Biology

• Respiration


  The need for cellular respiration
• Mitochondrion


  • Inner and outer mitochondrial membranes, cristae, matrix and mitochondrial DNA
• Photosynthesis is the process that allows energy to enter nearly all ecosystems, producing the organic hexose sugar glucose from inorganic carbon dioxide and water
• Plants (and any organisms that eat them) will need to respire in order to use the chemical energy in the bonds of glucose
• Flow of energy through a system

  1. Plants produce organic molecules

  2. Molecules are used in respiration to make ATP

  3. ATP is used to do work in the cell
• How ATP may be broken down and reformed

  ATP is very easily broken down, but this means it is not a good long-term store of energy. Instead, what is used by cells/organisms?
• ATP


  Small, water soluble, releases small quantities of energy, hydrolysed and reformed in one step
• Synthesis of ATP


  1. Substrate level phosphorylation

  2. Chemiosmosis
• Substrate level phosphorylation involves transfer of phosphate from a high-energy intermediate molecule to ADP, with the aid of an enzyme
• Chemiosmosis is a reaction which has resulted in a proton gradient being used to drive the synthesis of ATP
• The processes of the link reaction, krebs cycle and oxidative phosphorylation occur in a mitochondria
• Mitochondria


  • Presence of 70s ribosomes and naked DNA suggests they were once free-living prokaryotic cells
  • The inner membrane is permeable to H+
  • The cristae give a large surface area for the proteins of the electron transport chain and ATP synthase enzymes to attach
• Cofactor


  A non-protein component which is needed for an enzyme to carry out its role as a biological catalyst
• Coenzyme


  An organic cofactor
• Prosthetic group


  A permanent non-protein component of an enzyme/protein which is needed for it to carry out its function
• Glycolysis


  Phosphorylation of glucose to hexose bisphosphate, splitting of hexose bisphosphate into two triose phosphate molecules and further oxidation to pyruvate, production of a small yield of ATP and reduced NAD
• Coenzymes


  Vital in transferring protons, electrons and functional groups between the different reactions in respiration
• NAD


  Takes part in all stages of respiration, NADH is reoxidised in oxidative phosphorylation to produce 3 ATP molecules
• FAD


  Only involved in the krebs cycle and oxidative phosphorylation, where FADH is reoxidised to produce 2 ATP molecules
• Coenzyme A


  Transfers a 2 carbon acetyl fragment to the Krebs cycle
• Redox reactions are reactions in which one substance is oxidised and another is reduced, e.g. by transfer of oxygen, hydrogen or electrons
• NAD and FAD allow the oxidation of other substances (which lose hydrogen) by accepting hydrogen and becoming reduced</b>
• Glycolysis


  Occurs in the cytoplasm, 6 carbon glucose is split into two smaller, 3 carbon molecules of pyruvate
• Phosphorylation


  Addition of a phosphate group
• Lysis


  Breaking apart a larger molecule into smaller ones
• Oxidation/Dehydrogenation


  Removal of H
• For each molecule of glucose undergoing glycolysis, there is a net production of 2 ATP, 2 pyruvate, and 2 NADH
• Substrate level phosphorylation refers to the ATP produced in glycolysis (directly from the substrate without the ETC/oxidative phosphorylation)
• Glycolysis is the first stage of both aerobic and anaerobic respiration
• Link reaction


  Decarboxylation of pyruvate to acetate, reduction of NAD, combination of acetate with coenzyme A
• Krebs cycle


  Formation of citrate from acetate and oxaloacetate, reconversion of citrate to oxaloacetate, importance of decarboxylation, dehydrogenation, reduction of NAD and FAD, and substrate level phosphorylation
• Link reaction


  To include the decarboxylation of pyruvate to acetate, the reduction of NAD, and the combination of acetate with coenzyme A
• Krebs cycle


  To include the formation of citrate from acetate and oxaloacetate and the reconversion of citrate to oxaloacetate (names of intermediate compounds are not required) AND the importance of decarboxylation, dehydrogenation, the reduction of NAD and FAD, and substrate level phosphorylation
• The Link Reaction occurs in the matrix of the mitochondrion
• Link reaction


  1. Decarboxylation by pyruvate decarboxylase (CO2 is removed)

  2. Dehydrogenation by pyruvate dehydrogenase (two H are removed and used to reduce NAD - this is later used to produce ATP)

  3. Forming is a 2C molecule called an acetyl group which combines with coenzyme A (CoA) to form acetyl coenzyme A (acetyl CoA)
• The link reaction occurs twice for each molecule of glucose (two molecules of pyruvate are produced from glycolysis)
• Overall final products of the Link Reaction, from one molecule of glucose

  • 2 x acetyl co-enzyme A - to Kreb's cycle
  • 2 x CO2 - waste product, diffuses away
  • 2 x reduced NAD (NADH) - to oxidative phosphorylation
• Pyruvate


  3 carbon atoms
• Acetyl


  2 carbon atoms
• 2 acetyl CoA will be produced per molecule of glucose as one molecule of glucose yields two pyruvate molecules (which are converted to acetyl CoA)