Energy Harvesting Pathways

Glycolysis & Cellular Respiration

energy harvest

, storage

& transfe

rsFigure 7.1

energy transfers

•two ways to transfer metabolic energy from one molecule to another–as free energy during coupled exergonic/ endergonic reactions

–as “high energy” electrons during reduction/oxidation reactions

reduction reactions transfer energy

Figure 7.2

of course, some usable energy is lost in the transfer

NAD+ accepts reducing equivalents (H & e-)

Figure 7.4

(NADH+H+) + 1/2 O2 => NAD+ + H2O

G = -52.4 kcal·mol-1

NAD+/NADH shuttles reducing equivalentsFigure 7.3

retrieving energy from storage

•glucose is the most common metabolic fuel–other fuel molecules use the same catabolic pathway

•when glucose is completely oxidized (burned)C6 +6O2 => 6CO2+6H2O + energy G= -686 kcal/mol

•when glucose is oxidized metabolicallyC6 +6O2 => 6CO2+6H2O + energy

~ half of released energy is transferred to ATP

stages of

glucose

oxidation

Figure 7.5

retrieving energy from storage

•glucose is oxidized by a series of regulated metabolic pathways–glycolysis (cytoplasmic)•yields ATP, NADH & •two 3C pyruvates

–cellular respiration (mitochondrial)•converts pyruvate to CO2 & H2O, and•yields ATP, and •absolutely requires O2

fermentation:

partial oxidation

of glucose in the

absence of oxygen

OR,if O2 is

shortFigure 7.5

Cell Resp/Ferment LocationsTable 7.1

free energy changes duringglycoly

sisFigure 7.7

Investment, Isomerase,Harvest I,Harvest IIFigure 7.6

glycolysis

products:

NADH (2)ATP (2)pyruvate

(2)Figure 7.7

retrieving energy from storage

•glycolysis–a ten-step metabolic pathway –in the cytoplasm

•cellular respiration–NADH & pyruvate go to the mitochondrion•pyruvate is oxidized, and•decarboxylated–COOH functional group (carboxyl) is released as COO (CO2)

coenzyme A cycleFigure 7.8

citric acid

cycle,

tricarboxylic acid

(TCA) cycle,

Kreb’s cycleFigure 7.8

retrieving energy from storage

•pyruvate oxidation produces acetyl-CoA which enters the citric acid cycle

•2C acetate joins 4C oxaloacetate => 6C citric acid

•atoms are rearranged

•CO2 is released

•intermediates are oxidized•ATP is formed•more oxidation & rearrangement

final enzymatic disassembly

of glucose

by acyclic acetate burner

with energy capturing accessoriesFigure 7.8

energy yield of glycolysis

and citric acid

cycleFigure 7.9

retrieving energy from storage

•the major energy product of glycolysis and citric acid cycle is NADH

•the major metabolic energy demand is for ATP–citric acid cycle enzymes are in the mitochondrial matrix

–NADH reduces an enzymatic pathway on the inner mitochondrial membrane

fate of electrons from

glucoseFigure 7.10

change in free energy during

electron transport

Figure 7.11

electron transport proton pump

proton translocation during electron transport

Figure 7.12

retrieving energy from storage

•NADH drives electron transport•electron transport drives proton pumping

•proton pumping produces a transmembrane electrochemical gradient

•the phospholipid bilayer blocks diffusion of protons into the matrix

the ATP synthase proton channel relieves

the transmembrane proton gradient,

andthe proton gradient drives ATP

synthesis

chemiosmosis

Figure 7.12

a proton gradient

is sufficient to

generate ATP

Figure 7.13

retrieving energy from storage

•fermentation

–occurs when O2 is insufficient to drive cellular (aerobic) respiration

–IS NOT “anaerobic respiration”

–regenerates NAD+

lactic acid fermentation regenerates

NAD+

Figure 7.14

ethanolic fermentatio

n regenerates

NAD+

Figure 7.15

energy balance sheetFigure 7.16

interacting

metabolic

pathways

Figure 7.17

transamination forms an amino acidFigure 7.18

positive & negative feedback

coordinate the integrated

metabolic pathways

Figure 7.19

positive &

negative feedback control

glycolysis

Figure 7.20