metabolic diversity 1: energetics

continued growth requires a continual

gain of energy and continual radiation of heat

earth’s biosphere behaves as a giant thermal reactor because

metabolism of most life forms ultimately release most energy as heat

free energy (G)

a measure of available energy in a chemical reaction; how far a system is from its state of lowest free energy possible

enthalpy (H)

measure of how much heat and work are added or removed from a substance when changing at a constant pressure

entropy (S)

measure of how uncertain, random, and disordered a system is

three components of an organism’s type of metabolism

• carbon source for biomass: CO2? preformed organic molecules?

• energy source: light? chemical reactions?

• electron source: inorganic molecules (H2, H2S, etc.)? organica molecules (glucose, etc.)?

prefixes for carbon sources

• auto → fixes CO2

• hetero → uses preformed organic molecules

prefixes for energy source

• photo → from light

• chemo → from chemical rearrangement of molecules (like redox reactions)

prefexes for electron source

• lith → electrons from inorganic molecules

• organo → electrons from organic molecules

the ultimate goal of microbes is to

divide

• biosynthesis requires input of energy

• energy must come from catabolism

more/less negative delta G = more biomass?

more

• explains the diauxic route: organisms will prefer to catabolize more energetically favorable compounds like glucose first before they rely on another

which state of concentration gradient is the most disordered (state of highest entropy)?

randomly distributed uniformly

• explains why molecules will tend to diffuse down their concentration gradients

why are catabolic pathways used instead of having a single, high-energy yielding reaction step?

able to couple each small breakdown step with reactions that store energy in small molecules energy carriers

energy carriers

molecules that gain or release small amounts of energy in reversible reactions; may also transfer electrons; ATP, NADH, NADPH; “currency”

ATP stores

ENERGY in phosphodiester bonds

ATP transfers energy to cell processes in 3 ways

• hydrolysis releasing phosphate

• hydrolysis releasing pyrophosphate (PPi)

• transfer of a phosphate group (phosphorylation)

NADH can carry up to (?) times as much energy as ATP and functions as an electron carrier

2 or 3

FADH2

flavin adenine dinucleotide

• also an electron/energy carrier

• FADH2 → reduced form, FADH → oxidized form

• weaker electron donor than NADH but can be combined with a strong electron acceptor like O2

energy obtained from FADH2 vs NADH

2 ATP vs 3 ATP

why do different kinds of reactions use different energy carriers?

• different redox levels

• different amounts of energy

• regulation and specificity (ex. NADPH is only used for biosynthesis)

true/false: enzymes change the Gibbs free energy of a reaction

false - enzymes thought of as changing kinetics, NOT thermodynamics

true/false: enzymes speed up reactions by lowering the activation energy

true - allows more rapid conversion of reactants to products