BYA5 SECTION 14.8Respiration 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
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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
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| 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
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| 2) Link reaction → matrix of mitochondria |
- Pyruvate enters matrix of mitochondrion
for further reaction
- Net yield of 2reducedNADH per glucose
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| 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
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| 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
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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
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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
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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
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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]