Citric Acid Cycle & Oxidative Phosphrylation Flashcards
Gylcolysis ends with 2 molecules of what?
2 molecules of pyruvate
Under aerobic conditions, pyruvate is transported from where to where?
Pyruvate is transported from the cytosol into the mitochondria matrix
What is pyruvate dehydrogenase complex responsible for?
It is responsible for its conversion to CO2 and the acetyl group of acetyal-CoA
What is pyruvate dehydrogenasecomplex made of?
3 Smaller subunits
Name the 3 enzymes that are the subunits of pyruvate dehydrogenase complex
E1= Pyruvate dehydrogenase
E2= Dihydrolipoyl transacetylase
E3= Dihydrolipoyl dehydrogenase
Fill in the blank: Pyruvate dehydrogenase
Pyruvte + ___ + ____ ——> ____ + CO2
Pyruvate + Thiamine Pyrophosphate + Lipoamide ——> Acetyl-dihydrolipoamide + CO2
Fill in the blank: Dihydrolipoyl transacetylase (E2)
____ + CoA ——> _____ + _____
Acetyl-dihydrolipoamide + CoA ——> Acetyl-CoA + Dihydrolipoate
Fill in the Blank: Dihydrolipoyl dehydrogenase (E3)
Dihydroolipoate + ______ ——> lipamide + ____ ——> FAD + ____ + H+
Dihydrolipoate + Flavin adenine dinucleotide (FAD) ——> Lipamide + FADH2 ——> FAD + NADH + H+
How many protons does FAD accept?
FAD accepts 2 Protons
What are 2 additional enzymes involved in pyruvate dehydrogenase reactions but not part of the complex?
- Pyruvate dehydrogenase kinase (PDK)
- Pyruvate dehydrogenase phosphate (PDP)
What does pyruvate dehydrogenase kinase do?
It phosphorylates pyruvate dehydrogenase by using ATP at 3 possible sites
Out of the 3 phosphorylation sites, what one is most important?
Site 1
What does pyruvate dehydrogenase phosphate do?
It reverse the effects of pyruvate dehydrogenase kinase
The ratios of products and substrates for pyruvate dehydrogenase reactions are important for what reason?
Regulation
What is the citric-acid cycle?
It is the final common pathway for the oxidation of fuel molecules: Carbs, fats and protein.
What do carbohydrates, fatty acids and some amino acids enter the citric acid cycle as?
Acetyl coenzyme A (acetyl CoA)
What are 3 other terms for the citric acid cycle?
- Citrate cycle
- Krebs cycle
- Tricarboxylic acid (TCA) cycle
Glycolysis makes a net of how many ATP?
2 ATP
Only a small amount of ATP available from glucose is extracted during what?
Anaerobic glycolysis
What does the citric acid cycle start with and where does it occur?
Process starts with the complete oxidation of glucose derivatives to carbon dioxide in a sequence of reactions, all takes place in the mitochondrial matrix
During the citric acid cycle, acetyl CoA is activated and oxidised to what?
CO2 and H2O
In order for oxidation to take place, what must also occur?
Reduction reaction of something else must also occur for oxidation to take place.
Many ATP molecules can be made from what?
By reduced cofactors such as NADH and FADH2 in the electron transport chain, via oxidative phosphorylation.
Give an 8 step summary of the citric acid cycle
- Acetyl-CoA —> Citrate (2C + 4C —>6C)
- Citrate —> Isocitrate (OH + H rearrangement)
- Isocitrate —>α-Ketoglutarate (6C —>5C + CO2 + NADH)
- α-Ketoglutarate —>Succinyl-CoA (5C —>4C-CoA + CO2 + NADH)
- Succinyl-CoA —>Succinate (4C-CoA —>4C + CoA + GTP) —>ATP
- Succinate —>Fumarate (4C —>4C + FADH2)
- Fumarate —>Malate (4C + H2O —>4C)
- Malate —>Oxaloacetate (4C —>4C + NADH)
All happens twice. 8 reactions total. 2 ATP per 1 glucose is produced
What happens in reaction 1 of the citric acid cycle?
Reaction 1 = Citrate synthase
- Condensation of acetyle CoA with oxalocetate to form citrate ( a C4 molecule)
- reaction is catalysed by citrate synthase, which is an allosteric enzyme.
What is the following allosteric enzyme inhibited by: Citrate synthase
NADH, ATP and succinyl-CoA
What happens in reaction 2 of the citric acid cycle?
Reaction 2=Aconitase
- Citrate is isomerized
What happens in reaction 3 of the citric acid cycle?
Reaction 3= Isocitrate dehydrogenase
- 1st of 4 oxidation-reduction reactions
- Isocitrate is oxidised, there is a reduction of NADH and a loss of one carbon atom as CO2
What is the following allosteric enzyme inhibited and activated by: Isocitrate dehydrogenase
Inhibited= ATP and NADH
Activated= ADP and NAD+
What happens in reaction 4 of the citric acid cycle?
Reaction 4= a-ketoglutarate dehydrogenase complex
- 2nd oxidation reduction reaction
- a-ketoglutarate dehydrogenase is a multi enzyme complex
What happens in reaction 5 of the citric acid cycle?
Reaction 5= Succinyl-CoA synthase
-Succinyl CoA is a thioester
- Thioesters are energy rich. Cleavage of the bond is linked to the phoshorylation of GDP
What is GDP?
Guanosine diphosphate
What can be done to make additional ATP in reaction 5 of the citric acid cycle which isnt a step in the overall cycle
The GTP that was produced can be used to make additional ATP. The ATP is produced by phosphoryl transfer with ADP
What happens in reaction 6 of the citric acid cycle?
Reaction 6= Succinate dehydrogenase
- 3rd oxidation reduction reaction
- Succinate is oxidised to fumarate
- FAD is reduced to FADH2
What happens in reaction 7 of the citric acid cycle?
Reaction 7= Fumarase
- Condensation reaction
- Fumarate—> Malate
How many reactions are involved in the citric acid cycle?
8 reactions
What happens in reaction 8 of the citric acid cycle?
Reaction 8=malate dehydrogenase
- final oxidation reduction reaction
- Malate oxidised to oxalocetate
- NAD+ reduced to NADH
-Oxaloacetate can re-enter into reaction 1 of the cycle
How many ATP is produced in the citric acid cycle?
2 ATP
What are the 3 points of control within the citric acid cycle? And what is the control point outside the cycle?
WITHIN:
1. Citrate synthase
2. Isocitrate dehydogenase
3. A-ketoglutarate dehydrogenase complex
OUTSIDE
1. Pyruvate dehydrogenase
Why do we ned points of control in the citric acid cycle?
We don’t want the cycle to be running constantly without a break.
How many ATP molecules are produced from the citric acid cycle?
0 ATP molecules
What does the metabolism of pyruvate produce?
- 3 NADH+H+
- 1 FADH2
What does ATP synthase do?
It synthesises ATP
What happens during the electron transport chain and chemiosmosis?
- A series of membrane bound proteins which electrons pass through in a series of redox reactions
- this creates energy
- the energy is then either given off as heat or used to drive a series of proton pumps to produce a concentration gradient between the mitochondrial matrix and the inter membrane space
What are the complexes that are involved in the electron transport chain and chemiosmosis in order?
Complex 1
Complex 2
Complex Q
Complex 3
Complex 4
Complex 5
What is complex 1 in the electron transport chain made of?
3 smaller proteins
1. Ubiquinone oxidoreductase
2. NADH oxidised by this complex
3. (NADH+ H+) + CoQ + 4H+ —> NAD+ + CoQH2 + 4H+
What are 3 or more key points of complex 2 in the electron transport chain?
- No protons are pumped
- 2nd entry point in the electron transport chain
- 2 electrons from FADH are sent to join with those from complex 1
What is Coenzyme Q in the electron transport chain?
- Ubiquinone
- It is Quinone with a hydrophobic tail
- It is an electron carrier
- Transfers electrons to complex 3 through the Q cycle
What are 3 key points of complex 3 in the electrn transport chain?
- Cytochrome= Heme containing electron transport protien, can only transport 1 electron at a time using the Q cycle
- Releases 4 protons into the intermembrane space, now a total of 8 protons are in the space
- Cytocrome c redutase= cytochrome b + c and rieske subunits
The Q cycle happens within complex 3, what does this involve?
2 steps in total
Cycle 1:
- Ubiquinol binds to site 1 and donates 2 electrons that go into 2 separate pathways
- 1 goes to Fe-S clusters and then to cytochrome C which is reduced
- 1 goes to cytochrome b, then to CoQ bound at the second site which becomes the CoQH radical
- Pumps 2H+ into the intermembrane space
Cycle 2:
- a repeat of cycle 1
- Electron donated by cytochrome b stabilises the CoQH+ radical CoQH2
- Another 2 H+ ions are pumped out
What are 3 key points in complex 4 of the electron transport chain?
-Cytochrome c oxidase= cytochrome a +a3 + heme and copper groups
- Oxidises cytochrome c, transferring 2 electrons to oxygen which becomes water
- 2 protons pumped into the inter membrane space
What are 3 key points of complex 5 in the electron transport chain?
- ATP synthase= Synthesises ATP
- F0= forms a rotor mechanism that is constantly pronated an depronated
- F1= as F0 rotates, it changed the orientation and conformation of F1 , catalysing the formation of ATP from ADP
- Every 4 H+ = 1ATP
- What part of the cell contains the enzymes that perform the citrate cycle?
Mitochondrial matrix
- How many carbon atoms are in an oxaloacetate molecule, which joins with an acetyl group during the first reaction of the citrate cycle?
a. 2
b. 3
c. 4
d. 6
c. 4
- How many carbon atoms are in a citrate molecule?
a. 2
b. 3
c. 4
d. 6
d. 6
- Oxidative decarboxylation which occurs during steps 3 and 4 of the citrate cycle, is the removal of both——— and ——- from a substrate at the same time.
- carbon dioxide
- hydrogen
- How many ATPs are produced in the conversion of pyruvate to citrate? (Include ATP formed from the oxidative phosphorylation of reduced enzymes).
A. 1
B. 2
C. 3
D. 4
E. 5
c. 3
- Which one of the following statements concerning the citric acid cycle is correct?
A. The cycle produces 3 moles of NADH and 1 mole of FADH2 per mole of acetyl CoA oxidised to CO2 and H2O.
B. The cycle is inhibited by malate.
C. Elevated levels of NADH stimulate oxidation of acetyl CoA by the cycle.
D. The oxidation of acetate leads to a net consumption (loss) of oxaloacetate.
E. The conversion of one mole of isocitrate to one mole of succinate results in the formation of five moles of ATP (including those obtained form oxidative phosphorylation.
A. The cycle produces 3 moles of NADH and 1 mole of FADH2 per mole of acetyl CoA oxidised to CO2 and H2O
