Variation In Biochemistry & Cell Structure

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Variation In Haemoglobin

  • Red blood cells contain haemoglobin.
  • Haemoglobin is a protein with a quaternary structure.
  • Each chain has a haem group which contains iron.
  • Haemoglobin has a high affinity for oxygen; it can carry up to 4 oxygen molecules.
  • Oxygen joins to haemoglobin in the lungs to form oxyhaemoglobin.
  • This is a reversible reaction, since oxygen dissociates from haemoglobin at the body cells.
  • The partial pressure of oxygen (ppO2) is a measure of oxygen concentration.
  • At high ppO2, oxygen associates with haemoglobin.
  • At low ppO2, oxygen dissociates with haemoglobin.
  • Alveoli have a high ppO2, so oxygen associates with haemoglobin.
  • Oxygen dissociates with haemoglobin at respiring tissues.
  • Where ppO2 is high, haemoglobin has a high affinity for oxygen, and so a high saturation of oxygen.
  • Where ppO2 is low, haemoglobin has a low affinity for oxygen, and so a low saturation of oxygen.
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Variation In Haemoglobin

  • Carbon Dioxide Concentration Affects Oxygen Unloading:
    • Oxygen dissociates more readily at higher ppCO2.
    • When cells respire, they produce CO2, and so raise the ppCO2.
    • This increases the rate of oxygen unloading.
    • The saturation of blood with oxygen is lower, so more oxygen is released.
    • This is called the Bohr Effect.
  • Haemoglobin is different in different animals.
    • Organisms in environments with low oxygen concentration have haemoglobin with a higher affinity for oxygen.
    • This results in a dissociation cure to the left.
    • Active organisms with a higher oxygen demand have haemoglobin with a lower affinity for oxygen.
    • This results in a dissociation curve to the right.
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Variation In Carbohydrates & Cell Structure

  • Carbohydrates are made from monosaccharides.
  • Condensation reactions join monosaccharides together, and release water.
  • Glycosidic bonds join sugars together.
  • Plants store excess glucose as starch.
  • Starch is made from 2 alpha glucoses:
    • Amylose: Long, unbranched chain of alpha glucose. It has a coiled structure and is compact, so good for storage.
    • Amylopectin: Long, branched chain of alpha glucose. It's side branches allow enzymes to quickly break down the glycosidic bonds, so glucose is released quickly.
  • Starch is insoluble, so there is no osmosis.
  • Animals store excess glucose as glycogen, which is also an alpha glucose.
  • It has lots of side branches, so stored glucose is released quickly.
  • Glycogen is compact, and so good for storage.
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Variation In Carbohydrates & Cell Structure

  • Cellulose is long, unbranched chains of beta glucose.
  • There are straight bonds between the sugars, so the chains are strong.
  • The chains are linked by hydrogen bonds, forming strong microfibrils.
  • These microfibrils allow cellulose to provide structural support for the cells.
  • Similarities:
    • Plasma Membrane: Controls what goes in and out of cells.
    • Cytoplasm: Contains enzymes. Chemical reactions happen here.
    • Nucleus: Contains genetic material.
    • Mitochondria: Produces ATP for respiration.
    • Ribosomes: Protein synthesis.
  • Differences - Plant Cells have:
    • Cell Wall: Made of cellulose, it supports the cell.
    • Vacuole: Contains cell sap.
    • Chloroplasts: Where photosynthesis occurs.
      • They are surrounded by a double membrane.
      • They contain thylakoid membranes which stack to form grana.
      • The grana are linked by lamellae.
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