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Topic 8 - Metabolism HL revision list

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  • Topic 8 - Metabolism HL revision list

This pages gives outline details of the content of the topic together with essential questions and student skills and applications. Helpful for revision.

8.1 Metabolism

Metabolic pathways

  • A chain or a cycle of enzyme-catalysed reactions makes a metabolic pathway.
  • Enzymes catalyse chemical reactions by lowering the activation energy.

Essential Questions

  • If each enzyme is substrate specific how can enzymes perform complex reactions like glycolysis?
  • When chemicals collide with more energy than the "activation energy" a reaction happens. How do enzymes change this activation energy to speed up reaction rates?

Competitive inhibitors

  • Competitive inhibitors for example in medicine - ethanol and Fomepizole used as competitive inhibitors for antifreeze poisoning.

Essential Questions

  • How can we stop enzyme-catalysed chemical reactions?
  • How do cells control enzymes?

Non-competitive inhibitors

  • Non-competitive inhibitors. E.g. Drugs for treatment of malaria.
  • End-product inhibition can control metabolic pathways - e.g. In the pathway that converts threonine to isoleucine.

Essential Questions

  • How can doctors control enzymes to provide medical treatments?

Student skills and applications

  • The use of databases to identify potential new anti-malarial drugs. In the ER role play: students will have seen this
  • In the Enzyme inhibition experiment students will calculate and plot rates of reaction from raw experimental results.
  • They will also distinguish different types of inhibition from graphs at specified substrate concentration.

8.2 Respiration

Introduction to reactions in respiration

  • Cell respiration involves:
  • the oxidation and reduction of electron carriers.
  • the phosphorylation of molecules which makes them less stable.
  • decarboxylation removes a carbon atom from a molecule

Essential Questions

  • What are the three key reactions: oxidation, reduction and phosphorylation?

Glycolysis & the Krebs cycle

  • Glycolysis is the conversion of glucose to pyruvate in the cytoplasm giving a small net gain of ATP(without the use of oxygen.)
  • Aerobic cell respiration converts the pyruvate by decarboxylation and oxidation, into an acetyl compound.
  • In the link reaction acetyl is attached to coenzyme A to form acetyl coenzyme A.
  • In the Krebs cycle,
    • the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers, liberating carbon dioxide.
    • reduced NAD and FAD (NADH+H+ and FADH+) carry energy released by oxidation reactions to the cristae of the mitochondria.

Essential Questions

  • How can you summarise glycolysis  (glyco - sugar & lysis - splitting)?
  • Which parts of respiration are joined by the link reaction?

The electron transport chain & Mitochondrion structure.

  • the electron transport chain in the membrane of the cristae is coupled to proton pumping.
  • oxygen is the final electron acceptor.
  • In chemiosmosis protons diffuse through ATP synthase to generate ATP.
  • Oxygen binds with the free protons to maintain the hydrogen gradient and resulting in the formation of water.
  • The structure of the mitochondrion is adapted its function. Annotate a diagram of a mitochondrion to show these adaptations

Essential Questions

  • What do hydrogen carriers do?
  • What two things does the electron tansport chain "transport"?
  • What is the role of oxygen?
  • How do cristae, matrix and the position of enzymes in the inner membrane of a mitochondrion help it to carry out aerobic respiration?

Student skills and applications

  • Active mitochondria have been studies using electron tomography - images.
  • students will be able to identify where decarboxylation and oxidation reactions occur in diagrams of the pathways of aerobic respiration.
  • Guidance:
  • The names of the intermediate compounds in gylcolysis and the Krebs cycle are not required.

8.3 Photosynthesis

Light-dependent reactions

  • Happen in the thylakoid membranes and in the space inside them.
  • Reduced NADP (NADPH2) and ATP are produced in the light-dependent reactions.
  • Light absorbed by photosystems generates excited electrons.
  • Photolysis of water generates electrons for use in the light-dependent reactions.
  • Excited electrons are transfered between carriers in the thylakoid membranes.
  • Excited electrons from Photosystem II are used to generate a proton gradient.
  • ATP synthase in the thylakoids generates ATP using the proton gradient.
  • Excited electrons from Photosystem I are used to reduce NADP to NADPH2.

Essential Questions

  • Water is used in the light dependent reactions - what happens to it?
  • What happens to the hydrogen from the water molecule?

Light-independent reactions

  • Take place in the stroma.
  • RuBP carboxylase enzyme catalyses the carboxylation of ribulose bisphosphate (RuBP).
  • Glycerate 3-phosphate is reduced to triose phosphate using "reduced NADP" (NADPH2) and ATP.
  • Triose phosphate is used to regenerate RuBP and produce carbohydrates.
  • Ribulose bisphosphate (RuBP) is regenerated using ATP.

Essential Questions

  • How does the chloroplast trap CO2 from the air?
  • Which 'carbohydrates' do the light independent reactions make?
  • Which products from the light dependent reactions are used in the light independent reactions?

Chloroplast structure

  • The structure of the chloroplast is adapted to its function in photosynthesis.

Essential Questions

  • Where is the chlorophyll found in the chloroplasts?
  • Why are there so many membranes in a chloroplast?
  • What is a photosystem?

Student skills and applications

  • to recognise details of Calvin’s experiment to elucidate the carboxylation of RuBP.
  • to be able to annotate a diagram showing the adaptations of a chloroplast to its function.