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cell biology & haematology > protein sorting and transport > Flashcards

protein sorting and transport Flashcards

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AP® Biology flashcards Biology 101 flashcards
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
Q

what happens to severely misfolded proteins in the ER?

A

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

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26
Q

what does a mutation in alpha 1-antitrypsin lead to?

A

misfolding of the protein and retention in the ER

27
Q

what are the normal functions of alpha 1-antitrypsin?

A

protease inhibitor

involved in various immunoregulatory functions

28
Q

what are the effects of a mutation in alpha 1-antitrypsin ?

A

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
Q

what does the abbreviation ‘ERGIC’ stand for?

A

ER-golgi intermediate complex

30
Q

explain vesicular transport from the ER to the golgi

A

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
Q

what are the targeting sequences that cause proteins to be retained in the ER?

A

KDEL sequence: Lysine- Aspartic acid- Glutamic acid- Leucine
KKXX sequences

32
Q

what happens if proteins which are supposed to be retained in the ER are accidentally transported out?

A

they are recognised by KDEL receptors and are transported back to the ER

33
Q

what are the different regions of the golgi apparatus?

A

cis
medial
trans

34
Q

what are synthesised in the Golgi apparatus?

A

glycolipids and sphingomyelin

35
Q

what does the cisternae maturation model propose?

A

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
Q

what does the stable cisternae model propose?

A

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
Q

what is the constitutive secretory pathway?

A

continuous secretion of proteins from the cell

38
Q

what is regulated secretion?

A

specific proteins are secreted in response to environmental signals

39
Q

what regulates the formation of coated vesicles?

A

small GTP-binding proteins related to Ras and Ran

40
Q

explain budding and fusion of a transport vesicle.

A

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
Q

what are the 3 kinds of coated proteins?

A

COP I
COP II
clathrin coated

42
Q

what is the function of COP I- coated vesicles?

A

transport ER proteins marked by KDEL or KXX retrieval signals from the ERGIC or the cis golgi network to the ER

43
Q

what is the function of COP II coated vesicles?

A

bud from the ER and transports its cargo to the ERGIC or golgi apparatus

44
Q

what is the function of clathrin coated vesicles?

A

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
Q

what regulates the assembly of COPI and clathrin vesicles?

A

ARF GTPase

46
Q

what regulates the assembly of COPII vesicles?

A

Sar 1

47
Q

explain the initiation of clathrin-coated vesicles by ARF1

A

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
Q

explain coat disassembly of clathrin coated vesicles

A

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
Q

what are snare proteins?

A

membrane bound proteins that help a vesicle fuse with the cell membrane

50
Q

how do vesicles fuse with the cell membrane?

A

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
Q

what is Grescilli’s syndrome?

A

a rare disease caused by mutation in the gene encoding Rab27a

52
Q

what does Rab27a play a key role in transporting?

A

melanosomes
pigment-containing vesicles
exocytosis of vesicles in T lymphocytes

53
Q

what are the symptoms of Griscilli’s syndrome?

A

partial albinism

immunodeficiency

54
Q

what is the normal function of Rab27a?

A

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
Q

which type(s) of Grescilli’s syndrome causes loss of pigmentation?

A

1 and 3

56
Q

which type(s) of Grescilli’s syndrome causes neurological dysfunction?

A

1

57
Q

which type(s) of Grescilli’s syndrome causes immunological defects?

A

2

58
Q

what causes loss of pigmentation in Grescilli syndrome?

A

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
Q

what causes neurological dysfunction in Grescilli syndrome?

A

mutation in Myo5a gene prevents the transport of vesicles to neuronal synapses

60
Q

what causes immunological defects in Grescilli syndrome?

A

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
Q

how many degenerative enzymes do lysosomes contain?

A

60

62
Q

what causes Gaucher disease?

A

a deficiency of glucocerebrosidase
in the most common form only macrophages are affected
characterised by enlarged liver and spleen

63
Q

what is the function of glucocerebrosidase?

A

catalyses the hydrolysis of gucosylceramide to glucose and ceramide

64
Q

what is the effect of a missense mutation in the gene encoding for glucocerebrosidase?

A

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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