Respiration produces ATP which is the immediate form of energy

Biochemistry of Respiration

Oxidative breakdown of organic molecules to store energy as ATP Animals and plants respire; FAD and NAD are coenzymes

Aerobic respiration

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy Complete oxidation of an organic substrate to CO2 and H2O using free O2 Production of CO2, NADH + H+ and FADH + H+, 38ATP 1) Glycolysis → cytoplasm Glucose enters cell by facilitated diffusion ATP activates glucose to produce 2 unstable compounds Substrate-level phosphorylation produces 4ATP Net yield of 2ATP and 2reducedNAD per glucose molecule 2) Link reaction → matrix of mitochondria Pyruvate enters matrix of mitochondrion for further reaction Net yield of 2reducedNADH per glucose  3) Krebs cycle → matrix of mitochondria Citrate is gradually broken down to re-form oxaloacetate Substrate-level phosphorylation forms 2ATP Removal of hydrogen from respiratory substrate Net yield of 2ATP, 2reducedFADH, 6reducedNADH per glucose 4) Electron Transport Chain ETC → inner membrane/cristae of mitochondria Reduced coenzymes arrive at ETC Split into coenzyme + 2H+ + 2e- by hydrogen carriers 2e- are transferred to electron carriers (cytochrome) Pass down ETC by redox reaction and release energy as they go Energy produces ATP by oxidative phosphorylation Final electron acceptor 1/2O2 is reduced by 2H+ and 2e- to produce H2O Net yield of 34ATP (30NADH, 4FADH) per glucose //Cytochromes are iron-containing proteins → cytochrome a3 also contains copper and is irreversibly damaged by cyanide

Anaerobic respiration (fermentation)

Substrate-level phosphorylation: 2ADP + 2Pi → 2ATP directly by enzymes in glycolysis No O2 to accept electrons from NADH + H+ → no Krebs cycle or ETC NADH + H+ reduces (gives off H+ ions to) pyruvate to produce Lactate C3 in animal cells → can be re-oxidised Ethanol C2 in yeast cells → irreversible, CO2(g) lost Regenerates NAD NAD can be re-used to oxidise more RS/allows glycolysis to continue Can still form ATP/release energy when O2 is in short supply

Role of ATP

Adenosine (ribose + adenine) triphosphate (3 phosphate groups) Produced by adding Pi to ADP → phosphorylation Breaks down to ADP (adenosine diphosphate) and Pi (inorganic phosphate ion) by hydrolysis ATP is useful as an immediate energy source/carrier because Energy release only involves a single reaction Energy released in small quantities Easily moved around inside cells, but cannot pass through cell membranes Light-dependent reaction cannot be the only source of ATP "Photosynthesis cannot produce ATP in the dark Need more ATP than can be produced in photosynthesis Cannot be produced in plant cells lacking chlorophyll ATP cannot be transported"1 Central molecule in metabolism (ATP hydrolysis) Muscle contraction → changes of position of myosin head relative to actin Protein synthesis → ATP "loads" amino acids onto tRNA Active transport → driven by phosphorylation of membrane-bound proteins Calvin Cycle → cyclic reduction of CO2 to TP Nitrogen fixation → involves ATP-driven reduction of molecular nitrogen ATP in liver is used for active transport / phagocytosis / synthesise of glucose, protein, DNA, RNA, lipid, cholesterol / urea in glycolysis / bile production / cell division

Brown fat

White fat insulates the body and reduces heat loss Brown fat cells in mitochondrial membrane produce heat Mitochondria in other tissue / chemiosmosis H+ ions pass back from space between two mitochondrial membranes into matrix Through pores which are associated with the enzyme ATP synthetase Energy from the ETC will be used to produce ATP Mitochondria in brown fat H+ ions flow back through channels not associated with ATP synthetase Energy produces heat instead of ATP Found in chest, larger arteries for heat distribution round the body or in hibernating mammals

References and Further Reading
1) AQA (2003) Mark Scheme June 2003 GCE Biology/Human Biology A Unit BYA5, [PDF]
AQA (2006) GCE Biology/Biology (Human) 2006 specification, [PDF]