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cell biology & haematology > protein sorting and transport > Flashcards

protein sorting and transport Flashcards

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1
Q

what are proteins translated from?

A

mRNA

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2
Q

what are some functions of proteins?

A

receptor construction
supply components to the mitochondria
produces secretory proteins
produce components pf the cytosol

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3
Q

what are the functions of lysosomes?

A

protein degradation

phagocytosis and autophagy

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4
Q

what are the functions of the golgi complex?

A

protein processing and sorting

lipid and polysaccharide synthesis

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5
Q

what are the functions of the rough endoplasmic reticulum?

A

protein targeting
protein folding and processing
quality control

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6
Q

what is gated transport?

A

movement of proteins between the cytoplasm and nucleus

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7
Q

what is transmembrane transport?

A

movement of proteins across a membrane from the cytoplasm

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8
Q

what is vesicle transport?

A

building a vesicle from one membrane to another

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9
Q

what were Palades discoveries?

A

used pancreatic cells and conducted the ‘pulse chase’ experiment
found the first membrane organelle that the protein enters
protein enters the rough endoplasmic reticulum then vesicles
also discovered that newly synthesised proteins are labelled

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10
Q

what were Blobel and Sabatini’s discoveries?

A

discovered signal sequences

if the proteins are destined to be secreted into the cytoplasm then the protein has longer sequences

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11
Q

what are signal sequences?

A

a stretch of around 20 hydrophobic amino acids usually located at the amino terminus of the polypeptide
it tells the cell where the protein is destined for

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12
Q

what is co-translational translocation?

A

when proteins are targeted to the ER during translation

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13
Q

what is post-translational translocation?

A

when proteins are targeted to the ER after translation

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14
Q

explain co-translational targeting of secretory protein into the ER

A

translating proteins emerge from the ribosome and contains a signal sequence
signal recognition particle engages with the sequence bringing it to the signal recognition particle on the ER and is then released
translocon on the ER membrane opens
signal peptidases cleave the recognition sequence and translation continues

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15
Q

explain post-translational translocation of proteins into the ER.

A

proteins are synthesised on free ribosomes
signal sequence is recognised by receptor proteins (Sec 62/63 and Sec 70/71) that are associated with the translocon in the ER membrane
cytosolic heat shock protein 70 chaperones maintain the polypeptide in an unfolded conformation in the cytosol so they can enter the translocon
BiP pulls the polypeptide through the channel

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16
Q

are proteins destined for secretion translocated into the ER lumen or inserted into the ER membrane?

A

translocated into the lumen

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17
Q

are proteins destined for the plasma membrane translocated into the ER or inserted into the ER membrane?

A

inserted into the ER membrane

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18
Q

explain insertion of membrane proteins with internal transmembrane sequences.

A

signal recognition particle receptor binds to signal sequence and opens the translocon
translation occurs within the translocon and the protein is then inserted into the membrane with either is C or N terminus exposed

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19
Q

what are examples of post translational modifications?

A

phosphorylation

glycosylation

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20
Q

which Hsp70 chaperone ensures correct protein folding in the ER?

A

BiP

it binds to the polypeptide chain as it crosses the ER membrane

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21
Q

what proportion of proteins are misfolded in the ER?

A

half

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22
Q

which glycoprotein chaperones are sensors of misfolded proteins?

A

calnexin

calreticulin

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23
Q

what protein recognises severely misfolded glycoproteins?

A

EDEM1

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24
Q

what does EDEM1 remove?

A

mannose residues from glycoproteins

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25
what happens to severely misfolded proteins in the ER?
EDEM1 recognises the misfolded proteins and removes mannose residues protein is then returned to the cytosol through a ubiquitin ligase complex which labels the protein with a ubiquitin molecule which is recognised by a proteasome it is then degraded
26
what does a mutation in alpha 1-antitrypsin lead to?
misfolding of the protein and retention in the ER
27
what are the normal functions of alpha 1-antitrypsin?
protease inhibitor | involved in various immunoregulatory functions
28
what are the effects of a mutation in alpha 1-antitrypsin ?
lung tissue damage as it usually protects lungs from proteases so degradation of the ECM leads to COPD build up can lead to liver cirrhosis
29
what does the abbreviation 'ERGIC' stand for?
ER-golgi intermediate complex
30
explain vesicular transport from the ER to the golgi
luminal proteins containing export signal bind to transmembrane proteins they are then incorporated into a transport vesicle which buds from the ER the vesicle then binds with the cis golgi membrane and the protein enters
31
what are the targeting sequences that cause proteins to be retained in the ER?
KDEL sequence: Lysine- Aspartic acid- Glutamic acid- Leucine KKXX sequences
32
what happens if proteins which are supposed to be retained in the ER are accidentally transported out?
they are recognised by KDEL receptors and are transported back to the ER
33
what are the different regions of the golgi apparatus?
cis medial trans
34
what are synthesised in the Golgi apparatus?
glycolipids and sphingomyelin
35
what does the cisternae maturation model propose?
that secretory cargo travel in cisternal compartments that slowly mature from the cis-Golgi to the trans-Golgi says that the cisternae move and mature through accumulating trans then medial enzymes
36
what does the stable cisternae model propose?
that the cisternae remains in one place with unchanging enzymes secretory cargo travel from one golgi compartment to the next in COP I vesicles exit is clathrin coated vesicles from the trans golgi
37
what is the constitutive secretory pathway?
continuous secretion of proteins from the cell
38
what is regulated secretion?
specific proteins are secreted in response to environmental signals
39
what regulates the formation of coated vesicles?
small GTP-binding proteins related to Ras and Ran
40
explain budding and fusion of a transport vesicle.
assembly of coat proteins drives the budding of vesicles containing selected cargo proteins from the donor membrane the coats are removed at the target membrane allowing the membranes to fuse and the vesicles to be emptied
41
what are the 3 kinds of coated proteins?
COP I COP II clathrin coated
42
what is the function of COP I- coated vesicles?
transport ER proteins marked by KDEL or KXX retrieval signals from the ERGIC or the cis golgi network to the ER
43
what is the function of COP II coated vesicles?
bud from the ER and transports its cargo to the ERGIC or golgi apparatus
44
what is the function of clathrin coated vesicles?
responsible for the uptake of extracellular molecules from the plasma membrane by endocytosis and from trans golgi to endosomes, lysosomes or the plasma membrane
45
what regulates the assembly of COPI and clathrin vesicles?
ARF GTPase
46
what regulates the assembly of COPII vesicles?
Sar 1
47
explain the initiation of clathrin-coated vesicles by ARF1
ARF 1/ GDP binds to proteins in the golgi membrane ARF- guanine nucleotide exchange factor in the membrane stimulates the exchange of GDP to GTP ARF/GDP initiates budding by recruiting adapter proteins these serve as binding sites for clathrin as well as transmembrane proteins
48
explain coat disassembly of clathrin coated vesicles
GTP bound to ARF1 is hydrolysed to GDP ARF1/GDP is released from the membrane for recycling loss of ARF1 and the action of uncoating enzymes weakens the binding of the clathrin coat complex this allows chaperone proteins in cytoplasm to dissociate the coat
49
what are snare proteins?
membrane bound proteins that help a vesicle fuse with the cell membrane
50
how do vesicles fuse with the cell membrane?
Rab/GDP is converted to Rab/GTP by specific guanine exchange factors Rab/GTP interacts with effector proteins and v-SNARES to assemble a pre-fusion complex on the transport vesicle rab protein on target membrane organises effector proteins and t-SNARES when the vesicle comes close to the target membrane the effector proteins link membranes this stimulates Rab/GTP hydrolysis and allows v-SNARES to connect to t-SNARES
51
what is Grescilli's syndrome?
a rare disease caused by mutation in the gene encoding Rab27a
52
what does Rab27a play a key role in transporting?
melanosomes pigment-containing vesicles exocytosis of vesicles in T lymphocytes
53
what are the symptoms of Griscilli's syndrome?
partial albinism | immunodeficiency
54
what is the normal function of Rab27a?
functions as a motor adapter connects the melanosomes to actin motor myosin melanosomes are then transported to the plasma membrane by Rab27a, Slac2a and myosin 5a
55
which type(s) of Grescilli's syndrome causes loss of pigmentation?
1 and 3
56
which type(s) of Grescilli's syndrome causes neurological dysfunction?
1
57
which type(s) of Grescilli's syndrome causes immunological defects?
2
58
what causes loss of pigmentation in Grescilli syndrome?
a mutation in Rab27a or myosin 5a causes disturbance to movement to actin rich region in the plasma membrane ultimately stops the melanosome reaching the plasma membrane which prevents exocytosis
59
what causes neurological dysfunction in Grescilli syndrome?
mutation in Myo5a gene prevents the transport of vesicles to neuronal synapses
60
what causes immunological defects in Grescilli syndrome?
caused by mutations in either Rab27a or Munc13-4 Rab27a disturbs the targeting of secretory lysosomes of the cytotoxic T cells to the immunological synapse Munc13-4 disturbs the priming of lysosomes for fusion with the plasma membrane
61
how many degenerative enzymes do lysosomes contain?
60
62
what causes Gaucher disease?
a deficiency of glucocerebrosidase in the most common form only macrophages are affected characterised by enlarged liver and spleen
63
what is the function of glucocerebrosidase?
catalyses the hydrolysis of gucosylceramide to glucose and ceramide
64
what is the effect of a missense mutation in the gene encoding for glucocerebrosidase?
leads to misfolding in the ER prevents the breakdown of glucosylceramide which is toxic when it accumulates causes the affected cell to swell

cell biology & haematology (12 decks)

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