Respiration Flashcards
1
Q
define glycolysis
A
multi-step reaction in which a glucose molecule is broken down into two pyruvate molecules
2
Q
outline glycolysis
A
- each glucose molecule is phosphorylated twice in two separate processes by two ATP molecules (via kinase) to give fructose-1,6-biphosphate, raising the energy level of the molecule so that more useful energy can be extracted later for ATP synthesis (net 2 ATP molecules produced) via substrate-level phosphorylation
- each fructose-1,6-biphosphate molecule is split into two molecules of glyceraldehyde-4-phosphate (GALP) (via aldolase)
- oxidation of the two GALP molecules (via dehydrogenase and kinase) yields 2 molecules of pyruvate molecules, 4 ATP molecules and 2 reduced NAD molecules
- pyruvate molecules are then transported from the cytoplasm into the mitochondrial matrix, H atoms removed via glycolysis are carried to the mitrochondria via hydrogen carrier (NAD+) for oxidative phosphorylation, and then channeled across the mitochdonrial outer membrane to the cristae via a shuttle system
3
Q
what happens to pyruvate after glycolysis?
A
- glycolysis yields a net gain of 2 ATP molecules and 2 reduced NAD molecules per glucose molecule but this represents only a small amount of energy that can be extracted from glucose. much of the energy is still stored in its product, pyruvate. fate of pyruvate depends on presence of oxygen
- complete oxidation via link reaction, krebs cycle and oxidative phosphorylation: a lot of the energy released
- incomplete oxidation: no energy released, purpose is to regenerate NAD+
4
Q
define link reaction
A
link between glycolysis in the cytoplasm and krebs cycle in the mitochondrial matrix, involves oxidative decarboxylation of pyruvate and only occurs during aerobic respiration
5
Q
outline link reaction
A
- occurs in mitochondrial matrix
- carboxyl group removed from pyruvate molecule as CO2 (decarboxylation)
- 2 H atoms removed from each pyruvate molcule and carried by NAD+, forming one reduced NAD+ molecule per pyruvate (oxidation)
- reduced NAD+ molecule subsequently enters the electron transport chain for ATP synthesis via oxidative phosphorylation
- pyruvate combines with coenzyme A to form acetyl coenzyme A
- using a multi-enzyme complex (pyruvate dehydrogenase complex)
6
Q
state the purpose of the krebs cycle
A
series of enzymatically-driven reactions that occur in the mitochondrial matrix, H atoms released from organic molecules in the cycle are carried by hydrogen carriers (NAD+ and FAD) to the mitochondrial cristae for ATP synthesis via oxidative phosphorylation, substrate-level phosphorylation also occurs
7
Q
outline krebs cycle
A
- acetyl CoA from link reaction combines with oxaloacetate to form citrate, releasing coenzyme A to pick up more pyruvate molecules in the link reaction
- through decarboxylation and dehydrogenation, citrate is then oxidised into alpha-ketoglutarate, then succinate, then fumarate, then malate, with the regeneration of oxaloacetate at the end of the cycle to pick up more aceyl CoA
- 2 molecules of CO2 are released per turn of the cycle via oxidative decarboxylation (citrate to alpha-ketoglutarate, and alpha-ketoglutarate into succinate)
- H atoms released are carried by hydrogen carriers (NAD+ and FAD) to form reduced NAD (citrate to alpha-ketoglutarate, and alpha-ketoglutarate into succinate and malate to oxaloacetate) and reduced FAD (succinate into fumarate)
- each turn of the Krebs cycle yields 3 reduced NAD and 1 reduced FAD molecules, which then channel the H atoms to the mitochondrial cristae for ATP synthesis via oxidative phosphorylation
- each turn of the krebs cycle yields one ATP molecule directly via substrate-level phosphorylation (alpha-ketoglutarate to succinate)
- reduced NAD and reduced FAD will release electrons to the ETC for oxidative phosphorylation
8
Q
outline oxidative phosphorylation
A
- H atoms carried by hydrogen carriers (NAD+ and FAD) in the form of reduced NAD and reduced FAD to the mitochondrial cristae
- high-energy electrons in H atoms in reduced NAD are transferred to the first electron carrier of the ETC, electron carrier becomes reduced, NAD+ is regenerated for reuse in the link reaction and Krebs cycle
- high-energy electrons in H atoms in reduced FAD also transferred to an electron carrier in the ETC, regenerating FAD for reuse in the Krebs cycle
- in a series of redox reactions, excited electrons migrate from one electron carrier to another until they are finally accepted by oxyen, the final proton and electron acceptor. oxygen accepts protons from the mitochondrial matrix and electrons from ETC to form water
- electron carriers in the ETC are of progressively lower energy level. as electrons are transferred down the chain, energy is released
- electron carriers use this energy to pump protons in the matrix into the intermembrane space across the inner mitrochondrial membrane
- as the inner mitochondrial membrane is impermeable to protons, protons accumulate in the intermembrane space and this forms a proton reservoir, establishing a proton gradient across the inner mitochondrial membrane
9
Q
define chemiosmosis
A
energy-coupling mechanism that utilises energy stored in a proton gradient across a membrane to drive ATP synthesis
10
Q
outline chemiosmosis
A
- at the mitochondrial cristae, ATP synthases are present to permet protons to pass through via facilitated diffusion
- protons move down their proton gradient back into the matrix through ATP synthase, ATP synthases harnesses the proton motive force to drive ATP synthesis
- each reduced NAD molecule yields 3 ATP molecules while each reduced FAD molecule yields 2 ATP molecules
11
Q
outline anaerobic respiration
A
- in the absence of oxygen, there is no final proton and electron acceptor. electrons are not transferred down the chain, electron carriers remain reduced so reduced NAD and FAD are not able to release electrons into the ETC and no regeneration of NAD+ and FAD occurs. thus, link reaction, Krebs cycle and oxidative phosphorylation cannot occur, only glycolysis occurs (partial breakdown of glucose)
- pyruvate cannot be oxidised and accumulates in cytoplasm
- pyruvate accepts H atom from reduced NAD to form lactate (animals) or ethanol (plants and yeast), regenerating NAD+ to allow glycolysis to continue to generate net 2 ATP per glucose molecule
- much of the energy is still stored in lactate/ethanol so anaerobic respiration is inefficient compared to aerobic respiration (2 ATP vs 36/38 ATP)
12
Q
describe two ways in which the structure of the mitchondrion is adapted for oxidative phosphorylation
A
- inner membrane impermeable to protons, allowing proton pool to be built up in intermembrane space for chemiosmotic synthesis of ATP
- inner membrane is thrown into folds called cristae to increase surface area for more ATP syntheases and electron carriers to be embedded for increased rate of oxidative phosphorylation
13
Q
state the significance of oxidative phosphorylation
A
- produces a lot of ATP via chemiosmosis for energy-requiring processes
- NAD+ and FAD regenerated to pick up more H atoms to allow Krebs cycle and link reaction to continue
14
Q
explain why less glucose is required to maintain cell metabolism under aerobic conditions than under anaerobic conditions
A
- in aerobic conditions, a molecule of glucose is completely oxidised to give 36/38 ATP molecules
- in anaerobic conditions, one molecule of glucose is converted to lactate to give a net synthesis of 2 ATP molecules
- to supply the same energy demands, less glucose molecules needed under aerobic conditions
15
Q
describe the role of oxygen in oxidative phosphorylation
A
- final electron and proton acceptor
- allows electron carriers in ETC to be reoxidised to receive more electrons from reduced NAD and reduced FAD
- allows regeneration of NAD+ and FAD for reuse in link reaction and Krebs cycle
