jeannette (dreaminpink_tay) wrote in mst_children,

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i'm so behind in biology. totally forgot about cellular respiration

here's more for me and you to study (ignore the weird bullets or thingys):

KREBS CYLCLE: A CLOSER LOOK – takes place within the mitochondrial matrix; w/ help of enzymes, completes oxidation of organic fuel
~ generates 1 ATP per turn by substrate level phosphorylation
 If oxygen is present, 2 molecules of pyruvate enters mitochondrion and converted to a compound called acetyl CoA (junction between glycolysis & Krebs cycle)
o Pyruvate’s carboxyl group - removed & given off as molecule of O2
o NAD+ (extracted electrons) is transferred  NADH (stores energy)
o Coenzyme A (sulfur-containing compound) attaches to acetate (remaining two-carbon fragment; oxidized)
 Two carbons enter cycle in reduced form of acetate & two different carbons exit as CO2
 acetate joins cycle by enzymatic addition oxaloacetate – subsequent steps decompose citrate back to oxaloacetate, giving of CO2 as “exhaust”
 most of the energy made available is conserved in NADH – each acetate that enters the cycle:
o 3 molecules of NAD+ are reduced to NADH
o [in one oxidative step, e – are transferred to FAD]  FADH2 (reduced form) donates e – to electron transport chain
 There is a step ~ forms ATP molecule directly by substrate-level phosphorylation

 so far – glycolylsis and the Krebs cycle have only produced:
o 4 ATP molecules per glucose molecule by substrate-level phosphorylation
 So far – molecules of NADH and FADH2 accounts for most of the energy extracted from food
 First molecule of electron transport chain is flavoprotein – in the next redox reaction, flavoprotein returns to oxidized form & passes electrons to an iron-sulfur protein – the iron-sulfur protein then passes the electrons to a compound called ubiquinone (not a protein)
o Molst of the remaining electron carriers between ubiquinone and oxygen are proteings called cytochromes [their prosthetic group – nonprotein components essential for catalytic functions of certain enzymes – called a heme group, has four organic rings surrounding a single iron atom
o The last cytochrome of the chain, cytochrome a3 , passes its electrons to oxygen – picks up a pair of hydrogen ions from “aqueous medium” to form water … (For every 2 NADH molecules, one O2 molecule is reduced to two molecules of H2O)
 Another source of e – ~ FADH2, adds e – at a lower energy level than NADH, thus, the electron transport chain provies 1/3 less energy for ATP synthesis when the electron donor is FADH2 than NADH
~ ATP synthase – uses energy of an existing ion gradient to power ATP synthesis – the power source for ATP synthase is a difference in concentration of H+ on opposite sides of the inner mitochondrial membrane. [we can also think of this gradient as a difference in pH since pH is a measure of H+ concentration]
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