Biology: 3.3 Respiration Flashcards
What is respiration?
A series of enzyme catalysed reactions which release chemical energy from organic molecules in order to synthesise ATP.
Where does glycolysis take place?
In the cytoplasm and does not require oxygen.
What happens in glycolysis?
1: The phosphorylation of glucose
2: Splitting of 6C hexose bisphosphate formed into 2x 3C triose phosphate and then to glycerate-3-phosphate molecules
3: The oxidation of each of these to 3C pyruvate.
4: With a yield of 2xATP produced by substrate level phosphorylation and 2 molecules of NADH/H+
Where does the link reaction take place?
In the matrix of the mitochondrion.
What happens in the link reaction?
If oxygen is available, the pyruvate produced in the cytoplasm is transported into the matrix of the mitochondria.
1: 3C pyruvate molecules are converted to 2C acetate through the loss of a carbon atom.
2: Carbon dioxide is produced
3: Hydrogen is also lost
4: NAD is reduced by the hydrogen to HADH/H+
5: Acetate is activated by combining with co-enzyme A to produce acetyl co-enzyme A.
Where does the Krebs cycle take place?
Each acetyl co-enzyme A enters the krebs cycle. It takes place in the matrix of the mitochondria.
What happens in the Krebs cycle?
1: Acetate group from the acetyl co-enzyme A is picked up by a 4C acid, to produce a 6C compound - coenzyme A is regenerated in the process.
2: 4C acid regenerated via a series of 6C and 5C intermediates - 2 atoms of carbon lost in 2xCO2 (decarboxylation).
3: 8 hydrogen atoms are lost and are used to reduce NAD and FAD
4: 1xATP produced (by substrate level phosphorylation), 3x NADH/H+, 1x FADH/H+ and 2x CO2 produced for each turn of the Krebs cycle.
Describe the passage of electrons in the electron transport chain?
1: NADH/H+ donates electrons on the hydrogen atoms to the first of a series of electron carriers in the electron transport chain.
2: Electrons from these atoms provide energy for the first proton pump and protons from the hydrogen atoms are pumped into the inter-membrane space.
3: The electrons pass down electron carriers releasing electron energy to fuel the proton pumps.
4: At the end of the chain, the electrons combine with protons and oxygen to form water: 2H+ + 2e- + 1/2 02 > H2O.
Describe the passage of protons in the electron transport chain.
1: Inner membrane is impermeable to protons and so the protons accumulate in the inter-membrane space.
2: The concentration of protons in the inter-membrane space becomes higher than in the matrix, so a concentration gradient is set up, and maintained by the proton pumps.
3: In membrane are stalked particles which are channels through which protons flow back into the mitochondrial matrix. ATP synthetase is associated with each channel. Protons flow back through these channels and their electrical potential energy produces ATP: ADP + Pi > ATP + H2O.
4: Oxygen is final electron acceptor and combines with protons and electrons to form water.
Why can’t the link reaction and the krebs cycle take place under anaerobic conditions?
Coenzymes NAD and FAD can’t be reoxidised and therefore made available to pick up hydrogen.
How does anaerobic respiration occur in animals?
NADH/H+ transfers the hydrogen to pyruvate to form lactic acid. (Lactic acid production is reversible if oxygen becomes available.)
How does anaerobic respiration occur in plants?
NADH/H+ transfers the hydrogen to pyruvate to form ethanol and CO2. (alcoholic fermentation is not reversible - the ethanol is toxic and will eventually kill the cells.
What is the glucose yield under anaerobic conditions?
2ATP per molecule of glucose.
Why does the cell not generally produce the theoretical maximum number of ATP?
1: ATP is used to move pyruvate, ADP, NADH/H+ and FADH/H+ across the mitochondrial membrane.
2: The proton gradient may be compromised by proton leakage across the inner mitochondrial membrane, rather than passing through ATP synthetase.
3: Molecules may also leak through membranes.
What is the efficiency equation?
Actual value x100
Max possible value
