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Mitochondrial Energy Metabolism - Coggle Diagram
Mitochondrial Energy Metabolism
Mitochondria
site of anaerobic respiration
oxidation of pyruvate to form ATP
TCA cycle
mitochondrial electron transport (MET)
spherical or rod shaped
present in higher numbers in highly active cells such as guard cells and companion cells, and typically fewer present in plants than in plants
a single complex and highly reticulate network
utrastructure
dual membrane system
smooth inner/outer membranes
most metabolites and ions can pass pores of outer membrane
inner membrane utilizes transporters for metabolites and ions
inner invaginated membranes known as cristae
70% of composition made up of proteins
impermeable to H+
contains transporters for metabolites and ions
osmotically active
site of MET system
protein import typically occurs at appressed sites
inner/outer membrane close to cristae
protein translocation complexes
imported proteins have signal sequence
intermembrane space is aqueous space between inner and outer membranes surrounding mitochondria
matrix is aqueous space between cristae and inner membrane; site of TCA cycle enzymes
semiautonomous
endosymbiotic theory
theory that mitochondria derived from primitive proteobacterium
explains dual membrane system and maternal inheritance pattern
Prokaryotic features include:
divides by fission
replicates independently of nucleus
70S ribosomes for protein synthesis
Mitochondrial Genome
contains own expression machinery, including DNA, RNA and 70S Ribosomes
Contains limited number of genes
tRNAs
Ribosome components--rRNAs and ribosomal proteins
some MET components
Ploidy Levels
ct DNA + mt DNA equals about 1/3 Nuclear DNA
mitochondrial genome decreases polyploidy with maturity
meristem: polyploid
immature leaf: mtDNA > ctDNA
mature leaf: ctDNA > mt DNA
Most proteins imported from cytosol
Pyruvate/Malate Uptake
Monocarboxylate transporter conducts pyruvate/OH antiport
dicarboxylate transporter conducts malate/Pi antiport
Malic enzyme changes malate to pyruvate; a unique plant rxn
Tricarboxylic Acid Cycle (TCAC)
oxidizes pyruvate to CO2
synthesizes ATP, NADH, and FADH
NADH formed when 2e- and 2H+ are transferred from an organic compound to NAD+
FADH formed by succinate dehydrogenase, with FAD cofactor tightly bound to SDH in membrane
All of these synthesis reactions involved in conserving energy
oxidation of pyruvate yields 4 NADH, 1 FADH,
complete oxidation of glucose yields 8 NADH, 2 FADH, 2 ATP
located in mitochondrial matrix
enzymes located in matrix may form super-complex (including citrate synthase, aconitase, isocitrate dehydrogenase, fumarase, malate dehydrogenase)
formation of citrate by citrate synthase, with free energy of acetic anhydride bond used to form C-C bond
the enzymes located in the inner membrane include pyruvate dehydrogenase, a-ketoglutarate, succinic anyhydride, and succinate dehydrogenase
Anhydrides used as high -energy intermediates and CoA, a sulfur protein, contains enough free energy for bond formation in its thioester
ATP formed by substrate-level phosphorylation via Succinyl-CoA synthase
direct transfer of Pi from substrate to ADP
free energy in Succinyl-CoA synthase
decarboxylations completely convert pyruvate to CO2 via pyruvate dehydrogenase, isocitrate dehydrogenase, and a-ketoglutarate dehydrogenase
FAMILIARIZE WITH P15
Regulation
a-Ketoglutarate Dehydrogenase
activity sets cycle direction
irreversible reaction
bifurcated TCAC without enzyme
bifurcated TCA cycle operates in algae when O2 limited
NADH produced by a-ketoglutarate arm
NADH and FADH consumed by succinate arm
postulated to operate in higher plants
allosteric inhibition by NADH
Pyruvate dehydrogenase regulated by protein phosphorylation and allosteric regulators
Citrate synthase controlled by allosteric inhibitors ATP and NADH
Isocitrate dehydrogenase allosterically inhibited by NADH
"bottom up"
Unique Plant Features
Succinyl-CoA synthase: plants synthesize ATP (and sometimes GTP) while animals synthesize GTP
Malic Enzyme
converts malate to pyruvate
mechanism to oxidize malate: produced by glycolosis malate shunt and in TCA cycle
not present in animals
Anapleurotic Reactions
Acetyl CoA
changes fatty acids to lipids in membranes
changes isoprenoids to terpenes, gibberellins, carotenoids, sterols, and abscisic acid
a-Ketoglutarate changes glutamate to porphyrins (which then become chlorophylls, phycocyanins, phytochromes, cytochromes, and catalases) and to amino acids (which become proteins)
Oxaloacetate
creates Alanine, which becomes proteins
Adenylate Energy Charge (AEC)
primary control mechanism
decreased ATP synthesis occurs with increased ADP levels
Mitochondrial Electron Transport (MET)
converts energy in NADH/FADH into ATP
NADH oxidation via MET
2e- and 2H+ transferred from NADH to MET and used to reduce O2
up to 3 ATPs synthesized via chemiosmotic mechanism
FADH oxidation via MET
up to 2 STPs synthesized via chemiosmotic mechanism
contains protein complexes in inner membrane that diffuse through it to interact
Complex I
NADH dehydrogenase
associated with FMN cofactor and several Fe-S proteins
transfers electrons to ubiquinone
Complex II
Succinate dehydrogenase (SDH) component
FADH and 3 Fe-S proteins transfer e- to ubiquinone
Ubiquinone Pool
Complex III
Cytochrome C1
transfers electrons to COX
aqueous mobile carrier
analogous to PC
Complex IV
AKA COX
2 Cu centers
reduces O2 to H2O
Inhibited by cyanide
Complex V
ATP synthase
utilizes H+ gradient to synthesize ATP
electron flow-- MEMORIZE P58
Unique MET plant features:
Rotenone-Resistant NAD(P)H Dehydrogenase
bypasses one phosphorylation site to yield 2 ATP/NAD(P)H
resistant to drug rotenone
functions with NADH or NADPH
External NAD(P)H dehydrogenase
located on external face of membrane
bypasses one phosphorylation site to yield 2 ATP/NAD(P)H
Alternate Oxidase (AO)
resistant to cyanide
sensitive to SHAM, BHAM, CLAM
no energy conservation
dimer formation via disulfide bridge
activated by pyruvate and a-ketoglutarate
utility:
generates heat, attracting pollinators, making plants cold tolerant
electron overflow hypothesis
excess electrons shunted to AO
saturation of ubiquinone pool
ADP limiting
allosteric regulation
prevents accumulation of superoxides
addresses stress responses inhibiting respiration
MEMORIZE P64: MET ADDITIONS IN PLANTS
ATP Synthesis is coupled to MET
ADP/O ratio
ATP formed per 2 e- through MET
energy conservation along path (H+ ejection)
F0F1-ATPase
multimeric enzyme complex
F0: hydrophobic core
forms channel that H+ pass through
at least 3 protein subunits
3 ATP formed per 1 rotation
F1: Hydrophilic catalytic subunits
peripheral membrane protein complex on matrix side of F0
At least five different protein subunits
catalytic sites
regulatory subunits modulate activity
Chemiosmotic mechanism:
as H+ moves through complex internal F0 stalk, it rotates relative to F1
Free energy from rotary motion used to form phosphodiester bonds
Catalysis occurs on beta subunits of F1
3H+/ATP per one rotation of CF0
ATP yield per hexose
substrate level phosphorylation: 4ATP
2 from glycolysis
2 from TCA
oxidative phosphorylation
10 NADH
2 from glycolosis
8 from TCA
2 FADH from TCA
PMF Across Inner Mitochondrial Membrane
inner mitochondrial membrane impermeable to H+
MET generates negative PMF across inner mitochondrial membrane
H+ translocated from matrix to intermembrane space
dissipation of electrochemical gradient occurs through ATP synthase
[change in] E is main component of PMF in mitochondria; large buffering capacity of cytosol and matrix prevent large pH changes
H+ Gradient and Membrane Transport
phosphate transporter
moving OH- out equivalent to moving H+ in
electroneutral exchange consumes chemical potential but not electrical potential
as long as change in pH is maintained, PO4- in matrix sufficient for ATP synthesis
Adenylate transporter
active transport driven by change in electrical potential
ATP synthesized in matrix but used outside mitochondria
4 H+/ATP required to synthesize and move ATP out of mitochondria
other transporters driven by change in E
Oxidative phosphorylation
equals ATP synthsis via chemiosmotic mechanism
complex I, III, and IV generate H+ gradient across inner mitochondrial membrane
complex V (ATP synthase) uses H+ gradient to synthesize ATP
Complete oxidation of sucrose to CO2 via glycolysis and TCAC
ATP yield per sucrose
cytosolic NADH assumed to be oxidized via external dehydrogenase
non-phosphorylating pathways assumed to be inoperative
calculated using theoretical ADP/O values
free energy recovered from sucrose
recovery of free energy from ATP using only glycolysis: 4%
actual free energy of ATP formation in vivo is 50 kJ mol
free energy not recovered lost as heat
Whole Plant Respiration
affected by O2, temp, water status
developmental state
generally lower rates than in animals
respiration occurs in green tissue
respiration of 30-60% of photosynthate
incresaed metabolic activity = increased respiration
gas impact:
3-5% CO2 inhibits respiration
2-3% O2 inhibits respiration
injured by other oxidases