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Lecture 4

01:447:380 Lecture Notes - Lecture 4: Spliceosome, Consensus Sequence, Polyadenylation


Department
Genetic
Course Code
01:447:380
Professor
R Michaelis
Lecture
4

This preview shows pages 1-3. to view the full 20 pages of the document.
Special Sequences Tell The Spliceosome Where To Cut
There are consensus sequences around the intron/exon borders that orient the spliceosome
so it cuts at the right places
Alternative Splicing Allows One Gene To Make Different Proteins In Different Tissues
RNA Can Be Edited After Transcription
Guide RNAs bind to the mRNA and cause it to be cleaved and edited
Nucleotides can be added or deleted, and one nucleotide can be substituted for by another
The resultant mRNA base sequence and protein's amino acid sequence will not match those
that are predicted from the gene's coding sequence
Overview of Translation:
The ribosome reads the mRNA three bases at a time
Each 3-base unit is called a codon
Each codon instructs the ribosome to add one amino acid to the growing polypeptide
A STOP codon terminates translation and releases the polypeptide
The polypeptide is folded, adorned with chemical side groups and sent to where it needs to be
Some polypeptides join with others to form multimers
Some get cleaved into multiple independently active peptides; some are made in
inactive form and are activated by cleavage
Initiation of Translation: Proteins that bind to the 5’ cap and the poly-A tail help the ribosome bind
the mRNA
Elongation Factors Help The Ribosome Chain Amino Acids Together
Without protein synthesis would be much slower
64 possible codon; 61 possible anticodons in transfer RNA
Because 3 stop codons are needed
When ribosome encounter stop codon, you have releasing factors that bind to stop
codon and uncouple polypeptide from RNA
tRNAs Carry Amino Acids In For Translation
The mRNA codon sequence dictates which anticodon the tRNA must have:
Each tRNA with a given anticodon sequence always carries the same amino acid
This maintains the fidelity of the genetic code
§
There are 20 different aminoacyl-tRNA synthetases
Each one attaches a different amino acid to the appropriate tRNAs
ATP provides the energy for this procedure, known as tRNA charging
§
Note that tRNAs sometimes contain unusual bases, ex. inosine (I) or pseudouridine (ψ)
These bases can often pair with more than one of the other bases, increasing the
number of codons that the tRNA’s anticodon can bind to
§
A Consensus Recognition Sequence Orients The Ribosome In Prokaryotes
Orients the ribosome
The small subunit of the bacterial ribosome attaches to the Shine-Dalgarno sequence in
bacterial mRNAs
A ribosomal binding site in bacterial and archaeal messenger RNA, generally located around 8
bases upstream of the start codon AUG.
The RNA sequence helps recruit the ribosome to the messenger RNA (mRNA) to initiate
protein synthesis by aligning the ribosome with the start codon.
How would the cell know which AUG is the start codon?
Consensus (general) sequence, usually has a G after… Look below.
Translation Usually Begins At An AUG Codon
GUG and UUG may be used in rare cases
The first amino acid added in bacteria is N-formylmethionine
In archaea and eukaryotes it is methionine
A Consensus Recognition Sequence Identifies The Translation Initiation Codon In Eukaryotes
Not every AUG is a START codon; most AUG codons instruct the ribosome to incorporate
methionine
In eukaryotes, the START codon is usually the first AUG in the mRNA
In addition, there is a consensus sequence around the START codon, aka a Kozak
sequence, after Marilyn Kozak, who reported several types of consensus sequence,
including intron/exon boundary sequences
In eukaryotes, it is GCC(A/G)CCAUGG, where the START AUG is underlined, and the
(A/G) means that there could be either an A or a G in that position
Ex. The human beta-globin gene's sequence differs from the consensus sequence
by one base: GACACCAUGG
§
Initiation Factors Help The Ribosome Assemble --> illustrates their function in prokaryotic cells
In eukaryotes, the 5' cap and the 3' poly-A tail both bind to initiation factors
Missense And Nonsense Mutations
Missense mutation = one amino acid gets replaced by another
Effects range from no effect to abolishing protein’s activitya.
Translation continues properly after the mutation—downstream sequences get
translated
Amino acids (diff size and charged)i.
Folding into proper 3D shapeii.
Changes shape or movement can decrease the level of activity in a protein
(sometimes can increase)
iii.
b.
1.
Nonsense mutation = creates a STOP codon at the site of the mutation
Protein is truncated—usually abolishes protein’s activitya.
Translation stops at that point—downstream sequences do not get translatedb.
2.
The Ribosome Has A Reading Frame
The reading frame begins with the START codon (usually an AUG) and ends at the STOP codon
(UGA, UAG, UAA)
If someone has a deletion or insertion, if it involves a multiple of three nucleotides (an
in-frame deletion/insertion), it will not shift the ribosome’s reading frame
Amino acids will be missing (deletion) or novel amino acids will be incorporated (insertion),
but the protein will retain its normal amino acid sequence before and after the
deletion/insertion
The protein may still be able to function—depends on how many and which specific
amino acids are missing/added
If someone has a deletion or insertion that does not involve a multiple of three nucleotides, it
will shift the ribosome’s reading frame
Novel amino acids will be incorporated into the polypeptide
The ribosome will encounter a STOP codon at some point
The protein will probably not be able to function
It may even acquire a novel function, depending on the amino acids that are chained
together after the frame shift
The Ribosome Reads The mRNA One Codon At A Time
The polypeptide that has already been assembled sits in the P site, or peptidyl (peptide) site
The next amino acid gets carried in to the A (aminoacyl) site
Peptidyl transferase forms a peptide bond between the new amino acid's amino group
and the previous amino acid's carboxyl group
The peptidyl site then releases its amino acid, and the polypeptide sits momentarily in the A
site
The ribosome then moves down one codon, and the P site now contains the polypeptide
Proteins called elongation factors assist the process
The Ribosome Moves Down The mRNA One Codon At A Time
Translation Termination Codons, aka STOP Codons, Signal Termination Of Translation
Releasing Factors Terminate Translation
The Integrity Of The mRNA Is Monitored Before Translation
Nonsense-Mediated mRNA Decay Handles Premature STOPs
Nonsense mutation = mutation that creates a STOP codon at the site of the mutation
The polypeptide is not completed
When the pre-mRNA gets processed, proteins are bound to the exon-exon junctions in the
mRNA; the ribosome removes them
If the ribosome does not travel all the way to the end of the mRNA, some of these
proteins remain, acting as a signal to enzymes to degrade the mRNA
Preserves energy
§
Unstopped mRNAs Must Be Degraded Also
The ribosome can stall if:
Transcription is incomplete and there’s no STOP codon in the mRNA
A mutation changes the STOP codon to an amino acid codon
This causes the ribosome to get stuck on that mRNA, and leaves it unavailable to
perform more translation
Too much of this can have very serious consequences—drastic reduction in
protein synthesis capacity
§
Bacteria Use tmRNA To Rescue Translation When There Is No STOP Codon
To save translation, bacteria can use a special RNA called a tmRNA—part transfer RNA and
part mRNA
The tmRNA carries the amino acid alanine
The tmRNA binds to the ribosome’s A site, delivers the alanine to the polypeptide
The mRNA portion of the tmRNA causes 10 more amino acids to be added to the
polypeptide, then uses its STOP codon to release the stalled ribosome
Nonstop mRNA Decay
EUKARYOTES
If the ribosome gets to the end of the mRNA, and has not encountered a STOP codon,
the ribosome’s A site will be hanging off the edge of the mRNA--there is nothing to fill
the ribosome’s A site
This signals proteins that attach to the mRNA and degrade it from its 3’ end
forward
i.
a.
1.
PROKARYOTES (bacteria)
Use a tmRNA, which functions like a tRNA in that it carries alanine, and as a mRNA in
that it provides a stretch of sequence that the ribosome uses to add more amino acids
to the polypeptide
a.
The tmRNA delivers an alanine to the polypeptide, then is used as a mRNA that contains
10 amino acid codons and a STOP codon
b.
2.
Post-Translation Processing: Folding, Adornment, Placement And Cleavage:
The ribosome makes a polypeptide, which must be processed into a protein
Proteins must be folded into their 3D shape
Need to be located properly, some cleaved, some join with others, and adorn with chemical
side groups
Chemical Side groups Can Be Critical Determinants Of Function
Chemical Sidegroups Can Be Critical Determinants Of Function:
Glycoproteins--proteins adorned with Oligosaccharides (chain of ~3-20 sugars
The Amino Terminal Amino Acids Often Direct The Polypeptide To Its Destination, Then Get Cleaved
Some Proteins Join With Other Proteins To Make Multimeric Proteins
Hemoglobin is a heterotetramer-- 4 subunits, 2 alpha globin and 2 beta globin
Homo = subunits are identical
Hetero = not all subunits are identical
The Process Whereby Genes Make Protein Continued:
Friday, January 26, 2018
11:19 PM

Only pages 1-3 are available for preview. Some parts have been intentionally blurred.

Special Sequences Tell The Spliceosome Where To Cut
There are consensus sequences around the intron/exon borders that orient the spliceosome
so it cuts at the right places
Alternative Splicing Allows One Gene To Make Different Proteins In Different Tissues
RNA Can Be Edited After Transcription
Guide RNAs bind to the mRNA and cause it to be cleaved and edited
Nucleotides can be added or deleted, and one nucleotide can be substituted for by another
The resultant mRNA base sequence and protein's amino acid sequence will not match those
that are predicted from the gene's coding sequence
Overview of Translation:
The ribosome reads the mRNA three bases at a time
Each 3-base unit is called a codon
Each codon instructs the ribosome to add one amino acid to the growing polypeptide
A STOP codon terminates translation and releases the polypeptide
The polypeptide is folded, adorned with chemical side groups and sent to where it needs to be
Some polypeptides join with others to form multimers
Some get cleaved into multiple independently active peptides; some are made in
inactive form and are activated by cleavage
Initiation of Translation: Proteins that bind to the 5’ cap and the poly-A tail help the ribosome bind
the mRNA
Elongation Factors Help The Ribosome Chain Amino Acids Together
Without protein synthesis would be much slower
64 possible codon; 61 possible anticodons in transfer RNA
Because 3 stop codons are needed
When ribosome encounter stop codon, you have releasing factors that bind to stop
codon and uncouple polypeptide from RNA
tRNAs Carry Amino Acids In For Translation
The mRNA codon sequence dictates which anticodon the tRNA must have:
Each tRNA with a given anticodon sequence always carries the same amino acid
This maintains the fidelity of the genetic code
§
There are 20 different aminoacyl-tRNA synthetases
Each one attaches a different amino acid to the appropriate tRNAs
ATP provides the energy for this procedure, known as tRNA charging
§
Note that tRNAs sometimes contain unusual bases, ex. inosine (I) or pseudouridine (ψ)
These bases can often pair with more than one of the other bases, increasing the
number of codons that the tRNA’s anticodon can bind to
§
A Consensus Recognition Sequence Orients The Ribosome In Prokaryotes
Orients the ribosome
The small subunit of the bacterial ribosome attaches to the Shine-Dalgarno sequence in
bacterial mRNAs
A ribosomal binding site in bacterial and archaeal messenger RNA, generally located around 8
bases upstream of the start codon AUG.
The RNA sequence helps recruit the ribosome to the messenger RNA (mRNA) to initiate
protein synthesis by aligning the ribosome with the start codon.
How would the cell know which AUG is the start codon?
Consensus (general) sequence, usually has a G after… Look below.
Translation Usually Begins At An AUG Codon
GUG and UUG may be used in rare cases
The first amino acid added in bacteria is N-formylmethionine
In archaea and eukaryotes it is methionine
A Consensus Recognition Sequence Identifies The Translation Initiation Codon In Eukaryotes
Not every AUG is a START codon; most AUG codons instruct the ribosome to incorporate
methionine
In eukaryotes, the START codon is usually the first AUG in the mRNA
In addition, there is a consensus sequence around the START codon, aka a Kozak
sequence, after Marilyn Kozak, who reported several types of consensus sequence,
including intron/exon boundary sequences
In eukaryotes, it is GCC(A/G)CCAUGG, where the START AUG is underlined, and the
(A/G) means that there could be either an A or a G in that position
Ex. The human beta-globin gene's sequence differs from the consensus sequence
by one base: GACACCAUGG
§
Initiation Factors Help The Ribosome Assemble --> illustrates their function in prokaryotic cells
In eukaryotes, the 5' cap and the 3' poly-A tail both bind to initiation factors
Missense And Nonsense Mutations
Missense mutation = one amino acid gets replaced by another
Effects range from no effect to abolishing protein’s activitya.
Translation continues properly after the mutation—downstream sequences get
translated
Amino acids (diff size and charged)i.
Folding into proper 3D shapeii.
Changes shape or movement can decrease the level of activity in a protein
(sometimes can increase)
iii.
b.
1.
Nonsense mutation = creates a STOP codon at the site of the mutation
Protein is truncated—usually abolishes protein’s activitya.
Translation stops at that point—downstream sequences do not get translatedb.
2.
The Ribosome Has A Reading Frame
The reading frame begins with the START codon (usually an AUG) and ends at the STOP codon
(UGA, UAG, UAA)
If someone has a deletion or insertion, if it involves a multiple of three nucleotides (an
in-frame deletion/insertion), it will not shift the ribosome’s reading frame
Amino acids will be missing (deletion) or novel amino acids will be incorporated (insertion),
but the protein will retain its normal amino acid sequence before and after the
deletion/insertion
The protein may still be able to function—depends on how many and which specific
amino acids are missing/added
If someone has a deletion or insertion that does not involve a multiple of three nucleotides, it
will shift the ribosome’s reading frame
Novel amino acids will be incorporated into the polypeptide
The ribosome will encounter a STOP codon at some point
The protein will probably not be able to function
It may even acquire a novel function, depending on the amino acids that are chained
together after the frame shift
The Ribosome Reads The mRNA One Codon At A Time
The polypeptide that has already been assembled sits in the P site, or peptidyl (peptide) site
The next amino acid gets carried in to the A (aminoacyl) site
Peptidyl transferase forms a peptide bond between the new amino acid's amino group
and the previous amino acid's carboxyl group
The peptidyl site then releases its amino acid, and the polypeptide sits momentarily in the A
site
The ribosome then moves down one codon, and the P site now contains the polypeptide
Proteins called elongation factors assist the process
The Ribosome Moves Down The mRNA One Codon At A Time
Translation Termination Codons, aka STOP Codons, Signal Termination Of Translation
Releasing Factors Terminate Translation
The Integrity Of The mRNA Is Monitored Before Translation
Nonsense-Mediated mRNA Decay Handles Premature STOPs
Nonsense mutation = mutation that creates a STOP codon at the site of the mutation
The polypeptide is not completed
When the pre-mRNA gets processed, proteins are bound to the exon-exon junctions in the
mRNA; the ribosome removes them
If the ribosome does not travel all the way to the end of the mRNA, some of these
proteins remain, acting as a signal to enzymes to degrade the mRNA
Preserves energy
§
Unstopped mRNAs Must Be Degraded Also
The ribosome can stall if:
Transcription is incomplete and there’s no STOP codon in the mRNA
A mutation changes the STOP codon to an amino acid codon
This causes the ribosome to get stuck on that mRNA, and leaves it unavailable to
perform more translation
Too much of this can have very serious consequences—drastic reduction in
protein synthesis capacity
§
Bacteria Use tmRNA To Rescue Translation When There Is No STOP Codon
To save translation, bacteria can use a special RNA called a tmRNA—part transfer RNA and
part mRNA
The tmRNA carries the amino acid alanine
The tmRNA binds to the ribosome’s A site, delivers the alanine to the polypeptide
The mRNA portion of the tmRNA causes 10 more amino acids to be added to the
polypeptide, then uses its STOP codon to release the stalled ribosome
Nonstop mRNA Decay
EUKARYOTES
If the ribosome gets to the end of the mRNA, and has not encountered a STOP codon,
the ribosome’s A site will be hanging off the edge of the mRNA--there is nothing to fill
the ribosome’s A site
This signals proteins that attach to the mRNA and degrade it from its 3’ end
forward
i.
a.
1.
PROKARYOTES (bacteria)
Use a tmRNA, which functions like a tRNA in that it carries alanine, and as a mRNA in
that it provides a stretch of sequence that the ribosome uses to add more amino acids
to the polypeptide
a.
The tmRNA delivers an alanine to the polypeptide, then is used as a mRNA that contains
10 amino acid codons and a STOP codon
b.
2.
Post-Translation Processing: Folding, Adornment, Placement And Cleavage:
The ribosome makes a polypeptide, which must be processed into a protein
Proteins must be folded into their 3D shape
Need to be located properly, some cleaved, some join with others, and adorn with chemical
side groups
Chemical Side groups Can Be Critical Determinants Of Function
Chemical Sidegroups Can Be Critical Determinants Of Function:
Glycoproteins--proteins adorned with Oligosaccharides (chain of ~3-20 sugars
The Amino Terminal Amino Acids Often Direct The Polypeptide To Its Destination, Then Get Cleaved
Some Proteins Join With Other Proteins To Make Multimeric Proteins
Hemoglobin is a heterotetramer-- 4 subunits, 2 alpha globin and 2 beta globin
Homo = subunits are identical
Hetero = not all subunits are identical
The Process Whereby Genes Make Protein Continued:
Friday, January 26, 2018
11:19 PM

Only pages 1-3 are available for preview. Some parts have been intentionally blurred.

Special Sequences Tell The Spliceosome Where To Cut
There are consensus sequences around the intron/exon borders that orient the spliceosome
so it cuts at the right places
Alternative Splicing Allows One Gene To Make Different Proteins In Different Tissues
RNA Can Be Edited After Transcription
Guide RNAs bind to the mRNA and cause it to be cleaved and edited
Nucleotides can be added or deleted, and one nucleotide can be substituted for by another
The resultant mRNA base sequence and protein's amino acid sequence will not match those
that are predicted from the gene's coding sequence
Overview of Translation:
The ribosome reads the mRNA three bases at a time
Each 3-base unit is called a codon
Each codon instructs the ribosome to add one amino acid to the growing polypeptide
A STOP codon terminates translation and releases the polypeptide
The polypeptide is folded, adorned with chemical side groups and sent to where it needs to be
Some polypeptides join with others to form multimers
Some get cleaved into multiple independently active peptides; some are made in
inactive form and are activated by cleavage
Initiation of Translation: Proteins that bind to the 5’ cap and the poly-A tail help the ribosome bind
the mRNA
Elongation Factors Help The Ribosome Chain Amino Acids Together
Without protein synthesis would be much slower
64 possible codon; 61 possible anticodons in transfer RNA
Because 3 stop codons are needed
When ribosome encounter stop codon, you have releasing factors that bind to stop
codon and uncouple polypeptide from RNA
tRNAs Carry Amino Acids In For Translation
The mRNA codon sequence dictates which anticodon the tRNA must have:
Each tRNA with a given anticodon sequence always carries the same amino acid
This maintains the fidelity of the genetic code
§
There are 20 different aminoacyl-tRNA synthetases
Each one attaches a different amino acid to the appropriate tRNAs
ATP provides the energy for this procedure, known as tRNA charging
§
Note that tRNAs sometimes contain unusual bases, ex. inosine (I) or pseudouridine (ψ)
These bases can often pair with more than one of the other bases, increasing the
number of codons that the tRNA’s anticodon can bind to
§
A Consensus Recognition Sequence Orients The Ribosome In Prokaryotes
Orients the ribosome
The small subunit of the bacterial ribosome attaches to the Shine-Dalgarno sequence in
bacterial mRNAs
A ribosomal binding site in bacterial and archaeal messenger RNA, generally located around 8
bases upstream of the start codon AUG.
The RNA sequence helps recruit the ribosome to the messenger RNA (mRNA) to initiate
protein synthesis by aligning the ribosome with the start codon.
How would the cell know which AUG is the start codon?
Consensus (general) sequence, usually has a G after… Look below.
Translation Usually Begins At An AUG Codon
GUG and UUG may be used in rare cases
The first amino acid added in bacteria is N-formylmethionine
In archaea and eukaryotes it is methionine
A Consensus Recognition Sequence Identifies The Translation Initiation Codon In Eukaryotes
Not every AUG is a START codon; most AUG codons instruct the ribosome to incorporate
methionine
In eukaryotes, the START codon is usually the first AUG in the mRNA
In addition, there is a consensus sequence around the START codon, aka a Kozak
sequence, after Marilyn Kozak, who reported several types of consensus sequence,
including intron/exon boundary sequences
In eukaryotes, it is GCC(A/G)CCAUGG, where the START AUG is underlined, and the
(A/G) means that there could be either an A or a G in that position
Ex. The human beta-globin gene's sequence differs from the consensus sequence
by one base: GACACCAUGG
§
Initiation Factors Help The Ribosome Assemble --> illustrates their function in prokaryotic cells
In eukaryotes, the 5' cap and the 3' poly-A tail both bind to initiation factors
Missense And Nonsense Mutations
Missense mutation = one amino acid gets replaced by another
Effects range from no effect to abolishing protein’s activitya.
Translation continues properly after the mutation—downstream sequences get
translated
Amino acids (diff size and charged)i.
Folding into proper 3D shapeii.
Changes shape or movement can decrease the level of activity in a protein
(sometimes can increase)
iii.
b.
1.
Nonsense mutation = creates a STOP codon at the site of the mutation
Protein is truncated—usually abolishes protein’s activitya.
Translation stops at that point—downstream sequences do not get translatedb.
2.
The Ribosome Has A Reading Frame
The reading frame begins with the START codon (usually an AUG) and ends at the STOP codon
(UGA, UAG, UAA)
If someone has a deletion or insertion, if it involves a multiple of three nucleotides (an
in-frame deletion/insertion), it will not shift the ribosome’s reading frame
Amino acids will be missing (deletion) or novel amino acids will be incorporated (insertion),
but the protein will retain its normal amino acid sequence before and after the
deletion/insertion
The protein may still be able to function—depends on how many and which specific
amino acids are missing/added
If someone has a deletion or insertion that does not involve a multiple of three nucleotides, it
will shift the ribosome’s reading frame
Novel amino acids will be incorporated into the polypeptide
The ribosome will encounter a STOP codon at some point
The protein will probably not be able to function
It may even acquire a novel function, depending on the amino acids that are chained
together after the frame shift
The Ribosome Reads The mRNA One Codon At A Time
The polypeptide that has already been assembled sits in the P site, or peptidyl (peptide) site
The next amino acid gets carried in to the A (aminoacyl) site
Peptidyl transferase forms a peptide bond between the new amino acid's amino group
and the previous amino acid's carboxyl group
The peptidyl site then releases its amino acid, and the polypeptide sits momentarily in the A
site
The ribosome then moves down one codon, and the P site now contains the polypeptide
Proteins called elongation factors assist the process
The Ribosome Moves Down The mRNA One Codon At A Time
Translation Termination Codons, aka STOP Codons, Signal Termination Of Translation
Releasing Factors Terminate Translation
The Integrity Of The mRNA Is Monitored Before Translation
Nonsense-Mediated mRNA Decay Handles Premature STOPs
Nonsense mutation = mutation that creates a STOP codon at the site of the mutation
The polypeptide is not completed
When the pre-mRNA gets processed, proteins are bound to the exon-exon junctions in the
mRNA; the ribosome removes them
If the ribosome does not travel all the way to the end of the mRNA, some of these
proteins remain, acting as a signal to enzymes to degrade the mRNA
Preserves energy
§
Unstopped mRNAs Must Be Degraded Also
The ribosome can stall if:
Transcription is incomplete and there’s no STOP codon in the mRNA
A mutation changes the STOP codon to an amino acid codon
This causes the ribosome to get stuck on that mRNA, and leaves it unavailable to
perform more translation
Too much of this can have very serious consequences—drastic reduction in
protein synthesis capacity
§
Bacteria Use tmRNA To Rescue Translation When There Is No STOP Codon
To save translation, bacteria can use a special RNA called a tmRNA—part transfer RNA and
part mRNA
The tmRNA carries the amino acid alanine
The tmRNA binds to the ribosome’s A site, delivers the alanine to the polypeptide
The mRNA portion of the tmRNA causes 10 more amino acids to be added to the
polypeptide, then uses its STOP codon to release the stalled ribosome
Nonstop mRNA Decay
EUKARYOTES
If the ribosome gets to the end of the mRNA, and has not encountered a STOP codon,
the ribosome’s A site will be hanging off the edge of the mRNA--there is nothing to fill
the ribosome’s A site
This signals proteins that attach to the mRNA and degrade it from its 3’ end
forward
i.
a.
1.
PROKARYOTES (bacteria)
Use a tmRNA, which functions like a tRNA in that it carries alanine, and as a mRNA in
that it provides a stretch of sequence that the ribosome uses to add more amino acids
to the polypeptide
a.
The tmRNA delivers an alanine to the polypeptide, then is used as a mRNA that contains
10 amino acid codons and a STOP codon
b.
2.
Post-Translation Processing: Folding, Adornment, Placement And Cleavage:
The ribosome makes a polypeptide, which must be processed into a protein
Proteins must be folded into their 3D shape
Need to be located properly, some cleaved, some join with others, and adorn with chemical
side groups
Chemical Side groups Can Be Critical Determinants Of Function
Chemical Sidegroups Can Be Critical Determinants Of Function:
Glycoproteins--proteins adorned with Oligosaccharides (chain of ~3-20 sugars
The Amino Terminal Amino Acids Often Direct The Polypeptide To Its Destination, Then Get Cleaved
Some Proteins Join With Other Proteins To Make Multimeric Proteins
Hemoglobin is a heterotetramer-- 4 subunits, 2 alpha globin and 2 beta globin
Homo = subunits are identical
Hetero = not all subunits are identical
The Process Whereby Genes Make Protein Continued:
Friday, January 26, 2018 11:19 PM
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