PA-STEM
Immaculata Week, 2015
Biology
Orlando
Bioenergetics
Living organisms are made up of
organic molecules
• Contain carbon
backbones
– Carbohydrates (sugars)
– Lipids (fats)
– Proteins
– Nucleic acids (DNA, RNA)
Molecular Biology, Craig, Oxford, 2010
Organic Molecules
• Sources of raw material/energy in food
– (ex) sugars, fats, proteins in diet
• Ingested food:
– Broken down for energy
– Used as raw materials to create new body structures
and run bodily functions
• (ex) new growth, cell division, enzymatic reactions
“cut” apart
molecules
Metabolism
• All chemical reactions in the body
• Catabolism:
– Decomposition reactions (break bonds)
– Typically release energy
– (ex) break down complex carbs and fats for energy
• Anabolism:
– Synthesis reactions (form bonds)
– Typically require energy input
– (ex) production of proteins from amino acids
Carbohydrates
• Monosaccharides
– All have the same molecular
formula: C6H12O6
• All isomers of each other
Carbohydrates
• Disaccharides
– Sucrose: (table sugar): glucose + fructose
– Lactose; (milk sugar); glucose + galactose
– Maltose: (malt sugar): glucose + glucose
Carbohydrates
• Polysaccharides
– Cellulose: indigestible* cell walls of plants (dietary
fiber)
• (*indigestible to humans)
– Starch: digestible energy stores in plants
– Glycogen: digestible energy stores in animals
Carbohydrate Metabolism
• Dietary carbohydrate burned as fuel
• Glucose catabolism
C6H12O6 + 6 O2  6 CO2 + 6 H2O
• Function: to transfer energy from glucose to ATP by
breaking bonds
O2
O2
O2
+ O2
O2
O2
CO2
H2O
CO2
H2O
CO2 + H2O
CO2
H2O
CO2
H2O
CO2
H2O
Glucose Catabolism
• Series of small steps (each controlled by a separate
enzyme), in which energy is released in small
manageable amounts, and as much as possible, is
transferred to ATP (short-term energy currency)
• The rest is released as heat (not 100% efficient)
Glucose Catabolism
http://animagraffs.com/how-a-car-engine-works/
Glucose Catabolism
Aerobic Respiration
1
Glycolysis
Anaerobic Fermentation
Glucose
NADH
Glycolysis
ATP
Pyruvic
acid
2
Pyruvic acid
(or derivative)
Acetyl CoA
Fermentation
NADH
Krebs cycle
(Citric acid cycle)
FADH2
Kreb’s
cycle
NADH &
FADH2
ATP
3
Electron transport
chain
NADH
Fermentation
end-products
(lactic acid,
ethanol)
brewer’s
yeast
CO2
Electron
s
Electron
transport
chain 
ATP
synthase
ATP
O2
H2O
(Totora. Microbiology: An Introduction. 11ed 2011)
Aerobic Respiration
• Krebs cycle (Citric acid cycle)
– Carbons are removed from organic compounds
• (as CO2)
– Electrons are passed to carrier molecules
(NADH, FADH2)
Aerobic Respiration
• Carrier molecules (NADH and FADH2) bring electrons
to electron transport chain in mitochondria
• Oxygen is the final electron acceptor
– Combines with electrons and hydrogen ions to form water
– No oxygen, ETC backs up and shuts off!
ATP Generated by Aerobic Respiration
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glucose
2 ATP
(net)
Glycolysis
2 NADH + 2 H+
Cytosol
2 pyruvate
Mitochondria
34% Efficiency
(66% is lost as
body heat)
2 NADH + 2 H+
CO2
6 NADH + 6 H+
Citric acid
cycle
2 ATP
2 FADH2
Electron-transport
chain
O2
H2O
Complete aerobic
oxidation of
glucose to CO2
and H2O produces
32 ATP
4 ATP
25
Total 32
ATP
ATP
Fermentation
• Doesn’t use Krebs cycle or ETC
• Uses an organic molecule as the
final electron acceptor
• Produces only 1 or 2 ATP
• Organic end products:
– Lactic acid
– Ethanol + CO2
(a) Lactic acid
fermentation
(b) Alcohol fermentation
Table 5.4 Some Industrial Uses for Different Types of Fermentations*
Figure 5.23 A fermentation test.
Fermentation
1.
2.
3.
• Fermentation test: Incubate microbe with carbohydrate
source, pH indicator (turns yellow with acid), inverted
Durham tube (air bubble with CO2)
• Match tube to description below…
a. Bacteria produce acid but no CO2
b. Bacteria produce acid and CO2
c. Bacteria did not use carbohydrate source
Organisms can switch between
aerobic respiration and fermentation
• Respiration is more efficient
but…
• Fermentation does not require oxygen, and
can create some ATP quickly
• (ex) Eukaryotic muscle cells can produce lactic
acid when run out of oxygen
• (ex) Brewer’s yeast switch from aerobic
respiration to fermentation
Glycogen Metabolism
• ATP is quickly used after it is formed
– It’s an energy transfer molecule, not an energy storage molecule
• Convert extra glucose to other compounds needed for
the cell (proteins) or that are better suited for longterm energy storage (glycogen and fat)
Integration of Metabolism
• Many metabolic pathways have both catabolic
and anabolic functions
– joined through common intermediates, share
some metabolic pathways
• (ex) Krebs Cycle
– Can allow cell to monitor demand for reaction
products and adjust
• (ex) if ATP accumulates, shuts down glycolysis
• (ex) if run out of amino acids, use Krebs cycle to make
some
Krebs
cycle
CO2