(5) Respiration Flashcards
Need for cellular respiration
Organisms respire to use the energy stored in complex organic molecules to make ATP, it is the universal energy currency for biological processes.
Active transport, endocytosis and exocytosis, cell division (synthesis of new organelles), muscle contraction and movement.
Structure of mitochondria
Cytoplasm - site of glycolysis
Outer membrane
Inner membrane (cristae) - oxidative phosphorylation.
Matrix - link reaction and kerbs cycle.
Glycolysis
Occurs in the cytoplasm
Glucose (6C) is phosphorylated into hexose bisphosphate (6C) - uses 2 ATP and releases 2 ADP + Pi.
Hexose bisphosphate then splits into 2x triose phosphate molecules (3C) by the addition of a Pi.
Then into triose bisphosphate by dehydrogenation - 2 ADP into 2 ATP and NAD into reduced NAD (oxidation) into pyruvate (3C).
Produces 4 ATP, net 2 ATP, 2 reduced NAD and 2 pyruvate.
Link reaction
Occurs in the matrix.
Pyruvate (3C) is decarboxylated (loses 1 co2) and dehydrogenated/oxidised (NAD into reduced NAD) to form acetyl (2C).
Acetyl accepts coenzyme A and makes acetyl coA (2C).
Makes 2 reduced NAD, 2 co2, 2 acetyl coA.
Kerbs cycle
Occurs in the matrix.
Acetyl coA (2C), loses its coA and citric acid (6C) is formed from the acetyl group.
Citric acid loses one co2 (decarboxylation) and NAD into reduced NAD (dehydrogenation) into a 5C compound.
5C loses 1 co2, 1 NAD into reduced NAD = 4C intermediate.
4C - substrate level phosphorylation (ADP + Pi into ATP), FAD into reduced FAD.
4C into oxaloacetate (4C) - NAD into reduced NAD.
Per glucose - 2 co2, 1 ATP, 1 reduced FAD and 3 reduced NAD (x2).
Coenzymes
Temporarily bind to the enzymes active site.
NAD and FAD - help dehydrogenase enzymes to remove H atom from substrate. Then combines with H and becomes reduced. It is regenerated during oxidative phosphorylation - H atoms from reduced NAD/FAD are used for ATP.
Coenzyme A - carries acetate from pyruvate made in glycolysis to krebs cycle.
Oxidative phosphorylation
Occurs on the cristae - H+ moved over the membrane from the matrix into the intermembranal space.
Reduced NAD and FAD release H+ atoms, they split into protons and electrons.
Electrons pass down the electron transport chain, from carrier to carrier, releasing energy each time.
Energy released is used to pump H+ across the membrane into the intermembranal space.
H+ then diffuse back through the membrane via ATP synthase, down the proton gradient.
This causes the head of ATP synthase to spin - releasing energy to combine ADP and Pi to make ATP.
Oxygen is the final electron acceptor - it combines with electrons from the etc and H+ from chemiosmosis to make water.
Yields around 28 ATP.
Anaerobic respiration in eukaryotes
Lactate fermentation - Pyruvate (3C) into lactate (3C).
2H from reduced NAD into NAD by lactate dehydrogenase.
There is no o2, so this allows muscle cells to keep contracting by supplying a small amount of ATP.
NAD being regenerated means that it is available to accept more H atoms, allowing glycolysis to continue because it needs NAD.
Anaerobic respiration in yeast
Alcohol fermentation - Pyruvate (3C) into ethanal by losing 1 co2 (pyruvate decarboxylase).
Then ethanal into ethanol - 2 reduced NAD transfers 2H into ethanal using ethanol dehydrogenase.
NAD is regenerated so glycolysis can continue.
ATP yield in anaerobic respiration
ATP yield is lower than aerobic respiration because anaerobic respiration only includes one energy releasing stage, glycolysis, which only gets 2 ATP per glucose.
Krebs cycle and oxidative phosphorylation cannot occur because it’s requires o2
Respiratory substrates
Yield different amounts of ATP because most is generated from oxidative phosphorylation, so more H+ = more energy per gram.
Carbohydrates (16kJg-1) - stores are used up quick, glucose from stored starch of glycogen.
Proteins (17kJg-1) - amino acids released by digestion are respired, some fed into kerbs cycle, the rest is delaminated into urea.
Lipids (39kJg-1) - glycerol and fatty acids, glycerol is turned into carbohydrate for glycolysis, fatty acids are high with H aroma so high energy.
Respiratory quotient - co2 produced/o2 consumed.
