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MCG > LEC36: Transport into Mitochondria, Peroxisomes, & the Nucleus > Flashcards

LEC36: Transport into Mitochondria, Peroxisomes, & the Nucleus Flashcards

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1
Q

what % of proteins go through the secretory pathway versus stay in the cytosol and are targeted elsewhere? where else might they be targeted?

A

30% of proteins are handled by secretory pathway at the ER

70% stay in cytosol or are targeted to mitochondria, nucleus, or peroxisomes

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2
Q

what % of liver volume do mitochondria comprise?

A

25%

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3
Q

size of mitochondria?

A

0.5-1 micron diameter

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4
Q

function of mitochondria?

A

generate ATP to be used as cellular source of energy

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5
Q

important structural features of mitochondria?

A

outer mitochondrial membrane, inner mitochondrial membrane with cristae forming big folds, membrane space in between the 2 membranes, mitochondrial matrix in middle of it all

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6
Q

structure(s) of outer mitochondrial membrane?

A

porous to molecules up to 5-10 kDa

contains a protein translocation apparatus, TOM

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7
Q

structure(s) of inner mitochondrial membrane?

A

inner membrane is 70% protein, is impermeable even to protons

inner membrane is highly invaginated into cristae to increase surface area (cristae are variable)

has TIM complex for transport of peptides across it

membrane potential across inner membrane

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8
Q

what is within the inner membrane, re: proteins?

A

protein complexes of the electron transport chain and ATP synthase complex that catalyzes formation of ATP from ADP

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9
Q

what creates membrane potential across inner membrane?

A

delta psi

matrix (inner) is negatively charged; inter membrane space (out) is highly positively charged

protons moving into the intermembrane space creates membrane potential

thus inner membrane is sealed tight to protons

makes it hard to get proteins into the mitochodria

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10
Q

what’s different between mitochondria in the skeletal muscle vs. liver?

A

muscles have lots of cristae; liver do not have much cristae

b/c liver is more involved in metabolism, and muscle is dedicated to ATP production

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11
Q

what to mitochondrion do in sperm?

A

in flagella - so sperm can swim

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12
Q

what is lodged w/in the inner mitochondria membrane in terms of proteins and molecules?

A

channel proteins for translocation of metabolites:

pyruvate, malate, acyl-CoA, amino acids

ions

ADP/ATP transporter

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13
Q

what is in the intermembrane space?

A

between the 2 membranes

contains enzymes that phosphorylate other nucleotides apart from ADP, eg nucleoside diphosphate kinase, which converts GDP -> GTP

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14
Q

what is in the mitochondrial matrix?

A

1) hundreds of enzymes, including those for oxidation of pyruvate, fatty acids, ketone bodies to acetyl-CoA
2) enzymes that catalyze amino acid oxidation
3) enzymes of tricarboxyic acid cycle and urea cycle
4) mitochondrial genome, ribosomes, tRNAs, molecular chaperones for folding newly synthesized & newly imported proteins

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15
Q

what is the structure of the mitochondrial genome?

A

circular

16,589 bp

encodes 13 proteins

2-50 copies of genome per mitochondria, so up to 1000/cell

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16
Q

what does mitocondrial genome encode?

A

tRNAs and rRNAs for its own ribosomes

mitochondrial genes are txn into mRNA and tln in matrix on mitochondrial ribosomes

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17
Q

what proteins does the mitochondrial genome encode?

A

subunits for several components of respiratory chain, including cytochrome c oxidase, NADH dehydrogenase, apocytochrome b

genes for protein synthesis within matrix: 22 tRNAs, 12S and 16S rRNA for mitochondrial ribosomes

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18
Q

can gene migration occur btwn the universal and mitochondrial genomes?

A

no!

b/c mitochondrial genome has different genetic code than universal genetic code

i.e. UGA is universal STOP codon; it is Tryptophan in mitochondria

AGG is R in universal code, STOP in mitochondrial genome

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19
Q

how do mitochondria come to exist?

A

they aren’t assembled; divide into 2 from 1 existing mitochondria

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20
Q

how are mitochondria inherited in mammals?

A

maternally

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21
Q

what is evidence of mitochondria’s prokaryotic origin?

A

endosymbiotic origin from prokaryotes, like chloroplasts in plants

evidence: prokaryotic character of irbosomes, molecular chaperones, and circular genome

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22
Q

where do most mitochondrial proteins come from?

A

synthesized on cytosolic ribosomes before targeting to outer membraen and post-translational import

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23
Q

what is the nature of mitochondrial targeting sequence?

A

**15-35 residuce N-terminal sequence of positive, basic amino acids **

it is cleaved in matrix by an endoprotease

also has a non-cleaved internal targeting sequence

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24
Q

when do proteins destined for mitochondria get transported?

what is the state of the peptide?

A

post-translationally

unfolded state

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25
what brings peptide to mitochondria? what does it do?
Hsp70 chaperone important b/c protein is imported in unfolded conformation, which Hsp70 maintains
26
describe how peptide enters mitochondria once it is chaperoned there from the ribosome
1) Hsp-70 bound peptide binds to receptor on outer mitochondrial membrane; is presented to TOM complex; enter through aqueous TOM40 translocation channel no energy involved 2) positively charged pre-sequence of peptide opens TIM complex on inner mitochondrial membrane electrophoretic effect occurs, b/c targeting sequence is positive compared to inner part of matrix TIM opens enough for peptide to get in through inner mitochondrial membrane 3) once in matrix, mitochondrial version of Hsp70 binds protein 4) Hsp70 pulls protein into matrix, helps fold it
27
what are all of Hsp70's functions?
1) keep protein unfolded in cytosol 2) pull protein in to mitochondrial matrix after presequence has entered through TIM complex of inner mitochondrial membrane 3) helps protein fold after it has entered matrix
28
when does the mitochondrial targeting sequence get cleaved?
once peptide is within the matrix
29
what happens if have a mutation in mitochondrial DNA?
may have genotypic mutation, but it may not express disease phenotype (although it may!) penetrance determines this - more copies of a mutation you have in genotype, more experiences in phenotype
30
what is leber's hereditary optic neuropathy (LHON) caused by?
missense mutation in subunit 4 of NADH-coQ reductase causes sudden onset blindness, hearing loss, mental retardation
31
what causes dystonia?
NADH-coQ reductase missense mutation in subunit 4 same mutation as LHON
32
what does aging due to mitochondria DNA?
rearranges mitochondrial DNA probably result of accumulation of reactive oxygen species with time humans over age 40 have increased mitochondrial DNA rearrangements compared to humans under age 40 leads to decreased energy production w/ age
33
what is the structure of peroxisomes?
small, single membrane organelle
34
what do peroxisomes do?
fatty acid B-oxidation aka they oxidize long chain fatty acids this generates **hydrogen peroxide** which **catalase **reduces to water and oxygen do plasmalogen synthesis - phospholipids found in omst eukaryotic cells, myelin membranes
35
what encodes peroxisomal proteins? where are they synthesized? when are they transported? how?
nuclear genes synthesized on cytosolic ribosomes imported post-translationally in folded state into peroxisome 2 C-terminal target sequences: PTS1, it is SKL a.as
36
what does catalse do?
reduces hydrogen peroxide to water and molecular oxygen works in peroxisomes
37
what are diseases related to peroxisomes? what are they caused by?
1) zellwegers syndrome - no import of any peroxisomal enzyme 2) adrenoleukodystrophy (ALD) - oxidation of very long chain fatty acids is defective; ALD gene is membrane transporter for long-chain fatty acyl CoA synthase from cytosol to peroxisome matrix
38
what does nucleus separate?
genetic material inside, separate from cytosol separates txn and tln, allowing another level of regulation compared w/ prokaryotes
39
what activites occur inside nucleus?
transcription mRNA splicing DNA replication ribosome biosynthesis
40
when does nucleus form?
nucleus is disassembled prior to mitosis, reforms afterward
41
what is size of nucleus?
largest organelle in cell 5-10 um diameter
42
what is membrane of nucleus like?
double lipied bilayer inner = nuclear lamina, gives nucleus tensile strength outer layer = rough ER membrane, they are contiguous
43
what/where is nuclear lamina?
lines inner surface of nuclear membrane meshwork of intermediate filament type proteins, lamins
44
how does transport into/out of nucleus occur?
via aqueous pores, nuclear pore complexes
45
what is the organization of chromatin?
nucleus houses all all genes, in 46 chromosomes each chromosome is very long and thin; presents packing problem DNA is packaged into chromatin which is further compacted into a 30 nm fiber these 30 nm fiber are interphase nucleus chromatin structure
46
what is the nucleolus?
where rRNA is transcribed, synthesized where ribosomal subunits are assembled most prominent strucutre within nucleus
47
describe the chormatin of the interphase nucleus
euchromatin (10% of which is transcribed) and heterochromatin, which is highly condensed and not trnscribed highly condensed chromatin is in close apposition to the lamina **euchromatin and heterochromatin define the interphase nucleus ** during mitosis, chromosomes condense into metaphse chromosomes that're more highly organized
48
where are the genes that encode rRNA?
in nucleolus, 200 copies of these genes, including 5.8S, 18S, 28S on 5 different chromosomes all are synthesized as a 45S precursor these locii localize to the nucleolus
49
describe process of ribosomal RNA biogenesis
they congregate in the nucleolus of the nucleus ribosomal mRNA are synthesized on chromsomes all around the nucleus by RNA Pol II the mRNA are exported from nucleus; translated on cytplasmic ribosomes ribosomal proteins then reenter nucleus, are transported to nucleolus, as does 5S RNA there, assemble w/ rRNA individual 40S and 60S pre-ribosomal aprticles are then delivered to cytosol
50
how many protein molecules enter nucleus / minute? how many mRNA? tRNA? how?
60,000 protein 50-250 mRNA 1000 tRNA all via 3,000 nuclear pore complexes
51
what is the nuclear localization sequence?
can exist anywhere on protein usually 4-8 a.as, rich in Arg and Lys, usually contains Pro
52
in what conformation do proteins enter nucleus?
folded
53
are nuclear export signals = NLS?
no nuclear export signal is distinct from nuclear localization sequence
54
when/is the nuclear localization cleaved?
never! because proteins shuttle between nucleus & cytoplasm or have to reenter nucleus as it reforms after mitosis
55
how do proteins enter/exit nucleus?
through nuclear pore complexes: 8 subunits long ring bidirectional transport occurs through NPCs
56
what is structure of the NPC?
nuclear pore complex 3000-4000 per nucleus each composed of ~100 diff proteins, collective mass is 125 Md has an 8 fold symmetry, contains central aqueous channel of 9 nm diameter and 15 nm length is several ring assemblies that occupy cytoplasmic face, inner core and nucleoplasmic face of structure filamens radiate out from both cytoplasmic and nucleoplasmic sides
57
describe process of protein entry into the nucleus via the NPC
if protein is made in cytosol, wants to go back to nucleus to ribosome 1) protein binds to karyopherin receptor karyopherin enters through NPC w/ protein attached 2) RAN-GTP causes disassembly of karyopherin complex, cargo protein is released 3) karyopherin is bound to RAN-GTP, they undergo export through NPC back to cytosol 4) cytosolic RAN-GAP protein promotes disassembly of karyopherin:RAN complex by catalyzing GTP hydrolysis in Ran karyopherin now free to recycle, pick up new cargo; Ran GDP can return into nucleus, and Ran ntd exchange factor, RAN Nef, catalyzes formation of Ran GTP to start cycle again
58
what is Ran? what are its forms/where? relations to GAP and GEF?
a small GTPase w/ co-factors that regulate nucleotide hydrolysis (Ran GAP) and ntd exchange (Ran GEF) Ran GAP: cytosol, so Ran GDP Ran GEF: nuclear, so Ran GTP
59
during process of secretion: is there a signal seuqnce? is signal sequence cleavable? co or post translational?
yes, signal sequence yes, cleavable, co-translational
60
during transport into mitochondria, is signal sequence cleavable? co or post translational?
yes cleavable post translatoinal
61
re: transport to nucleus, is signal sequence cleavable? co or post translational?
not cleavable post translational
62
for peroxisome, is signal sequence cleavable? co or porst translational?
not cleavable, and at C terminus post translational

MCG (77 decks)

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