Chapter 12: ATP production and respiration

What is ATP? - Adenosine triphosphate, the universal energy currency of cells.

What is the structure of ATP? - A ribose sugar, an adenine base, and three phosphate groups.

How does ATP release energy? - By hydrolysis to ADP and inorganic phosphate (Pi).

Write the equation for ATP hydrolysis. - ATP + H₂O ⇌ ADP + Pi.

How is ATP synthesised? - By combining ADP with inorganic phosphate using energy.

What are the two ways ATP is synthesised? - Transfer of phosphate in substrate-linked reactions and chemiosmosis.

What is substrate-linked phosphorylation? - The synthesis of ATP by direct transfer of a phosphate group from another molecule to ADP.

Where does substrate-linked phosphorylation occur? - Glycolysis and the Krebs cycle.

Why is ATP the universal energy currency? - It is small, water-soluble, easily transported, rapidly hydrolysed, releases manageable amounts of energy, and is readily regenerated.

What is ATP used for? - Active transport, movement, and anabolic reactions.

What are anabolic reactions? - Reactions that build complex molecules from simpler molecules.

Give examples of anabolic reactions. - DNA replication and protein synthesis.

Why do living organisms need energy? - For active transport, movement, and anabolic reactions.

What is respiration? - The process whereby chemical potential energy from organic molecules is used to synthesise ATP.

What is a respiratory substrate? - A molecule from which energy can be released during respiration.

Why do lipids have a higher energy value than carbohydrates and proteins? - Lipids contain more hydrogen atoms per unit mass.

Why do lipids yield more ATP than carbohydrates? - More hydrogen atoms result in more reduced NAD and FAD and therefore more ATP production.

What is the energy density of carbohydrates? - 15.8 kJ g⁻¹.

What is the energy density of proteins? - 17.0 kJ g⁻¹.

What is the energy density of lipids? - 39.4 kJ g⁻¹.

How is energy density determined? - By burning a known mass in a calorimeter.

What is the respiratory quotient (RQ)? - The ratio of carbon dioxide produced to oxygen consumed during respiration.

Write the equation for respiratory quotient. - RQ = CO₂ produced ÷ O₂ consumed.

What is the RQ of carbohydrates? - 1.0.

What is the RQ of proteins? - 0.9.

What is the RQ of lipids? - 0.7.

What does a change in RQ indicate? - A change in the respiratory substrate being respired.

What is the RQ of alcoholic fermentation? - Infinity.

Why is the RQ of alcoholic fermentation infinity? - Carbon dioxide is produced but oxygen is not consumed.

Why can no RQ be calculated for lactate fermentation? - No carbon dioxide is produced.

Where does glycolysis occur? - Cytoplasm.

Where does the link reaction occur? - Mitochondrial matrix.

Where does the Krebs cycle occur? - Mitochondrial matrix.

Where does oxidative phosphorylation occur? - Inner mitochondrial membrane.

Name the four stages of aerobic respiration. - Glycolysis, link reaction, Krebs cycle, and oxidative phosphorylation.

What is glycolysis? - The breakdown of glucose into two pyruvate molecules.

Does glycolysis require oxygen? - No.

What happens to glucose at the start of glycolysis? - It is phosphorylated using ATP.

What is formed after glucose is phosphorylated? - Fructose 1,6-bisphosphate.

What happens to fructose 1,6-bisphosphate? - It is split into two triose phosphate molecules.

What happens to triose phosphate molecules? - They are oxidised to pyruvate.

How many ATP molecules are used in glycolysis? - 2 ATP.

How many ATP molecules are produced in glycolysis? - 4 ATP.

What is the net ATP gain in glycolysis? - 2 ATP.

How many reduced NAD molecules are produced during glycolysis? - 2 reduced NAD.

What are the products of glycolysis? - 2 pyruvate, 2 reduced NAD, and a net gain of 2 ATP.

What happens to pyruvate when oxygen is available? - It enters the mitochondrion and takes part in the link reaction.

What is the link reaction? - The conversion of pyruvate into acetyl coenzyme A.

What happens first in the link reaction? - Pyruvate is decarboxylated.

What is decarboxylation? - Removal of carbon dioxide.

What happens after decarboxylation in the link reaction? - Dehydrogenation.

What is dehydrogenation? - Removal of hydrogen.

What happens to NAD during the link reaction? - It is reduced.

What is formed after decarboxylation and dehydrogenation of pyruvate? - A 2-carbon acetyl group.

What happens to the acetyl group? - It combines with coenzyme A.

What are the products of the link reaction per glucose molecule? - 2 acetyl CoA, 2 CO₂, and 2 reduced NAD.

What is coenzyme A? - A coenzyme that carries acetyl groups.

What is the role of coenzyme A? - To transfer acetyl groups into the Krebs cycle.

What is the first step of the Krebs cycle? - Acetyl CoA combines with oxaloacetate.

What is oxaloacetate? - A 4-carbon compound that accepts the acetyl group.

What is formed when acetyl CoA combines with oxaloacetate? - Citrate.

How many carbons does citrate contain? - 6 carbons.

What reactions occur in the Krebs cycle? - Decarboxylation and dehydrogenation.

What happens to NAD in the Krebs cycle? - It is reduced.

What happens to FAD in the Krebs cycle? - It is reduced.

How many reduced NAD molecules are produced per turn of the Krebs cycle? - 3.

How many reduced FAD molecules are produced per turn of the Krebs cycle? - 1.

How much ATP is produced per turn of the Krebs cycle? - 1 ATP.

How much carbon dioxide is produced per turn of the Krebs cycle? - 2 CO₂.

What is regenerated at the end of the Krebs cycle? - Oxaloacetate.

What are the products of one turn of the Krebs cycle? - 3 reduced NAD, 1 reduced FAD, 1 ATP, and 2 CO₂.

What are the products of the Krebs cycle per glucose molecule? - 6 reduced NAD, 2 reduced FAD, 2 ATP, and 4 CO₂.

What is the main role of the Krebs cycle? - To generate reduced NAD and reduced FAD for oxidative phosphorylation.

What is NAD? - Nicotinamide adenine dinucleotide, a hydrogen carrier coenzyme.

What is the role of NAD? - To accept and transport hydrogen atoms and electrons.

What is reduced NAD? - NADH.

Write the equation for NAD reduction. - NAD⁺ + H⁺ + 2e⁻ ⇌ NADH.

What is FAD? - Flavin adenine dinucleotide, a hydrogen carrier coenzyme.

What is the role of FAD? - To accept and transport hydrogen atoms and electrons.

What is reduced FAD? - FADH₂.

Write the equation for FAD reduction. - FAD + 2H⁺ + 2e⁻ ⇌ FADH₂.

What is the role of NAD and FAD in respiration? - They transfer hydrogen to carriers in the inner mitochondrial membrane.

What is NADP? - A hydrogen carrier used in photosynthesis.

What is oxidative phosphorylation? - ATP production using energy released from electrons moving through the electron transport chain.

What happens to hydrogen atoms during oxidative phosphorylation? - They split into protons and energetic electrons.

What is the electron transport chain? - A series of electron carriers in the inner mitochondrial membrane.

What happens to energetic electrons during oxidative phosphorylation? - They pass along the electron transport chain and release energy.

How is the energy released by electrons used? - To transfer protons across the inner mitochondrial membrane.

What is a proton gradient? - A difference in proton concentration across a membrane.

What is an electrochemical gradient? - A gradient caused by differences in proton concentration and charge across a membrane.

What is chemiosmosis? - ATP synthesis using energy from protons moving down an electrochemical gradient.

How do protons return to the mitochondrial matrix? - By facilitated diffusion through ATP synthase.

What provides energy for ATP synthesis during oxidative phosphorylation? - The return of protons through ATP synthase.

What is ATP synthase? - An enzyme that synthesises ATP from ADP and inorganic phosphate.

What is the final electron acceptor in aerobic respiration? - Oxygen.

What happens when oxygen accepts electrons and protons? - Water is formed.

Why is oxygen essential for aerobic respiration? - It acts as the final electron acceptor.

What is anaerobic respiration? - Respiration in the absence of oxygen.

Why is the energy yield from aerobic respiration much greater than the energy yield from anaerobic respiration? - Aerobic respiration includes oxidative phosphorylation and complete breakdown of glucose, whereas anaerobic respiration only produces ATP through glycolysis.

What happens to the electron transport chain when oxygen is absent? - It stops functioning.