Download Anaerobic Fermentation

Degredative pathways to release ATP energy for cell functions
(catabolic)
Evolution of Catabolic pathways
 Anaerobic Fermentation – evolved in primitive
bacteria still used by some unicellular organisms
Anaerobic Fermentation
Steps: Glycolysis then regeneration of NAD+
(Glycolysis breaks glucose in ½)
 A) 2 ATP added to glucose
 B) unstable intermediate forms
 C) NAD+ picks up H from glucose
 D) Intermediate splits into 2 pyruvates
 E) 4 ATP generated (net gain of 2 ATP)
 F) NADH drops hydrogen off on pyruvates
 G) CO2 and alcohol by products form

 Net gain of 2ATP is enough energy for a
unicellular organism….
 but not for a multicellular organism
Advent of non-cyclic
photosynthesis
 Caused free O2 to build up in the ocean
Build up of O2 in atmosphere
 Obligate Anaerobes: die in presence of O2
 Present day obligate anaerobes regulated to
anaerobic environments. Form endospores
against the O2 laden air.
 Example disease causing bacteria:
 Botulism (Clostridium botulinum), Tetnus
(Clostridium tetani)
 Other lines evolved anti-oxidants/defense against
 the oxidative properties of O2 can
 survive the presence of free oxygen
 Some organisms found ways to use the O2 to
generate more energy per glucose :

aerobic cellular respiration
 Some organisms can use aerobic respiration when
O2 is present then switch to anaerobic
fermentation when in anaerobic conditions

= facultative aerobes (yeast)
Aerobic Respiration
 Evolved a way to use e- on NAD+ in electron
transport chain to get more ATP /glucose.
 Anaerobic fermentation => 2 ATP gain
 Aerobic respiration => 32 ATP gain
 Some bacteria became obligate aerobes
 Animals plants fungi…..
Aerobic Respiration 4 Parts
 Step 1 ..Glycolysis
 Step 2 .. Acetyl-CoA formation
 Step 3…Krebs Cycle (citric acid cycle)
 Step 4… Electron transport and oxidative
phosphorylation
Aerobic Glycolysis
 Glucose split in cytoplasm (before entering mito.)
 2ATP added to Glucose
 Unstable intermediate forms then splits
 NAD+ reduced into NADH
 4 ATP made
 Net gain = 2 ATP per glucose
 1) Substrate level phosphorylation creates
unstable intermediate
 2) Intermediate splits then forms 2 PGAL
 3) NAD+ is reduced
 4) NADH carries e- and H+ to mitochondria
 5) Each PGAL has enough energy to make 2 ATP
 6) 2 pyruvates (pyruvic acids) move to mito
Acetyl-CoA formation
 The pyruvate enters the mitochondrial matrix

(in prokaryotes stays in cytoplasm)
 One C is removed and converted to CO2
 One NAD+ is reduced to NADH
 Coenzyme A binds to the remaining 2 C
forming Acetyl-CoA
Krebs cycle : Citric Acid Cycle
 Acetyl Co-A drops off 2 C onto oxaloacetate to form
citrate
 CoA is thereby regenerated and returns to pick up
more C from pyruvate
 3NAD+ and 1FAD reduced to form NADH and
FADH2
 To do this, a series of intermediates have all their
Hydrogens removed
 Remaining C and O released as 2CO2
 1 ATP is produced
 Oxaloacetate is reformed
 Cycle runs one time for each pyruvate
Electron Transport Chain
 e- brought to ET chain by NADH & FADH2
 NADH and FADH2 come from Glycolysis & Kreb’s
 e- passed down chain of proteins in a series of
oxidation/reduction reactions
 Protein pumps use energy from e- to pump H+
 H+ build up in intermembrane space creating
electrochemical gradient (lots of Potential E)
 e- at end of chain picked up by O2
 Chemiosmosis = energy coupling mechanism
 converts potential energy of chemical gradient
into chemical energy (ATP)
Oxidative phosphorylation
 Producing ATP using the energy of oxidation
reactions in the e- transport chain
 Generates 26 – 28 ATP per glucose
Electrons from Glycolysis
 Passed through mito membrane by
transport proteins to NAD+ or FAD on
inside of mito
 Slightly less ATP is formed if FAD pick up e-
Lack of Oxygen in mitochondria
 Oxygen = final electron acceptor in aerobic resp
 If no O2 oxidizes the last protein in e- transport
chain, chain stops
 Oxidative phosphorylation stops
 NADH &FADH2 build up, NAD+ & FAD run out
 Kreb cycle stops
 NADH from glycolysis can’t drop of e- at mito
Lactic Acid Fermentation-animals
 NADH drops off electrons onto pyruvate
 pyruvate is converted to Lactic acid
Other Macromolecules as fuel
 Only Glucose runs entire aerobic resp pathway
 Carbs converted to glucose before being used
 When carbs run out Fats used
 Triglycerides break into ……

fatty acids & glycerol
 Glycerol converted to PGAL & enters….

Glycolysis
 Fatty acids are converted into acetyl-CoA

enters Kreb’s
 Proteins broken into ….

amino acids
 Amino acids break into
 a) NH3 (nitrogenous waste) converted to urea
 b) carbon backbone converted to pyruvate or
Acteyl Co-A