Component 1.3 - Aerobic Respiration Flashcards
Overview of respiration
- Metabolic pathway as it is a series of enzyme catalysed reactions
- The reactions are catabolic
- Break down of energy rich molecules containing high energy C-H, C-C, C-OH bonds to form low energy bonds (difference is released and used to attach P to ADP)
Definition of aerobic respiration
The release of large amounts of energy made available as ATP, from the breakdown of molecules, with oxygen as the terminal electron acceptor.
Where does glycolysis occur?
In the cytoplasm
Why does glycolysis occur in the cytoplasm?
Because glucose cannot pass through the mitochondrial membrane
Why is it important that glucose is phosphorylated in glycolysis?
- It will be more reactive so less activation energy for enzyme controlled reactions
- Polar and therefore less likely to diffuse out of the cell.
What are the steps of glycolysis?
1) Glucose is phosphorylated by two molecules of ATP
2) This produces hexose biphosphate (6C)
3) Hexose biphosphate splits into two molecules of triose phosphate (3C)
4) The two triose phosphate molecules are dehydrogenated
5) This makes two molecules of reduced NAD and oxidises the molecules to 2 pyruvate
6) This synthesis produces 2x2(4) molecules of ATP by substrate-level phosphorylation
What is the net gain of ATP in glycolysis per molecules of glucose?
2 molecules of ATP are used,
4 molecules of ATP are made by substrate level phosphorylation
6 are made by oxidative phosphorylation.
Net gain of 8 molecules of ATP
Describe substrate-level phosphorylation in glycolysis
The phosphate from the triose phosphate converts ADP to ATP without the involvement of an electron transport chain.
How many molecules of ATP can one molecule of reduced NAD make?
3
Overall reaction of glycolysis
Glucose + 2NAD(oxidised) + 2ADP + 2Pi -> 2 pyruvates + 2NAD(reduced) + 2ATP + heat
Where does the link reaction occur?
The mitochondrial matrix
What happens in the link reaction?
1) Pyruvate is dehydrogenated
2) This forms one molecule of reduced NAD
3) Pyruvate is also decarboxylated (forming CO2)
4) This leaves acetate (2C) and coenzyme A (coA) which combine to form acetyl coenzyme A
Describe the Krebs cycle
1) Acetate from Acetyl coenzyme A combines with 4C acid to form 6C acid and coA is regenerated
2) 6C acid is dehydrogenated and decarboxylated, making reduced NAD, co2 and 5C acid.
3) 5C is dehydrogenated and decarboxylated, making reduced NAD and regenerated 4C. One molecule of ATP is made my substrate level phosphorylation.
4) 4C is dehydrogenated twice forming reduced NAD and reduced FAD
4) 4C can combine with AcCoA to repeat the cycle
What is the function of the Krebs cycle?
Liberating energy from carbon bonds via reduced intermediates to provide ATP and NAD, with the release of carbon dioxide.
What else is fed into the Krebs cycle at 3 different points?
H2O
How many times does decarboxylation happen in krebs and where?
Twice, between 6C and 5C and between 5C and 4C by decarboxylase
At the end of the Krebs cycle what has happened to the acetate fragment?
Completely broken down into CO2 and water
How many times does dehydrogenation happen in krebs and where?
4 times, between 6C and 5C, 5C and 4C, 4C and 4C, 4C and 4C which combines with AcCoA
Overall what does Krebs produce?
One ATP
Three molecules of reduced NAD
One molecule of reduced FAD
Two molecules of carbon dioxide
What does per molecule of glucose mean?
Due to hexose biphosphate splitting into two molecules of triose phosphate this causes two link reactions and two turns of the Krebs cycle meaning you have to double the numbers.
How many molecules of ATP can reduced FAD make?
2, due to it being oxidised in the electron transport chain
Where is the electron transport chain located?
The cristae of the inner mitochondria/ inner mitochondrial membrane
Describe the passage of electrons in the electron transport chain
1) Reduced NAD and FAD donates electrons of its hydrogen atoms to the electron carriers.
2) High energy electrons provide energy for the first proton pump to pump H+ ions into the inter-membrane space.
3) The electrons pass along the chain, providing energy for each of the proton pumps
Describe the passage of H+ ions in the electron transport chain
1) Proton pumps powered by NAD on inner mitochondrial membrane pump H+ ions into inter-membrane space
2) Concentration of H+ ions higher in inter membrane space than matrix
3) This creates an electrochemical gradient which is maintained by proton pumps
4) H+ ions flow back through protein channels down a conc gradient (chemiosmosis). Flow through ATP synthetase and this causes the combination of ADP and a phosphate ion to make ATP.
5) Oxygen is the final electron acceptor and combines with electrons and protons to form water.
Why is 38 molecules of ATP a theoretical yield?
1) ATP is used to move Pyruvate, ADP, reduced NAD and FAD across the mitochondrial membrane
2) The proton gradient may be compromised by proton leakage across the inner mitochondrial membrane rather than through ATP synthetase
3) Molecules can leak through membranes
Describe what is meant by decarboxylated and dehydrogenated?
What enzymes perform these reactions?
Decarboxylation - removal of CO2 by decarboxylase
Dehydrogenation- removal of hydrogen by dehydrogenase
Why is not all energy made available to the cell?
- Some is lost as heat
- Trapped as chemical energy in ATP
How many molecules of ATP are yielded from one molecule of glucose?
Glycolysis - 2 x NAD = 6
- 2 from substrate level phosphorylation
Link reaction - 2 x NAD = 6
Krebs cycle - 6 x NAD = 18
- 2 x FAD = 4
- 2 from substrate level phosphorylation
Total = 38
What could be the problem if there is a low oxygen consumption in mitochondria?
1) Enzymes are not functioning properly
2) No NAD being produced for electron transport chain so no O2 is needed
Why does a drug that stops proton gradient cause weight loss and an increase in body temp.
- Reduced proton gradient
- No ATP produced by ATP synthetase
- More glucose broken down by respiration so fat is used as respiratory substrate
- Heat is byproduct and therefore heat produced
- more active transport
Why are isotonic and cold solutions used?
Isotonic to prevent cell lysis and cold to slow enzyme activity.
