Citric Acid Cycle & Oxidative Phosphorylation Flashcards
What is the role of the Citric Acid Cycle in catabolism?
- Oxidise Acetyl-CoA to CO2
- Energy produced is conserved in NADH and FADH2
What did Hans Kreb discover stimulated pyruvate oxidation in the Citric Acid Cycle?
Certain organic acid anions
Dicarboxylic & Tricarboxylic Acids
What is the name of the enzyme that converts Pyruvate to Acetyl CoA?
Pyruvate Dehydrogenase (PDH)
How many enzyme types are in pyruvate dehydrogenase?
3
E1, E2, & E3
What does the pyruvate dehydrogenase reaction do to pyruvate?
Oxidises and Decarboxylates
What part of the cell does pyruvate dehydrogenase localise to?
Mitochondrial matrix
How is pyruvate dehydrogenase regulated?
Allosterically / Covalently
PDH OFF when ample fuel available and ON when energy low
Give an overview of what happens in the Citric Acid Cycle
- 4C Oxaloacetate & 2C Acetyl CoA condense to form 6C Citrate.
- 6C Citrate oxidised and decarboxylated back to 4C Oxaloacetate in a cycle of 7 enzymes
What are the products of the Citric Acid Cycle?
3x NADH
1x FADH2
1x GTP
2x CO2
Which of the metabolic intermediates in the Citric Acid Cycle are DICARBOXYLIC ACIDS?
4 carbon
* Succinate
* Fumarate
* Malate
* Oxaloacetate
5 carbon
* α-ketoglutarate
Which of the metabolic intermediates in the Citric Acid Cycle are TRICARBOXYLIC ACIDS?
6 carbon
- Citrate
- Isocitrate
What enzyme types are active in the Citric Acid Cycle?
- Synthase
- Isomerase
- Dehydrogenase
- Synthetase
- Hydratase
What is the sequence of metabolites in the Citric Acid Cycle?
Our City Is Kept Safe and Secure From Mobsters
1. Oxaloacetate
2. Citrate
3. Isocitrate
4. α-Ketoglutarate
5. Succinyl-CoA
6. Succinate
7. Fumarate
8. Malate
Give an overview of the metabolic transformations that occur in the Citric Acid Cycle
What is the energy output of the citric acid cycle?
1x GTP to 1x ATP
How many NADH and FADH2 are formed in one cycle of the Citric Acid Cycle?
3x NADH
1x FADH2
Why is the Citric Acid Cycle known as the “hub” of metabolism?
Because metabolites are constantly feeding IN for degredation and OUT for synthesis
Does the Citric Acid Cycle have a role to play in both catabolic and anabolic pathways?
Yes
What enzymes are regulated in the Citric Acid Cycle?
- Citrate Synthase
- Isocitrate Dehydrogenase
- α-Ketoglutarate-Dehydrogenase
Regulation of Pyruvate Dehydrogenase also important
How are the enzymes regulated in the Citric Acid Cycle?
Regulated allosterically by:
* Energy indicators e.g when energy indicators are HIGH (NADH, ATP), enzymes are turned OFF
* Product accumulation
* Substrate availability
What is Oxidative Phosphorylation?
The process of ATP formation due to electron transfer from NADH/FADH2 to O2
Is oxygen needed for Oxidative Phosphorylation?
Yes.
ALL catabolism in the presence of O2 converges to Oxidative Phosphorylation
Where does Oxidative Phosphorylation occur in the cell?
Inner Mitochondrial Membrane
Where respiratory electron carrier proteins & ATP synthase reside
How many membranes do mitochondria have?
2
Inner & Outer
Is the inner mitochondrial membrane more or less permeable that the outer mitochondrial membrane?
Inner membrane = LESS permeable
Outer membrane = MORE permeable
How many enzyme complexes make up the electron transport chain?
4
On inner mitochondrial membrane
How is the Proton Motive Force created during electron transfer?
By pumping of protons (H+) from mitochondrial matrix to mitochondrial intermembrane space through 3 of the protein complexes (I, III, & IV)
What are the THREE major types of electron transfer?
- Direct Transfer of electrons
- Transfer as hydrogen atom
- Transfer as hydride ion
Describe the sequence of electron transport in Oxidative Phosphorylation
Does proton pumping cause the inside of the inner mitochondrial membrane to be more negative than the outside?
Yes.
Creates electrical potential:
* INSIDE membrane -ve
* OUTSIDE membrane +ve
Name the major electron transport biomolecules that accept and donate electrons during the electron transport process
- Ubiquinone
- Iron-Sulfur Proteins
- Cytochromes
The last two are iron containing proteins
Which complex does Antimycin inhibit?
Complex III & IV
Which complex does Rotenone inhibit?
Complex I & Q
Which complex does Cyanide inhibit?
Complex IV & O2
How many protons are pumped across the inner mitochondrial membrane in the transport of electrons from 1 NADH to terminal oxygen?
10
How many protons are pumped across the inner mitochondrial membrane in the transport of electrons from 1 FADH2 to terminal oxygen?
6
What is the sequence of electrons carriers and complexes in the resiratory chain?
- Complex I: Transfers 2x electrons from NADH to Ubiquinone
- Complex II: Transfers electrons from Succinate to FADH2 to Ubiquinone
- Complex III: Transfers 2x electrons to 2 x 1 Cyt C & expulsion of 4 more protons from matrix to intermembrane space
- Complex IV: Transfers electrons from Cyt C to O2 & 2 protons transferred from matrix to intermembrane space
Does inhibition of electron transport block ATP synthesis?
Yes.
Inhibitors of electron transport block ATP synthesis and vice versa
What does ATP synthase make?
Makes ATP required to sustain life by a rotary mechanism
What type of enzyme is ATP synthase?
F-Type ATPase
Has two functional domains; F1 & F0
Is the F1 part of ATP synthase a peripheral or integral membrane protein?
Peripheral
How many subunits does the F1 part of ATP synthase possess?
9 subunits
5 different types
Describe the Fo part of ATP synthase
- Integral membrane protein
- Makes up proton pore
- Composed of 3 subunits
Who won a Nobel Prize for describing how ATP synthase works using the proton motive force?
John Walker
What type of reaction forms Citrate?
Condensation Reaction
Acetyl-CoA (2C) condenses with Oxaloacetate (4C) to form Citrate (6C)
Which enzyme is involved in the synthesis of Citrate?
Citrate Synthase
What type of reaction forms Isocitrate?
Isomerisation Reaction
Citrate isomerises to Isocitrate
Which enzyme is involved in the synthesis of Isocitrate?
Citrate Aconitase
What type of reaction forms α-Ketoglutarate?
1st Oxidative Decarboxylation
Key Exergonic Step:
* Oxidation of Isocitrate (6C) to α-Ketoglutarate (5C)
* First CO2 released
* NADH formed
Which enzyme is involved in the synthesis of α-Ketoglutarate?
Isocitrate Dehydrogenase
What type of reaction forms Succinyl-CoA?
2nd Oxidative Decarboxylation
2nd Key Exergonic Step:
* Addition of CoA & Oxidation of α-Ketoglutarate (5C) to Succinyl-CoA (4C)
* Second CO2 released
* Second NADH formed
Which enzyme is involved in the synthesis of Succinyl-CoA?
α-Ketoglutarate Dehydrogenase
Which enzyme is involved in the synthesis of Succinate?
Succinyl-CoA Synthetase
* Removal of CoA
* 1x GTP forms which converts to 1x ATP
What type of reaction forms Fumarate?
Oxidation
Succinate (4C) to Fumarate (4C)
Which enzyme is involved in the synthesis of Fumarate?
Succinate Dehydrogenase
* Flavoprotein
* Removal of 2H
* Formation of 1x FADH2
What type of reaction forms Malate?
Hydration
Fumarate (4C) to Matate (4C)
Which enzyme is involved in the synthesis of Malate?
Hydratase (Fumarase)
What type of reaction forms Oxaloacetate?
Oxidation
Malate (4C) to Oxaloacetate (4C)
Which enzyme is involved in the synthesis of Oxaloacetate?
Malate Dehydrogenase
* Removal of 2H
* Formation of NADH + H+
How many NADH molecules are produced in one turn of the citric acid cycle?
a) 2
b) 3
c) 12
d) 7
e) 4
3
Which ONE of the following set of enzyme reactions results in the production of NADH in the Citric Acid Cycle?
a) Isocitrate decarboxylase, Protein kinase A, Citrate synthase
b) Isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, Malate dehydrogenase
c) Isocitrate dehydrogenase, Isocitrate synthase, Malate dehydrogenase
d) Isocitrate dehydrogenase, Isocitrate synthase, Malate dehydrogenase
e) Fumarase, Succinate dehydrogenase, Citrate synthase
b) Isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, Malate dehydrogenase
Which ONE of the following intermediates of the Citric Acid Cycle has 5x carbons and 2x COO- (Carboxylic Acid anions)?
a) Succinate
b) Fumarate
c) Malate
d) Citrate
e) α-Ketoglutarate
e) α-Ketoglutarate
Which ONE of the following enzymes performs an oxidative decarboxylation to produce α-Ketoglutarate from Isocitrate?
a) Isocitrate decarboxylase
b) Citrate synthase
c) Isocitrate kinase
d) Isocitrate dehydrogenase
e) Isocitrate isomerase
d) Isocitrate dehydrogenase
Which ONE of the following is a major regulatory enzyme in the Citric Acid Cycle?
a) Isocitrate decarboxylase
b) Citrate synthase
c) Malate dehydrogenase
d) Aconitase
e) Hexokinase
b) Citrate synthase
Which ONE of the following enzymes converts Pyruvate to Acetyl-CoA?
a) Succinate dehydrogenase
b) Pyruvate decarboxylase
c) Pyruvate dehydrogenase
d) Pyruvate kinase
e) None of the above
c) Pyruvate dehydrogenase
The Citric Acid Cycle occurs in which ONE of the following locations?
a) Cytosol
b) Mitochondria
c) Endoplasmic reticulum
d) Nucleus
e) Plasma membrane
b) Mitochondria
Oxidation of one NADH results in the pumping of which ONE of the following number of protons into the mitochondria inter-membrane space?
a) 10
b) 8
c) 6
d) 4
e) 2
a) 10
Which ONE of the following is a mobile electron carrier in the electron transport chain?
a) Cytochrome C
b) Cytochrome A
c) Cytochrome A3
d) Cytochrome B
e) None
a) Cytochrome C
Which ONE of the following statements describes the F1 component of ATP synthase?
a) Is an integral membrane protein with 9 subunits
b) Is a peripheral membrane protein with 20 subunits
c) Is a peripheral membrane protein with 9 subunits
d) Is a channel through which protons flow
e) None of the above
c) Is a peripheral membrane protein with 9 subunits
