LGS A-Level OCR Biology - Unit 5 - Respiration
Respiration is the process of releasing energy from complex organic molecules and transferring it into ATP, the cell’s energy currency. This involves breaking bonds through hydrolysis and forming new ones to drive metabolic processes.
Respiration
Process by which energy stored in complex organic molecules is released and immediately transferred to ATP
Energy is released through hydrolysis (making new bonds)
Key Terms
Respiration
Process by which energy stored in complex organic molecules is released and immediately transferred to ATP
Energy is released through hydroly...
Why do animals need energy
Active transport
Endo/exocytosis
Synthesis of protein
DNA replication
Cell division
Movement
Activation of a ch...
Catabolic
Releasing energy
Anabolic
Energy consuming
ATP
Intermediary between catabolic and anabolic reactions
Relatively stable, only broken down by hydrolysis by enzyme catalysis (energy released ...
Hydrolysis of ATP
Catalysed by ATPase
ATP is hydrolysed to produce ADP then again to produce AMP
ATP –> ADP (-30.5), ADP –> AMP (-30.5), AMP —> ...
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| Term | Definition |
|---|---|
Respiration | Process by which energy stored in complex organic molecules is released and immediately transferred to ATP Energy is released through hydrolysis (making new bonds) |
Why do animals need energy | Active transport Endo/exocytosis Synthesis of protein DNA replication Cell division Movement Activation of a chemical (phosphorylation) |
Catabolic | Releasing energy |
Anabolic | Energy consuming |
ATP | Intermediary between catabolic and anabolic reactions Relatively stable, only broken down by hydrolysis by enzyme catalysis (energy released can be controlled) Easily moved around a cell when in solution |
Hydrolysis of ATP | Catalysed by ATPase ATP is hydrolysed to produce ADP then again to produce AMP ATP –> ADP (-30.5), ADP –> AMP (-30.5), AMP —> A (-13.8) |
Structure of ATP | Ribose attached to adenine (phosphodiester bond) Phosphorylated nucleotide |
Processes in aerobic respiration | Glycolysis Link reaction Krebs cycle Oxidative phosphorylation |
Glycolysis | Occurs in cytoplasm Phosphorylation —> hexose biphosphate (2 phosphate groups from 2 ATP) Hexose biphosphate splits into two Oxidation (removal of H atoms) - accepted by NAD to make NADH Breaks down glucose into pyruvate (3C), 2 NADH and 2 ATP |
Where does glycolysis occurs | Cytoplasm |
Why are ATP used in the first stage of glycolysis | Provide activation energy |
Where does oxidative phosphorylation occur | Cristae |
Role of ATP in the cell | Universal currency of energy Phosphates can be removed by hydrolysis to release 30 kJ/mol energy Energy used in metabolic reactions Energy released in small quantities to prevent cell damage |
Where does the Kreb’s cycle occur | Matrix of mitochondria |
Coenzymes in leaf | NAD and FAD can be reduced to NADH and FADH2 and act as hydrogen carriers NADPH reduces molecules by adding e- ATP phosphorylates Coenzyme A carries acetate to Kreb’s cycle |
Link reaction | Pyruvate is decarboxylated to acetate (+ CO2) Combines w/ CoA to make acetyl coenzyme A Happens twice for glycolysis Produces 2 NADH |
Kreb’s cycle | CoA is recycled back to link reaction Acetate combines with oxaloacetate to make citrate Decarboxylated 2x to give orig. 4C compound, oxaloacetate Produces 6 NADH, 2 FADH2 , 2 ATP and 4 CO2 (substrate level phosphorylation) |
Which cofactor is part of the ETC | Fe^2+ |
What’s found in the matrix | Enzymes NAD FAD Oxaloacetate Mitochondrial DNA Mitochondrial ribosomes |
Mitochondrial DNA | Codes for mitochondrial enzymes and other proteins |
Mitochondrial ribosomes | Where proteins are assembled |
Where can fatty acids be used in respiration | Fatty acids can produce acetate and enter the Kreb’s cycle directly |
Where can glycerol be used in respiration | Can be converted to pyruvate and enter the link reaction |
Where does the link reaction occur | Matrix of mitochondrion |
Theoretical yield of ATP from 10 NADH | 25 |
Total theoretical yield of ATP per pyruvate | 25 - NAD 1 - Krebs cycle 2 - glycolysis =30 |
Why is the yield of ATP not 100% | ATP has to be used for active transport of pyruvate and NADH |
RQ | Vol. of CO2/ Vol. of O2 per unit time |
RQ value for glucose | 1 |
RQ value for amino acids | 0.8/0.9 |
RQ value for triglycerides | 0.7 |
Investigating respiration rates of yeast | Put a known vol. and conc. of a substrate sol. into a tt Add a known vol. of buffer soln. - keep pH constant Place tt in water bath (25 degrees) Add known mass of dry yeast After yeast has dissolved, place a bung on the tt which is attached to a gas syringe (should be set to 0) Start the stopwatch Record vol. of CO2 produced at regular intervals and calculate rate |
Using a respirometer to measure O2 consumption | Set up respirometer - one w/ glass beads and the other w/ woodlice of same vol. Add KOH to both - absorbs CO2 produced Use syringe to set fluid in manometer to known level Measure distance travelled by liquid in manometer - gives you vol. of O2 used up (pi r^2 h - need diameter of capillary tube) |
Why does the liquid move in the manometer | As the organisms use up the O2, the pressure decreases causing coloured liquid in manometer to move. |
Limitation of using respirometer | Difficult to accurately read the meniscus of the fluid in the manometer |
Substrate level phosphorylation | ATP is formed by the direct transfer of Pi to ADP | Only occurs in Glycolysis and Kreb's cycle |
Substrate level phosphorylation in glycolysis | 2 ATP per each glucose, when Trios-biphosphate is converted to pyruvate | 4 - 2 = 2 |
Substrate level phsophorylation in Kreb's cycle | 1 per each turn | Occurs when 5C compound is converted to oxaloacetate |
NAD vs FAD | NAD used in all stages but FAD only in Kreb's NAD accepts 1 H, FAD accepts 2 H's NADH is oxidised at the start of the etc releasing e- and H+ while FADH2 is oxidised further along the chain NADH synthesises 3 ATP but FADH2 synthesises 2 ATP |
Oxidative phosphorylation | FADH2 and NADH deliver H to etc in cristae H dissociates into H+ and e- (used in synthesis of ATP through chemiosmosis) Energy is released as e- travel down etc, creates a proton gradient At end of etc, e- combines w/ H+ and O2 --> water Etc cannot operate w/out oxygen |
Obligate anaerobes | Cannot survive on the presence of oxygen at all |
Facultative anaerobes | Synthesie ATP by aerobic respiration if oxygen is present but can switch to anerobic e.g. yeast |
Obligate aerobes | Can only synthesise ATP in the presence of oxygen e.g. mammals |
Fermentation | Produces ATP through substrate level phosphorylation only, no involvement of electron transport chain |
Alcoholic fermentation | Occurs in yeast and some root cells Glycolysis occurs and pyruvate is decarboxylated to ethanal Ethanal accepts H+ from NADH to produce ethanol and NAD (recycled) Produces ethanol and CO2 |
Lactate fermentation | Carried out in animal cells and produces lactate Glycolysis occurs as normal Lactate dehydrogenase causes pyruvate to accept H from NADH and is converted to lactate and NAD (recycled) Allows glycolysis to keep occurring |
Where is lactic acid converted back to glucose | Liver but requires oxygen --> oxygen debt after exercise |
Why can lactate fermentation not occur indefinitely | Reduced ATP isn't enough to sustain vital processes | Accumulation of lactic acid leads to fall in pH, proteins denature (respiratory enzymes) |