5.2.2 - respiration

• Organisms need to respire as it produces ATP as an energy currency and it releases heat energy for thermoregulation
• ATP produced from respiration is used by organisms for:

  active transport against concentration gradients (eg, to absorb nutrients)

  metabolic reactions

  muscle contraction
• Mitochondria are surrounded by a double membrane. The folded inner membrane forms cristae which is the site of the electron transport chain. The fluid matrix contains mitochondrial DNA, respiratory enzymes, lipids and proteins.
• The four main stages of respiration and where they occur are:

  • glycolysis - cytoplasm
  • link reaction - mitochondrial matrix
  • Krebs cycle - mitochondrial matrix
  • oxidative phosphorylation - membrane of cristae
• Stages of glycolysis:

  glucose is phosphorylated into hexose bisphosphate by 2 lots of ATP

  hexose bisphosphate splits into 2 lots of triose phosphate (TP)

  Each triose phosphate is oxidised into pyruvate.
• pyruvate enters the mitochondria via active transport
• during the link reaction:

  Oxidation of pyruvate to acetate - net gain of 1 CO2 per pyruvate molecule (Decarboxylation) and 2 hydrogen atoms (used to reduce NAD)

  acetate combines with coenzyme A (CoA) to form acetylCoA
• link reaction in equations:

  pyruvate + NAD + CoA ——> Acetyl CoA + reduced NAD + CO2
• In the Krebs cycle:

  a series of redox reactions produces:

  • ATP by substrate level phosphorylation
  • reduced coenzymes
  • co2 from decarboxylation

  begins when acetyl group from acetyl CoA (2C) reacts with oxaloacetate (4C) which the cycle regenerates
• krebs cycle:

  Oxaloacetate reacts with acetyl CoA to release CoA and produce citrate. Undergoes decarboxylation and loses 2 lots of CO2, forms

  • 3 x of NADH
  • 1 x ATP
  • 1 x FADH2
• electron transfer chain is a series of carrier proteins embedded in the membrane of the cristae of mitochondria. produces ATP through oxidative phosphorylation via chemiosmosis during aerobic respiration.
• In the etc, electrons released from reduced NAD and FAD undergo successive redox reactions. The energy released maintains proton gradient or is released as heat. Oxygen acts as the final electron acceptor.
• chemiosmosis produces ATP during aerobic respiration as some energy released from the etc actively transports H+ ions from mitochondrial matrix into intermembrane space. H+ ions move down concentration gradient into mitochondrial matrix via ATP synthase. ATP synthase catalyses ADP + pi ——> ATP
• in aerobic respiration, oxygen acts as the final electron acceptor in the electron transport chain.

  oxygen joins with electrons and protons to form water as a byproduct.
• ATP is produced by substrate level phosphorylation in

  glycolysis

  krebs cycle
• during anaerobic respiration in animals:

  only glycolysis continues to produce NADH and pyruvate as well as ATP from substrate level phosphorylation.

  reduced NAD + pyruvate ——> NAD + lactate
• during anaerobic respiration in some microorganisms (yeast and some plants):

  only glycolysis continues so much less ATP is produced compared to aerobic.

  pyruvate is then decarboxylated into ethanal. ethanal is then reduced to ethanol using reduced NAD to form NAD for further glycolysis.
• Benefits of anaerobic respiration:

  ATP production for vital metabolic processes continues.

  Production of ethanol / lactate converts NADH back into NAD so glycolysis can continue to make the maximum yield of ATP in the conditions.
• a student could investigate the effect of a variable on rate of respiration by using a respirometer (pressure changes in boiling tube cause a drop of coloured liquid to move)

  use a dye as the terminal electron acceptor for the etc.
• sodium hydroxide in a respirometer absorbs CO2 so that there is a net decrease in pressure as O2 is consumed
• calculate rate of respiration using a respirometer by:

  volume of co2 consumed / time x mass

  volume = distance moved by coloured drop x pi r^2
• other molecules that can be used as respiratory substrates are:

  • amino acids from proteins
  • glycerol and fatty acids from lipids
• respiratory quotient = carbon dioxide produced / oxygen consumed
• Respiratory quotient can be used to determine the respiratory substrate being used…

  0.7 = lipids

  0.9 = proteins

  1.0 = carbohydrates

  >1 = anaerobic respiration
• Different respiratory substrates have different relative energy values because it depends on the number of hydrogens in the structure which are oxidised to water.

  lipids is the greatest substrate as it has the most hydrogens
• cells need a supply of ATP molecules to act as an energy source for:

  • active transprot
  • maintaining resting potential in neurones
  • muscle contraction
  • cell division and growth
  • most metabolic reactions
• respiration is required to generate heat in mammals.
• respiration is required in plants for movement of sucrose in mass flow
• respiration is required to generate ATP for mitosis in bacteria
• ATP synthase is embedded in the cristae
• matrix is the fluid like substance inside of the mitochondria that contains enzymes needed for the krebs cycle
• Intermembrane space is where the protons are pumped into to create a concentration gradient
• cristae is the folding of the inner membrane of mitochondria and increases the surface area for attachment of enzymes
• Mitochondria contains ribosomes used for protein synthesis
• DNA present in mitochondria codes for proteins made by ribosomes
• Outer membrane of mitochondria separates cell contents from cytoplasm - compartmentalisation

  controls entry and exit of substances like pyruvate, oxygen, ATP and co2
• Phosphorylation: addition of a phosphate group to a molecule - usually from ATP
• lysis: splitting or breaking down of a molecule
• glucose to hexose bisphosphate using 2 ATP is phosphorylation
• Hexose bisphosphate breaking down into two lots of triose phosphate is lysis