higher biology unit 2

• Metabolic Pathways


  Integrated and controlled pathways of enzyme-catalysed reactions within a cell
• Metabolic Pathways


  • Can have reversible steps
  • Can have irreversible steps
  • Can have alternative routes
• Anabolic Reactions


  Build up large molecules from small molecules and require energy

  
• Catabolic Reactions


  Break down large molecules into smaller molecules and release energy
• Membranes


  • Consist of proteins and phospholipids
  • Phospholipids create a bilayer and are constantly moving, giving the membrane flexibility

  
• Channel-forming proteins


  Create pores which control the diffusion of small molecules across the cell
• Diffusion


  Movement of molecules from an area of high concentration to an area of low concentration
• Active transport


  Movement of molecules from an area of low concentration to an area of high concentration and requires energy in the form of ATP
• The Sodium-Potassium pump is an example of a carrier protein involved in active transport
• ATP Synthase is an example of a membrane embedded enzyme which produces ATP from ADP + Pi

  
• Activation Energy


  The energy required to initiate a chemical reaction
• Enzymes


  Lower the activation energy required for a reaction to take place

  
• Affinity


  • The activity of enzymes depends on their flexible and dynamic shape
  • Substrate molecules have high affinity for the active site of an enzyme (bind readily)
  • Products of enzyme reactions have a low affinity for the active site of an enzyme, allowing them to leave the active site

  
• Induced Fit


  The enzyme is flexible and the substrate can induce the active site to change shape to better fit the substrate after the substrate binds

  
• Direction of enzyme-controlled reactions


  1. Presence of a substrate or removal of a product will drive a sequence of reactions in a particular direction

  2. Most enzymes can also work in reverse

  
• As the concentration of Substrate or Enzyme increases


  The rate of an enzyme-controlled reaction increases

  
• If either enzyme or substrate concentration is limited


  The rate reaction will only increase up to a point, beyond which the rate of reaction remains constant

  
• Competitive Inhibitors


  • Bind at the active site of the enzyme, preventing the substrate from binding
  • Competitive inhibition can be reversed by increasing substrate concentration

  
• Non-competitive Inhibitors


  • Bind away from the active site (at an allosteric site) but change the shape of the active site, preventing the substrate from binding
  • Non-competitive inhibition cannot be reversed by increasing substrate concentration

  
• Feedback Inhibition


  The end-product in the metabolic pathway reaches a critical concentration and then inhibits an earlier enzyme, blocking the pathway and preventing further synthesis of the end-product

  
• Cellular respiration


  An enzyme-controlled series of reactions in which a respiration substrate such as Glucose is broken down to generate energy in the form of ATP

  
• Glycolysis


  1. Breakdown of Glucose to Pyruvate

  2. Occurs in the cytoplasm of the cell

  3. ATP is required for the phosphorylation of glucose and intermediates during the energy investment phase

  4. Results in a net gain of ATP

  
• Citric Acid Cycle


  • The Aerobic phase of respiration takes place in the Matrix of Mitochondria
  • Pyruvate is broken down to an Acetyl Group that combines with Coenzyme A forming Acetyl Coenzyme A
  • The Acetyl group from Acetyl Coenzyme A combines with Oxaloacetate to form Citrate
  • Citrate is gradually converted back into Oxaloacetate which results in the generation of ATP and release of Carbon Dioxide

  
• Dehydrogenase enzymes


  • Remove hydrogen ions and electrons and pass them to the Coenzyme NAD, forming NADH
  • This occurs in both Glycolysis and the Citric Acid Cycle
• Electron Transport Chain


  1. A series of carrier proteins attached to the inner mitochondrial membrane

  2. Electrons are passed along the Electron Transport Chain releasing energy

  3. This energy allows Hydrogen ions to be pumped across the inner mitochondrial membrane

  4. The flow of these ions back through the membrane protein ATP Synthase results in the production of ATP

  5. Hydrogen ions and electrons combine with oxygen to form water

  
• Fermentation


  • In the absence of oxygen, fermentation takes place in the cytoplasm
  • Glycolysis takes place as normal, however the Pyruvate formed cannot enter the Citric Acid cycle
  • In animal cells, the Pyruvate is converted to Lactate
  • In plant & yeast cells, the Pyruvate is converted to Ethanol and CO2
  • Fermentation results in much less ATP being produced than in aerobic respiration

  
• Role of ATP


  • ATP is used to transfer energy to cellular processes which require energy
  • E.g the ATP released during aerobic respiration provides the energy required for Protein Synthesis

  
• Metabolic rate


  Can be measured by the rate of oxygen consumption, carbon dioxide production, or heat production
• Measuring metabolic rate


  Use respirometers, oxygen probes, carbon dioxide probes, calorimeters
• Organisms with high metabolic rates


  • Require more efficient delivery of oxygen to cells
• Organisms ranked by metabolic rate

  • Birds & Mammals
  • Reptiles & Amphibians
  • Fish
• Birds & Mammals


  • Have a Complete Double circulatory system with 2 Atria & 2 Ventricles
• Complete Double circulatory system


  • Enables higher metabolic rates to be maintained
  • No mixing of oxygenated & deoxygenated blood
  • Oxygenated blood can be pumped out at higher pressure
  • Enables more efficient oxygen delivery to cells
• Amphibians & Reptiles


  • Have an Incomplete Double circulatory system with 2 Atria & 1 Ventricle
• Incomplete Double circulatory system


  • Less efficient in the delivery of oxygen to cells
  • Mixing of oxygenated and deoxygenated blood in the single ventricle

  
• Fish


  • Have a single circulatory system with 1 Atrium & 1 Ventricle
  • Blood only passes through the heart ONCE in each complete circuit around the body

  
• As blood passes through a capillary bed (e.g. at the gills)

  • There is a drop in blood pressure
  • Blood is delivered to the capillary bed in the body tissues at LOW PRESSURE

  
• Conformers


  Organisms whose internal environment is dependent upon their external environment
• Conformers


  • Use behavioural responses to maintain optimum metabolic rate
  • Have low metabolic costs
  • Have a narrow range of ecological niches
• Regulators


  Organisms that can maintain their internal environment regardless of their external environment