BIOL 130L Cellular Respiration Notes

1
CELLULAR RESPIRATION

Key concepts
 In cells, endergonic reactions needed for life are paired with exergonic reactions requiring ATP
 There will be lots of electrons flowing back and forth
 OIL RIG → oxidation is loss, reduction is gain
 Components of metabolic pathways include:
o Energy source—glucose
o Enzymes
o Electron carriers (NAD+, FAD)
o Terminal electron acceptor (oxygen)

Metabolism and nutrition
 Metabolic reactions contribute to homeostasis by harvesting chemical energy from consumed nutrient
to contribute to body’s growth, repair, and normal functioning
 Metabolism—denotes sum of all body chemical reactions
o Energy-balancing act between catabolic and anabolic reactions
 Molecule that participates most often in energy exchanges in living cells is ATP
 Couples energy-releasing catabolic reactions to energy-requiring anabolic
reactions
o Anabolism—building up smaller molecules into larger molecules
 Anabolic reactions consume more energy than they produce
 Endergonic—consume heat
o Catabolism—breaking down larger molecules into smaller molecules
 Catabolic reactions provide more energy than they consume
 Exergonic—liberate heat
 Transfer energy into “high-energy” phosphate bonds of ATP, where it can be
released quickly and easily
 Electrons are more important source of chemical potential energy in cells
o Amount of potential energy in an electron is based on position relative to positive and negative
changes
 Electrons closer to negative charges (from other electrons) and farther from positive
charges (in nuclei of nearby atoms) have higher potential energy

Cellular respiration
 Process by which cells acquire energy by breaking down nutrient molecules by photosynthesis
o Glycolysis
o Pyruvate processing
o Citric acid cycle
o Electron transport and chemiosmosis
 Requires oxygen and gives off carbon dioxide
 Usually involves breakdown of glucose to carbon dioxide and water
o Step-wise process allows for efficiency in production and storage of ATP
o Oxidation-reduction enzymes include NAD + and FAD as coenzymes
 Full breakdown of glucose results in 36-38 ATP molecules

Glucose breakdown: reaction summary

, 2
 Electrons are removed from substrates and received by oxygen, which combines with H + to become
water
 Glucose is oxidized and O2 is reduced
 Reducing agent—electron donor
 Oxidizing agent—electron receptor
 Some redox reactions do not transfer electrons but change electron sharing in covalent bonds
o Example: reaction between methane and O2

Redox reactions
 Oxidation of glucose by “burning it” in cells through a series of electron transfers to ultimately yield
water, carbon dioxide, and ATP
o Leaves product with decrease in potential energy
 Many steps in burning glucose require oxidation via a dehydrogenation (redox) reaction
o Liberated electron pair are lost along with a hydrogen atom
 Called a hydride ion and represented along with its electron pair (H:-)
+
Coenzymes NADand FAD
 NAD+—nicotinamide adenine dinucleotide
o Called coenzyme of oxidation-reduction
 Oxidizes a metabolite by accepting electrons
 Reduces a metabolite by giving up electrons
o Each NAD+ molecule used over and over again
o Usually accepts 2 high-energy e- and one H + resulting in NADH
 FAD—flavin adenine dinucleotide
o Also a coenzyme of oxidation-reduction
o Sometimes used instead of NAD+
o Accepts two electrons and two hydrogen ions (H+) to become FADH2

Role of electron carriers
 Energy harvested in stepwise process
o Electrons transferred to electron carriers, which represent reducing power (easily transfer
electrons to molecules)
 Raise energy level of recipient molecule
o NAD+/NADH
o NADP+/NADPH
o FAD/FADH2
 NADH passes electrons to electron transport chain
 Unlike uncontrolled reaction, electron transport chain passes electrons in series of steps instead of on
explosive reaction
 O2 pulls electrons down chain in energy-yielding tumble
 Energy yielded is used to regenerate ATP

Carbohydrate metabolism
 Glucose is body’s preferred source of fuel
o During digestion, polysaccharides and disaccharides are hydrolyzed into monosaccharides
 Glucose—80%
 Fructose and galactose—20%