metabolism, respiration and photosynthesis

• A substrate and competitive inhibitor share...

  • A similar molecular shape / size
  • So they both can fit into / bind / are complementary to the enzyme’s active site

  A substrate and competitive inhibitor differ…

  • A competitive inhibitor may stay irreversibly bound to the enzyme whereas a product will always unbind from the enzyme
  • No product is formed with a competitive inhibitor whereas a substrate will form products
• Copper (II) ions work to inhibit the activity of catalase by:

  • Inhibitor binds to allosteric site (on the enzyme) 
  • Changes tertiary/3D structure of enzyme active site so it is no longer complementary to substrate OR changes tertiary/3D structure of enzyme active site so that the substrate and enzyme/active site cannot bind/fit (together) / E-S complex cannot form
• Similarities between competitive and non-competitive inhibition:

  • The inhibitor binds to the enzyme (surface)
  • There is a reduction in the enzyme’s rate (of catalysis)
  • The rate of initial reaction is inversely proportional to inhibitor concentration / as inhibitor concentration increases, rate of reaction decreases
• Differences between competitive and non-competitive inhibition:

  • The specific site of binding differs, competitive inhibitors bind to the active site AND non-competitive inhibitors bind to an allosteric site
  • So, in competitive inhibition, the active site is blocked AND in non-competitive inhibition, the active site is distorted / changes shape
  • Increasing substrate concentration will decrease the effect of competitive inhibition BUT will not affect non-competitive inhibition
• Oxidative phosphorylation:

  • Electrons are passed along the electron transport system
  • Within the inner membrane/cristae of the mitochondria
  • Energy is released as electrons move from one carrier to the next
  • Carrier is oxidised as it loses an electron to the next carrier
  • The energy released during electron transport causes proton pumping
  • Protons pumped against concentration gradient from matrix to intermembrane space
  • Protons move down their concentration gradient back through the ATP synthase
  • The passage of protons through ATP synthase causes phosphorylation of ADP/ production of ATP
• The role of co-enzymes and carrier proteins in the synthesis of ATP is:

  • NAD/FAD are reduced / hydrogen ions attach/bond to NAD/FAD/co-enzymes
  • Hydrogen ions / electrons are passed on in a series of REDOX reactions
  • The REDOX reactions take place on carrier proteins (embedded in the cristae membrane)
  • Energy is released as the electrons are transferred
  • The energy is used to synthesise ATP from ADP and phosphate (using ATP synthase enzyme)
• The techniques used by Calvin to identify the Calvin cycle were...

  • Use of apparatus called the lollipop which was thin to enable light to be shone through to reach all algae
  • Use of paper chromatography which separated out the different carbon compounds made by the algae
  • Use of autoradiography which enabled radioactive carbon compounds to be identified
• Ferredoxin is involved in the reduction of NAPD by...

  • It accepts photoactivated electrons
  • (From the) reaction centre P700 in photosystem 1
  • Ferredoxin is reduced (by the electrons)
  • Ferredoxin donates/passes the electrons to NADP (thereby reducing it)
• Light energy is used by crop plants during the light-dependent reaction in the following way...

  • Light energy excites electrons to a higher energy level
  • Electrons excited from PS II are used to produce a proton gradient
  • Electrons from PS I are used to reduce NADP
  • The electrons move along the electron transfer chain releasing energy
  • The energy is used to join ADP with Pi to form ATP
  • Photolysis of water produces electrons, oxygen and protons
  • NADP is reduced by electrons
•  During the light-independent reaction...

  • RuBP (5C) combines binds CO2
  • To form glycerate 3-phosphate (2*3C)
  • Using ATP and reduced NADP
  • Two molecules of glycerate 3-phosphate form a hexose sugar (6C)
  • All the ribulose bisphosphate/RuBP is regenerated
  • 10 molecules glycerate 3-phosphate (3C) are formed from 6 molecules of RuBP (5C); [1 mark]
• The role of protons in the light dependent reaction are...

  • H⁺ are pumped from the stroma into the intermembrane space (using energy from photoactivated electrons)
  • Photolysis of water provides a sources of H⁺
  • High concentration of H⁺ builds up
  • H⁺ move down their concentration gradient
  • Through ATP synthase
  • Aiding chemiosmosis
• Similarities of ETC in respiration and photosynthesis include:

  • Both involve the movement of electrons down a series of transport proteins through REDOX reactions
  • Both drive the movement of H+ protons across the membrane to produce an electrochemical/proton gradient
  • Both produce ATP through ATP synthase
  • Both require coenzymes to function
  • Chemiosmosis is used in both processes
• Differences of ETC in respiration and photosynthesis include:

  • In the ETC of photosynthesis electrons are provided from chlorophyll when photons hit PS II; the ETC of respiration obtains electrons from NADH/FADH
  • In respiration, oxygen is the final electron acceptor; in photosynthesis, NAD is the final electron acceptor
  • In respiration water is formed at the end from oxygen, electrons and H+ protons; in photosynthesis, water is split in photolysis to provide electrons to replace those lost from PSII
• Differences of ETC in respiration and photosynthesis include:

  • The products of the ETC in respiration are H2O/NAD/FAD; in photosynthesis the products are reduced NADP/NADPH2 /O2
  • In respiration, the coenzymes/NADH/FADH become oxidised in the ETC; in photosynthesis, the coenzyme/NADP becomes reduced
• The role of water in photosynthesis is:

  • Water is involved only in non-cyclic phosphorylation, split by photolysis
  • Photolysis occurs in PS II in the light dependent reactions
  • Photolysis produces oxygen, electrons and H+
  • The electrons replace those lost from PS II to be passed through the electron transport chain/to photosystem I
  • Electrons reduce NADP
  • Oxygen is diffused out of the leaf as a waste product
  • The protons are picked up by NADP to make NADPH/reduced NADP
• Explain how chemical energy is generated in the ETC:

  1. NAD/FAD is reduced by gaining two electrons in glycolysis/link reaction/Krebs cycle
  2. reduced NAD/FAD delivers electrons to ETC in mitochondrial inner membrane/cristae
  3. electrons release energy as they flow along the chain
  4. electrons from ETC accepted by oxygen
  5. protons pumped into intermembrane space
  6. energy «from electrons» used to pump protons into intermembrane space generate a proton gradient
  7. energy released as protons pass through ATP synthase
  8. converts ADP to ATP/phosphorylates ADP