bio u3 aos2

• Where does the Light Independent Stage occur?

  The Calvin Cycle occurs in the fluid-filled interior of the chloroplast; stroma.
• What happens during the Light Independent Stage (outline the steps)

  
  

  1. ATP and hydrogen (carried by NADPH) are transported to the stroma.
  2. Hydrogen combines with carbon dioxide to form complex organic compounds (e.g carbohydrates and amino acids)
  3. Then the RUBISCO enzyme fixes the carbon and the ATP provides chemical energy so the molecules can merge.
• What happens in the Light Dependent Stage?


  This stage occurs in the flat membranous disks (thylakoids) of leaves.

  > Light is absorbed by chlorophyll pigments which leads to the release of energised electrons.

  > The energy enters the electron transport chain (ETC) which leads to ATP production.

  
  

  > Light can also be absorbed by water, and then split (thru. photolysis) to create separate oxygen and hydrogen molecules. This is carried by the NADPH coenzyme.

  > Hydrogen and ATP are used in the process and oxygen is expelled out thru. the stroma as waste.
• What is photosynthesis?


  Photosynthesis is the process by which plants convert sunlight, carbon dioxide, and water into glucose and oxygen.

  > 6CO2 + 6H2O = C6 H12 O6 + 6O2
• What are chloroplasts?


  > They are membrane bound organelles in plant and autotroph cells that act as sites for photosynthesis.

  • They have a stroma(fluid), a thylakoid (sac-like and has a membrane that contains chlorophyll), lumen (fluid inside thylakoid), and granum (stack of thylakoid).
• C3 Calvin Cycle

  > Less efficient in dry and hot environments as stomata have to remain closed to retain plant water storage (minimise transpiration).

  • 6 CO2 molecules ara absorbed and combined with the other 30 carbons already in the cycle
  • > They leave the cycle as a glucose molecule and the other 30 are released back into the cycle.
• C4 Calvin Cycle


  The Rubisco enzyme warms up which causes it to undergo a conformational change. In doing so it becomes more complementary to oxygen molecules compared to carbon dioxide molecules. This results in it using oxygen as a substrate. This results in photorespiration - a much slower rate of photosynthesis, and the calvin cycle continues.
• C4 - Maximising Photosynthesis

  1. CO2 enters mesophyll cells

  2. CO2 fixed by PEP carboxylase enzyme

  3. PEP carboxylase adds carbon from CO2 to 3C molecule to create 4C molecule (oxaloacetate)

  4. Oxaloacetate converted to 4C molecule (malate) capable of being transported to bundle-sheath cells

  5. Malate breaks down in bundle-sheath cell, releasing CO2 which enters Calvin cycle

  6. Pyruvate formed from breakdown of malate transported back to mesophyll cell and converted to PEP with ATP

  7. PEP ready to contribute to fixation of CO2 and production of oxaloacetate, continuing the cycle
• PEP carboxylase


  • Enzyme responsible for initial carbon fixation in C4 plants
  • Has no affinity to bind to O2 (unlike Rubisco)
• Malate breaks down in bundle-sheath cell

  Releases CO2 which enters Calvin cycle
• How does temperature impact enzyme function?


  > warmer temperatures help facilitate faster chemical reactions as more kinetic energy is produced

  > however, there is a threshold for this. each enzyme has a specific optimal temperature where its activity is the most efficient (most frequent enzyme and substrate binding)

  too hot: the enzyme denatures and its active site shape suffers an irreversible conformational change -> no binding

  too cold: enzyme activity decreases significantly and may freeze (become inactive) however it can regain functionality when put under warmer conditions
• tolerance range


  > a wide temperature range in which an enzyme can function under; not to be confused with optimal temperature range.
• How does PH impact enzyme function?

  A scale used to measure the acidity or alkalinity of a substance

  > acids : low ph under 7

  > alkaline : high ph values over 7

  Like temperature, enzymes have an optimal PH they function well under.
• Competitive Inhibition


  Substrate and the inhibitor trying to bind to the active site @ the same time

  > Molecule in active site completey occupies and covers the enzyme's active site which prevents substrate from binding and the function can't occur/be catalysed.

  To bind with an active site the competitive inhibitor must have a complementary shape therefore it must have similair shape to the substrate.
• Enzyme inhibitors:


  > Molecules that bind to an enzyme to prevent it from initiating a function.
• Non-competitive inhibition:


  Molecules bind to an allosteric site (not active site).

  > this causes a conformational change in the enzyme's active site

  • thus preventing a reaction as the substrate can't bind to it
• Reversible Inhibition


  Weak temporary bonds formed between an enzyme and an inhibitor that can be broken

  > This means reversible inhibitors typically slow the rate of a given enzyme-catalysed reaction, but do not stop it indefinitely.
• How can reversible inhibition be overcome?

  The inhibitor can have its effects overcome by increasing the amount of substrate present. This provides a greater chance of substrate binding to the enzyme and not an inhibitor, increasing overall enzyme functioning
• Irreversible Inhibition


  Inhibitors will form strong bonds that are unbreakable. This means that if an irreversible inhibitor binds to an enzyme, the enzyme is unable to bind with any substrate or catalyse any reactions indefinitely. This means that regardless of how much extra substrate is present, the reaction can never occur
• What are enzymes?


  Enzymes are molecules that are organic catalysts. They increase level of chemical reaction (sometimes to a faster rate than normal) without their sources being depleted.
• Enzyme Binding Steps


  > Substrate will enter the active site of the enzyme and bind to it

  > The enzyme and substrate will undergo slight conformational changes to fit eachother. Chemical bonds hold them together

  > The reaction occurs and the products are made. They are then released allowing for the enzyme to catalyse further reactions.
• What is the collision theory?


  The collision theory states that chemical reactions occur when particles collide with sufficient kinetic energy and proper orientation, because it overcomes the activation energy.
• Anabolic reaction


  Two or more smaller molecules combine to create a larger one
• Catabolic reaction


  A larger molecule turning into two or more smaller molecules.
• Activation energy


  Input of minimum amount of energy required for a chemical reaction to start
• Glycolysis Inputs


  1 glucose (C6H12O6)

  2 ADP + 2 Pi

  2 NAD+ + 2 H+
• Glycolysis Outputs


  2 pyruvate

  2 ATP

  2 NADH
• Kreb's Cycle Inputs


  2 acetyl-CoA (derived from 2 pyruvate)

  2 ADP + 2 Pi

  6 NAD+ + 6 H+

  2 FAD + 4 H+
• Kreb's Cycle Outputs


  4 carbon dioxide (CO2)

  2 ATP

  6 NADH

  2 FADH2
• The electron transport chain

  Location: the cristae of the mitochondria

  Inputs

  6 oxygen (O2) + 12 H+

  26 or 28 ADP + 26 or 28 Pi

  10 NADH 10

  2 FADH2

  Outputs

  6 water (H2O)

  26 or 28 ATP

  10 NAD+ + 10 H+

  2 FAD + 4 H+