AQA A level Biology
AQA A level Biology
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Topic 5: Energy transfers in and between organisms
Topic 5: Energy transfers in and between organisms
Respiration
Respiration
Respiration uses glucose to produce ATP
Respiration uses glucose to produce ATP
Respiration can occur in two forms:
Aerobic respiration: In the presence of oxygen.
Anaerobic respiration: In the absence of oxygen.
The function of respiration is to produce Adenosine triphosphate (ATP) using the energy stored in glucose.
ATP is the main cellular energy storage molecule. ATP is:
Very efficient.
Allows energy to be released in small, manageable amounts.
Stores less energy than glucose, making it easier to utilize.
The energy in ATP is released when it is hydrolysed by an ATPase enzyme:
ATP → ADP + Pi
When ATP donates a phosphate group to another molecule it increases that molecule's reactivity. In this way, ATP is needed for:
Active transport.
Synthesis of proteins/enzymes and DNA.
Muscle contraction.
Stages of respiration
Stages of respiration
Glycolysis (Occurs in the cytoplasm)
Glucose is phosphorylated twice by ATP to form glucose phosphate.
Glucose phosphate splits into two triose phosphate (3C) molecules.
Triose phosphate is oxidised through several steps to form pyruvate (3C).
This produces a net gain of:
2 ATP molecules (produced from substrate-level phosphorylation).
2 reduced NAD molecules (NADH).
Link Reaction (Occurs in the mitochondrial matrix)
Pyruvate (3C) is converted to acetate (2C) by losing:
A molecule of CO₂ (diffuses into the blood).
Electrons to form reduced NAD.
Acetate binds with coenzyme A to form acetyl CoA, which enters the Krebs cycle.
Krebs Cycle (Occurs in the mitochondrial matrix)
Acetyl CoA (2C) combines with a 4C molecule to form a 6C molecule.
The 6C molecule undergoes a series of oxidation-reduction reactions to regenerate the 4C molecule.
CO₂ is released as a waste product.
Electrons are transferred to NAD and FAD to form reduced NAD and FAD.
ATP is produced via substrate-level phosphorylation.
Electron Transfer Chain (Occurs in the inner mitochondrial membrane)
Reduced NAD and FADH transfer their electrons to proteins embedded in the inner mitochondrial membrane.
Electrons are passed along the chain, releasing energy to pump H⁺ ions into the intermembrane space.
H⁺ ions flow back into the matrix through ATP synthase, releasing energy to synthesize ATP (oxidative phosphorylation).
Oxygen is the final electron acceptor, combining with H⁺ ions to form water.
Anaerobic respiration
Anaerobic respiration
In the absence of oxygen pyruvate is converted to:
Ethanol (in plants and yeast).
Lactate (in animals) using reduced NAD. NAD is regenerated to allow glycolysis to continue.
Definitions
Definitions
Acetyl coA: two carbon molecule formed in the link reaction from pyruvate and coenzyme A.
Adenosine triphosphate (ATP): an activated nucleotide containing ribose sugar, adenine base and three phosphate groups; acts as an energy carrier in cells.
Aerobic: occurring in the presence of oxygen.
Anaerobic: occurring in the absence of oxygen.
ATP synthase: enzyme used to synthesise ATP from ADP + Pi.
Cristae: folded inner membrane structure in a mitochondrion, where electron transport occurs in aerobic respiration
Electron transport chain: occurring on the folded inner membrane of a mitochondrion, this is the site of series of oxidation-reduction reactions that lead to the production of a proton gradient.
Ethanol: product of anaerobic respiration in plants and microorganisms.
Glucose phosphate: phosphorylated form of glucose that breaks down in glycolysis to form triose phosphate.
Glycolysis: first part of cellular respiration that produces pyruvate in the cell cytoplasm.
Krebs cycle: a series of redox reactions that occur in the mitochondrial matrix and cause the breakdown of acetyl CoA resulting in the formation of reduced coenzymes and ATP.
Lactate: product of anaerobic respiration in animals.
Link reaction: process linking glycolysis to the Krebs cycle in the matrix of the mitochondria, where pyruvate converted to carbon dioxide and acetyl CoA.
Matrix: liquid portion of the mitochondria.
Mitochondria: organelle where aerobic respiration takes place.
NAD: a coenzyme that, when reduced, carries electrons to the electro transport chain.
Oxidative phosphorylation: the formation of ATP when oxygen is required as an electron acceptor, such as during the electron transport chain in aerobic respiration.
Pyruvate: the final three carbon product of glycolysis.
Substrate-level phosphorylation: the production of ATP when a phosphate group is transferred from a high energy molecule to ADP, such as during glycolysis.
Triose phosphate: three carbon intermediate in glycolysis, produced from glucose phosphate.
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