Respiration

• During respiration, a chemical reaction occurs in which sugars are oxidised to release energy, with carbon dioxide and water being released during these reactions
• Glucose enters cells by diffusion and facilitated diffusion
• When there is a shortage of oxygen, anaerobic respiration occurs in muscles to produce lactate
• To remove lactate, an individual has to breathe heavily to increase oxygen uptake, this is known as oxygen debt
• What is metabolism?

  The sum of all the chemical reactions in the body
• What are metabolic pathways?

  When one chemical is transformed through a series of enzyme controlled reactions into another chemical
• What are the two types metabolic reactions?

  Catabolic and anabolic
• What are catabolic reactions?

  When complex molecules are broken down into smaller molecules, releasing energy as it is a hydrolysis reaction
• What are anabolic reactions?

  When molecules that the body needs are synthesised, requiring energy as it is a condensation reaction
• Some cells will have large amounts of mitochondria to provide large amounts of ATP for certain functions
• What are some reasons for cells needing large amounts of ATP?

  Building complex molecules, protein synthesis, movement, cell division, Endocytosis and exocytosis and transmission of nerve signals
• What is a respiratory substrate?

  Any organic molecule broken down to release energy from the synthesis of ATP
• What are some examples of respiratory substrates?

  Glycogen, which can be converted into glucose and fats, proteins and lactate that can be broken down into pyruvate
• What is the order of net energy release of biological molecules?

  Lipids > alcohols > proteins > carbohydrates
• The respiratory quotient of a substrate is the ratio of carbon dioxide to oxygen produced or consumed to break down that molecule
• How can the amount of oxygen consumed by a molecule be measured?

  Using a respirometer
• Respiratory quotient = carbon dioxide produced / oxygen consumed
• If a respiratory quotient is >1, it indicates that anaerobic respiration is occurring, as more carbon dioxide is being produced than oxygen is being consumed
• What is the respiratory quotient of carbohydrates?

  1
• What is the respiratory quotient of proteins?

  0.8 - 0.9
• What is the respiratory quotient of lipids?

  0.7
• Glucose is the main respiratory substrate used by cells
• Anaerobic respiration is the process of breaking down a respiratory substrate in order to produce ATP (using oxygen)
• How many ATP molecules is produced within a respiration cycle?

  32
• What are the four stages of respiration?

  Glycolysis, Krebs cycle, electron transport chain, oxidative phosphorylation.
• Any ATP produce in the first three stages of respiration is called substrate level phosphorylation
• Glycolysis occurs in the cytoplasm of cells
• What are the three processes in glycolysis?

  Phosphorylation, oxidation and dephosphorylation
• Describe the process of glycolysis?

  Glucose gains two phosphate ions from two ATP, forming hexose biphosphate, which splits and forms two triose phosphates, another phosphate ions joins to form two triose biphosphates

  The triose biphosphate is oxidised, losing H+, which is transferred to NAD -> NADH

  Phosphates are removed to form 4 ATP through substrate level phosphorylation, producing pyruvate
• What are the products of glycolysis?

  2 NADH

  2 Pyruvate

  (net) 2 ATP
• Why is pyruvate formed in glycolysis?

  It can enter the mitochondria easier than glucose
• Once oxygen is available, pyruvate will move across the double membrane of the mitochondria into the matrix space via active transport
• Describe the process of the link reaction?

  Pyruvate is oxidised (carbon dioxide and H+ are removed) to produce acetate, the H+ is accepted by NAD -> NADH

  Acetate combines with coenzyme A to form acetyl coenzyme A
• What is a coenzyme?

  A molecule that helps an enzyme carry out its function but is not used in the reaction itself, it is not an enzyme itself
• What are the products of the link reaction?

  Carbon dioxide, NADH and acetylcoenzyme A
• The link reaction occurs in the mitochondrial matrix
• The krebs cycle occurs in the mitochondrial matrix
• Describe the process of the Krebs cycle?

  Acetate (2C) is removed from acetyl CoA and combines with oxaloacetic acid (4C) to form citrate (6C)

  Citrate is decarboxylated and dehydrogenated twice to form 2 NADH and 2 carbon dioxide molecules

  A phosphate is lost and is used to generate a molecule of ATP and is dehydrogenated twice to form FADH, NADH and oxaloacetic acid
• What are the products of the Krebs cycle?

  3 carbon dioxide molecules

  3 NADH

  1 FADH

  1 ATP

  1 oxaloacetic acid
• How many NADH molecules are formed from one molecule of glucose?

  10