickingRER
Signalis removed“budding”
Completed proteininside ER
Transport vesicle“shuttle”to Golgi
Fusion with Golgi
Golgi“modifications” occurthat provide sorting signals
“budding”
Secretory vesicleStorage vesicle
Fate #1
Immediate secretionRegulated secretion
Fate #2
Stimulus Applied
“shuttle”to membrane
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Pathway
• In the Golgi it is modified and sorted
• Bud forms from the Golgi– Secretory vesicle– Leaves via exocytosis
Fig. 4.11
Protein Trafficking
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Pathway
• Two possibilities for secretion– Immediate release– Regulated storage
• Vesicles stay in cell for a while as storage vesicles
• e.g. neurons and endocrine cells
Fig. 4.11
Protein Trafficking
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Protein
Trafficking
Synthesis begins
DNA
mRNA
Free ribosomal subunits
in the cytoplasm
mRNA
Ribosome subunits
associate with mRNA
Signal
sequence
“element” in cytoplasm
recognizes signal
and moves
whole complex to the
surface of the RER
Signal sequence is
translocated across
membrane of the ER
to the inside
whole protein threads
into the interior
of the ER
RER
Initial sequence of
amino acids is a
SIGNAL that directs
protein to
the ER
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Transport vesicle
RER
Golgi
An enzyme inside the RER
will cleave off
the signal
sequence
Protein is liberated into
the interior of the RER
once translation ends
The ribosome dissociates
from the mRNA
The signal piece will be degraded; the remainder of the protein will be
further processed
Eventually the protein
is moved into a membrane “bud”
which will generate a
transport vesicleThe transport
vesicle
shuttles the protein
to the Golgi
The transport vesicle
fuses with the Golgi and
releases the protein inside
After more processing, the protein
is moved into a membrane “bud”
which will generate a
secretory vesicle
Secretory vesicle
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Secretory vesicleStorage vesicle
Fate of the Secretory Vesicle
In some cases the secretory vesicle
will transition to the plasma membrane
for immediate secretion of the contents
into the extracellular space
Plasma membranePlasma membrane
In some cells the vesicle can remain as a storage vesicle
for a period of time;
this is true in cells that have Regulated Secretion
Regulated Secretion requires that a stimulus
(trigger event) be applied to the cell to make the
storage vesicle release its contents
into the extracellular space
STIMULUS!
Regulated secretion Secretion into the extracellular space