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SBI4U Cellular Respiration and Photosynthesis Review: ch2&3
Cellular Respiration: Big Picture
-the process by which living organisms break down organic molecules to obtain energy.
-the bonds in glucose (main source of energy) are broken and rearranged into more stable,
lower energy molecules of CO2 and H2O, resulting in the release of free energy which is
used to make ATP
-overall: C6H12O6 + 6O2 --> 6CO2 + 6H2O + 36 ATP
-this reaction has a high activation energy, so it occurs stepwise with enzyme catalysts
-4 main stages: glycolysis, pyruvate oxidation, Kreb’s cycle, electron transport chain
Glycolysis
-10 step reaction in cytoplasm that breaks down glucose to 2 pyruvates in absence of O2
-2ATP are added (activation energy) to convert it to fructose-1,6-biphosphate
-next it is split into 2 molecules of G3P (3C)
-each molecule of G3P:
-produces 1 NADH, 1 ATP, 2H2O removed, then rearranged to PEP
-1 more ATP produced, forms pyruvate
Pyruvate Oxidation (once for each pyruvate)
-3 step reaction to prepare for Kreb’s cycle, pyruvate converted to acetyl-coA
-1 carboxyl group removed, 1NADH formed coenzyme A added
-acetyl-coA is where other biological molecules can enter respiration (fats, proteins)
Kreb’s Cycle (once for each acetyl-coA)
-8 step reaction in the mitochondria that converts acetyl-coA to 2CO2
-acetyl-coA(2C) binds to oxaloacetate(4C), loses coA, forms citrate (6C)
-CO2 removed, produce 1 NADH, forms α-ketoglutarate (5C)
-2nd CO2 removed, produce 1 NADH, 1ATP, form succinate (4C)
-1 FADH2 produced, add 1 H2O, 1 NADH produced, oxaloacetate reformed.
-overall: 2 acetyl-coA + 2 H2O--> 4CO2 + 6NADH + 2ATP + 2FADH2
Electron Transport Chain (mitochondrial membrane)
-high energy e- on carriers used to build a H+ gradient, which makes ATP
-e- transferred to cytochromes from NADH and FADH2 (enters on 2nd cytochrome)
-as electrons move to stronger cytochromes, H+ is pumped across the membrane
-e- from NADH pump 3H+, e- from FADH2 pump 2H+, forming gradient
-H+ move back across membrane, through ATPase channel, producing ATP
-electrons end up on O2 with H+, forming H2O
Metabolism
-need continual supply of O2 and glucose, total of 36ATP/glucose
-fastest at 1 year old, decreases with age- efficiency, less growth/activity/muscle
-controlled by 3 feedback loops (ATP, citrate, NADH)
-anaerobic resp. results in fermentation (either alcohol or lactic acid) to recycle NAD+
Photosynthesis: Big Picture
-use light, CO2, H2O to make organic molecules (glucose)
6CO2 + 6H2O + light energy--> 1 glucose (C6H12O6)
-occurs in chloroplasts, using chlorophyll and rubisco
-light dependent and independent (Calvin cycle) stages
Light reactions
-light energy (photon) excites e- on chlorophyll in photosystem II
-excited e- move down ETC, pumping 4H+ into thylakoid, e- end up on photosystem I
(Z enzyme splits water into O2, 4H+, 2 e-, which replace e- on chlorophyll)
-e- are re-excited on PS I by another photon, have 2 options:
-return to ETC, pump 4H+, return to PS I to get excited (cyclic pathway-->ATP)
-2e- with H+, bind to carrier to form NADPH, enter Calvin cycle (non-cyclic)
-chemiosmosis (H+ gradient) produces 1ATP for every 4H+ that leave thylakoid
(Called photophosphorylation)
Calvin Cycle (light independent)
-CO2 added to RuBP (5C), split into 2PGA (3C) by enzyme rubisco
-1ATP, 2e- from NADPH (from light reactions) added to each produce 2G3P(3C)
-every 3 cycles produces 6G3P, of which 5 are recycled as 3RuBP(costing 3ATP), last
one is used by the cell to make sugars (glucose)
-2/3 of glucose converted to sucrose, used by rest of plant, 1/3 stored as starch
Alternate Pathways
-in presence of O2, photorespiration occurs in C3 plants
-C4 (4C acids) and CAM plants (day/night reactions) prevent photorespiration
-rate of photosynthesis dependent on light intensity, temperature, O2 concentration
Comparing Cellular Respiration and Photosynthesis
-see p179-181*, questions p182 # 3-6
Review Questions: Respiration p134 # 2,4,5,9,10,13,16,18,22,27
Photosynthesis p192 # 3,4,8,10-13,15,19