17 Gene to Protein Flashcards
(181 cards)
1
Q
“___ are the links between genotype and phenotype”
A
Proteins
2
Q
What does ’gene expression’ refer to?
A
The process by which DNA directs the synthesis of specific proteins.
3
Q
What does ’alkaptonuria’ refer to?
A
A hereditary condition in which the body lacks an enzyme to break down ‘alkapton’ causing it the be present in urine, which appears black.
4
Q
What does the ’one gene, one enzyme hypothesis’ refer to?
A
The idea that every gene codes for and thus leads to a phenotype by leading to the formation of an enzyme.
Note: this theory is disproven
5
Q
What is did the ‘one gene, one enzyme hypothesis’ get replaced with?
A
The ‘one gene, one protein’ as some genes code for proteins other than enzymes
6
Q
What does ’complete growth medium’ refer to?
A
A growth medium which includes salts, glucose and vitamins align with all 20 amino acids
7
Q
What are the basic steps of the conversion of DNA to proteins?
A
Transcription, ‘RNA processing’ and Translation
8
Q
What does ‘mRNA’ stand for?
A
Messenger RNA
9
Q
What molecule does transcription form?
A
‘pre-mRNA’
10
Q
What can pre-mRNA be called?
A
The ‘primary transcript’
11
Q
What does ’primary transcript’ refer to?
A
The RNA formed directly by transcription i.e. the unprocessed pre mRNA
12
Q
What are the bases of DNA?
A
A, C, T and G
13
Q
What are the bases of RNA?
A
A, C, U and G
14
Q
What is ‘U’ in terms of the RNA base?
A
Uracil, which replaces thymine
15
Q
What is the DNA base that is replaced by uracil?
A
Thymine
16
Q
What is the basic principle behind ’transcription’?
A
The information in the DNA is transferred to messenger RNA by the formation of an RNA strand that is complementary to the template strand.
17
Q
Which strand of DNA is used as the ‘template strand’?
A
For any given gene, the same strand
is used as the template every time the gene
is transcribed.
For other genes on the same DNA molecule, however, the opposite strand may be the one that always functions as the template.
18
Q
What is the basic principle behind ’translation’?
A
The information encoded in the mRNA is translated into a sequence of amino acids and thus a polypeptide
19
Q
Where does ’transcription’ occur?
A
In a prokaryote in the cytoplasm.
In a eukaryote it occurs in the nucleus
20
Q
Where does ‘RNA processing occur’?
A
Prokaryote: DOES NOT OCCUR
Eukaryote: nucleus
21
Q
Where does ’translation’ occur?
A
Prokaryote/Eukaryote: cytoplasm (in ribosomes)
22
Q
What does ’codon’ refer to?
A
A nucleotide triplet which codes for a specific amino acid etc.
23
Q
What are the basic types of ‘codon’?
A
’Start codon’, ’Stop codon’ and those that code for amino acids.
24
Q
What are the sequences of the ’start codons’?
A
AUG which codes for the amino acid ‘Met’ or acts as a start codon.
25
What are the sequences of the ’stop codons’?
UAA, UAG and UGA
26
What does ’reading frame’ refer to?
The frame of reference with with the triplet codons are interpreted.
For example _ACT_UAG_GCT
A point mutation would shift the farm of reference and thus lead to missense/nonsense
27
What are the stages of ’transcription’?
‘Initiation’,’elongation’ and ’termination'
28
In what direction is RNA formed an thus which direction does RNA polymerase move?
RNA is formed 5’ to 3’
Therefore the RNA polymerase must move 3’ to 5’ down the template strand so that the mRNA is antiparallel.
29
What is an important consideration when converting a DNA sequence to a series of amino acids?
DNA is typically read 5’ to 3’. However the RNA polymerase must form the mRNA so that it produced 5’ to 3’.
To ensure that the mRNA is antiparallel to the DNA the RNA polymerase must move down the template strand in a 3’ to 5’ direction.
Therefore if asked to translate a series of DNA to amino acids one must also read it 3’ to 5’
Also remember that the RNA formed is complementary (not identical) to the DNA. Thus ACT on the DNA would become UGC
30
What does ’triple code’ refer to?
The fact that each codon is a triplet of 3 nucleotides
31
Based on the fact that 3 nucleotides code for one amino acid, what property does DNA/RNA have?
It is a ’triplet code'
32
What happens during the ‘initiation’ stage of transcription?
RNA polymerase binds to the ‘promoter', the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand.
Note that no primer is formed
33
Is a primer needed during translation?
Nope
34
What happens during the ‘elongation’ stage of transcription?
The polymerase moves downstream (3’ to 5'), unwinding the DNA and elongating the RNA transcript 5′ → 3′. In the wake of transcription, the DNA strands re-form a double helix.
35
What is the ’termination’ phase of transcription?
The RNA transcript is released, and the polymerase detaches from the DNA.
Transcription is complete
36
What does ’downstream’ refer to in the context of genetics?
In transcription and DNA replication it refers to the direction the RNA/DNA polymerase moves.
Therefore ‘downstream is 3’ to 5'
37
How is transcription guided?
The RNA polymerase binds to a special region on the template strand called the ‘promoter’
It then moves ‘downstream’ through the ’transcription unit’ which is the length of DNA which is actually transcribed
In prokaryotic transcription is reaches a region called the ’terminator’ which instructs it to stop. In eukaryotes termination is signalled differently.
38
What are the specific RNA polymerases used in transcription?
In prokaryotes there is only one generic polymerase that is used.
Eukaryotes have at least three types of RNA polymerase in their nuclei. The one used for mRNA synthesis is called RNA polymerase II. The other RNA polymerases transcribe RNA molecules that are not translated into protein.
39
What specifically happens during the ‘initiation phase’ of transcription?
The promoter of a gene includes the transcription start point (the nucleotide where RNA synthesis actually begins)
RNA polymerase binds in a precise location and orientation on the promoter to determine where transcription starts and which DNA strand is used as the template strand.
In bacteria, the RNA polymerase itself specifically recognizes and binds to the promoter. In eukaryotes, a collection of proteins called 'transcription factors' mediate the binding of RNA polymerase and the initiation of transcription. The complex of transcription factors and RNA polymerase II bound to the promoter is called a transcription initiation complex.
Once the appropriate transcription factors are firmly attached to the promoter DNA and the polymerase is bound in the correct orientation, RNA nucleotides the enzyme unwinds the two DNA strands and starts transcribing the template strand.
40
What does ’promotor’ refer to?
The region of DNA that the RNA polymerase binds to. This initiates transcription and is found in eukaryotes and prokaryotes
41
What does ’terminator’ refer to?
The DNA sequence found in bacteria which acts as the signal to stop transcription
42
What does ’transcription unit’ refer to?
The actual region of the template strand which is transcribed
43
What is the DNA sequence from which transcription is initiated called?
The ‘promotor'
44
What is the region of DNA which in bacteria signals the termination of transcription called?
The ’terminator'
45
What is the actual region of the template strand which is transcribed called?
The ’transcription unit'
46
What is an example of a specific promoter region?
The ’TATA’ box which is used in many eukaryotic genes as the promotor region and consists of the nucleotide sequence ‘TATA’ i.e. thymine, adenine etc.
47
How is the binding of the RNA polymerase to the promoter mediated?
In bacteria the RNA polymerase recognises and binds directly to the promoter region.
In eukaryotes ’transcription factors’ bind to the promotor region and in turn bind to the polymerase. This complex of a polymerase and its ’transcription factors’ is called a ’transcription initiation complex'
48
What does ’transcription factor’ refer to?
The proteins which in eukaryotes bind to the promoter region and in turn the polymerase to mediate the attached of the polymerase to the promotor
49
What are those things which bind to the promoter region so that the polymerase can be attached?
’Transcription factors'
50
What does ’transcription initiation complex’ refer to?
A polymerase and its bound transcription factors.
51
What is a polymerase and its bound transcription factors called?
A ’transcription initiation complex'
52
What is typical transcription rate in eukaryotes?
Around 40 nucleotides per second
53
How can the transcription rate be increased?
A single gene can be transcribed simultaneously by several molecules of RNA polymerase following each other, with each forming an individual RNA strand
The congregation of many polymerase molecules simultaneously transcribing a single gene increases the amount of mRNA transcribed from it, which helps the cell make the encoded protein in large amounts.
Therefore it is particularly useful in secretory cells.
54
How is transcription terminated?
In bacteria, transcription proceeds through a terminator sequence in the DNA. The transcribed terminator (an RNA sequence) functions as the termination signal causing the polymerase to detach from the DNA and release the transcript, which requires no further modification before translation.
In eukaryotes, RNA polymerase II transcribes a sequence on the DNA called the 'polyadenylation signal sequence', which codes for a polyadenylation signal (AAUAAA) in the pre-mRNA.
This triggers proteins to cut the RNA strand free form the polymerase and thus transcription is complete
55
How does RNA transcription termination work in eukaryotes?
The polymerase transcribes a region called the ‘polyadenylation signal sequence’ which codes for the ‘polyadenation signal’ (AAUAAA) which terminates transcription
56
What does ’polyadenation signal sequence’ refer to?
The region of DNA which codes for the ‘polyadenation signal’ (AAUAAA) which terminates transcription
57
What does ’polyadenation’ refer to?
AAUAAA which when transcribed stops transcription.
58
What is the first step of RNA processing?
Each end of the RNA molecule is modified in a particular way.
At the 5’ end a ‘5’ cap’ is added which consists of a modified form of a guanine (G) nucleotide.
At the 3’ end an enzyme adds 50-250 adenine nucleotides to form a ‘poly-A tail'
59
What does ’5’ cap’ refer to?
The modified guanine nucleotide added to the 5’ (start) of the pre-mRNA
60
What does ’poly-A tail’ refer to?
The long sequence of adenine nucleotides added to the end of the pre-mRNA
61
What is the function of the 5’ cap and the poly-A tail?
They seem to facilitate the export of the mature mRNA from the nucleus.
They help protect the mRNA from degradation by hydrolytic enzymes.
They help ribosomes attach to the 5' end of the mRNA once the mRNA reaches the cytoplasm.
62
What regions does a pre-mRNA molecule after the 5’ cap and poly-A tail have been added?
In order from 5’ to 3’:
```
5’ Cap
5’ UTR
Start codon
‘Protein coding segment’
Stop codon
3’ UTR which includes the ‘polyadenylation signal’
Poly-A tail
```
(UTR = untranslated region)
63
What does ’protein coding segment’ refer to?
The actual region of mRNA which will become proteins although it does included introns which will be spliced out.
64
After the addition of the 5’ cap and poly-A tail, what happens in RNA processing?
'RNA slicing'
65
How long is a typical protein?
400 amino acids long
66
What does ’UTR’ refer to?
Untranslated region
67
Put simply, what happens during RNA splicing?
The non-coding ‘intron’ segments are cut out to leave a continuous stream of coding ‘exons'
This remaining block of ‘exons’ is called the ‘coding segment'
68
What does ’exon’ refer to?
The region of the pre-mRNA that is left in after splicing and thus remains to code for a protein.
69
What does ’intron’ refer to?
The region of pre-mRNA that is spliced out of the pre-mRNA during RNA splicing
70
What is the region of RNA which is left in after splicing called?
The ‘exon'
71
What is the region of RNA which is cut out during splicing called?
Intron
72
What is the continuous coding sequence formed after RNA processing called?
The 'coding segment'
73
What does ’coding segment’ refer to?
The continuous region of coding DNA
74
How does RNA splicing occur?
Particles called small nuclear ribonucleoproteins, (snRNPs) are found in the cell nucleus and recognise the splice sites.
Small nuclear ribonucleoproteins (snRNPs) and other proteins form a molecular complex called a ‘spliceosome.’
Within the spliceosome, snRNA base-pairs with nucleotides at specific sites along the intron. The spliceosome cuts the pre-mRNA which releases the intron for degradation while simultaneously joining the exons.
75
What are ’snRNPs’ composed of?
They composed of RNA and protein molecules. The RNA in a snRNP particle is called a small nuclear RNA (snRNA); each snRNA molecule is about 150 nucleotides long.
76
What does ’snRNP’ refer to?
The protein-nucleic acid complex which are part of the splicesome
77
What does ’spliceosome’ refer to?
The structure composed of multiple snRNPs which splice the introns out of pre-mRNA
78
What is the RNA inside the snRNPs called?
snRNA
79
What does ’snRNA’ refer to?
The RNA inside the snRNPs
80
What is snRNA an example of?
A ribozyme
81
What is a ribosome an example of?
A ribozyme.
82
What is a ‘ribozyme’?
A RNA molecule which acts as an enzyme i.e. catalyses reaction.
83
What is a catalytic RNA molecule called?
A ‘ribozyme'
84
What properties of RNA allows it to be used in ribozymes?
RNA is single-stranded so region of an RNA molecule can base-pair with a complementary region elsewhere in the same molecule. This gives it the specific 3D shape need to be a catalyst.
Like certain amino acids in an enzyme, some of the bases in RNA contain functional groups that may participate in catalysis
RNA can hydrogen-bond with other nucleic acid molecules (either RNA or DNA). This adds specificity to its catalytic activity.
85
What is the evolutionary importance of RNA splicing?
It allows for ‘alternative RNA splicing'
86
What is ‘alternative splicing?'
The concept in which the specific exons which are left in can be regulated.
Therefore alternative versions of an active site could be present as two exons. A third exon would code for the generic non-active site region.
This allows one gene to code for multiple polypeptides such as multiple versions of a similar enzyme which work at slightly different temperatures.
87
What is a variation in which exons remain in the final mRNA called?
‘Alternative RNA splicing'
88
What does a ’domain’ refer to?
A specific region of a protein. For example one domain might act as the active site and another could anchor the protein to the plasma membrane.
89
What is specific region of a protein called?
A 'domain'
90
How do exons link to protein structure?
During alternative RNA splicing a specific exon typically codes for a specific domain of the protein i.e. the active site.
This is how alternative RNA splicing leads to variation in protein structure.
91
What is the principle by which alternative RNA splicing leads to the evolution of proteins called?
‘Exon shuffling'
92
What is ‘exon shuffling’?
The spaces between the exons caused by the introns increases the rate of crossing over and thus exchange of exons between genes as this allows more space for the chiasmata to form.
Therefore the intron make the exons more likely to be separated and thus for new proteins to form through the combination of exons from both parents.
93
What principle explains the importance of introns?
‘Exon shuffling'
94
What is the basic principle of translation?
In a ribosome transfer RNA molecules (tRNA) bind ot specific nucleotide sequences. This causes the amino acids they carry to be added to the growing polypeptide chain.
95
What is the structure of a tRNA molecule and how does this help it perform its function?
At one end is a nucleotide triplet called the ‘anticodon’ which base-pairs with a complementary base sequence on the mRNA.
At the 3’ end of the tRNA molecule is an amino acid. tRNA molecules with different amino acids have different ‘anticodons’ and thus the correct.
96
What is a protein bonded to a carbohydrate called?
A glycoprotein
97
Where on the tRNA molecule is the amino acid attached to?
The 3’ end
98
What is the structure which carries amino acids to the mRNA called?
tRNA (transfer RNA)
99
What is the region of the tRNA which binds to the mRNA called?
The ‘anti codon'
100
What does ’anti-codon’ refer to?
The region of the tRNA which binds to the mRNA.
101
What factors are required to ensure the accurate translation of mRNA?
Each tRNA must have the correct amino acid joined to it.
Also only the tRNA with the anti-codon for the codon of the mRNA should bind to the mRNA.
102
How are the amino acids added to the tRNA?
The enzyme ‘aminoacyl-tRNA’ binds to an amino acid and an ATP molecule. Two phosphate groups are released so that AMP is left bonded to the amino acid.
An appropriate tRNA molecule binds with the amino acid. This displaces the AMP. The tRNA with amino acid is then release.
103
What is a tRNA with an amino acid called?
'Aminoacyl tRNA' aka ‘charged tRNA'
104
What does ’aminoacyl tRNA’ refer to?
A tRNA with an attached amino acid
105
What does ’charged tRNA’ refer to?
A tRNA with an attached amino acid.
106
How does tRNA account for the fact that multiple base sequences code for the same amino acid?
The rules for base pairing between the third nucleotide base of a codon and the corresponding base of a tRNA anticodon are relaxed compared to those at other codon positions.
For example, the nucleotide base U at the 5' end of a tRNA anticodon can pair with either A or G in the third position (at the 3' end) of an mRNA codon.
The flexible base pairing at this codon position is called 'wobble'.
Wobble explains why the synonymous codons for a given amino acid most often differ in their third nucleotide base, but not in the other bases.
107
What is flexible base pairing of the tRNA called?
Wobble
108
Why is ‘wobble’ important?
It prevents the need for 64 tRNAs to handle the redundancy in the codons.
109
What does ’wobble’ refer to?
Flexible bas pairing of the tRNA so that multiple base sequences can lead to one amino acid
110
Why do the redundant base sequences for amino acids typically differ in the 3rd nucleotide?
‘Wobble’ typically occurs in the third nucleotide.
111
What is the structure of a ribosome?
It consists of two subunits (one large, one small)
Each subunit is made up of ribosomal RNA (rRNA) and associated proteins (3 proteins in bacteria, 4 proteins in eukaryotes)
112
What does ’rRNA’ refer to?
Ribosomal RNA i.e. the RNA which ribosomes are made of.
113
How are ribosomes produced?
In eukaryotes, the subunits are made in the nucleolus. Ribosomal RNA genes are transcribed, and the RNA is processed and assembled with proteins imported from the cytoplasm.
The resulting ribosomal subunits are then exported
via nuclear pores to the cytoplasm.
In both bacteria and eukaryotes, large and small subunits join to form a functional ribosome only when they attach to an mRNA molecule.
114
What is the most abundant type of RNA in a cell?
rRNA
115
How does ’streptomycin’ work?
It impairs the function of bacterial ribosomes which are different enough to the ribosomes of humans that they do not harm the human.
116
What it the structure of the ribosome and how is this specific to its function?
It has a binding site for mRNA and three more binding sites called the E site, P site and A site.
117
What is the E site of the ribosome also known as?
The ‘exit site'
118
What is the P site of the ribosome also known as?
‘peptidyl-tRNA binding site'
119
What is the A site of the ribosome also known as?
'aminoacyl-tRNA binding site'
120
How can the binding sites of a ribosome be memorised?
They are “E, P, A” i..e the Environmental Protection Agency
121
What are the basic stages of translation?
‘Ribosome association and initiation’, ‘elongation’ and ’termination'
122
What happens during ‘Ribosome association and initiation’?
A small ribosomal subunit binds to a molecule of mRNA. A specific tRNA molecule called the ‘initiator tRNA’ binds to the start codon and carries the amino acid Met
The large subunit bonds to the small subunit. This lease to a ’translation initiation complex’
The combination of the subunits is controlled by proteins called ‘initiation factors’ The energy needed is provided by the hydrolysis of GTP.
The initiator tRNA is in the P site; the A site is available to the tRNA bearing the next amino acid.
123
What direction does the ribosome move down the mRNA?
It moves from the 5’ end of the mRNA to the 3’ end
124
How is the energy needed for ribosome association provided?
By GTP
125
What is the molecule which binds to the mRNA and thus leads to initiation? (not small subunit)
‘initiator tRNA'
126
What does ’initiator tRNA’ refer to?
The specific ‘charge tNA’ which binds to the ’start codon’ and thus ends the initiation of translation.
127
What does ’translation initiation complex’ refer to?
The two ribosomal subunits and the bound mRNA which is thus ready for translation.
128
What is the bound ribosome and mRNA called?
The ’translation initiation complex'
129
What molecules are needed to combine the small subunit+mRNA to the large sub unit?
‘Initiation factors’ and ‘GTP'
130
What does ’initiation factors’ refer to?
The proteins which mediate the binding of the small and large subunits and thus the formation of the ’translation initiation complex'
131
What substances regulate the elongation phase of translation?
’Translation factors'
132
What does ’translation factors’ refer to?
The proteins which regulate the process of translation.
133
What can the elongation phase of translation be divided into?
‘Codon recognition’, ‘Peptide bond formation’ and ’translocation'
134
What happens during the ‘codon recognition phase’ of the elongation phase of translation?
The anticodon of an incoming aminoacyl tRNA base-pairs with the complementary mRNA codon in the A site.
Hydrolysis of GTP increases the accuracy and efficiency of this step.
Note that many aminoacyl tRNAs are presented but only the one with an anticodon that is complementary to the mRNA actually binds
135
What happens during the ‘peptide bond formation’ phase of the elongation phase of translation?
An rRNA molecule of the large ribosomal subunit catalyzes the formation of a peptide bond between the amino group of the new amino acid in the A site and the carboxyl end of the growing polypeptide in
the P site.
This step removes the polypeptide from the tRNA in the P site and attaches it to the amino acid on the tRNA in the A site and adds it to the elongating polypeptide chain.
136
What happens during the ’translocation phase’ of the elongation phase of translation?
The ribosome translocates the tRNA in the A site to the P site. At the same time, the empty tRNA in the P site is moved to the E site, where it is released.
The mRNA moves along with its bound tRNAs, bringing the next codon to be translated into the A site.
137
How is translation terminated?
A ‘release factor’ is a protein shaped as a tRNA. It has an anticodon that binds to one of the stop codons.
The release factor promotes hydrolysis of the bond between the tRNA in the P site and the last amino acid of the polypeptide, thus freeing the polypeptide from the ribosome.
Using the energy from GTP the ribosomal subunits dissociate and are thus reused.
138
When is energy used in the termination of translation? How is this energy provided an in what quantity?
Energy is needed to breakdown down the translation assembly i..e ribosome
This energy comes form the hydrolysis of 2 GTP molecules.
139
What phases of elongation require energy. How is this energy provided and in what quantity?
Codon recognition and Transloction require the energy from the hydrolysis of one GTP each.
139
What phases of elongation require energy. How is this energy provided and in what quantity?
Codon recognition and Transloction require the energy from the hydrolysis of one GTP each.
140
How much energy would be needed to transcribe a 300 nucleotide mRNA strand?
100 ATP molecules would be needed to add the amino acids to the tRNAs
1 GTP would be needed to form the translation initiation complex.
200 GTP, two per triplet, would be needed for the elongation
Finally 2 GTP would be needed for termination of translation
Thus a total of 100 ATP and 203 GTP would theoretically be needed.
140
How much energy would be needed to transcribe a 300 nucleotide mRNA strand?
100 ATP molecules would be needed to add the amino acids to the tRNAs
1 GTP would be needed to form the translation initiation complex.
200 GTP, two per triplet, would be needed for the elongation
Finally 2 GTP would be needed for termination of translation
Thus a total of 100 ATP and 203 GTP would theoretically be needed.
141
How can the rate of translation be increased?
With ‘polyribosomes'
141
How can the rate of translation be increased?
With ‘polyribosomes'
142
What does ’polyribosome’ refer to?
The fact that many ribosomes can be found on a single mRNA strand.
142
What does ’polyribosome’ refer to?
The fact that many ribosomes can be found on a single mRNA strand.
143
In what direction is mRNA translated?
5’ to 3'
143
In what direction is mRNA translated?
5’ to 3'
144
What does ’polysomes’ refer to?
Polyribosomes
144
What does ’polysomes’ refer to?
Polyribosomes
145
In what organisms are polyribosomes found?
Both bacteria and eukaryotes
145
In what organisms are polyribosomes found?
Both bacteria and eukaryotes
146
What happens to the protein after translation?
It undergoes ‘post translational modification’ then is targeted to a specific place in the cell.
146
What happens to the protein after translation?
It undergoes ‘post translational modification’ then is targeted to a specific place in the cell.
147
What happens during ‘post-translational modification’?
The protein ‘chaperoning’ helps the polypeptide fold correct.
Certain amino acids may be chemically modified by the attachment of sugars, lipids, phosphate groups, or other additions.
Enzymes may remove one or more amino acids from the leading (amino) end of the polypeptide chain.
In some cases the complete polypeptide may be cleaved into two.
147
What happens during ‘post-translational modification’?
The protein ‘chaperoning’ helps the polypeptide fold correct.
Certain amino acids may be chemically modified by the attachment of sugars, lipids, phosphate groups, or other additions.
Enzymes may remove one or more amino acids from the leading (amino) end of the polypeptide chain.
In some cases the complete polypeptide may be cleaved into two.
148
What does ’amino end’ refer to?
The leading end of a polypeptide i.e the one translated first.
148
What does ’amino end’ refer to?
The leading end of a polypeptide i.e the one translated first.
149
What does ’chaperonin’ refer to?
A protein which aids in the folding of polypeptides
149
What does ’chaperonin’ refer to?
A protein which aids in the folding of polypeptides
150
What does ’chaperon protein’ refer to?
A protein which aids in the folding of polypepetides
150
What does ’chaperon protein’ refer to?
A protein which aids in the folding of polypepetides
151
What is a protein which aids in the folding of polypeptide called?
A chpaeronin or ‘chaperone protein‘
151
What is a protein which aids in the folding of polypeptide called?
A chpaeronin or ‘chaperone protein‘
152
What is an example of protein which is formed from a polypeptide which is cleaved during ‘post-transaltional modification'?
Insulin.
152
What is an example of protein which is formed from a polypeptide which is cleaved during ‘post-transaltional modification'?
Insulin.
153
How is insulin formed?
After being translated it undergoes ‘post translational modification’ in which it is cleaved in half by an enzyme.
This results in a protein made up of two polypeptide chains connected by disulphide bridges.
168
How is insulin formed?
After being translated it undergoes ‘post translational modification’ in which it is cleaved in half by an enzyme.
This results in a protein made up of two polypeptide chains connected by disulphide bridges.
169
What happens after a protein has complete ‘post-translational modification’?
It is targeted for transport to a specific location in/out of the cell.
170
Where are proteins destined for secretion produced?
In bound ribosomes on the endomemebrane system
171
Where are proteins destined to be used in the endomembrane system i.e. by a lysosome produced
In bound ribosomes on the endomemebrane system
172
What does ’N-terminus’ refer to?
The leading end of a polypeptide i.e. the bit translated first
173
What is the leading end of the polypeptide called?
The ’N-terminus'
174
How are mRNAs destined to be produced by the endomembrane system translated?
The mRNA binds to a free ribosome and translation occurs. As the polypeptide forms the first 20 nucleotides translated form a sequence called the ’signal peptide’
A 'signal-recognition particle’ (SRP) in the cytosol binds to this signal peptide. This SRP carries the ribosome and mRNA to the ER. As the ribosome is carried translation stops (note that the free ribosome becomes a bound ribosome)
The SRP binds to a ’translocation complex’ in the membrane of the ER. This translocation complex includes a ’signal cleaving enzyme’ which removes the signal peptide from the polypeptide. The translocation complex also includes a pore through with the polypeptide is threaded into the lumen of the ER.
175
What does ’SRP’ refer to?
Signal recognition particle.
176
What does ’signal peptide’ refer to?
A specific peptide sequence which when translated leads to the binding of an SRP and thus the completion of translation bound to the ER.
177
What does ’translocation complex’ refer to?
The site on the ER membrane to which the SRP binds.
This complex contains a ’signal-cleaving enzyme’ and a pore
178
What is the translated polypeptide which specifies that translation should continue at the ER called?
the ’signal peptide'
179
What is the protein which binds to the signal peptide and carries the ribosome to the ER called?
SRP (Signal recognition particle)
180
What does ’signal recognition particle’ refer to?
The site on the ER membrane to which the SRP binds.
This complex contains a ’signal-cleaving enzyme’ and a pore
181
What is the region of the ER membrane which the SRP binds to called?
The ’translocation complex'
