unit 2

• Metabolic pathway

  An integrated series of enzyme-controlled reactions
• Metabolism

  All the reactions that take place within a cell
• Types of metabolic reactions

  • Anabolic reactions (build up simple molecules into more complex molecules)
  • Catabolic reactions (break down complex molecules into simpler molecules)
• Anabolic reactions

  Build complex molecules from more simple building blocks, require energy
• Catabolic reactions

  Break down complex molecules into smaller ones, release energy
• Anabolic and catabolic pathways are closely linked, with ATP from catabolic reactions used for anabolic reactions
• Metabolic pathways

  • Some can be reversed
  • Some are irreversible
  • Some have alternative pathways
• Cell membranes

  Control what molecules can enter and exit the cell
• Membrane-bound organelles

  Such as mitochondria and chloroplasts, contain compartments where different metabolic reactions occur
• Structure of mitochondria

  • Have an outer membrane and a folded inner membrane, enzymes and metabolites required for reactions are concentrated in the inner membrane
• Structure of cell membranes

  • Made up of proteins and a double layer of phospholipids (fluid mosaic model)
• Membrane proteins

  Pores (allow diffusion), pumps (actively transport molecules/ions, require energy), enzymes (catalyse reactions)
• Enzymes

  Biological catalysts that speed up the rate of metabolic reactions
• Activation energy

  Energy required to break chemical bonds and start a reaction
• Enzymes

  Lower the activation energy required for reactions to occur, allowing them to proceed rapidly at low temperatures
• Enzyme features

  • Induced fit (active site changes shape to fit substrate)
  • Affinity (substrates have high affinity for active site, products have low affinity)
• Enzyme inhibition

  • Competitive inhibitors (compete with substrate for active site)
  • Non-competitive inhibitors (bind elsewhere, change active site shape)
  • Feedback inhibition (final product inhibits first enzyme in pathway)
• Cellular respiration

  A series of metabolic pathways that break down glucose into energy in the form of ATP
• ATP

  A high-energy compound consisting of adenosine and three phosphate groups
• Cellular respiration

  1. Glycolysis

  2. Citric acid cycle

  3. Electron transport chain
• Glycolysis

  • Takes place in the cytoplasm
  • Occurs with or without oxygen present
• Energy investment phase (of glycolysis)

  2 ATP molecules are used up
• Energy payoff phase (of glycolysis)

  4 ATP molecules are produced
• Net gain of 2 ATP molecules from glycolysis
• Dehydrogenase


  Enzyme that removes hydrogen ions and electrons, passing them to NAD to form NADH
• Citric acid cycle

  • Takes place in the matrix of the mitochondria
  • Requires oxygen to proceed
• Citric acid cycle

  1. Pyruvate converted to acetyl CoA

  2. Acetyl CoA combines with oxaloacetate to form citrate

  3. Citrate converted back to oxaloacetate, releasing CO2
• NADH

  Coenzyme formed from NAD and hydrogen ions/electrons, used in electron transport chain
• Electron transport chain

  • Takes place in the inner mitochondrial membrane
  • Requires oxygen
  • Generates 36 ATP molecules
• ATP synthase


  Enzyme that uses the flow of hydrogen ions to generate ATP
• Total of 38 ATP molecules produced during aerobic respiration (2 from glycolysis, 36 from electron transport chain)
• Fermentation

  Anaerobic process that produces 2 ATP molecules and either lactate (in animals) or ethanol + carbon dioxide (in plants/yeast)
• Ways to measure metabolic rate

  • Volume of oxygen consumed per unit of time
  • Volume of carbon dioxide produced per unit of time
  • Heat produced per unit of time
• Respirometer measures the volume of oxygen consumed per unit of time as a measure of respiration
• A control (e.g. marble, glass bead, rock) is used in a respirometer to account for factors other than the organism
• Organisms with higher metabolic rates

  • Birds
  • Mammals
• Organisms with lower metabolic rates

  • Reptiles
  • Amphibians
  • Fish
• Organisms with higher metabolic rates require more efficient delivery of oxygen to their cells
• Complete double circulatory system

  Found in birds and mammals, has two atria, two ventricles, and no mixing of oxygenated and deoxygenated blood
• Incomplete double circulatory system

  Found in amphibians and reptiles, has two atria, one ventricle, and mixing of oxygenated and deoxygenated blood