Lecture 16: Peroxisomes Flashcards
(102 cards)
1
Q
peroxisomes carry out a ____
A
variety of essential functions in a wide spectrum of organisms
2
Q
peroxisome (descr.)
A
single membrane organelle that has fine granular matrix
3
Q
peroxisomes are generally _____
A
spherical with diameters of 0.2 to 1 um
4
Q
number and composition of peroxisomes _____
A
vary widely depending on physiological needs
5
Q
peroxisomes are distributed _____
A
evenly in human cell
6
Q
peroxisomes size depends on ____
A
diet of organism
7
Q
peroxisomes under EM
A
electron dense surrounded by membrane
8
Q
peroxisomes are organelles that ____
A
use molecular oxygen and hydrogen peroxide to carry out oxidative reactions
9
Q
peroxisomes: 2 essential enzymes
A
-oxidase (produces H2O2)
-catalase (decomposes H2O2)
10
Q
oxidase reaction
A
RH + O2 -> R + H2O2 (produces H2O2)
11
Q
catalase reaction
A
decomposes H2O2
12
Q
peroxisomes detoxify _____
A
several toxic molecules (ex. ethanol)
13
Q
peroxidation (def.)
A
H2O2+ R’H2 —> R’+ 2H2O
14
Q
site of lipid metabolism in mammalian cells
A
mitochondria & peroxisomes
15
Q
site of B-oxidation of long chain fatty acids in mammalian cells
A
mitochondria & peroxisomes
16
Q
site of bile synthesis in mammalian cells
A
mitochondria & peroxisomes
17
Q
site of B-oxidation of long chain fatty acids in yeast cells
A
peroxisomes
18
Q
peroxisomes are central to _______
A
lipid metabolism
19
Q
Peroxisomes control ____
A
extent of oxidative stress with catalase by controlling levels of reactive oxygen species (ROS)
20
Q
peroxisome function requires tethering to _____ (2)
A
lipid sources (lipid droplets)
lipid metabolizing organelles (mitochondria,ER)
21
Q
lipid metabolizing organelles (2)
A
mitochondria
ER
22
Q
size of peroxisome = how ____
A
metabolically active the cell is
23
Q
2 types of disorders with peroxisomes
A
-protein deficiencies
-deficiencies in biogenesis of peroxisomes
24
Q
peroxisomes disorders help to identify ____
A
human genes required for peroxisome function
25
class of inherited disorders that affect biogenesis of peroxisomes
Zellweger Spectrum Disorders
26
peroxisomes are required for proper ____
human development and physiology
27
peroxisomes function + neural defects
they catalyze 1st reaction in formation of plasmalogens (phospholipids in myelin)
defects in peroxisomes biogenesis -> neural defects
28
peroxisomes are the signaling platform for ____
antiviral response
29
immunity: increasing peroxisomes leads to ____ by ___
increased capacity of innate immunity
inhibiting RNA viral replication
30
Interferon (def.)
group of signaling proteins made and released by host cells in response to the presence of several viruses
-part of innate immunity
31
peroxisomes and interferon relationship
increase peroxisomes = increase activity of interferon simulated gene
32
interferon simulated gene (ISGs) (def.)
a gene that can be expressed in response to stimulation by interferon
33
Zellweger Spectrum Disorders (ZSS) and other peroxisomal diseases leads to the accumulation of _____
very long chain fatty acids in blood and many tissues
34
ZSS is the result from defects in at least of how many pex genes?
14
35
protein targeting to peroxisomes involves two pathways: _____
-direct import from cytoplasm
-import machinery of the ER
36
peroxisomes lack _____ and _____
genome
protein synthesis machinery
37
all peroxisomal protein are encoded in _____ and synthesized by ____
nucleus
ribosomes in cytosol
38
peroxisomes are completely dependent on ____ for biogenesis
completely dependent on import of protein for biogenesis
39
signal needed for the import of peroxisome matrix proteins
Peroxisome Targeting Signal (PTS)
40
two types of signals (PTS) for import of peroxisome matrix proteins
-PTS1
-PTS2
41
most common PTS signal
PTS1
42
PTS1 (descr.)
conserved C-terminal tripeptide sequence (SKL)
43
PTS1 is the primary _____
targeting signal used by majority of matrix proteins
44
PTS1 is ___ and ____ for targeting to peroxisomes (needed and enough for transport)
essential and sufficient
45
GTP with PTS1 motif is transported where?
peroxisomes
46
PTS2 (descr.)
conserved N-terminal nonapeptide (9 a.a.)
47
PTS2 sequence
(R/K)(L/V/I)(X5)(H/Q)(L/A)
48
PTS2 is used by ____
smaller subset of matrix proteins
49
characterization of pex targeting mutants is done with_____ because ____
yeast
B-oxidation of fatty acids only occurs in peroxisomes
50
characterization of pex targeting mutants method
*Mutagenize yeast cells in culture
*Divide in many aliquots
*Plate each aliquot on standard plate
*Replica plate
*Identify mutants that grow on complete medium, but fail to grow on plates with long chain fatty acids as sole carbon source
51
two proteins recognize proteins that have PTS1 or PTS2 bearing proteins
Pex5p
Pex7p
52
Pex5/7 ____ produces Pex5/7p (___)
gene
protein
53
Pex5p recognizes protein with _____ targeting signal
PTS1
54
Pex7p recognizes protein with _____ targeting signal
PTS2
55
recognition of PTS2 involves ____ and _____
Pex7p
factor X (varies from species to species)
56
recognition of PTS1 involves ____
Pex5p
57
Pex5p and Pex7p require ___
docking proteins/channels/translocation complex
58
Pex13p/Pex14p form complex exposed to ___
cytosolic surface of peroxisomal membrane
59
Pex13p/Pex14p are resistant to extraction with ___ so they are _____
-high pH carbonate buffers (still in pellet)
integral membrane proteins
60
peroxisome extraction: pellet
imbedded with membrane
61
peroxisome extraction: supernatant
inside the peroxisome
62
Pex14p binds to ___
both PTS receptors (Pex5p and Pex7p)
63
Pex14p is the docking site for both _____
Pex5p and Pex7p complexes
64
overall pex14p mechanism
pex14 binds and internalizes PTS receptors (like a channel) with the help of other membrane proteins
65
import of matrix proteins is ___ and doesn't require ___ (not like ER)
post-translational
unfolding
66
matrix proteins are stabilized with ____ before import into peroxisome
disulfide bonds and chemical cross-linkers
67
size of several matrix proteins
> 450 kDa (ex. catalase)
68
9nm gold particles with PTS1 is where?
peroxisome
69
Pex5p/7p found in the matrix of peroxisomes suggest that ___
PTS receptors are co-imported with their substrates
70
Pex5 shuttling between cytosol and matrix steps
1) Pex5 forms complex with proteins with PTS1
2)Pex5 docks on peroxisomal membrane through Pex14
3)Part or all of complex translocated into peroxisomal matrix
4) Cargo released in matrix
5) Pex5p is mono-ubiquinated
6) Pex5p is de-unbiquinated and exported back to cytosol in ATP-dependent process
71
Pex5p is _____ and then ______ to be exported back in cytosol
mono-ubiquinated
de-ubiquinated
72
Different types of ubiquination have ___
drastically different function
73
polyubiquination leads to ____
protein degradation
74
import process of PTS receptors is poor understood but ____
Pex5 oligomer may act as a transient pore
75
polysome (def.)
group of ribosomes bound to an mRNA molecule like “beads” on a “thread
76
most integral membrane proteins of peroxisome are synthesized _____
on free polysome
77
integral membrane proteins are targeted and inserted _____
post-translationally into peroxisomal membrane
78
integral membrane proteins are targeted to peroxisome by various ____
membrane related PTS (mPTS)
79
mPTS have no ____
clear consensus sequence
80
hydrophobic trans-membrane segments of integral membrane proteins interact with ____
specific chaperone to prevent aggregation
81
integral membrane proteins and chaperone form ____ that is then _____
complex
targeted to receptor on peroxisomal membrane
82
PMP stands for ___
peroxisomal membrane proteins
83
chaperone/transporter for peroxisomal membrane proteins
pex19p
84
receptor for peroxisomal membrane proteins
pex3p
85
some organisms require an additional membrane protein receptor:
pex16p
86
PMP inserted into membrane through what mechanism?
unknown mechanism
87
Mature peroxisomes are generated by the uptake of ____
membrane and matrix proteins to distinct intermediates
88
peroxins (def.)
several protein families found in peroxisomes
89
peroxisome biogenesis method
1) early peroxins (ex. pex3p) are targeted to ER and translocated by Sec61p complex
2) peroxins are sorted to specific pre-peroxisomal domains within ER then exported into small vesicles/pre-peroxisomes
3)additional PMPs imported into pre-peroxisomes
4) additional matrix proteins imported to form peroxisomes
5) peroxisomes continue to grow by fission
90
1st peroxins that are used to make peroxisomes
pex3p - receptor for integral membrane protein
91
pre-peroxisomes also called___
ghosts
92
pre-peroxisomes become peroxisomes by the addition of ____ after ___
matrix proteins
integral proteins
93
organelle the contributes membranes for de novo peroxisome biogenesis
ER
94
Yeast: Peroxisomes originate from
modifying vesicular pathways at the ___
ER
95
Mammals: Peroxisomes originate from
combination of modifying vesicular pathways at the ____
ER and mitochondria
96
____ is a key factor for the formation of pre-peroxisomal vesicles
Pex3
97
lipid droplets are tethered to peroxisomes by tethering protein: ____
spastin
98
effect of lipid droplet tethering to peroxisomes on lipid metabolism (2)
1) decrease of the size of a lipid droplet over time
2) degradation of lipids from the droplet accelerates
99
spastin knockdown with RNAi result
reduced lipid transfer to peroxisomes
100
glycosome (def.)
variant of peroxisome
101
Trypanosoma brucei (the parasite that causes ____) compartmentalizes glycolysis in the _____
sleeping sickness
glycosome
102
Identification of divergent T. brucei Pex3 led to the discovery that _____
glycosome biogenesis is essential for parasite growth
