Cellular Respiration The Details
LEARNING GOALS By the end of the lesson you will be able to; 1. Describe in detail the 4 stages of cellular respira;on 2. Track the crea;on of ATP and energy carrier molecules 3. Calculate ATP yield 4. Understand why ATP yield varies 5. Describe as a whole, the process of cellular respira;on
Stage 1: Glycolysis (Sugar- spli<ng) (10 rxn. s) We start HERE! RECALL Occurs in cytoplasm Breaking 6 carbon glucose into (2) 3- carbon pyruvate molecules Crea;on of 2 net ATP by substrate- level phosphoryla;on Crea;on of 2 NADH for further processing
GLYCOLYSIS Can be divided into 3 main sec;ons; o Investment (Steps 1-3) o Cleavage (Steps 4-5) o Harves;ng (Steps 6-10)
GLYCOLYSIS Investment (Steps 1-3) o Step 1: Glucose Phosphoryla;on (hexokinase) o Step 2: G6P isomeriza;on to F6P (phospho- glutamase) o Step 3: F6P phosphoryla;on to F1, 6BP (phospho- fructokinase) Investment of 2 ATP molecules Addi;on of 2 phosphate groups primes the molecule to be cleaved
GLYCOLYSIS Cleavage (Steps 4-5) o Step 4: Cleavage of F1, 6BP to G3P & DHAP (aldolase) o Step 5: Isomeriza;on of DHAP to G3P (triosephosphate- isomerase) Conversion of DHAP à G3P means 2 G3Ps in total per glucose molecule All the rxn. s from 6-10 are doubled (not shown)
GLYCOLYSIS Harves;ng (Steps 6-10) o Step 6: Redox of NAD+ à NADH crea;on & G3P phosphoryla;on (Pi NOT from ATP) to become BPG (triosephosphate- dehydrogenase) o Step 7: BPG dephosphoryla;on to from 3PG & ATP (phospho- glyceratekinase) o Step 8: 3PG conversion to 2PG (phospho- glucomutase) First site of NADH crea;on; 2NADH First site of ATP crea;on; 2ATP
GLYCOLYSIS Harves;ng (Steps 6-10) o Step 9: loss of H2O and conversion of 2PG to PEP (enolase) o Step 10: PEP dephosphoryla;on to from pyruvate & ATP (pyruvate kinase) Another crea;on of 2ATPs (4 total) Thus concludes glycolysis; 2NADH & 2ATP net! Recall: Oxygen has not been necessary YET!
Glycolysis alone is not a highly efficient mechanism for harnessing energy. Two moles of ATP is 62 kj vs. Complete oxida;on of one mole of glucose is 2870 kj Only about 2.2 % of the available free energy is converted to ATP in glycolysis. Some E lost as thermal energy, but most is spll stored in two pyruvate molecules and two NADH molecules, for further processing in aerobic respira;on.
Stage 2: Pyruvate OxidaPon (1 rxn.) Occurs in mitochondrial matrix Breaking 3- carbon pyruvate molecule into 2- carbon acetly group joined to Coenzyme A (CoA) (i.e. 2 sulfur- containing acetyl- CoA molecules) Crea;on of 2 CO 2 Crea;on of 2 NADH for further processing
1. Decarboxyla;on of (- COO - ) to form CO 2 2. Redox of NAD+ à NADH 3. Addi;on of sulfur- containing Coenzyme A (CoA) ***2 acetyl- CoA molecules are high- energy intermediates
2 molecules of acetyl- CoA enter next stage, Kreb s Cycle, to be further broken down 2 molecules of NADH proceed to Stage 4 to produce ATP by oxida;ve phosphoryla;on 2 molecules of CO 2 diffuse out of mitochon. and then out of cell as low energy waste product (i.e. exhale) 2 H + ions remain dissolved in matrix Keep coun*ng SO FAR (Glycolysis + Pyruvate Oxida;on), Created 2 ATP & 4NADH
Stage 3: The Citric Acid Cycle aka The Krebs Cycle (8 rxn. s) We start HERE! Occurs in mitochondrial matrix Compete breakdown of what s lej (acetyl- CoA) to 4 CO 2 Crea;on of 2 ATP Crea;on of 6 NADH Crea;on of 2 FADH 2 ***3 NADH, 1 FADH 2, 1 ATP (substrate- level phosphoryla;on) per acetyl- CoA molecule that enters Krebs cycle Cyclical; oxaloacetate (product of step 8), is the reactant in Step 1 (Oxaloacetate) + + (Oxaloacetate)
KREBS Step 1: Citrate forma;on (citrate synthase) Step 2: Isomeriza;on to Isocitrate (aconitase)
Step 3: NADH reduc;on & CO 2 forma;on (isocitrate dehydrogenase) Step 4: NADH reduc;on, CO 2 forma;on & addi;on of CoA (α- ketoglutarate dehydrogenase)
Step 6: FADH 2 reduc;on Step 5: CoA release & ATP forma;on
Step 8: NADH reduc;on Step 7: Addi;on of H2O (Fumarate à Malate)
Stage 3: The Citric Acid Cycle aka The Krebs Cycle (8 rxn. s) Things to no;ce: Two acetyl- CoA molecules enter Krebs cycle In Step 1, the acetyl group reacts with oxaloacetate to form one molecule of citrate (i.e. citric acid cycle) Steps 3, 4, 5, 6, and 8, form power molecules NADH, ATP, and FADH 2 o Steps 3, 4, and 8 reduce NAD + to form NADH o Step 5 produces ATP by substrate- level phosphoryla;on o Step 6 reduces FAD to form FADH2 Because one glucose molecule yields two pyruvate molecules, each glucose molecule generates two turns of the citric acid cycle
By end of Krebs cycle, the original glucose molecule is en;rely dismantled; the six carbon and some oxygen atoms released as six low- energy CO2 waste products All that s lej of original glucose is its energy in the form of free ATP and reduced coenzymes, NADH and FADH2 The E in these reduced coenzymes are transferred o ATP in the next (final) stage of cellular respira;on (Oxaloacetate) + + (Oxaloacetate)
Stage 4: Electron Transport Chain & Chemiosmosis (MulPstep) We start HERE! Occurs in the inner mitochondrial membrane & intermembrane space Through a series of steps, all the chemical poten;al E in the carrier molecules, NADH & FADH 2 is harvested to form ATP The 2 NADH molecules created in glycolysis are converted to either NADH or FADH 2 NADH à 3 ATP or FADH 2 à 2 ATP
Electron Transport Chain (ETC) Involves a series of proteins that perfectly illustrate a series of redox reac;ons with oxygen as the final e- acceptor e- s xfr from NADH & FADH 2 to proteins (driven by increasing electronega;vity) E of xfr pumps H+ into intermembrane space à electrochemical gradient
Chemiosmosis H + in intermembrane space are impermeable to inner mitochondrial membrane, so forced to enter via channel in ATP synthase ATP synthase uses kine;c E of moving H + to join ADP & Pi à ATP
Things to note: Proteins in ETC (increasing electronega;vity) 1. NADH Dehydrogenase i. Ubiquinone aka Q (mobile protein carrier) 2. Cytochrome b- c1 complex ii. Cytochrome c (mobile protein carrier) 3. Cytochrome oxidase complex
Things to note: e- s at Cyt. Oxidase have lost so much E, that the only thing strong enough to oxidize it is Oxygen (i.e. final e- acceptor) o Oxygen + 2 e- s + 2 H + à H 2 O FADH 2 skips NADH dehydrogenase o Smaller complex oxidizes it then it moves to Cyt. b- c1 (via Q) and so on à less H + pumping than NADH à less ATP forma;on than NADH
Stage 4: Electron Transport Chain & Chemiosmosis (MulPstep) The 2 NADH molecules created in glycolysis are converted to either NADH or FADH 2 o NADH produced in glycolysis occurs in cytoplasm (i.e. cytosolic NADH) o NADH is impermeable to inner mitochondrial membrane, so it has 2 shuple systems that can help pass e- s from cytosolic NADH in the intermembrane space into matrix i. Glycerol- Phosphate shu\le; passes e- s from cytosolic NADH to FAD in matrix à FADH 2 à 2 ATP ii. Aspartate shu\le; passes e- s from cytosolic NADH to NAD + in matrix à NADH à 3 ATP Let s see it!
Cellular RespiraPon Summary Let s see it ALL!