Transcript Protein and Lipid Catabolism

Tricarboxcylic acid cycle
• Anaerobic, cell membrane or mitochondria
• Each pyruvate gives up its carbon as CO2
– 6 total
• Oxaloacetate is regenerated with every turn
– Pick up molecule
• 2 ATP are produced
– Substrate level phosphorylation
TCA cycle occurs twice per glucose
Net yield of product per glucose
molecule:
•6 CO2
•2 ATP
•8 NADH = 3 ATP
•2 FADH2 = 2 ATP
ELECTRON TRANPORT
• Aerobic or anaerobic
• Final electron acceptor:
– aerobic respiration - oxygen
– anaerobic respiration - CO2, NO3-, SO42
• Inner mitochondrial membrane or plasma membrane
• Electrons move down chain and set up H+ gradient
– drives chemiosmosis
Electron transport systems consist of separate protein complexes
Oxidative Phosphorylation – series of redox reactions creating a
stepwise release of energy
Proton Motive Force generated by chemical and electrical gradient
Proton flow across membrane is exerogonic
Using the PMF, ATP synthesis is catalyzed by ATP synthase (ATPase),
through a process called chemiosmosis
Complete Aerobic Catabolism of
Glucose
• C6H12O6 + 6O2 + 36ADP + 36P → 6CO2 + 6H2O + 36ATP
– (eukaryote)
• C6H12O6 + 6O2 + 38ADP + 38P → 6CO2 + 6H2O + 38ATP
– (prokaryote)
Typical net energy yield:
36 ATP for eukaryotes
38 ATP for prokaryotes
By-products of aerobic respiration are H2O and CO2
Substrate-Level Phosphorylation
– 2 ATP (net gain Glycolysis)
– 2 ATP (TCA cycle)
– 4 Total from substrate-level
phosphorylation
Oxidative Phosphorylation
– 6 ATP (NADH Glycolysis)
– 28 ATP (NADH/FADH2 TCA
cycle)
– 34 total from oxidative
phosphorylation
Total ATP gain ~ 36 to 38
Anaerobic Respiration
Many compounds can serve as terminal electron acceptors
• E.coli
– Nitrate reduction
– N03- + 2e- + 2H+
N02-+ H20
• Paracoccus, Bacillus and Pseudomonas
– Denitrification
– N03N02-
NO
N2O
N2
Nitrate reduction and ammonification
Denitrification in Paracoccus
• Desulfovibrio
– Reduce sulfate
– acetate + SO4-2 + 3H+
2CO2 + H2S + 2H2O
• Archaea
– Methanogens that reduce carbonate
– HC03- + 4H2 + H+
CH4 + 3H2O
• Common
– Not associated with any one phylogenetic group
– Except methanogenesis
• Involves:
– membrane system
– generation of ion gradient
– formation of ATP via ATP synthase
• Less efficient than aerobic respiration
– Electron acceptors have less positive reduction
potentials than oxygen
– lower energy yield
Fermentation
• Used by organisms that can’t respire
– lack of suitable inorganic electron acceptor or
lack of electron transport chain
• Anaerobic; Occurs in the cytoplasm
– Partial oxidation of substrate
• NADH oxidized back to NAD+
• Uses organic compound as terminal electron
acceptor
– Typically pyruvate or derivative
• NO oxidative phosphorylation so ATP yield is low
• Lactic acid fermentation
– pyruvate reduced to lactate
– pyruvate accepts electrons and protons from NADH
• Alcohol fermentation
– pyruvate decarboxylated to form acetaldehyde
– NADH transfers electrons and protons to acetaldehyde
reducing it to ethanol
Catabolism of Other Organic
Compounds
• Carbohydrates are the main energy source
– glucose
• Microbes may also utilize lipids and proteins
– Both must be broken down into their individual
components
– Each component is oxidized separately
Lipid Catabolism
• Lipases
• Fatty acids and glycerol
– Fatty acid converted into acetyl CoA, enters TCA cycle
– Glycerol converted into DHAP, enters glycolysis
Protein Catabolism
• Proteases
• Amino acids
–
–
–
–
can NOT be catabolized directly
transamination
decarboxylation
dehydrogenation