Brainscape's Knowledge GenomeTM

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


See full index

MBB164 > Hettema - Cell destination > Flashcards

Hettema - Cell destination Flashcards

1
Q

where are the majority of proteins synthesised?

A

cytosol

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

define targeting

A

movement of newly synthesised proteins from the cytosol to the membrane of an organelle

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

define translocation

A

process of moving a protein across a membrane

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

define sorting

A

portein travelling from one membrane bound compartment to another

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

explain the signal sequence (SS) hypothesis

A

proteins containing a short a/a sequence that directs a protein to a specific cell location

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

describe Gunther Blobel’s experiment that led to the SS hypothesis

A

label a/a’s in secretory proteins with a radioactive label
homogenise cells (leads to microsome formation)
protease protection assay (use detergent to remove microsome membrane - protease degrades secretory protein)

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

what did Cesar Milstein’s experiment prove?

A

evidence for signal sequence and co-translational import

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

describe Cesar Milstein’s experiment

A

cell-free protein synthesis with one half having microsomes added at the beginning and one with microsomes added later on
when the microsomes are added later there is no incorporation into proteins and the signal seq isn’t removed
when microsomes are added at the beginning the proteins are incorporated and the signal seq is removed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

describe the cotranslational import of a soluble protein

A

signal sequence recognition particle (SRP) binds to the signal sequence
SRP blocks translation temporarily
SRP binds specific receptor on the ER membrane
Transfer of polypeptide/ribosome complex to translocon leads to translocon opening.
When SRP and SRP receptor dissociate from translocon they hydrolyse each of their GTP.
SS enters ER lumen and is cleaved off polypeptide chain by signal peptidase and rapidly degraded.
Transl. begins again and polypeptide enter ER lumen through translocon.

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

describe the insertion of a type I transmembrane protein

A
  • Same as cotranslational import of soluble proteins until ribosome/nascent protein complex binds to translocon. The signal peptidase removes the SS. Nascent chain elongated until hydrophobic stop-transfer sequence. The nascent chain can no longer elongate into ER lumen. Stop-transfer sequence moved laterally into membrane and translocon closes. The chain begins to elongate again until stop codon is reached. (N-terminus in ER and C-terminus in cellular env)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

describe the insertion of a type II transmembrane protein

A
  • Same as cotranslational import of soluble proteins until the ribosome/nascent protein complex binds to translocon. NO SS PRESENT – hydrophobic signal-transfer sequence acts as a ER signal and membrane-anchor sequence. At the N-terminus end of the nascent protein there is a positive charge (just before the stop-transfer sequence), this orients the N-terminal end into the cellular env and not the ER lumen. As the chain is elongated the signal-anchor sequence is moved laterally out of the translocon and into the membrane. (N-terminus in cellular env and C-terminus in ER)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

describe the post-translational import of secretory protein

A

signal sequence binds translocon and is cleaved by signal peptidase
Hsp70 pulls the unfolded polypeptide chain in by ATP hydrolysis
chaperones help fold the nascent mRNA

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

name 3 types of protein modification and where and when they occur

A

when: happen to newly synthesised proteins
- glycosylation: in ER and Golgi
- disulphide bond formation: in ER
- proper folding and multimeric complex formation: in ER

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

why do proteins undergo glycosylation?

A
  • may promote folding
  • stabilises some secreted proteins
  • involved in cell to cell interactions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

name 2 pieces of evidence that suggest glycosylation promotes protein folding

A

tunicamycin inhibits glycosylation (and secondary protein folding in ER)
mutation of glycosylation site in haemagglutinin (HA) = build up of unfolded HA in ER

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

describe n-linked glycosylation

A

added to nascent chain in RER
linked to Asn residue
complex oligosaccharide

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

describe o-linked glycosylation

A

added to nascent chain in RER
linked to ‘OH’ group of Thr/Ser residue
simple oligosaccharide

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

describe the processing and folding of n-linked oligosaccharides in the RER

A

1) glycosylation occurs in translocation
2) glucosidases trim core glycans
3) if the protein isnt folded correctly UGGT (UDP-glucose: glycoprotein glucosyltransferase) adds glucose again
4) mannose is removed and the oligosaccharide is transferred to the Golgi

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

what happens to incorrectly folded proteins?

A

transferred to cytosol to be degraded by proteosome

20
Q

describe the target sequence and location for ER-bound peptides

A

N-terminus

6-12 h.phobic a/a’s preceded by +ve a/a

21
Q

describe the target sequence and location for mitochondrial-bound peptides

A

N-terminus

amphipathic helix, 20-50 a/a’s. Arg and Lys on one side and h.phobic on the other side

22
Q

describe the target sequence and location for chloroplast-bound peptides

A

N-terminus

usuallly rich in Ser, Thr and smalll h.phobic a/a’s. Usually low in Glu and Asp

23
Q

describe the target sequence and location for peroxisome-bound peptides

A 
PTS1 signal (Ser-Lys-Leu) for C-terminal
PTS2 signal for N-terminus
24
Q

describe the post-translational uptake of precursor proteins into the mitochondria

A

type of protease protection assay

1) uptake-targeting seq &mitochondrial protein made in cell-free system
2a) add yeast mitochondria (to half of solution)
3a) add trypsin - no degradation as there has been uptake into mitochondria
2b) add trypsin (to half of solution) - degradation as there has been no uptake into mitochondria

25
Q

describe protein import into the mitochondrial matrix

A

1) unfolded precursor binds receptor
2) protein inserts into outer membrane channel
3) threads through TOM and TIM complexes pulled by Hsp70
4) protein folded into active conformation
(this requires inner and outer membrane contact)

26
Q

describe the interaction between methotrexate (MTX) and chimeric DHFR

A

MTX binds DHFR which folds it, meaning it cannot pass through the translocon and only the signal sequence is removed
DHFR would otherwise enter the mitochondrial matrix and be folded
(this requires inner and outer membrane contact)

27
Q

describe peroxisomal import

A

PTS1 binds receptor receptor which binds to membrane

receptor is recycled after PTS1 dissociation (requires ATP hydrolysis)

28
Q

what is hyperoxaluria type I?

A

heritable kidney stone disease which leads to calcium oxalate

29
Q

why do people get hyperoxaluria type I?

A

70% lack AGT enzyme
30% have AGT enzyme but with incorrect AGT targeting sequence - double mutation of Pro11Leu and Gly170Arg creates mitochondrial targeting signal and leads to slowed dimerisation and folding of AGT

30
Q

what does the Pro11Leu mutation do in the AGT gene?

A

has a weak mitochondrial targeting sequence therefore goes mainly to peroxisomes

31
Q

describe the pulse-chase experiment by george palade

A

labelled slices of tissue with radioactive Leu (pulse)
washed out leu
incubated for set times - saw proteins moving from ER to Golgi to post-golgi

32
Q

describe video microscopy of GFP labelled VSV-G protein

A

temp sensitive mutant stays in ER at high tmp
at lower temp transporter to golgi and PM
lowered temp and say the fluorescence levels increase in golgi first, then PM as they decreased in the ER

33
Q

describe what happens to glycoproteins when they enter the golgi from ER and what happens when theyre treated with endoglycosidase D

A

mannose sugars trimmed in golgi
trimmed in golgi means sensitive to endoglycosidase D
untrimmed ER protein not sensitive to endonuclease D
used temp sensitive mutants to show how fraction of endonuclease D sensitive proteins increased over time

34
Q

describe the steps in vesicular transport

A

1) coat assembly and concentration of cargo in bud
2) budding
3) uncoating
4) docking and fusion

35
Q

name 3 coat proteins

A

clathrin
cop I
cop II

36
Q

how do coat proteins drive budding

A

by oligomerisation on the membrane and thereby bending the membrane
Coat proteins bind sorting signals
vSNAREs direct vesicle to organelles

37
Q

describe vesicle formation at ER membrane

A

Coat assembly under control of GTPase.
Sar1-GDP binds Sec12 on ER membrane, the exchange of GDP for GTP anchors Sar1 into the membrane.
Sar1-GTP (in mem) drives polymerisation of soluble coat factors (leads to budding). Sorting signals in cargo receptors are recognised by coat proteins.
GTP hydrolysis initiates uncoating.
Vesicle type COPII (ER –> cis-Golgi) uses GTPase Sar1// COPI (cis-Golgi –> ER) uses ARF as does clathrin.

38
Q

describe vesicle fusion with PM

A
  • Rab-GTP on vesicles binds complex on PM. 3 helices on PM and vSNARE helix interact and form SNARE complex. The membranes fuse. ATP hydrolysis disassembles the SNARE complex. GTP hydrolysis on Rab results in Rab dissociation. The vSNARES are brought back into the vesicle to be recycled.
39
Q

describe anterograde transport

A

coat assembly and budding from ER
coat is released and vesicle meets golgi membrane
specificity factors vesicle membrane and donor membrane pair = fusion

40
Q

describe retrograde transport

A

KDEL containing peptide bind to specific receptor in golgi stack
complex gets incorporated into retrograde vesicle
delivered to er
retrieval of KDEL bearing peptides to ER

41
Q

describe the two models of transport through the Golgi complex

A 
stationary cisternal model
transport between stacks by vesciles
cisternal maturation model
retrograde transport 
trans turns to medial etc
42
Q

describe the transport from the golgi to the lysosomes

A

Man-6-P added in cis-Golgi.
Man-6-P protein binds to receptor in trans-Golgi and is incorporated into clathrin-coated vesicle.
After vesicle formation the coat is disassembled and fuses with the late endosome (LE).
Protein is released from the receptor and dephosphorylated.
The LE then fuses with the lysosome and the receptor and coat proteins are recycled.

43
Q

what causes I-cell disease

A

formation of mannose-6-P is affected

44
Q

describe clathrin receptor-mediated endocytosis

A
  • Adaptor proteins bind receptors, clathrin, membrane, factors required for vesicle formation and release. Dynamin then pinches off the vesicle (by GTP hydrolysis) forming a vesicle.
45
Q

describe endocytosis of LDL

A
  • Ligand binding of LDL to the LDL-receptor. Incorporation of LDL and receptor into a clathrin-coated vesicle. Vesicle is then uncoated and fused with the LE. LDL dissociates from the receptor (requires pH <5) and the LE fuses with the lysosome The LDL receptor is recycled.
46
Q

what happens at pH 7 and pH 5 in LDL release

A

pH7 ligand binding receptor to LDL particle (bound on mem)

pH5 beta propellor domain becomes positively charged and ligand binding arm attaches (releases in endosome)

47
Q

what is familial hypercholesterolaemia

A

LDL high in serum
mutations in the LDL receptor
fat deposition in certain cell types

MBB164 (9 decks)

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