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
2
Q
Organelle biogenesis
A
- includes protein targeting, membrane assembly, morphology, motility,
replication, degradation, and inheritance during cell division
3
Q
Semi-autonomous
A
- organelle replication controlled by both nuclear genome & organelle genome
- both mitochondria and chloroplast are
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
5
Q
Mitochondrial outer membrane
A
- permeable to ions & small molecules
- contains porins (‘barrel-shaped’ integral membrane proteins with large internal channel)
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
7
Q
Mitochondrial intermembrane space
A
- high [H + ]
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
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)
10
Q
Fusion
A
- the combining of a mitochondrial inner and outer membrane to form a singular mitochondria
11
Q
Fission
A
- processes of a mitochondria/chloroplast dividing to form two sister mitochondria/cloroplasts
12
Q
Organelle homeostasis
A
- rates of fission versus fusion control number, size and extent of inter-connections
of mitochondrial network
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
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
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
16
Q
Lipid microdomain
A
- mediates recruitment of Drp1 (and ER tubule) in
mitochondrial outer membrane - enriched in cardiolipin (mitochondrial-specific membrane phospholipid)
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)
18
Q
Photosynthesis
A
- happens in chloroplasts
- CO2+H2O+sun -> O2+energy-rich carbs -> CO2+ATP
19
Q
Chloroplast envelope
A
consists of outer and inner membranes
20
Q
Chloroplast Outer Membrane
A
- contains porins
- not as permeable to ions/small molecules as OMM
21
Q
Chloroplast intermembrane space
A
between outer and inner chloroplast membranes
22
Q
Chloroplast inner membrane
A
- highly impermeable
- various transporters
23
Q
grana thylakoids
A
flattened membranous discs arranged in stacks
24
Q
Stromal thylakoids
A
flattened membranous discs arranged between stacks
25
thylakoid membrane
* site of ATP synthase
* maintain H+ gradient in thylakoid lumen
26
thylakoid lumen
* aqueous interior of thylakoid
* high H+ concentration
27
stroma
* aqueous interior - inside envelope, outside of thylakoids
* enzymes involved in carb synthesis and plastid genome
* contains ribosomes
28
stromules
* long stroma-filled membrane tubules
* connect chloroplast
29
Organelle tethering complex
- ***formed by the linking of Mfn1/2 together in a GTP-dependent manner during mitochondrial fusion of outer membrane***
30
chloroplast fission
* how chloroplasts multiply
* ring-like structures formed by FtsZ and PD tighten and pinch organelle into two daughter chloroplasts
31
FtsZ division machinery
* involved in chloroplast fission
* internal machinery - on stromal side of inner membrane
32
FtsZ1 and FtsZ2
* FtsZ division machinery
* soluble stromal proteins
* spontaneously assemble into long, filamentous polymers at equator on inner membrane surface
33
FtsZ-(Z-) ring
formed by FtsZ1/2 at future chloroplast division site
34
ARC3, MinD, MinE
* soluble, stromal proteins
* mediate initial positioning of FtsZ proteins at equator
35
Bak and Bax
- ***mediate proper Mfn1/2 binding (e.g., prevention of ‘self’ binding)***
36
ARC6
* 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
Plastid dividing (PD) machinery
* in chloroplast outer membrane
* recruited by ARC6
* PDV1/2
38
PDV1 and PDV2
* 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
PD-ring
* wraps around outside of chloroplast
* tightening causes constriction of outer envelope (GTP hydrolysis)
40
ARC5
* cytoplasmic, soluble dynamin-related GTPase protein
* assembles into "spiral-like" structures to form PD-ring
41
Stromal import sequence
* 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
TOC complex
* stromal import sequence recognized by this complex at surface of chloroplast
* multi-protein complex
* binding involves GTP
43
TIC complex
* precursor protein transferred through Toc complex and then through this adjacent complex
* adjacent to each other at contact sites
44
stromal processing enzyme
cleaves stromal-import sequence
45
Phospholipiase D
- ***converts cardiolipin (moves from inner
to outer membrane) into phosphatidic acid***
46
Hsp93
* 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
Thylakoid targeting sequence
* how folded protein is imported into thylakoid membrane
* contains di-arginine sequence
48
SRP-dependent pathway
* 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
Phosphatidic acid
- ***‘cone-shaped lipid’***
- causes outer membrane curvature inward and promotes
Mfn1/2-mediated membrane fusion (via GTP hydrolysis)
50
pH-dependent import pathway
* 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
OPA1
- ***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
Thylakoid lumenal protease
removes thylakoid-targeting sequence on mature protein
53
Thylakoid molecular chaperones
mediate folding of mature protein in thylakoid lumen
54
Prohibitin
- ***ensures that OPA1-mediated fusion occurs only between ‘different’ inner membranes (i.e. prevents ‘self’ fusion of cristae within same mitochondrion)***
55
Matrix targeting sequence
- ***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
Cytosolic molecular chaperones
- ***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
Cytosolic Hsp70
- ***a cytosolic molecular chaperone maintain conformation of nascent protein in
partially unfolded, import-competent state***
58
mRNA localization
- ***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
Mitochondrial RNA cloud
- ***mRNAs encoding mitochondrial proteins often enriched in cytoplasm surrounding
mitochondria***
60
Import receptor complex
- ***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
Tom20 and Tom22
- ***integral outer mitochondria membrane proteins that make up the import receptor complex***
62
General import pore
- ***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
Tom40
- ***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
Inner membrane channel
- ***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
Time 23 and Tim17
- ***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
Membrane contact sites
- ***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
Matrix processing protease
- ***cleaves matrix-targeting sequence***
68
Matrix Hsp70
- ***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
H+ electrochemical gradient
- ***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
Matrix molecular chaperones
- ***required for final folding of imported, cleaved protein in matrix***
- represents an additional (4th ) requirement for energy
input in mitochondrial matrix protein import
71
Chloroplasts
- ***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
