Metabolism Part 2

• A healthy diet consists of much more than just glucose
• Vitamins and minerals

  Act as coenzymes and cofactors (necessary for the substrate to bind to an active site of an enzyme)
• Most of a healthy diet is used for Energy And proteins. Fats are used for this purpose too.
• Cellular respiration

  1. Carbohydrates (ex: starch) are broken down by enzymes like amylase to make glucose

  2. Proteins are broken down by proteases into amino acids

  3. Amino acids are deaminated (the amino group is removed)

  4. Lipase enzymes break Fats down into Fatty acids and glycerol

  5. Glycerol is converted to G3P and used in glycolysis

  6. Fatty acids enter the mitochondria and carbon atoms are removed 2 at a time, making acetyl-CoA
• Ethanol fermentation

  1. Occurs in the absence of Oxygen (anaerobic conditions)

  2. Molecule: pyruvate (produced during glycolysis)

  3. End products: pyruvate, CO₂ + Ethanol

  4. Purpose: regenerates NAD to fuel glycolysis
• Lactate Fermentation

  1. Also occurs under anaerobic conditions

  2. Molecule: Pyruvate (from Glycolysis)

  3. End product: Pyruvate, Lactate

  4. Purpose: generates NAD for continued glycolysis
• Photosynthetic organs of plants

  • Structure maximizes Surface area and limits distance gases (O₂) have to travel
  • Have a waxy cuticle to protect from over-absorption of water/excessive sunlight
  • Have special photosynthetic cells called mesophyll
  • Have guard cells that create tiny openings called Stomata that regulate exchange of CO₂ and oxygen and allow water vapour to enter or escape by transpiration
  • Have Vascular bundles ("veins") that transport water and minerals to roots and leaves and carry carbohydrates from the leaves to the roots
• Chlorophyll


  • Green coloured pigments that absorb light
  • Components: porphyrin ring with Mg at the centre, alternating single and double bonds, delocalized e- that absorb light, hydrocarbon tail that anchors the chlorophyll molecule in the membrane
• The Light Reactions

  1. Photoexcitation: absorption of a photon and excitation of an electron of chlorophyll

  2. Electron transport: transfer of the excited electron through a series of membrane-bound electron carriers, resulting in the pumping of a proton through the photosynthetic membrane, which creates an H+ reservoir and eventually reduces an electron acceptor

  3. Chemiosmosis: the movement of protons through ATP synthase to drive the phosphorylation of ADP to ATP
• Photoexcitation

  • Excitation: the absorption of energy by an electron, raising it to a higher energy level
  • Fluorescence: rapid loss of energy (in the form of light)
• Photosystem

  • Complex of chlorophyll molecules, accessory pigments and proteins embedded in the thylakoid membrane
  • Two parts: 1) antenna complex (chlorophyll molecules and accessory pigments) and 2) Reaction centre (a number of chlorophyll a molecules)
• Antenna Complex

  A number of chlorophyll molecules and accessory pigments embedded in the thylakoid membrane that absorb a photon and transfer the energy from pigment to pigment until it reaches a Chlorophyll molecule in the reaction centre
• Reaction Centre

  A transmembrane protein complex containing Chlorophyll a whose electrons absorb light energy and begin the process of photosynthesis
• Photosystem I (P700)

  Chlorophyll a with absorption spectrum peaking at 700 nm (red light)
• Photosystem II (P680)


  Chlorophyll a with absorption spectrum peaking at 680 nm (red light)
• Non-cyclic Electron Flow and Chemiosmosis

  1. Occurs on the thylakoid membrane and in the thylakoid lumen

  2. Reactants: Sunlight (photons), chlorophyll, ADP, Pi, NADP+, water

  3. Products: NADPH, ATP, oxygen

  4. Energy from sun photon strikes PSII, exciting an electron in Chlorophyll

  5. Energized electron is picked up by plastoquinone (PQ)

  6. PQ passes electrons to cytochrome complex, causing it to pump H+ into the thylakoid lumen

  7. Proton gradient in lumen leads to ATP synthesis via ATP synthase (chemiosmosis)

  8. Electrons from PSII are replaced by "Z" enzyme splitting water, releasing O₂ as waste

  9. Plastocyanin (PC) picks up electrons and passes them to PSI, where they are struck by photons again

  10. Excited electrons from PSI are picked up by ferredoxin (Fd) and used to reduce NADP+ to NADPH
• Carbon Fixation (Calvin Cycle)

  1. 3 CO₂ molecules are captured by 3 RuBP (5-C) molecules, catalyzed by rubisco

  2. The resulting 6 unstable 6-C compounds break into 6 3-C PGA

  3. ATP and NADPH from light reactions provide energy to reduce PGA to G3P

  4. One G3P is removed to make glucose, another is removed for the next cycle

  5. Remaining G3P molecules go through "sugar shuffle" reactions and are phosphorylated by ATP to reform RuBP, continuing the cycle