Respiration Flashcards
What are the stages of aerobic respiration?
Glycolysis: the splitting of 6-C glucose into two 3-C pyruvate molecules.
Link reaction: the 3-C pyruvate molecules form 2-C acetylcoenyme A.
Krebs Cycle: acetylcoenzyme A goes into a cycle of oxidation-reduction reactions to yield some ATP and a large quantity of reduced NAD and FAD.
Oxidative phosphorylation: electrons, reduced NAD and FAD synthesise ATP and produce water as a by-product.
What is glycolysis?
The first stage of aerobic and anaerobic respiration.
It occurs in the cytoplasm.
It is the process by which a hexose sugar is split into two molecules of 3-carbon pyruvate.
What is the phosphorylation of glucose to glucose phosphate (glycolysis 1)?
Glucose is made more reactive by adding two phosphate molecules.
The phosphate comes from the hydrolysis of two ATP molecules to ADP.
This provides the energy to activate glucose and lowers the activation energy for later enzyme-controlled reactions.
What is the splitting of the phosphorylated glucose (glycolysis 2)?
Each glucose molecule is split into two 3-carbon molecules called triose phosphate.
What is the oxidation of triose phosphate (glycolysis 3)?
Hydrogen is removed from each of the two triose phosphate molecules and transferred to a hydrogen carrier molecule NAD to form reduced NAD.
What is the production of ATP (glycolysis 4)?
Enzyme controlled reactions convert each triose phosphate into another 3-carbon molecule pyruvate.
2 ATP molecules are regenerated from ADP in the process.
What is the energy yield from glycolysis?
Two molecules of ATP.
Two molecules of reduced NAD.
Two molecules of pyruvate.
How is glycolysis indirect evidence for evolution?
The enzymes for glycolysis are found in the cytoplasm of cells and so glycolysis does not need any organelle or membrane.
It doesn’t need oxygen, and the pyruvate produced in its absence can be converted to lactate or ethanol.
This is neccessary to re-oxidise NAD.
What is the Link reaction?
The pyruvate molecules are actively transported to the matrix of the mitochondria.
The 3-C pyruvate is oxidised to acetate. It loses a carbon dioxide molecule and two hydrogens - accepted by NAD to form reduced NAD.
The 2-C acetate combines with coenzyme A to produce coacetylenzyme A.
What is the Krebs cycle?
The 2-C acetylcoenzyme A combines with a 4-C molecule to form a 6-C molecule.
This loses carbon dioxide and hydrogen to give a 4-C molecule and a single molecule of ATP (produced as a result of substrate-level phosphorylation).
The 4-C molecule can now combine with a new acetylcoenzyme A to begin again.
What is the yield from the link reaction and Krebs cycle?
Each molecule of pyruvate produce:
Reduced coenzymes NAD and FAD.
1 molecule of ATP
3 molecules of carbon dioxide.
2 pyruvates are produced for each original glucose, so these quanities are doubled.
What is the significance of the Krebs cycle?
Breaks macromolecules (pyruvate) into smaller ones (carbon dioxide).
Produces hydrogen atoms that are carried by NAD to the electron transport chain and provide energy for oxidative phosphorylation.
Regenerates 4-C molecule that combines with acetylcoenzyme A.
Is a source of intermediate compounds used by cells to manufacture fatty acids, amino acids and chlorophyll.
What is the importance of mitochondria?
The site of oxidative phosphorylation, the cristae are where the enzymes and other proteins are.
They occur in great numbers in metabollically active cells, which also have a more densely packed cristae to provide a greater surface area.
What is the electron transfer chain (oxidative phosphorylation)?
Hyrdogen atoms combine with coenzymes NAD and FAD.
The reduced NAD and FAD donate electrons to the first molecule in the chain.
The electrons pass along the chain in oxidation-reduction reactions. The energy they release causes the active transport of protons across the inner mitochondrial membrane and into inter-membranal space.
The protons accumulate here before diffusing back through ATP synthase channels.
At the end of the chain, electrons combine with these protons and oxygen to form water.
What is the importance of oxygen?
It acts as the final acceptor of the hydrogen atoms produced in glycolysis and the Krebs cycle.
Without this removing of hydrogen atoms, the protons and electrons would ‘back up’ and respiration would stop.
