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A2 biology 4
OCR biology - respiration
| Question | Answer |
|---|---|
| What is the purpose of respiration? | Releases chemical potential energy from glucose to produce ATP, universal energy currency. Hydrolysis of ATP is exergonic and is coupled to endergonic reactions to provide an immediate source of energy (manageable amount, doesn't damage cells) |
| What is the structure of ATP? | Adenosine (adenine, a purine (nitrogenous base) and ribose, a pentose sugar) + 3 phosphoryl groups = a phosphorylated nucleotide |
| What are the equations for the hydrolysis of ATP? | 1. ATP + H2O -> ADP + Pi (30.6 kJ/mol) 2. ADP + H2O -> AMP + Pi (30.6 kJ/mol) 3. AMP + H2O -> adenosine (14.2 kJ/mol) |
| What are some possible uses of ATP? | Anabolic reactions e.g. protein synthesis. Catabolic reactions. Membrane transport e.g. active transpot (Na/K pumps) and bulk transport (endocytosis/exocytosis). Movement of cilia, undulipodia, flagella. Interphase: replication of DNA and organelles |
| What is an indication of the continuous hydrolysis + resynthesis of ATP? | Only 5g in body at one point in time, but 25-50 kg of ATP used per day |
| Define ultrastructure | The detailed structure of the components of a cell as seen under an electron microscope |
| What are the features of mitochondria in metabolically active cells? | Many mitochondria, with densely packed cristae |
| Describe structure of envelope of mitochondria | 2 phospholipid bilayers separated by intermembrane space. Outer = normal lipid composition. Inner = different lipid composition, impermeable to small ions, ATP synthase enzymes, cristae large SA for electron transport chain (oxidoreductase enzymes) |
| Describe the matrix of mitochondria | A semi-rigid, gel-like medium, site of the Krebs cycle. Contains: NAD+, oxaloacetate, prokaryote-type ribsoomes (70s), enzymes, mitochondrial DNA (circular, naked) |
| What is the difference between cofactors and coenzymes? | Cofactors are non-protein moelcules required for enzyme activity. COenzymes are a subset of cofactors: large, organic molecules required for enzyme activity |
| Describe NAD structure and function | 2 nucleotides (adenine + nicotinamide, vitamin B3), 2 ribose sugars, 2 phosphates. nicotinamide ring accepts H atoms after dehydrogenase enzyme has removed them from a species |
| Describe FAD structure and function | 2 nucleotides (adenine + riboflavin, vitamin B2), 1 ribose, 2 phosphate. Riboflavin accepts H atoms after dehydrogenase has removed them from a species in Krebs cycle |
| Describe CoA structure and function | Pantothenic acid (vit B5), adenine, cysteine, 3 phosphoryl, 1 ribose sugar. Carries acetate made in link reaction to krebs cycle |
| Where do the 4 stages of respiration take place? | Glycolysis = cytoplasm. Link reaction = mitochondrial matrix. Krebs cycle = mitochondrial matrix. OP = inner mitochondrial membrane |
| Describe glycolysis | Glucose -> glucose 6-phsophate -> fructose 6-phsophate -> fructose 1,6-bisphosphate -> 2 triose phosphates -> intermediate (dehydrogenase, SLP) -> pyruvate (SLP) |
| What are the net products of glycolysis for 1 glucose molecule? | 2 pyruvate, 2 NADH, 2 ATP |
| Describe the link reaction | Pyruvate -> acetate - dehydrogenase oxidises pyruvate by removing 2H which reduce NAD+ to NADH + H+, decarboxylase removes carboxyl group ->CO2. Acetate + CoA -> acetyl CoA, carries acetate to Krebs cycle. Matrix. 2NADH, 2CO2, 2acetyl CoA |
| Describe the Krebs cycle | Acetyl CoA -> acetate + CoA. Acetate + oxaloacetate -> citrate -> 5C (dehydrogenase, decarboxylase) -> 4C (dehydrogenase, decarboxylase) -> 4C (SLP) -> malate (dehydrogenase, FAD -> FADH2) -> oxaloacetate (dehydrogenase |
| Is the Krebs cycle aerobic or anaerobic + why? | Aerobic - doesn't directly require oxygen but needs NAD+ and FAD produced by oxidation of NADH and FADH2 during oxidative phosphorylation in presence of O2. Absence of O2 = accumulation of H+, low pH can cause denaturation |
| What are the net products of the Krebs cycle per 1 glucose molecule? | 6NADH, 2FADH2, 2ATP, 4CO2 |
| Define: oxidative phosphorylation | Where ATP is synthesised from the phosphorylation of ADP in the presence of oxygen, across inner mitochondrial membrane |
| Describe the role of ECCI | ECCI (NADP-coenzyme Q reductase) oxidises NADH+H+ to NAD+ (reused in other stages) and 2H, 2H-> 2H+ + 2e-. e- reduce Fe3+ to Fe2+ which is less stable, e- transferred to coenzyme Q so haem cofactor regains stability releasing energy, pump H+ |
| Describe the role of ECCII | ECCII oxidises FADH2 to FAD (reused in Krebs cycle) and 2H, 2H -> 2H+ + 2e-, protons remain in matrix, e- transferred to ECIII |
| What happens at ECIII and ECCIV? | ECCIII receives 4e-, reduce Fe3+ to Fe2+ which is less stable, e- are transferred to cytochrome C so haem cofactor regains stability releasing energy used to pump H+ into intermembrane space. e- reduce Fe3+ in ECCIV, transferred to O2 (final e- acceptor) |
| How is water produced during respiration and how many water molecules per glucose? | O2 + 4e- (from ECCIV) + 4H+ -> 2H2O, byproduct of respiration, excreted |
| Describe chemiosmosis | High [H+] in intermembrane space =H+ electrochemical gradient, maintained by H+ -> H2O in matrix. Inner mitochondrial membrane impermeable to H+. Diffuse into stroma down gradient through ATP synthase channel, proton motive force, KE -> chemical energy |
| What is the maximum ATP yield and why is this rarely achieved? | 1 glucose: 10 NADH -> 26 ATP in OP, 4 ATP via SLP- total = 30. Some ATP is used to actively transport pyruvate into mitochondria/ to shuttle reducing agent into mitochondria. Some protons leak across inner membrane so proton motive force is weaker |
| What happens if there is a shortage of oxygen during OP? | ECCIV remains reduced, e- accumulate in ETC, NADH and FADH2 aren't reoxidised, shortage of NAD+ and FAD disrupts glycolysis, link reaction, krebs cycle. Very acidic |
| What is some evidence for chemiosmosis? | pH of intermembrane space lower than matrix, membrane potential more negative on matrix side, rupturing outer membrane=acidic solution, no electron transfer in mitoblasts, no ATP when headpiece removed/oligomycin, lots of protins released from matrix |
| What is anaerobic respiration? | Where glucose is respired in absence of O2, only source of ATP is SLP during glycolysis (2ATP per glucose), 2% efficiency because glucose isn't broken down fully, fermentation oxidises NADH to NAD+ for glycolysis again, 2 types in eukaryotes |
| What is lactate fermentation? | Animals: vigorous exercise, oxygen deficit. Lactate dehydrogenase oxidises NADH+H+ to NAD+ by removing 2H which reduce pyruvate to lactate |
| What is an issue with lactate fermentation and how is this resolved? | Lactate accumulates in muscle cells, low pH, denatures enzymes. In presence of O2, lactate is oxidised to pyruvate in liver, pyruvate -> glucogen/ glucose/ enters krebs cycle |
| What is ethanol fermentation? | In waterlogged root hair cells + fungi: C6H12O6 -> 2CO2 + 2C2H5OH. Pyruvate -> ethanal - pyruvate decarboxylase. Ethanal -> ethanal - ethanol dehydrogenase oxidises NADH+ H+ to NAD+ by removing 2H which reduce ethanal. Yeast is facultative |
| Why can't animals undergo ethanol fermentation? | Lack pyruvate decarboxylase enzyme which converts pyruvate to ethanal |
| Define respiratory substrate | Organic substance used for respiration |
| How are carbohydrates respired? | Glucose is respired (produced by isomerisation/ break down of glycogen/starch), aerobically or anaerobically, only 32% efficient, energy mainly used for thermoregulation, mean energy value: 15.8 kJ/g |
| How are proteins respired? | Keto acid from deamination in liver -> glycogen or fat. Prolonged exercise/fasting/starvation - protein in muscle is hydrolysed into amino acids - converted to pyruvate, acetate or enter Krebs cycle directly. Aerobic, mean energy value: 17 kJ/g |
| How are lipids respired? | Glycerol -> glucose. Fatty acids - B-oxidation pathway: combine with CoA (energy + 2Pi from hydrolysis of ATP), fatty acid-CoA complex splits into acetyl groups (1NADH, 1FADH2), enter krebs cycle (3NADH, 1FADH2, 1ATP). mean energy value: 39.4kJ/g, aerobic |
| Why is the mean energy value for lipid respiration greatest? | Most hydrogen atoms: proton motive force is the strongest, most ATP is synthesised. Both glycerol and fatty acids can be respired |
| How does a respirometer work? | Submerge in water to prevent more O2 entering. Invertebrates use up O2, CO2 released is absorbed by KOH, volume/ pressure decrease, water enters tubing. If T/P of gases are constant, volume of water enters glass tubing proportional to volume of O2 used up |
| Why do you leave the open end of the glass tubing out of the water for 5 minutes? | To allow invertebrates to acclimitise so rate of respiration stabilises + to minimise changes in the volume of gas due to pressure/ temperature changes |
| Why must a control with glass beads be done? | Glass beads = same volume. To calculate the volume of O2 that was actually taken up by the invertebrates, and identify what volume changes are due to changes in the temperature/ pressure of the gas |
| How do you calculate the mean volume of oxygen taken up by the invertebrates per minute? | 1) mean distance travelled by the meniscus per minute for invertebrates. 2) mean distance travelled by the meniscus per minute for glass beads. 3) mean volume of oxygen taken up by invertebrates per minute = (1-2) x πr2 |
| What variables need to be kept constant? | Number, species, age of invertebrates. Concentration and volume of KOH. Temperature of water |
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