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MCB2050 > Mitochondria and Chloroplast > Flashcards

Mitochondria and Chloroplast Flashcards

1
Q

Endosymbiont theory

A
  • irst eukaryotic common ancestor – formed from engulfed prokaryotic ‘ancestor’ cell
    developing internal membrane compartments (e.g., nucleus)
  • common ancestor cell engulfed and maintained endosymbiotic organism and other
    additional changes gave rise to cellular features now common in all eukaryotic cell
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2
Q

Organelle biogenesis

A
  • includes protein targeting, membrane assembly, morphology, motility,
    replication, degradation, and inheritance during cell division
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3
Q

Semi-autonomous

A
  • organelle replication controlled by both nuclear genome & organelle genome
  • both mitochondria and chloroplast are
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4
Q

Mitochondria

A
  • double-membrane-bound organelle
  • organelle possesses wide range of shapes & sizes
  • contain their own DNA (genome)
  • organelle biogenesis
  • semi-autonomous
  • mitochondria often form ‘mitochondrial network’
  • highly dynamic structure
  • mitochondrial tubules are mobile and undergo fusion and fission
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5
Q

Mitochondrial outer membrane

A
  • permeable to ions & small molecules
  • contains porins (‘barrel-shaped’ integral membrane proteins with large internal channel)
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6
Q

Mitochondrial inner membrane

A
  • lies adjacent to outer membrane; forms ‘folds’ (cristae) that
    extend into organelle’s interior (provide increased surface area)
  • impermeable; maintains H + gradient, site of ATP synthase
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7
Q

Mitochondrial intermembrane space

A
  • high [H + ]
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8
Q

Mitochondrial matrix

A
  • aqueous interior
  • site of TCA cycle, ATP from oxidative phosphorylation
  • contains mitochondrial genome; circular DNA, varies
    between species in size, copy and gene number
  • contains ribosomes; used for translation of
    mitochondrial genome-encoded proteins
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9
Q

Mitochondrial network

A
  • highly branched, long & interconnected
    series of tubules
  • allows for cell-wide co-ordination of organelle’s functioning and biogenesis
  • highly dynamic structure; mitochondrial tubules are mobile and undergo fusion and fission (occurs in response to environmental stimuli, developmental status, and/or overall energy requirements of cell)
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10
Q

Fusion

A
  • the combining of a mitochondrial inner and outer membrane to form a singular mitochondria
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11
Q

Fission

A
  • processes of a mitochondria/chloroplast dividing to form two sister mitochondria/cloroplasts
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12
Q

Organelle homeostasis

A
  • rates of fission versus fusion control number, size and extent of inter-connections
    of mitochondrial network
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13
Q

ER tubules

A
  • encircle mitochondrion (via change in ER shape) at future fission site and initiate constriction = ER subdomain MAM
  • mediated by lipid ‘microdomain’ in mitochondrial outer membrane
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14
Q

Drp1

A
  • member of dynamin GTP-binding protein family responsible for scission of other cellular membranes
  • recruited from cytoplasm to constriction site and assemble into helices (DRP1 ‘ring’) around surface of mitochondrial outer membrane
  • recruitment mediated by lipid ‘microdomain’ in mitochondrial outer membrane
  • interacts with cardiolipin at constriction site
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15
Q

Cardiolipin

A
  • mitochondrial-specific membrane phospholipid
    normally only found in inner membrane - recruited from inner to outer membrane at constriction site
  • found plentifully in lipid ‘microdomain’ in
    mitochondrial outer membrane
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16
Q

Lipid microdomain

A
  • mediates recruitment of Drp1 (and ER tubule) in
    mitochondrial outer membrane
  • enriched in cardiolipin (mitochondrial-specific membrane phospholipid)
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17
Q

Mitofusins: Mfn1 and Mfn2

A
  • integral outer membrane proteins; possess cytoplasmic-facing GTPase domain and long, coiled-coil, protein-protein interaction domain
  • located on adjacent mitochondria - link together in
    GTP-dependent manner to form ‘organelle tethering complex’
  • proper Mfn1/2 binding (e.g., prevention of ‘self’ binding)
    regulated by other mitochondrial outer membrane
    proteins (Bak and Bax)
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18
Q

Photosynthesis

A
  • happens in chloroplasts
  • CO2+H2O+sun -> O2+energy-rich carbs -> CO2+ATP
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19
Q

Chloroplast envelope

A

consists of outer and inner membranes

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20
Q

Chloroplast Outer Membrane

A
  • contains porins
  • not as permeable to ions/small molecules as OMM
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21
Q

Chloroplast intermembrane space

A

between outer and inner chloroplast membranes

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22
Q

Chloroplast inner membrane

A
  • highly impermeable
  • various transporters
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23
Q

grana thylakoids

A

flattened membranous discs arranged in stacks

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24
Q

Stromal thylakoids

A

flattened membranous discs arranged between stacks

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25
Q

thylakoid membrane

A
  • site of ATP synthase
  • maintain H+ gradient in thylakoid lumen
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26
Q

thylakoid lumen

A
  • aqueous interior of thylakoid
  • high H+ concentration
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27
Q

stroma

A
  • aqueous interior - inside envelope, outside of thylakoids
  • enzymes involved in carb synthesis and plastid genome
  • contains ribosomes
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28
Q

stromules

A
  • long stroma-filled membrane tubules
  • connect chloroplast
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29
Q

Organelle tethering complex

A
  • formed by the linking of Mfn1/2 together in a GTP-dependent manner during mitochondrial fusion of outer membrane
30
Q

chloroplast fission

A
  • how chloroplasts multiply
  • ring-like structures formed by FtsZ and PD tighten and pinch organelle into two daughter chloroplasts
31
Q

FtsZ division machinery

A
  • involved in chloroplast fission
  • internal machinery - on stromal side of inner membrane
32
Q

FtsZ1 and FtsZ2

A
  • FtsZ division machinery
  • soluble stromal proteins
  • spontaneously assemble into long, filamentous polymers at equator on inner membrane surface
33
Q

FtsZ-(Z-) ring

A

formed by FtsZ1/2 at future chloroplast division site

34
Q

ARC3, MinD, MinE

A
  • soluble, stromal proteins
  • mediate initial positioning of FtsZ proteins at equator
35
Q

Bak and Bax

A
  • mediate proper Mfn1/2 binding (e.g., prevention of ‘self’ binding)
36
Q

ARC6

A
  • controls tightening of FtsZ-ring
  • interaction with ring signals stard of chloroplast constriction process
  • binds to plastid dividing (PD) machinery in chloroplast outer membrane
37
Q

Plastid dividing (PD) machinery

A
  • in chloroplast outer membrane
  • recruited by ARC6
  • PDV1/2
38
Q

PDV1 and PDV2

A
  • hetero-dimeric, integral outer transmembrane proteins recruited by binding to ARC6 at midway point in dividing chloroplast
  • IMS-facing domains interact with IMS-facing domain of ARC6
  • also bind to ARC5 at division site on outer membrane surface
39
Q

PD-ring

A
  • wraps around outside of chloroplast
  • tightening causes constriction of outer envelope (GTP hydrolysis)
40
Q

ARC5

A
  • cytoplasmic, soluble dynamin-related GTPase protein
  • assembles into “spiral-like” structures to form PD-ring
41
Q

Stromal import sequence

A
  • at protein’s N-terminus
  • Encriched in hydroxylated residues (S/T) and small hydrophobic residues (no amphipatic a-helix like mitochondria)
  • cleaved ollowing protein import into stroma
42
Q

TOC complex

A
  • stromal import sequence recognized by this complex at surface of chloroplast
  • multi-protein complex
  • binding involves GTP
43
Q

TIC complex

A
  • precursor protein transferred through Toc complex and then through this adjacent complex
  • adjacent to each other at contact sites
44
Q

stromal processing enzyme

A

cleaves stromal-import sequence

45
Q

Phospholipiase D

A
  • converts cardiolipin (moves from inner
    to outer membrane) into phosphatidic acid
46
Q

Hsp93

A
  • chaperone protein
  • acts as molecular motor (ATP conformational changes that pull protein into stroma and prevents back sliding of protein back into cytoplasm and assists with protein folding
  • recognizes emerging precursor protein
47
Q

Thylakoid targeting sequence

A
  • how folded protein is imported into thylakoid membrane
  • contains di-arginine sequence
48
Q

SRP-dependent pathway

A
  • pathway where the thylakoid-targeting sequence is recognized by an SRP which binds an SRP receptor on the thylakoid membrane to translocate protein into lumen
  • precursor protein in stroma maintained in partially unfolded, import-competent state
49
Q

Phosphatidic acid

A
  • ‘cone-shaped lipid’
  • causes outer membrane curvature inward and promotes
    Mfn1/2-mediated membrane fusion (via GTP hydrolysis)
50
Q

pH-dependent import pathway

A
  • pathway where the folded protein is imported into the thylakoid lumen by di-arginine-containing thylakoid targeting sequence and unique receptor/translocon complex at thylakoid membrane
  • precursor protein fully folded in stroma
  • relies on energy from proton gradient
51
Q

OPA1

A
  • integral inner membrane-bound mitofusin;
    contains intermembrane space-facing GTPase domain
  • mediates inner membrane fusion mediated
  • OPA1 proteins on adjacent inner membranes
    interact in GTP-dependent manner to promote
    membrane fusion (via GTP hydrolysis)
  • OPA1 binding regulated by other mitochondrial
    inner membrane proteins (e.g., Prohibitin)
52
Q

Thylakoid lumenal protease

A

removes thylakoid-targeting sequence on mature protein

53
Q

Thylakoid molecular chaperones

A

mediate folding of mature protein in thylakoid lumen

54
Q

Prohibitin

A
  • ensures that OPA1-mediated fusion occurs only between ‘different’ inner membranes (i.e. prevents ‘self’ fusion of cristae within same mitochondrion)
55
Q

Matrix targeting sequence

A
  • signal sequence located at nascent protein’s N terminus
    consisting of amphipathic a-helix (enriched in positively-charged residues (R/K) on one side of helix and hydroxylated (S/T) residues on other side)
  • responsible for targeting nascent matrix protein
    to cytoplasmic surface of mitochondrion AND
    subsequent translocation across outer and
    inner membranes
  • most matrix-destined proteins possess a 20-50
    amino-acid-long matrix targeting sequence
56
Q

Cytosolic molecular chaperones

A
  • maintain conformation of nascent protein in
    partially unfolded, import-competent state
  • in cytoplasm, precursor (matrix-destined) protein
    synthesized on free ribosomes and recognized
    by cytoplasmic molecular chaperones
  • Ex. cytosolic Hsp70
  • enriched in vicinity of mitochondria surface due to
    diffusion and….. mRNA localization
57
Q

Cytosolic Hsp70

A
  • a cytosolic molecular chaperone maintain conformation of nascent protein in
    partially unfolded, import-competent state
58
Q

mRNA localization

A
  • mRNAs encoding mitochondrial proteins often enriched in cytoplasm surrounding
    mitochondria - ‘mitochondrial RNA cloud’
  • mediated by RNA-binding proteins located on mitochondrial outer surface
  • results in mitochondrial protein synthesis (translation)
    taking place immediately adjacent to mitochondrial surface
  • allows for site-specific (spatial) control of mitochondrial protein gene expression; facilitates efficient (post-translational) protein targeting to mitochondria
59
Q

Mitochondrial RNA cloud

A
  • mRNAs encoding mitochondrial proteins often enriched in cytoplasm surrounding
    mitochondria
60
Q

Import receptor complex

A
  • consist primarily of two integral mitochondrial outer membrane proteins, Tom20 and Tom22
  • binds and recognizes protein’s matrix-
    targeting sequence at the surface of the mitochondrion
  • also consist of several accessory proteins
61
Q

Tom20 and Tom22

A
  • integral outer mitochondria membrane proteins that make up the import receptor complex
62
Q

General import pore

A
  • consists primarily of integral outer mitochondrial membrane protein Tom40
  • referred to as “general” import pore; all (most) mitochondrial proteins (both matrix and membrane-bound) access mitochondria initially through Tom40
  • precursor protein passed from import receptor
    to general import pore in outer mitochondrial membrane
63
Q

Tom40

A
  • integral outer mitochondrial membrane protein that makes up the general import pore
  • forms transmembrane channel allows for protein translocation across (or into, for membrane proteins) the outer membrane
64
Q

Inner membrane channel

A
  • consists of integral inner mitochondrial membrane proteins Tim17, Tim23, and TIM44
  • precursor protein transferred through general
    import pore and then through adjacent inner
    membrane channel
  • general import pore and inner membrane channel
    adjacent to each other at contact sites
65
Q

Time 23 and Tim17

A
  • integral inner mitochondrial membrane proteins that (Tim44), make up the inner membrane channel
  • general import pore and inner membrane channel
    adjacent to each other at contact sites - contact sites maintained by interactions of Tom40 and Tim23/17 intermembrane-space-facing domains
66
Q

Membrane contact sites

A
  • places where outer and inner membranes are closely appressed – intermembrane space reduced or absent at contact sites
  • general import pore and inner membrane channel
    adjacent to each other at contact sites (maintained by interactions of Tom40 and Tim23/17 intermembrane-space-facing domains)
67
Q

Matrix processing protease

A
  • cleaves matrix-targeting sequence
68
Q

Matrix Hsp70

A
  • inner membrane channel accessory protein
  • located at matrix-face of inner membrane channel via binding to Tim44
  • acts as molecular motor (‘ratchet’); Tim44-bound Hsp70 undergoes ATP-dependent conformational changes that ‘pulls’ protein into matrix AND prevents ‘back sliding’ of protein back into cytoplasm
69
Q

H+ electrochemical gradient

A
  • during protein translocation into the mitochondria, import is driven partially by H+ electrochemical gradient
    across inner membrane – established during electron
    transport
  • [H +] intermembrane space > [H +] matrix
  • positively-charged residues in amphipathic matrix-
    targeting sequence are attracted (‘pulled’) to less
    positively-charged matrix
70
Q

Matrix molecular chaperones

A
  • required for final folding of imported, cleaved protein in matrix
  • represents an additional (4th ) requirement for energy
    input in mitochondrial matrix protein import
71
Q

Chloroplasts

A
  • double-membrane-bound plant cell organelle
  • semi-autonomous
  • site of photosynthesis (Ps)
  • involved in several other important metabolic processes (fatty acid and amino acid biosynthesis, nitrogen and sulfur assimilation, etc.)
  • highly mobile; move along cytoskeleton elements via molecular motors
  • chloroplasts often connected via stromules (ong, stroma-filled membrane tubules)
  • multiply by fission

MCB2050 (5 decks)

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