Week 3=> Electron Transport and OxiPhos, Mito Transporters, one-carbon and nuc meta Flashcards
(90 cards)
1
Q
Where is most energy from ATP synthesis derived from?
A
From the oxidation of the reduced electron carriers made during glycolysis and the citric acid cycle
2
Q
Hoe much NADH and FADH2 are generated per mole of glucose?
A
10 moles of NADH and 2 moles of FADH2
3
Q
Where are the electron transport complexes bound?
A
Inner mitochondrial membrane
4
Q
Why is the surface area of the inner mitochondria dramatically greater than the outer membrane?
A
Due to folds termed cristae
5
Q
What does green fluorescent protein (GFP) label?
A
Mitochondria in cultured cells => specifically the mitochondrial cristae
6
Q
What does magenta dye labelled?
A
Mitochondrial DNA
7
Q
Mitophagy
A
Degradation of damaged mitochondria by the autophagy pathway
8
Q
What is nutrient availability and mitochondrial efficiency coupled to?
A
Fission and fusion
9
Q
Fission characteristic
A
- Nutrient excess
- Impaired OxPhos and ATP synthesis
- Increased mito fission
- Severe stress and mito damage
- Between hyperfused and tubular morphology
10
Q
Fusion characteristics
A
- Nutrient limited
- Increased OxPhos and ATP synthesis
- Increased mito fusion
- Mild stress
- more fragmented (or short tubular) morphology
11
Q
Mitochondrial complex that contains succinate dehydrogenase from the TCA cycle
A
Complex II
12
Q
Mitochondrial complex that transfer protons into the intermembrane space
A
Complexes I, III, and IV
13
Q
Mitochondrial complex that the ATP synthase couples proton import to ATP synthesis
A
Complex V
14
Q
What shuttles bring NADH generated in the cytosol into the mitochondrial matrix?
A
DHAP/glycerol-3-phosphate shuttle or malate/aspartate shuttle
15
Q
Enzymes, other proteins, and other cofactors involved in electron transfer complex I
A
Receives electrons from oxidation of NADH and passes to coenzyme Q (CoQ)
16
Q
Enzymes, other proteins, and other cofactors involved in electron transfer complex II
A
Electrons from oxidations of succinate are passed to CoQ
17
Q
Enzymes, other proteins, and other cofactors involved in electron transfer complex III
A
Oxidizes reduced to CoQ and reduces cytochrome C
18
Q
Enzymes, other proteins, and other cofactors involved in electron transfer complex IV
A
oxidizes cytochrome c and reduces O2 to H2O
19
Q
Faraday’s constant
A
96.5 kJ mol-1 V-1
20
Q
ΔEo’
A
Difference in reduction potential between redox couples [Eo’(acceptor)-Eo’(donor)]
21
Q
Exergonic
A
reactions release energy (-ΔG)(lower product)
22
Q
Endergonic
A
reactions absorb energy (+ΔG)(higher product)
23
Q
The standard free energy change (ΔGo) for the hydrolysis of for ATP under standard conditions?
A
31 kJ/mol
24
Q
Describe the redox reactions in the respiratory chain?
A
Each redox reaction in the respiratory chain is exergonic and electrons from from low to high potential carriers
25
Coenzyme Q
* hydrophobic electron carrier embedded in the inner mito membrane by long isoprenoid chain
* Undergoes hydrogenation of ring carbons to alternate between and oxidized quinone (ketone) and reduced hydroquinone (alcohol)
26
Cytochromes
* heme-containig proteins with distinct visible spectra based on the redox state
27
The efficiency of oxidative phosphorylation =
number of molecules of ATP synthesized per pair of electrons transported
28
Evidence of chemi-osmotic coupling
* Proton and electrochemical (∆Ψ) gradients can be measured.
* An intact inner mito membrane is required for coupling
* Electron transport complexes span the membrane
* Uncoupling agents dissipate the proton gradient
* artificial generation of proton gradient permits ATP synthesis without electron transport
29
What dissipates the H+ Gradient?
Uncoupling agents
30
Which complex appears as a nod-like projection into the matric from the inner membrane of the cristae?
Complex V
31
What is the outer mitochondrial membrane (OMM) permeable to?
to molecules <10 kDa due to the voltage-dependent anion channel (VDAC)
32
How does VDAC work for the mitochondria?
VDAC closes when mitochondria are stressed and under hypoxic conditions
33
Hypoxic conditions
conditions where there is a lack of oxygen in the body or in the environment
34
What is the inner mitochondrial membrane (IMM) permeable to?
Is permeable to small, uncharged ad hydrophobic molecule s(water, oxygen, and CO2 pass easily)
35
What is the inner mitochondrial membrane (IMM) impermeable to?
Impermeable to large, charged, or hydrophobic molecules
36
Symport
solution is co-transport of ions of opposite charge
37
Antiport
Counter-transport of ions with same charge (preferred mechanism in most instances)
38
ATP synthase/complex X
H+ into matrix
39
Adenine nucleotide translocase
ATP towards OMM/cytosol, and ADP towards matrix
40
Phosphate antiport
OH- towards OMM/cytosol, and H2PO4- towards matrix
41
Phosphate symport
2H+ and HPO4 2- towards Matrix
42
Pyruvate symport
2H+ and pyruvate towards matrix
43
Dicarboxylate antiport
Dicarboxylate, HPO4 2- towards OMM/cytosol, and decarboxylate towards matrix
44
Tricarboxylate antiport
Citrate towards OMM/cytosol, and Dicarbocylate towards matrix
45
Solute carrier 25 (SLC25) family
* Family of membrane proteins
* Transport across IMM
* 53 specificities
* Most antiport
* Encoded by nuclear genes and have common structure and mechanism
46
What do SLC25 transport?
Phosphate, ADP/ATP, carboxylates, co-factors and amino acids acids the IMM
47
Proton-coupled monocarboxylate transport system for pyruvate?
SLC16 family
48
"Gate" steps for mechanisms of SLC25 solute antiport
1) Solute in cytosol
2) m opens and c closed => transition of solute from cytosol across IMM
3) solute released into matrix
2) c opens while m closes => solute from matrix transition across IMM
4) solute released into cytosol
49
Most passively diffused by monocarboxylate transport across inner and outer membrane
acetate> propionate > beta-hydroxybutyrate > short-chain fatty acids
50
SLC16
* pyruvate carrier
* major substrate for mitochondrial oxidation and is generated outside mitochondria
* mechanisms of import is via a proton gradient driven symport (H+ and pyruvate anion cross membrane along the h+ ion gradient
51
Monocarboxylate transporters
SLC25 and pyruvate carrier (SLC16)
52
Dicarbocylate transporters
Malate carrier (SLC25S10) and alpha-ketoglutarate/malate transporter (SLC25A11)
53
Tricarboxylate transport
Citrate carrier (SLC25A1 or CIC)
54
SLC25A3
* phosphate transport
* At neutral pH there is a mic of HPO4 -2 and H2PO4- and passive diffusion will be slow or non-existent
* Transport of H2PO4- in exchange for hydroxyl anion probably predominates in the intermembrane space
* Presence of proton gradient favors the influx of phosphate in matrix via the symport or antiport mechanism
55
Phosphate pKa
2.1, 7.2, 12.3
56
Adenine Nucleotide Transporter (SLC24A4-6)
* specific for ATP and ADP
* most abundant mito membrane protein
* Active as dimer of 30 kDa monomers
* Strongly inhibited by low temp
* transport regulated by the proton gradient, which in actively respiring mitochondria favors ADP uptake and ATP export from the matrix
57
Specific inhibitors for Adenine Nucleotide Transporter (SLC24A4-6)
* bonkrekic acid and carboxytractylate bind to matric (m) and cytosolic (C) exposed conformation of the permease, respectively
58
SLC25A51
The IMM NAD+ transporter (because the IMM is impermeable to NADH and therefore "shuttle" mechanisms are used to transfer reducing equivalents across the inner membrane)
59
Malate/Aspartate shuttle system
Active in liver and heart and coupled to the reduction of NAD to Mito
60
Glycerol-3-phsophate/dihydroxyacetone phosphate (DHAP) shuttle
* important shuttle in brain and muscle and coupled to FAD reduction
* Glycerol-3-pohsphate is made by hydrolysis of triacylglycerol, which is prominent energy source of muscle. DHAP is a glycolytic intermediate
* Enzyme is on external side of the IMM
* Transfers electrons from FADH2 to Coenzyme Q of ETC
61
Genetic defects in SLC25 transporters
* 13 rare diseases related to mutations in SLC25 genes, all are autosomal recessive
* Difficult to treat and often lethal. Organ transplants are performed in some cases
62
Malate carrier (SLC25A10)
* also has low affinity for oxaloacetate, fumarate and succinate
* operates by an antiport mechanism; import of malate (or succinate) in exchange for HPO4 2-
* Role is to supply malate that is the counter ion for the tricarboxylate transporter
63
alpha-ketoglutarate/malate transporter (SLC25A11)
* Important transporter for the import of reducing equivalents into mitochondrial matrix (coupled with glutamate/aspartate carrier)
* Depends on reciprocal transport of phosphate
* In isolation, a main function of the carrier is to generate glutamate in the cytoplasm
64
Citrate Carrier (SLC 25A1 or CIC)
* Antiport type carrier that exports citrate to the cytoplasm
* Citrate export supplies cytosolic acetyl-CoA for fatty acid and cholesterol biosynthesis
* Depends on conversion of citrate to malate in cytoplasm by ATP-citrate lyase; malate is then used for counter transport of more citrate
65
One-carbon metabolism
Metabolic pathways that are connected to reaction involving the transfer of a single carbon (methyl group) in different oxidation states equivalent to methanol, formaldehyde, and formate
66
Most important carriers of C-1 groups
Folic acid and S-adenosylmethionine
67
What is S-adenosylmethionine a derivative of?
Methionine
68
One-Carbon groups
* Methanol (most reduced): methyl (-CH3)
* Formaldehyde: methylene (-CH2-)
* Formate (most oxidized): Formyl (-CHO) and methenyl (-CH=)
69
What are two major medical conditions that Folate decreases prevalence of?
Spina bifida and Anecephaly
70
Major carrier of 1-C units of amino acid and nucleotide metabolism?
Tetrahydrofolate (THF)
71
How does THF work?
Carriers methyl groups in different oxidation states
72
What is the source of the methyl group on THF?
Serine transfers a methyl-group to THF and is converted to glycine. Serine hydrocymethyltransferase
73
SAM or AdoMet
s-adenisyl-homocysteine
74
SAH or AdoHcy
S-adenosyl-homocysteine
75
Major chemicals in the methionine cycle and methylation
1) Methionine
2) S-adenosyl-methionine
3) S-adenosyl-homocysteine
4) Homocysteine
76
Methyltransferases reactions requiring SAM products
* Phosphatidylcholine
* Methylated proteins
* Creatine
* Other Methylated acceptors
77
Requirements for one-carbon metabolism and methylation
* folate
* serine
* Methionine
* B6 Riboflavin
* B12 Cobalamin
Additional methyl groups from betaine (BHMT)
78
What intermediate in 1-C pathways leads to production of both pyrimidines and purines?
5-methyltetrahydrofolate (5,10-CH3 THF)
79
Important application of methylation reactions
* DNA methylation
* Phosphatidylcholine synthesis
* Synthesis of carnitine, creatine, epinephrine, etc...
* Purine synthesis
80
DNA methylation application
* Methylation of cytosine to 5-methylcytosine on CpG 'islands"
* Catalyzed by DNA methyltransferases (DNMT)
* Inhibits transcription without changes in DNA sequence
81
Nucleotide synthesis de novo pathway
Bases are synthesized from amino acids, CO2, folate derivatives and PRPP
82
Nucleotide synthesis salvage pathway
Free bases from breakdown of nucleotide DNA or RNA react with PRPP
83
PRPP
Phosphoribosyl-pyrophosphate (PRPP) = Activated Ribose 5-phosphate
84
Pyrimidine nucleotide synthesis first forms ___
Uridine monophosphate (UMP)
85
Purine nucleotide synthesis first forms ___
inosine monophosphate (IMP)
86
Required substrates for IMP
PRPP, glutamine, glycine, aspartate, bicarbonate, methyl group for formyl tetrahydrofolate
87
What are the two regulatory sites of Ribonucleotide Reductase?
* One site to regulate overall activity
* One site to regulate substrate specificity
* This regulates of overall synthesis versus the relative amount of the different dNTPs
88
Nucleotide Degradation
1) Phosphorylase acts on nucleoside to generate base and ribose-1-phosphate
2) Purines are degraded to uric acid, which is secreted in urine. Pyrimidines are degraded into amino acids
89
What are purines degraded into?
Uric acid (for terrestrial reptiles, primates and many insects)
90
What do "other" organisms do to further process uric acid before excretion?
* Mammals (other than primates) ozidize uric acid to allantoin
* Bony fish oxidize uric acid to allantoic acid
* Cartilaginous fish and amphibian degrade allantoic acid to urea
* Marine invertebrates decompose urea to NH4+
