Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Cell Biology > Cell Biology Chapter 8 - Protein Synthesis and Sorting > Flashcards

Cell Biology Chapter 8 - Protein Synthesis and Sorting Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

The Central Dogma of Molecular Biology

A

DNA polymers code RNA polymers which code Amino Acid polymers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Three challenges

A
  1. DNA to RNA or RNA to protein subject to mistakes?
  2. How do cells ensure the right information occurs at the right time and place?
  3. How does a cell ensure information is efficiently passed from one form to another?
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Transcription

A

Converts the DNA Genetic Code into RNA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

The major difference between DNA replication and Transcription

A

Transcription is HIGHLY selective

*Only defined portions of DNA are transcribed to RNA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

RNA Polymerases

A

Transcribe Genes In A “Bubble” Of Single-stranded DNA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Transcription bubble

A

Similar to replication bubble

  • Unidirectional
  • Single strand

*On rare occasions in prokaryotes, two replication bubbles can cross in opposing directions to read different templates on different DNA strands

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Transcription Occurs In Three Stages

A
  1. RNA is synthesized 5’3’ and the DNA is “read” in the opposite direction
  • In eukaryotes, three different RNA polymerases are used to transcribe different forms of RNA
    RNA polymerase I, II, II (pol I, II, III)
    Pol II makes mRNA and is the most studied
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Transcription Begins After

A

A RNA Polymerase Binds To A Promoter Site On DNA

  • Prokaryotic RNA polymerase is simple
  • Eukaryotic RNA polymerase has about 12 subunits
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Location of Promoter sites

A

Prokaryotic promoters are short and lie close to the actual transcription start site

Eukaryotic promoters may be spread out over hundreds of DNA base pairs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Transcription Factors

A

Can bind DNA or other DNA-binding proteins

Basal Transcription factors or the Basal Transcription Complex are the smallest group of proteins required to produce any transcription

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

6 factors make up the basal transcription factors

A

TFIIA, TFIIB, TFIID, TFIIE, TFIIF, and TFIIH

  • Some of these are made of multiple polypeptide subunits each
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Transcription: Initiation

A

RNA synthesis begins when basal transcription factors bind to the promoter nearest to where transcription begins

*This is NOT mark the beginning of translation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Core promoter

A

(essential for transcription) on which the basal transcription factors assemble

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Assembly of the Initiation Complex (continued)

A

TFIID is recruited to the TATA box

TFIIH
- binds specifically the template strand and it also has helicase activity

  • With TFIIE it “caps” RNA Pol II and holds it in place
  • It has kinase activity and phosphorylates RNA Pol II activating it
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Order of TF adding sequence

A
  1. TFIID (has affinity for the minor groove of the DNA) —>
  2. TFIIA
  3. TFIIB
  4. TFIIF
  5. TFIIE
  6. TFIIH

RNA polymerase only appears after all the basal transcription factors have been assembled.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

TFIIH

A

The “H” stands for helicase activity and helps unwind it. Phosphorylates RNA pol and activates it.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

TFIIE

A

“E” Binds hold RNA poly II and holds it in place. “The Escape claw”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

RNA transcript

A

transcript is extended in the 5’-to-3’ direction as the RNA polymerase reads the template DNA strand in the 3’-to-5’ direction

The entire replication bubble is within the space occupied by RNA pol II

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Supercoiling Solved by Two Enzymes

A

Gyrase reverses extra positive supercoiling ahead of the transcription bubble by inducing negative supercoiling

Topoisomerase relaxes negative supercoiling behind the transcription bubble

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Stage 3 of Transcription: Termination

A

Termination results in the release of the mRNA transcript and RNA pol from the DNA template

Prokaryotes and Eukaryotes use different termination methods

Three features of termination are especially important

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Three Important Features of Termination

A
  1. Prokaryotes (not eukaryotes) have termination encoded within the DNA sequence : called terminators
    Fold into hairpin loops of semi-stable double-stranded RNA

2) Bacterial rho protein is an example of an RNA pol binding-protein necessary for termination of some transcription

3) Terminators are not universally effective
Anti-terminators can suppress termination
Polycistronic RNA and operons result when adjacent or clusters of genes are transcribed on a single RNA molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

One of the most striking differences between Prokaryotic and Eukaryotic transcription is that mRNA structure is modified by Eukaryotes prior to their use

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

The Spliceosome Controls RNA Splicing

A

Introns are removed from the primary transcript and exons are stitched together in a transesterification reaction at the exon-exon boundary

Alternative splicing can generate a large variety of proteins from a single DNA sequence

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

RNA Modifications

A
  • 5’ methylguanosine cap

- Poly(A) tail

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Eukaryotic mRNA has a methylated 5’ cap

A

The cap protects the 5’ end of mRNA from nucleases and may be methylated at several positions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

RNA Export

A
  • poly(A)-binding protein (PABP) at 3’ end
  • Sometimes the mRNA with all associated proteins is called the heterogeneous nuclear ribonucleoprotein particle (hnRNP)
  • After RNA processing is complete, also called the messenger ribonucleoprotein particle (mRNP)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Proteins Are Synthesized By ______?

A

Ribosomes Using An mRNA Template

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Translation

A

is the term used to describe the conversion of mRNA information into polypeptides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Translation requires cooperation

A

between ribosomal RNAs, transfer RNAs, messenger RNAs, and numerous proteins.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

The steps of translation are grouped into three stages:

A

initiation, elongation, and termination

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

The Stoke’s Radius

A

Radius is Based on the Time it Takes to Migrate Through a Gel

Prokaryotic Ribosomes
Typically 70S (composed of 50S and 30S subunits)
Eukaryotic Ribosomes
Typically 80S (composed of 60S and 40 S subunits)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Aminoacyl tRNAs

A

Contain a three-letter “anti-codon” that will match up with the three-letter “codon” on the mRNA

Aminoacyl tRNA synthetase uses ATP energy to couple the amino acid to the hydroxyl group of the 3’ end of the tRNA
This “charges” the tRNA with the energy needed to generate the peptide bond!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Translation Factors

A
  • Initiation Factors and Elongation Factors
  • Form a critical link between RNA processing and translation
  • Found in eukaryotes and prokaryotes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

The Ribosome Has Three tRNA-binding Sites

A

A Site – is where the aminoacyl tRNA first attaches to the ribosome

P Site – is where the newly arrived amino acid is removed from its charged tRNA and added to the growing chain

E Site – Is where the tRNA is ejected from the ribosome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Stage 1of translation: Initiation requires base pairing between mRNA and rRNA

A

Goal = bring all of the elements necessary for translation together into a giant cluster

Once the mRNA and small subunit are properly aligned, the first tRNA (initiator tRNA) binds to the AUG, and the large ribosomal subunit clamps down on the small subunit, forming an intact ribosome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Prokaryotic Initiation

A

Bacteria use a specific mRNA sequence called the Shine-Delgarno sequence that base pairs with a portion of the rRNA on the small subunit

Shine-Delgarno sequence is upstream of a translation start sequence called the initiation site
-5’-AUG-3’

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Eukaryotic Initiation

A

5’-methylated G cap on mRNA binds eIFs (eukaryotic initiation factors)
Once the cap is identified, the small ribosomal subunit crawls towards the initiation site in the 3’ direction

Since AUG is a common sequence, it doesn’t necessarily stop at the first one it sees. Surrounding sequence helps it.

At least a dozen different translation factors attach to the complex at this time.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Stage 2: ElongationProkaryotic Elongation as a Model

A

Proofreading Step
EF-Tu
Ensures a perfect codon/anticodon match

Peptide Bond Formation
Peptidyl-transferase is part of the large ribosomal subunit

Moving On
EF-G-GTP provides the energy to shove the ribosome forward a codon

Chain Elongation
Occurs at the P site

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Translation stop sequences

A

UAA, UAG, UGA

Do not bind to any tRNAs
Instead, these bind release factors that fit into the A-site on the ribosome
occurs when the bond holding the polypeptide to tRNA is hydrolyzed

Water is the acceptor in this hydrolysis reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

Three Important Themes

A

The sequence of bases in the coding region of a gene is directly reflected by the sequence of amino acids in a protein
Differences in amino acid sequence result in great variation in protein shape

Controlling protein shape is the mechanism cells use for controlling protein location

Controlling protein shape is the mechanism cells use for controlling protein function

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

Signal Sequences Code For Proper Targeting Of Proteins

A

Important: The Cytosol is the default destination for all proteins synthesized there

Proteins without signal sequences stay in the cytosol
Proteins with signal sequences are transported
“ticket analogy”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

Nuclear Transport

A

Dilemma: How to keep Chromosomes in and Organelles out?

Transcription enzymes need to get in and mRNA needs to get out

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

Consider the following statements:
i. The origin of replication is the site where transcription of a gene begins.
ii. The basal transcription complex binds to the promoter of a gene.
iii. RNA polymerase is modified by phosphorylation, DNA polymerase is not.
iv. The DNA replication fork contains two DNA polymerase enzymes.
v. The pre-initiation complex on DNA establishes whether a gene will be transcribed or not.
Which of these are true?

A

ii, iii, and iv

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

Central Dogma of Molecular Biology

A

DNA —> RNA —> Amino Acids —> Proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

DNA transcription is always in the ______ direction

A

3’ -to- 5’

There are no primers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

Transcription stages

A

Initiation —> Elongation —> Termination

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

Eukaryotes express three different RNA polymerase. Each specialized to generate a different kind of RNA molecule

A

RNA pol I

RNA pol II

RNA pol III

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

RNA pol I

A

synthesizes a single large ribosoma RNA which is later cut into the 3 parts of the rRNA found in ribosomes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

RNA pol II

A

synthesizes messenger RNAs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

RNA pol III

A

synthesizes tRNAs

51
Q

Promoters

A

Mark the designated sites of DNA transciption

NB// Where as replication begins at sequences called “origins of replication”, transcription begins at sequences called promoters.

52
Q

Proteins that control transciption are called ________

A

transcription factors

53
Q

Basal transciption factors

A

they literally form the base upon which the regulatory structures are built.

For RNA pol II, six factors make up this complex
TFIIA, TFIIB, TFIID, TFIIE, TFIIF, and TFIIH

54
Q

Transcription: Initiation

A

begins when basal transcription factors bind to the promoter nearest to where transcription begins. This site is called the transcription startpoint

55
Q

The promoter is subdivided into distinct sequences. The portion near the transcription start point is called _______

A

core promoter because its is absolutely essential for transciption

56
Q

The core promoter is called

A

TATA box.

5’ -TATAA- ‘3

The TATA box binds TFIIID

57
Q

Basal transciption factors binding sequence

A

TFIIID + 3 other BTF

These form a pocket for RNA pol II

After pol II binds TFIIIE & TFIIIH attach to cap the polymerase.

58
Q

TFIIIH —>

A

Ensure pol II reads the right template.

Contains kinase enzyme that add phosphate and initiate conformational change. BTF are the activated

59
Q

TFIIIE —>

A

partially unwinds DNA double helix

60
Q

RNA pol has no proof reading abilities

A

True

61
Q

Stage 2 of Transcription: Elongation

A

RNA transcript is extended in the 5’-to-3’ direction as the RNA polymerase reads the template DNA strand in the 3’-to-5’ direction

62
Q

Supercoiling Solved by Two Enzymes

A

Gyrase reverses extra positive supercoiling ahead of the transcription bubble by inducing negative supercoiling

Topoisomerase relaxes negative supercoiling behind the transcription bubble

63
Q

Stage 3 of Transcription: Termination

A

Prokaryotes and Eukaryotes use different termination methods

I prokaryotes its encoded by specific sequences called terminators.this forms a sei stable double-stranded RNA called hairpin loop.

64
Q

Termination - may require additional protein

A

some terminators require additional proteins (Rho protein in bacteria) to bind RNA polymerase to induce shape change and stop transcription.

65
Q

Terminators are not universally effective

A

Terminators are not universally effective
Anti-terminators can suppress termination
Polycistronic RNA and operons result when adjacent or clusters of genes are transcribed on a single RNA molecule

66
Q

RNA processing

A

One of the most striking differences between Prokaryotic and Eukaryotic transcription is that mRNA structure is modified by Eukaryotes prior to their use.

The Spliceosome Controls RNA Splicing

67
Q

RNA Splicing

A

Nucleotide sequences at the boundries of of introns and exons on mRNA facilitae the breakng and forming of the suger phosphate backbone by a process called transeterification

68
Q

Alternative splicing

A

Alternative splicing can generate a large variety of proteins from a single DNA sequence by “mixing & matching” exons after introns have been spliced out.

69
Q

RNA Modifications

A

5’ methylguanosine cap

poly(A) tail

70
Q

RNA Export

A

Is Unidirectional And Mediated By Nuclear Transport Proteins

71
Q

RNA Export: Function of the Poly A-tail

A

poly(A)-binding protein (PABP) at 3’ end

72
Q

mRNA with all associated proteins is called

A

…..the heterogeneous nuclear ribonucleoprotein particle (hnRNP) or ribonucleoprotein particle (mRNP)

73
Q

Translation Occurs In Three Stages

A

initiation, elongation, and termination

74
Q

The first goal of initiation is for the ribosomal subunit to find the ______

A

Ribosomal binding site (Specific translation start point)

Bacteria and eukaryotes accomplish this differently

75
Q

Ribosomal binding site in bacteria is the _____

A

Shine Delgarno sequence…..forms complementary pairing with a section of the small subunit of the ribosome.

5’ -AUG- 3

76
Q

Once small subunit of ribosome pairs with shine Delgarno sequence _______

A

1st tRNA called initiator tRNA binds to the AUG

77
Q

Prokaryotic Ribosomes size _____

A

Typically 70S (composed of 50S and 30S subunits)

*based on The Stoke’s Radius

78
Q

Eukaryotic Ribosomes size _____

A

Typically 80S (composed of 60S and 40 S subunits)

79
Q

Eukaryotes dont have a Shine Delgarno sequence.

A

True. instead they capitalize on the 5 methylguanine cap that is added to the 5’ of the mRNA.

Small subunits in eukaryotes bind to initiation proteins (eIFs) on the 5’ methylguanine cap

80
Q

elongation - Three inputs are required

A
  1. Charged tRNA linked to an amino acid
  2. EF-Tu-GTP protein
  3. Translation factor complex EF-G-GTP
81
Q

Stage 3: Termination

A

Translation stop sequences: UAA, UAG, UGA
Do not bind to any tRNAs
Instead, these bind release factors that fit into the A-site on the ribosome
occurs when the bond holding the polypeptide to tRNA is hydrolyzed
Water is the acceptor in this hydrolysis reaction

82
Q

What cellular activity does the term gene splicing describe?

A

It describes the removal of nucleotides from a primary transcript RNA

83
Q

What distinguishes transport of proteins into the nucleus from other modes of protein transport?

A

Proteins targeted to the nucleus are transported in a fully folded, functional state

84
Q

Which statement best explains the difference between transcription and translation in eukaryotic cells?

A

Transcription occurs in the nucleus, translation occurs in the cytosol.

85
Q

Removal of a TATA box from a eukaryotic gene would likely result in which of the following outcomes?

A

No transcription of that gene

86
Q

Which statement best explains the difference between transcription and translation?

A

Transcription copies one nucleotide sequence to another, translation converts a nucleic acid sequence into an amino acid sequence.

87
Q

During the elongation phase of translation, what occurs at the P site on a ribosome?

A

A peptide bond is formed between adjacent amino acids in the growing polypeptide

88
Q

Which statement most accurately describes how translation is terminated?

A

Release factor binds to the stop codon, so the P site cannot form any more peptide bonds.

89
Q

Signal Sequences Code For Proper Targeting Of Proteins

A

The Cytosol is the default destination for all proteins synthesized there.

Proteins without signal sequences stay in the cytosol

Proteins with signal sequences are transported
“ticket analogy”

90
Q

Nuclear Transport

A

Dilemma: How to keep Chromosomes in and Organelles out?

Transcription enzymes need to get in and mRNA needs to get out

91
Q

signal sequences that permit entry to and exit from the nucleus are called ______

A

Nuclear localization sequences (NLS) nad nuclear export sequences (NES). These bind to receptor proteins Importin and Exportins

Nuclear Transport is Bidirectional
Proteins transported in/out of nucleus in folded, functional state

92
Q

Nuclear Transport

A

Simple Diffusion
Colloidal Gold diffusion into nucleus was inversely related to particle diameter (10 nm or larger were entirely excluded)
Small particles diffuse in through tiny, 8 aqueous diffusion channels in the pore complex
Thought to be permeable to ions and small proteins and ATP, GTP, CTP, TTP used for DNA replication

93
Q

Nuclear Import – Step by Step

A
  1. Importin recognizes proteins with an NLS sequence
    This Importin-cargo complex goes through the nuclear pore complex
  2. Ran-GTP (a small G protein) binds to Importin causing release of the cargo
    Ran-GTP bring importin back to the nucleus for another round
    GTP hydrolysis triggers release of importin back in the cytosol
94
Q

Nuclear Export – Step by Step

A

Usually RNA, rather than protein
Proteins with nuclear export signals (NES) bind RNA
Exportin binds Ran-GTP
This triggers cargo loading onto Exportin
Cargo-Exportin-Ran-GTP travels through the nuclear pore complex to the cytosol
Complex falls apart with GTP hydrolysis
Exportin goes back to the nucleus for another round

95
Q

Proteins Targeted To The Peroxisome contain ________

A

Contain Peroxisomal Targeting Signals (PTS)

96
Q

Peroxisome functions include

A
  1. Oxidation of long-chain fatty acids
  2. amino acids synthesis and breakdown,
  3. Glycerol synthesis and
  4. degradation of dangerous molecules called reactive oxygen species (ROS)
97
Q

Aminoacyl tRNA synthetase:

A

forms a covalent bond between amino acids and tRNAs in the cytosol

98
Q

Protein import into the peroxisome most closely resembles protein import in:

A

the chloroplast

99
Q

If a cell was transfected with a plasmid encoding Green Fluorescent Protein, and the result was accumulation of GFP in the nucleus, which statement best explains this result?

A

The GFP gene was engineered to include a Nuclear Localization Sequence.

100
Q

Consider the following statements:
i. The origin of replication is the site where transcription of a gene begins.
ii. The basal transcription complex binds to the promoter of a gene.
iii. RNA polymerase is modified by phosphorylation, DNA polymerase is not.
iv. The DNA replication fork contains two DNA polymerase enzymes.
v. The pre-initiation complex on DNA establishes whether a gene will be transcribed or not.
Which of these are true?

A

ii, iii, and iv

101
Q

What is the function of aminoacyl-tRNA synthetase?

A

It adds an amino acid to tRNA.

102
Q

Which statement best describes the peptidyl transferase function of a ribosome?

A

It adds the growing polypeptide to the aminoacyl tRNA

103
Q

Which statement best describes the core promoter?

A

It encodes the sequences that promote expression of the core proteins in the nuclear pore complex

104
Q

Transport into the ER

A

Secreted Proteins And Proteins Targeted To The Endomembrane System Contain An ER Signal Sequence

105
Q

Transport into the ER

A

Transport into the ER is cotranslational (as it is being synthesized by the ribosome)

Transport into the ER requires that the protein be in its unfolded state

Transport into the ER is unidirectional

As Proteins Enter the ER Lumen, They May Be Post-Translationally Modified

106
Q

Terminally Misfolded Proteins In The ER Are Degraded In The Cytosol

A

Misfolded polypeptides in ER are “reverse translocated” back into cytosol
Once in the cytosol, misfolded polypeptides are ubiquitinated and subsequently degraded by proteosomes

Process of identifying, reverse translocating, and destroying these polypeptides is called ER-assisted degradation (ERAD)

The Unfolded Protein Response (UPR) is triggered when unfolded proteins begin to accumulate in the ER lumen

Heat shock proteins to the rescue!

107
Q

NLS

A

Nucleus localization sequence

108
Q

NES

A

Nucleus Export Signals

109
Q

RAN

A

Controls the direction nucleus transport

110
Q

Proteins Targeted To The Peroxisome

A

Peroxisome Contain Peroxisomal Targeting Signals (PTS)

111
Q

True / False

Proteins are transported into the peroxisomal matrix in their properly folded, functional state

A

True

112
Q

ERoS

A

ER Signal Sequence

113
Q

Secreted Proteins And Proteins Targeted To The Endomembrane System Contain An ER Signal Sequence

A

True

114
Q

True or False

Transport into the ER requires that the protein be in its unfolded state

A

True

Transport into the ER is unidirectional

115
Q

Transmembrane Proteins

A

There are The four classes of transmembrane proteins, according to the Singer classification system.

C N N (or C) N (or C) / C (or N)
| | |
N C C (or N)

116
Q

SRP

A

Signal recognition particle (Contains 6 subunits and forms RNA called small cytosolic RNA. Uses GTP

117
Q

Proteins destined for any portion of the endo membrane system express at least one signal sequence called _________

A

ER signal sequence

118
Q

discuss the process from SRP —–> translocation.

A

Go…

119
Q

As Proteins Enter the ER Lumen, They May Be Post-Translationally Modified

A

N-linked glycosylation transferase in the translocon attaches clusters of suger called core oligosaccharides to some polypeptides.

Then…

Chaperone Proteins Assist in the Proper Folding of ER Proteins. BiP (Binding proteins) binds to exposed hydrophobic patches in recently translocated proteins.

120
Q

reverse translocated

A

Misfolded polypeptides in ER are “reverse translocated” back into cytosol
Once in the cytosol, misfolded polypeptides are ubiquitinated and subsequently degraded by proteosomes

121
Q

ER-assisted degradation (ERAD)

A

Process of identifying, reverse translocating, and destroying these polypeptides is called ER-assisted degradation (ERAD)

122
Q

Unfolded Protein Response (UPR)

A

The Unfolded Protein Response (UPR) is triggered when unfolded proteins begin to accumulate in the ER lumen
Heat shock proteins to the rescue!

123
Q

Cytosolic Proteins Targeted To Mitochondria Or Chloroplasts Contain An _________

A

N-terminal Signal Sequence.

Signal Sequences
Mitochondrial signal sequences
Chloroplast transit peptides
Bind Membrane Protein Receptors (TOMs and TIMs)
Transport is post-translational and in an unfolded state
Requires ATP energy

124
Q

The Cytoskeleton Immobilizes And Transports mRNAs

A

mRNAs were previously thought to float through the cytosol
mRNAs preferetially localize to certain areas of the cytosol
They associate with actin filaments and microtubules and are transported by motor proteins
Example – zipcode sequence in b-actin mRNA

Cell Biology (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions