Photosynthesis and Cellular Respiration Stuff

• Photosynthesis


  The process that converts energy from the Sun into chemical energy that is used for living cells, solar energy is converted into chemical energy in the form of glucose
• Photosynthesis


  1. 6 CO2 (g) + 12 H2O (l) + photons → C6H12O6 (aq) + 6 O2 (g) + 6 H2O (l)

  2. carbon dioxide + water + light energy → glucose + oxygen + water
• Organisms that carry out photosynthesis

  • Plants
  • Bacteria
  • Phytoplankton such as algae
• Greater than 70% of net photosynthesis on Earth is carried out by phytoplankton in the world's oceans
• Photosynthesis Overview


  • Photosynthesis is the most important large-scale chemical process on Earth – we rely on it for food and oxygen
  • All organic materials are constructed using the building blocks and energy supplied by photosynthesis (see wood, paper, cotton, drugs, fossil fuels etc)
  • Currently humans consume about 40% of the Earth's primary production to meet our daily needs
• Chlorophyll


  Green pigment in photosynthetic organisms that absorbs sunlight
• Cellular Respiration Overview


  • The set of the metabolic reactions and processes that take place in organisms' cells to convert biochemical energy from nutrients (glucose) into adenosine triphosphate (ATP, usable energy), and then release waste products
  • Used to release energy for all kinds of work, glucose is broken down by oxygen and free electrons are transferred to cells to carry out work by ATP – Adenosine Tri-Phosphate
• Cellular Respiration


  1. C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 12H2O + Energy (ATP)

  2. Glucose + Oxygen → Carbon Dioxide + Water + Energy (ATP)
• Photosynthesis and Cellular Respiration


  • These two biochemical reactions are coupled, photosynthesis produces the oxygen required for cellular respiration and cellular respiration provides the CO2 required to make photosynthesis work
  • Cellular respiration breaks down the sugar produced from photosynthesis in order to provide the energy required to create ATP
• Oxidation


  A molecule or atom loses electrons (energy released)
• Reduction


  A molecule or atoms gains electrons (energy gained)
• LEO goes GER!
• Examples of oxidation and reduction


  • ATP/ADP + Pi – Energy is released for cellular functions when ATP is broken down to ADP, ATP is oxidized (loses electrons), ADP is reduced (gains electrons) – the transfer of electrons is what releases the energy
  • NADP+/NADPH
  • NAD+/NADH
  • Glucose breakdown
  • FAD+/FADH2
• 2 main sets of reactions in Photosynthesis

  • I) Light Dependent Reactions – Light energy excites chlorophyll, reduces NADP+ to NADPH through electron transport and chemiosmosis
  • II) Light Independent Reactions – DO NOT NEED SOLAR ENERGY, Calvin Cycle and carbon fixation to create glucose
• Chloroplast Structure


  • Light is harvested into energy in the form of glucose in chloroplasts, the internal structure of this organelle is necessary to understand to be able to follow how photosynthesis proceeds
  • There is an inner membrane and an outer membrane with an INTERMEMBRANE SPACE B/T the two (important for chemiosmosis)
  • Stroma – (like a cell's cytoplasm), protein-rich gelatinous matrix, holds a chloroplast together
• Thylakoids

  • Thylakoids are stacks of photosynthetic material, housed within the stroma
  • A stack of thylakoids are called GRANA, each chloroplast has approx. 60 grana, each grana houses 30-50 thylakoids
  • Chlorophyll is found on the thylakoid membrane, the inside of a thylakoid is fluid filled, called the LUMEN
  • Between grana, there may be unstacked thylakoids called lamellae, these connect grana to exchange the raw materials of photosynthesis
• Light Dependent Reactions


  • Happens in the THYLAKOIDS
  • Chlorophyll and photosynthetic pigments are arranged in structures called PHOTOSYSTEMS, of which there are two, photosystem I and II, named after the timeline of their discovery
  • The purpose of the light dependent reactions is to release energy from electrons to fuel the light independent reactions and to reduce NADP+ to NADPH, an electron carrier molecule, which transports electrons to the dark reactions
• Light Dependent Reactions – How they work


  1. Photons of light energy penetrate PS II (actually the 1st photosystem) and PS I (the 2nd photosystem)

  2. Pigments in the photosystem absorb light energy and pass it onto the REACTION CENTRE, a specialized chlorophyll a molecule

  3. The light energy absorbed by the reaction centre energizes electrons within it, the electron leaves the reaction centre and is carried from PS II to the 1st electron transport chain involved in photosynthesis
• Photolysis


  The same time an electron is liberated from the reaction centre of PS II, sunlight splits a water molecule within the chloroplast, this releases electrons which replenish lost electrons in the reaction centre, oxygen and hydrogen are also released. This is the oxygen creating part of photosynthesis, the H+ ions are used in chemiosmosis to create ATP
• Photolysis


  2 H2O + light energy → 4 H+ + O2 + 4 e-
• Electron Transport Chains


  • Exist in both cellular respiration and photosynthesis, 2 in photosynthesis, crucial parts of the energy creating process
  • Electron transport chains are collections of proteins (called cytochromes) in which electrons are passed through, redox reactions occur along the ETC's as the electrons are passed along cytochromes, releasing energy every time a redox reaction occurs
  • ETC I in photosynthesis uses the energy provided from electron exchange to aid in ATP creation, ETC II creates NADPH
• Electron Transport Staircase


  1. As electrons are passed along the ETC from cytochrome to cytochrome, they lose energy at every step, eventually ending up with no energy

  2. At the end of ETC I is PS I – the now de-energized electron enters the reaction centre of PS I

  3. At the same time this de-energized electron enters PS I, light energy has energized another electron from this photosystem to enter the 2nd ETC, the de-energized electron replaces the electron that got bumped up to ETC II

  4. The energy from the 2nd ETC is used to reduce NADP+ to NADPH

  5. NADPH is used to provide the raw materials to create sugar in the dark reactions
• Chemiosmosis


  • How exactly is ATP created? Remember, ATP is the main molecule used by biological organisms to fuel metabolic reactions
  • A combination of photolysis, ETC's, and protein complexes in the thylakoid membrane create a "biological battery" across this membrane to provide the energy to create ATP
• How Chemiosmosis Works


  1. As water is split via photolysis, H+ ions are freed up as well as electrons

  2. H+ ions are used to create a concentration gradient across the thylakoid membrane between the stroma of the chloroplast and the lumen of the thylakoids

  3. The energy from the ETC pumps H+ ions into the lumen of the thylakoid, they are given energy as they move against their concentration gradient to an area of high H+ concentration, this is ACTIVE TRANSPORT

  4. The active transport of H+ into the lumen creates a potential difference, or charge, across the thylakoid membrane, inside the lumen is more positively charged than the stroma

  5. A special protein channel in the thylakoid membrane allows energized H+ ions to move back down their concentration gradient into the stroma of the chloroplast, as they move back to equilibrium concentrations, H+ ions release a lot of energy, catalyzing the creation of ATP
• Light Independent Reactions


  • NADPH and ATP enter the stroma after they are created from Electron Transport and Chemiosmosis
  • The dark reactions occur in the STROMA
  • The dark reactions use a biochemical process called the CALVIN CYCLE to create glucose from the products of the light reactions
• The Calvin Cycle


  1. I) Carbon Fixation – CO2 taken in from the environment bonds to a 5C carbon compound called Ribulose Biphosphate (RuBP) – the 6C compound is unstable and breaks up into TWO 3C compounds

  2. II) Reduction: The newly formed 3C compounds are poorly energized, to raise their energy state, 1st ATP phosphorylates (adds phosphates) to activate the molecule then NADPH reduces it by adding electrons, the newly molecule from these reactions is called G3P (glyceraldehyde-3-phosphate)

  3. III) RuBP recovery – the reduced molecules of G3P remaining in the Calvin Cycle are recycled to make for RuBP. Energy supplied by ATP breaks the bonds in G3P to rebuild RuBP molecules

  4. Because only 2 molecules of G3P leave the Calvin Cycle for every 12 produced, the cycle must turn 6 times to produce one molecule of glucose

  5. The oxidized electron carrier molecules (ADP and NADP+), return to the light reactions to be reduced again
• Cellular Respiration


  • Set of metabolic reactions that occurs in living organisms to release the energy stored in glucose
  • Provides energy to sustain work for all sorts of energy consuming processes including basal metabolism, digestion, exercise, movement, higher brain functions (thinking, sensation, perception, etc), essentially everything we do to sustain our daily activities
• Cellular Respiration


  1. glucose + oxygen -> carbon dioxide + water + energy (ATP)

  2. C6H12O6 (s) + 6O2 (g) -> 6CO2 (g) + 12H2O + energy (ATP)
• Three Types of Reactions Necessary for Cellular Respiration

  • ReDox reaction
  • endergonic/exergonic
  • Catabolism/anabolism
• Redox Reactions


  • Review – for energy exchange, there must be an exchange of electrons
  • LEO goes GER
  • When glucose breaks down, the hydrogen ions get transferred to oxygen and makes water. The electrons from this breakdown are transferred to ADP, ADP gain a P to make ATP
• Ized electron carrier molecules

  ADP and NADP+
• Photosynthesis


  Process where ized electron carrier molecules return to the light reactions to be reduced again
• Cellular Respiration


  Set of metabolic reactions that occurs in living organisms to release the energy stored in glucose
• Cellular Respiration


  • Provides energy to sustain work for all sorts of energy consuming processes including basal metabolism, digestion, exercise, movement, higher brain functions (thinking, sensation, perception, etc) - essentially everything we do to sustain our daily activities
• Cellular Respiration


  glucose + oxygen -> carbon dioxide + water + energy (ATP)
• Three Types of Reactions Necessary for Cellular Respiration

  • Redox reaction
  • Endergonic/exergonic
  • Catabolism/anabolism
• Redox Reactions


  For energy exchange, there must be an exchange of electrons. LEO goes GER. When glucose breaks down, the hydrogen ions get transferred to oxygen and makes water. The electrons from this breakdown are transferred to ADP, ADP gain a P to make ATP
• Endergonic/exergonic


  Endergonic reactions absorb energy for work (ADP + P -> ATP), molecules are built. Endergonic reactions always happen in unison with exergonic reactions, which breakdown molecules to release energy to perform work (glucose -> carbon dioxide + water + energy)
• Catabolism/Anabolism


  Catabolic reactions break down large molecules to their constituent parts, we break down carbs, proteins, and fats into glucose to be stored as glycogen in the liver for future metabolic work. Anabolism builds large molecules from smaller ones. We breakdown molecules of food into their basic parts (catabolism), reorganize them, and rebuild them in the configurations our bodies need (anabolism)
• Overall efficiency of Cellular Respiration is only 36%. That means 64% of the potential energy available in ONE glucose molecule is lost, released as heat