OXPHOS, fatty acids Flashcards
(126 cards)
1
Q
Why can’t animals make glucose from fatty acids?
A
Because Acetyl-CoA can’t be converted back to pyruvate (link reaction is one-way)
2
Q
What is linoleic acid known as?
A
Omega 6 - the 1st n you hit when counting backwards is 6 in
3
Q
What is the main stored form of fat in adipose tissue?
A
Triacylglycerol (TAG)
4
Q
Which hormones stimulate lipolysis of TAG in adipose tissue?
A
Glucagon, epinephrine, cortisol
5
Q
What enzyme breaks down TAG into fatty acids and glycerol?
A
Hormone-Sensitive Lipase (HSL)
6
Q
What are the products of TAG breakdown?
A
3 free fatty acids (FFA) and 1 glycerol
7
Q
Where does glycerol from TAG go? What for?
A
To the liver for gluconeogenesis
8
Q
What must happen to fatty acids before they can be oxidised?
A
They must be activated by attaching to CoA
9
Q
Which enzyme activates fatty acids?
A
Acyl-CoA synthetase
10
Q
How are long-chain fatty acids transported into mitochondria?
A
Via the carnitine shuttle
11
Q
What does the carnitine shuttle exchange?
A
Acyl-CoA and carnitine to form acyl-carnitine
12
Q
Where does β-oxidation occur?
A
In the mitochondrial matrix
13
Q
What are the 4 repeating steps of β-oxidation?
A
Oxidation, hydration, oxidation, thiolysis
14
Q
What are the enzymes of β-oxidation in order? Remember this is oxidation, hydration, oxidation, thiolysis
A
Acyl-CoA dehydrogenase, enoyl-CoA hydratase, hydroxyacyl-CoA dehydrogenase, β-ketothiolase
15
Q
What is the ATP yield from complete oxidation of palmitate (16C)?
A
Approximately 106 ATP
16
Q
What is different about oxidation of unsaturated fatty acids?
A
They require extra enzymes (e.g. isomerase, reductase)
17
Q
What is the final product of odd-chain fatty acid oxidation?
A
Propionyl-CoA, which will enter TCA as succinyl-CoA not Acetyl-CoA
18
Q
How is propionyl-CoA converted to succinyl-CoA?
A
By carboxylation and rearrangement reactions
19
Q
Which cofactor is required for methylmalonyl-CoA mutase?
A
Vitamin B12
20
Q
Can animals convert fat into glucose?
A
No, because the link reaction is irreversible
21
Q
Why can’t acetyl-CoA be used to make glucose?
A
Because its carbons are lost as CO₂ in the TCA cycle
22
Q
What does the liver convert acetyl-CoA into during starvation?
A
Ketone bodies
23
Q
Name the three ketone bodies.
A
Acetoacetate, β-hydroxybutyrate, acetone
24
Q
Which organs prefer to use ketone bodies?
A
Brain, heart, skeletal muscle
25
Which ketone body is reduced from acetoacetate?
β-hydroxybutyrate
26
Which enzyme interconverts acetoacetate and β-hydroxybutyrate?
β-hydroxybutyrate dehydrogenase
27
What determines the ratio of β-hydroxybutyrate to acetoacetate?
The mitochondrial NAD⁺/NADH ratio
28
Where does fatty acid synthesis occur?
In the cytoplasm
29
How is acetyl-CoA transported out of the mitochondria?
As citrate
30
What happens to citrate in the cytoplasm?
It is cleaved to acetyl-CoA and oxaloacetate
31
How is NADPH generated for fatty acid synthesis?
From conversion of malate to pyruvate
32
What is the committed step in fatty acid synthesis?
Acetyl-CoA → Malonyl-CoA
33
What enzyme catalyzes the committed step?
Acetyl-CoA carboxylase
34
Which cofactor is used by acetyl-CoA carboxylase?
Biotin
35
What activates acetyl-CoA carboxylase?
Citrate
36
What inhibits acetyl-CoA carboxylase?
AMP-activated protein kinase (AMPK), glucagon, epinephrine
37
What is the fatty acid synthase complex?
A multi-enzyme polypeptide with all FA synthesis steps
38
What is the carrier protein in fatty acid synthesis?
Acyl Carrier Protein (ACP)
39
What molecule is the growing fatty acid attached to during synthesis?
ACP
40
How many carbons are added per cycle of fatty acid synthesis?
2 carbons
41
What is the final product of fatty acid synthesis?
Palmitate (16C saturated fatty acid)
42
What reducing agent is used in FA synthesis?
NADPH
43
Which antibiotic inhibits enoyl-ACP reductase?
Triclosan
44
How are fatty acids transported in the blood?
Bound to serum albumin
45
How are triglycerides transported in blood?
In lipoproteins (e.g. chylomicrons, VLDL)
46
Which lipoprotein transports dietary fat from the intestine?
Chylomicrons
47
Which lipoprotein delivers liver-made fat to tissues?
VLDL
48
Which lipoprotein delivers cholesterol to tissues?
LDL
49
Which lipoprotein removes cholesterol from tissues?
HDL
50
What is oxidative phosphorylation?
The mitochondrial process that uses electrons from NADH and FADH₂ to drive ATP synthesis via the electron transport chain (ETC) and ATP synthase.
51
Where does oxidative phosphorylation occur?
In the inner mitochondrial membrane.
52
What are the two mitochondrial membranes?
Outer membrane (porous) and inner membrane (impermeable to polar molecules).
53
What are cristae?
Highly folded structures of the inner membrane that increase surface area for oxidative phosphorylation.
54
What are the two NADH shuttles?
Glycerol-3-phosphate shuttle and malate-aspartate shuttle.
55
Where is the glycerol-3-phosphate shuttle used?
In muscle; it converts cytoplasmic NADH to mitochondrial FADH₂.
56
Where is the malate-aspartate shuttle used?
In liver and heart; it transports NADH into the mitochondrial matrix.
57
What is E° (standard reduction potential)?
A measure of a molecule's affinity for electrons; more positive means higher tendency to be reduced.
58
How is ΔG° related to ΔE°?
ΔG° = -nFΔE°, where n = # of electrons and F = Faraday constant (96.5 kJ/V·mol).
59
What is the total ΔE° from NADH to oxygen?
+1.14 V
60
How much free energy is released by oxidation of NADH?
Approximately -220 kJ/mol
61
How much energy is needed to make 1 ATP?
About +30.5 kJ/mol
62
How many ATP are produced per NADH?
~2.5 ATP
63
How many ATP are produced per FADH₂?
~1.5 ATP
64
What is the electron donor to Complex I?
NADH
65
What is the electron donor to Complex II?
FADH₂ (via succinate in the TCA cycle)
66
What is the electron acceptor of Complex IV?
Oxygen (O₂), which is reduced to water.
67
What is Complex I called?
NADH-Coenzyme Q Oxidoreductase (or NADH dehydrogenase).
68
What cofactors does Complex I use?
Flavin mononucleotide (FMN) and 6-7 iron-sulfur (Fe-S) centers.
69
How many protons does Complex I pump?
4 H⁺ per NADH
70
What is Complex II called?
Succinate-Coenzyme Q Oxidoreductase
71
What enzyme is shared between Complex II and the TCA cycle?
Succinate dehydrogenase
72
What cofactor does Complex II use?
FAD (covalently bound)
73
Does Complex II pump protons?
No
74
What is the role of Coenzyme Q (ubiquinone)?
A lipid-soluble mobile electron carrier between Complexes I/II and III.
75
What is Complex III called?
Coenzyme Q–Cytochrome c Oxidoreductase
76
What are the main components of Complex III?
Fe-S center, cytochrome b, and cytochrome c₁
77
How many protons does Complex III pump?
4 H⁺ per pair of electrons
78
What is cytochrome c?
A small, water-soluble protein that carries electrons from Complex III to IV.
79
What is Complex IV called?
Cytochrome c oxidase
80
What does Complex IV contain?
Cytochromes a and a₃, and copper ions (CuA and CuB)
81
How many protons does Complex IV pump?
2 H⁺ per pair of electrons
82
What is the final electron acceptor in the ETC?
Oxygen (½O₂), forming H₂O
83
What is the proton motive force?
The electrochemical gradient of protons across the inner membrane used to drive ATP synthesis.
84
What are the two parts of ATP synthase?
F₀ (membrane channel) and F₁ (catalytic subunits in the matrix)
85
What subunit rotates in ATP synthase?
The γ (gamma) subunit
86
What is the function of the β subunits in ATP synthase?
They perform the catalytic synthesis of ATP.
87
What is the ATP-ADP translocase?
A transport protein that exports ATP and imports ADP across the inner membrane.
88
Why does exporting ATP cost energy?
ATP is more negatively charged than ADP, so it weakens the electrical gradient.
89
How much of the proton gradient is used by ATP-ADP translocase?
About 25%
90
What are reactive oxygen species (ROS)?
Highly reactive byproducts from partial reduction of oxygen in the ETC.
91
Name three ROS molecules.
Superoxide (O₂⁻), hydrogen peroxide (H₂O₂), hydroxyl radical (OH•)
92
What enzyme removes superoxide?
Superoxide dismutase (SOD)
93
What enzyme removes hydrogen peroxide?
Catalase
94
What inhibits Complex I?
Rotenone (insecticide), Amytal (barbiturate)
95
What inhibits Complex IV?
Cyanide, azide, and carbon monoxide (CO)
96
How does cyanide inhibit Complex IV?
It binds ferric iron (Fe³⁺) in cytochrome a₃, blocking electron flow.
97
What is tight coupling in mitochondria?
Electron transport is tightly linked to ATP synthesis; no ATP is made without ADP and O₂.
98
What happens to ETC if no ADP is present?
Electron transport stops; proton gradient becomes too strong to pump more H⁺.
99
How is oxidative phosphorylation regulated?
Primarily by the availability of ADP and oxygen (respiratory control).
100
What is the efficiency of oxidative phosphorylation?
About 40% (rest is lost as heat)
101
Which proton pumping complex pumps the least protons per pair of electrons?
Complex IV
102
Describe how molecules with different standard reduction potentials work on each other
↑+veEo Oxidises ↓ +veEo
– ↓ +veEo Reduces ↑+veEo
103
What is the committed intermediate in fatty acid synthesis?
Malonyl-CoA
104
What is the function of ubiquitin in protein metabolism?
It tags proteins for degradation by the proteasome.
105
What is the sequence of enzymes in ubiquitination?
E1 (activating), E2 (conjugating), E3 (ligase).
106
What is the 26S proteasome composed of?
19S regulatory subunit (recognition) and 20S core (protease activity).
107
Where does amino group removal primarily occur?
In the liver.
108
Which amino acids are primarily degraded in muscle?
Branched-chain amino acids (leucine, isoleucine, valine).
109
What do aminotransferases do?
Transfer an α-amino group to α-ketoglutarate to form glutamate.
110
What vitamin is required for transaminase activity?
Pyridoxal phosphate (from vitamin B6).
111
What enzyme performs oxidative deamination of glutamate?
Glutamate dehydrogenase.
112
Where is glutamate dehydrogenase found?
In the mitochondria, mainly in the liver.
113
What is the first step of the urea cycle?
NH₄⁺ + CO₂ + 2 ATP → carbamoyl phosphate via carbamoyl phosphate synthetase I.
114
Which enzyme converts carbamoyl phosphate and ornithine into citrulline?
Ornithine transcarbamoylase.
115
Where does citrulline go after it's formed in the mitochondria?
It is transported into the cytosol.
116
What is formed by argininosuccinate synthetase?
Argininosuccinate from citrulline and aspartate.
117
What does argininosuccinase produce?
Arginine and fumarate.
118
What enzyme completes the urea cycle by producing urea?
Arginase.
119
What happens to the fumarate produced in the urea cycle?
Converted to malate, then oxaloacetate, and can enter gluconeogenesis.
120
What is the glucose–alanine cycle?
Muscle converts amino acids to alanine, which goes to the liver to become glucose.
LIKE THE LACTATE PYRUVATE CYCLE BUT WITH AMINO ACIDS INSTEAD
121
What is nitrogen fixation?
Conversion of atmospheric N₂ into NH₄⁺ by nitrogenase in bacteria.
122
What is glutamine synthetase?
Enzyme that forms glutamine from glutamate and NH₄⁺ using ATP.
123
What defines an essential amino acid?
It cannot be synthesized by the body and must come from the diet.
124
What is a limiting amino acid?
The essential amino acid present in the shortest supply relative to the body’s needs.
125
What is a high-quality protein?
A protein that contains all essential amino acids in the correct proportions.
126
What are examples of high-quality protein sources?
Animal proteins like eggs, meat, and dairy.
