5.2 - Respiration
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What is ATP synthesised from?
ADP + inorganic phosphate (P)
Name three biological processes that require the use of ATP.
Active transport, endocytosis, DNA replication.
What is a catabolic reaction?
A reaction where large molecules are broken into smaller molecules.
What is an anabolic reaction?
A reaction where small molecules are combined into larger molecules.
What is glycolysis?
The first stage of respiration, where glucose is converted into pyruvate.
What is NAD?
A coenzyme (nicotinamide adenine dinucleotide) that carries protons and electrons to the cristae.
What is phosphorylation in glycolysis?
The attachment of two phosphate groups to glucose to form hexose bisphosphate using 2 molecules of ATP.
What is hexose bisphosphate split into during glycolysis?
2 molecules of triose phosphate.
What is triose phosphate converted into during the oxidation stage of glycolysis?
Pyruvate.
How many carbons are found in a molecule of pyruvate?
Which molecule accepts the hydrogen atoms from triose phosphate when it is oxidised?
NAD.
What are the products of glycolysis for every molecule of glucose?
2 x pyruvate, 2 molecules of ATP, and 2 reduced NAD.
What is the net gain of ATP in glycolysis?
2 (four are made but two are used).
Why is glycolysis an anaerobic process?
It occurs in the cytoplasm without the need for oxygen.
What is the cristae?
The inner highly folded mitochondrial membrane.
What is the mitochondrial matrix?
The fluid-filled inner part of the mitochondria.
What is the average length of mitochondrion?
2-5 micrometers.
Where does the link reaction occur in the mitochondria?
The mitochondrial matrix.
What are the names of the two coenzymes found in the mitochondria?
NAD and FAD.
Where is the electron transport chain found in the mitochondria?
The cristae of the inner membrane.
What is the name of the enzyme that synthesises ATP in the cristae?
ATP synthase.
What is decarboxylation?
The removal of a carboxyl group from a substrate molecule.
What is dehydrogenation?
The removal of a hydrogen atom from a substrate molecule.
What is substrate level phosphorylation?
The production of ATP from ADP and inorganic phosphate during glycolysis and the Krebs cycle.
Why is pyruvate said to be decarboxylated and dehydrogenated during the link reaction?
Pyruvate loses a molecule of carbon dioxide and reduces NAD to become acetyl.
What does the acetyl group in the link reaction join with before entering the Krebs cycle?
Coenzyme A.
How is one molecule of glucose formed into two molecules of acetyl coenzyme A?
Glycolysis followed by the link reaction.
What molecule enters the Krebs cycle?
Acetyl CoA.
How many carbons are found in a molecule of acetyl CoA?
What molecule does acetyl CoA join to in the Krebs cycle?
Oxaloacetate.
How many carbons does citrate contain?
What two molecules combine to form citrate in the Krebs cycle?
Oxaloacetate and Acetyl CoA.
What happens to citrate in the Krebs cycle?
It is decarboxylated and dehydrogenated into a 5C compound.
What happens to the 5C compound in the Krebs cycle?
It is decarboxylated and dehydrogenated into a 4C compound.
Where does substrate level phosphorylation occur in the Krebs cycle?
The 4C molecule combines temporarily with coenzyme A to produce a molecule of ATP.
What are the products of one turn of the Krebs cycle?
3 reduced NAD, 1 reduced FAD, 2 molecules of CO2, and 1 molecule of ATP.
What is the final stage of aerobic respiration called?
Oxidative phosphorylation.
Define chemiosmosis.
The flow of protons down their concentration gradient across a membrane through channels associated with ATP synthase.
What is oxidative phosphorylation?
The formation of ATP using energy released from the electron transport chain in the presence of oxygen.
Where does oxidative phosphorylation take place?
In the mitochondria.
What is the electron transport chain?
A chain of electron carrier proteins that contain an Fe ion, using energy to pump protons across the inner mitochondrial membrane.
What is the name of the enzyme embedded in the cristae involved in oxidative phosphorylation?
ATP synthase.
Which two coenzymes deliver hydrogen atoms to the electron transport chain?
Reduced NAD and reduced FAD.
How do reduced NAD and FAD release hydrogen atoms at the electron transport chain?
They are reoxidised.
What happens to the hydrogen atoms released at the electron transport chain?
They are split into protons and electrons.
When electrons are released at the electron transport chain from reduced NAD and FAD, what is their fate?
They are passed along the chain of electron carriers and accepted by oxygen to form water.
Where are protons pumped into by the electron transport chain?
The intermembrane space.
What forms when protons are pumped into the intermembrane space?
A proton gradient.
What is the source of potential energy in the intermembrane space?
The proton gradient accumulates and creates a chemiosmotic potential.
As protons flow from the high concentration in the intermembrane space, why must they flow through ATP synthase?
The protons cannot easily flow through the lipid bilayer of the mitochondrial membranes.
How does the flow of protons cause ATP to be formed?
The protons cause a conformational change in ATP synthase allowing ADP and inorganic phosphate to combine.
What is the final electron acceptor?
Oxygen.
How is water formed during oxidative phosphorylation?
Oxygen accepts the electrons and combines with protons from chemiosmosis.
Which stage of photosynthesis also involves chemiosmosis?
Photophosphorylation in the light dependent reaction.
How many ATP can be formed from a molecule of reduced NAD?
3 ATP (2.5).
How many ATP can be formed from a molecule of reduced FAD?
2 ATP (1.5).
How many molecules of ATP can be formed from glycolysis by 1 molecule of glucose?
How many molecules of ATP can be formed from the link reaction by 1 molecule of glucose?
How many molecules of ATP can be formed from the Krebs cycle by 1 molecule of glucose?
How many molecules of ATP can be formed from oxidative phosphorylation by 1 molecule of glucose?
What is the total yield of ATP from one molecule of glucose during aerobic respiration?
Why is the theoretical yield of 32 ATP per glucose molecule rarely achieved?
Some ATP is used; some protons may leak through the mitochondrial membrane.
Why is the pH of the intermembrane space lower than the mitochondrial matrix and the cytoplasm?
There is an accumulation of protons.
What are the two metabolic pathways used by eukaryotic cells to reoxidise NAD?
Ethanol fermentation and lactate fermentation.
Which stage of respiration is the same for both aerobic and anaerobic respiration? Why?
Glycolysis; it occurs in the cytoplasm.
In ethanol fermentation, what enzyme decarboxylates pyruvate into ethanal?
Pyruvate decarboxylase.
What does the enzyme pyruvate decarboxylase convert pyruvate into during ethanol fermentation in yeast?
Ethanal.
Which enzyme is used to help ethanal accept hydrogen from reduced NAD in ethanol fermentation in yeast?
Ethanol dehydrogenase.
Why is yeast described as a facultative anaerobe?
It can respire aerobically or anaerobically depending on the environment.
Write out the two steps involved in ethanol fermentation.
Pyruvate → Ethanal + CO2; 2. Ethanal + H+ from reduced NAD → Ethanol.
What is the name of the enzyme that allows pyruvate to accept hydrogen from reduced NAD in lactate fermentation?
Lactate dehydrogenase.
Write out the equation for formation of lactate in anaerobic respiration in eukaryotic cells.
Pyruvate + H+ from reduced NAD → Lactate.
What is the fate of lactate?
It is moved to the liver where it is either converted back into pyruvate or recycled to glucose.
Lactate and ethanol fermentation do not produce any ATP. Suggest how these processes still allow the production of some ATP.
Both processes allow glycolysis to continue, which has a net gain of 2 ATP.
What is a respiratory substrate?
An organic substance that can be oxidised by respiration, releasing energy to make ATP.
How can glycerol be used as a respiratory substrate?
It is converted to triose phosphate and then respired.
How are fatty acids used as respiratory substrates?
They combine with acetyl CoA and enter the Krebs cycle.
How are proteins used as respiratory substrates?
Different amino acids can enter various stages of aerobic respiration.
Which respiratory substrate can be converted into acetate and enter the Krebs cycle via the link reaction?
Fatty acids.
Which molecule can be deaminated, allowing the rest of the molecule to enter the Krebs cycle directly?
Amino acids.
Why do lipids have the highest mean energy value per gram?
They contain large chains of hydrocarbons, which are a source of protons.
What is the formula for the respiratory quotient (RQ)?
CO2 produced / O2 consumed.
What is the RQ value for glucose?
What is the RQ value for fatty acids?
0.7.
What is the RQ value for proteins?
0.8.
What does an RQ value of over 1 suggest?
Anaerobic respiration is taking place.
In an investigation, if the RQ value was calculated as 0.82, which respiratory substrate was likely being used?
Protein.
In an investigation, if the RQ value was calculated as 0.99, which respiratory substrate was likely being used?
Glucose.
In an investigation, if the RQ value was calculated as 0.70, which respiratory substrate was likely being used?
Fatty acids.
In an investigation, if the RQ value was found to be 2.3, what can be deduced from these findings?
Anaerobic respiration has occurred.