Digestion

• Calorie requirements


  When fewer calories are taken in than are expended, fuel is taken out of storage deposits & oxidized (digested)
• Calorie balance


  1. Breakdown (digest) glycogen from liver & muscle cells

  2. Metabolize (digest) fat
• When calories taken in exceed calories expended

  Energy is stored
• Malnutrition


  Can occur due to ongoing imbalance of intake/output of calories, including underweight, overweight and obesity
• Carbohydrates


  • Contain carbon, hydrogen, and oxygen atoms
  • Range in size and complexity from polysaccharides to monosaccharides
• Monosaccharides


  Have general structure C6H12O6
• Carbohydrate functions


  • Main human energy source
  • Help control blood glucose and insulin metabolism
  • Participate in cholesterol and triglyceride metabolism
  • Energy storage
• Simple carbohydrates


  • Mono and disaccharides (also called sugars)
  • Easily utilized for energy- cause rapid rise in blood sugar (High GI- glycaemic index)
• Simple carbohydrates


  • Fructose
  • Lactose
  • Sucrose
  • Glucose
• Complex carbohydrates


  • Oligo and polysaccharides
  • Take longer to digest and have slow effect on blood sugar (Low GI)
• Complex carbohydrates


  • Cellulose
  • Amylose
• Starches


  • Complex CHOs with a lot of glucose
  • Found in potatoes, pasta and wheat
• Fiber


  • Non-digestible complex CHO with a lot of cellulose and pectin
  • Insoluble: Good for healthy bacterial growth in colon and help with defecation
  • Soluble: helps decrease blood cholesterol
• Proteins


  • Linear polymers built of monomer units called amino acids
  • Function dependent on individual structure, determined by sequence of 20 possible amino acids
  • Contain C, H, O, N and often S, P
• Protein functions


  • Provide between 15-25% total food energy intake
  • Catalysts (enzymes)
  • Transport and store other molecules
  • Generate movement
  • Transmit nerve impulses
  • Control growth and differentiation
• Lipids


  • Group of compounds usually insoluble in water
  • Contain C, H, and small amounts of oxygen
  • Made up of glycerol and fatty acids
  • Triacylglycerols make up 95% of dietary lipids
• Lipid functions


  • Serving as energy storage
  • Constituents of membranes
  • Hormones
  • Vitamins A, D, E and K (fat soluble)
  • Oxygen/ electron carriers
• Vitamins


  Organic substances (containing carbon) with important roles in metabolism such as co-enzymes or co-factors
• Vitamins


  • A: retinol production (eyesight)
  • C: protein metabolism
  • D: required for calcium absorption
  • E: antioxidant
  • K: required for blood clotting
  • B: 8 different vitamins, needed in energy metabolism
• Vitamin deficiencies can cause scurvy, rickets, blindness, and anemia
• Minerals


  • Inorganic substances (don't contain carbon)
  • Required in diet in very small amounts
  • Roles in biological processes
• Minerals


  • Calcium
  • Iron
  • Iodine
• Mineral deficiencies can cause osteoporosis, goiter, and iron deficiency anemia
• Enzymes


  • Proteins that are biological catalysts
  • Reduce the energy required to start a reaction
  • Speed up reactions in the body
  • Essential to sustain life
• Enzyme structure and function

  • Each enzyme is involved in a specific reaction
  • It assists in the building or breaking of molecules (substrates)
  • Each enzyme has a specific substrate
  • Enzymes either speed up the breakdown of one substrate into multiple products or speed up the process for turning multiple substrates into one product
• Enzyme optimum conditions


  • The enzyme will work to its full capacity at its optimum temperature and pH
  • High temperature or altered pH can permanently change the active site and denature the enzyme
  • Low temperature will inactivate the enzyme
• Enzymes lower the activation energy of reactions, allowing them to occur more quickly
• Factors affecting enzyme rate

  • pH
  • Temperature
  • Enzyme concentration
  • Substrate concentration
  • Inhibition
• Enzymes work best at the temperatures they are found in, e.g. 37°C for the human body
• Effect of temperature on enzymes

  • Increase in temp = increase in activity
  • Increase in activity = increase in collisions between substrate and enzyme → faster rate of reaction
  • If temperature is too high, bonds break and the protein loses its functional shape (becoming permanently denatured)
• Effect of pH on enzymes


  • Each enzyme has an optimum pH at which it works
  • Most work effectively at pH7 (neutral)
  • Optimal pH relates to the environment in which the enzyme works
  • Change in pH from the optimum can change the shape of an enzyme and affect its ability to combine with its substrate
• Effect of enzyme concentration

  • If the amount of enzyme is increased, the amount of product made per unit time increases
  • Enzyme molecules are not used up in a reaction and are available for reuse
• Effect of substrate concentration

  • Amount of substrate or enzyme present in a reaction mix can limit the amount of product produced
  • Increase in substrate concentration increases the rate of reaction
• pH


  Neutral (pH 7)
• Optimal pH of an enzyme


  • Relates to the environment in which it works
• Enzymes and their optimal pH

  • Pepsin in the stomach (pH 2)
  • Catalase in cells of the liver (pH 7)
  • Alkaline phosphatase in bone (pH 9.5)
• Change in pH from the optimum

  Can change the shape of an enzyme and affect its ability to combine with its substrate
• Enzyme is less able to combine with its substrate

  Unable to act and the rate of the metabolic reaction declines
• Enzyme concentration


  Only a very small number of enzyme molecules are usually involved in a reaction and these produce a given amount of product per unit time
• If the amount of enzyme is increased


  The amount of product made per unit time increases