Ch. 13: Introduction to Metabolism

the ultimate energy source on earth

sunlight

metabolism

the sum of all chemical reactions in a cell

anabolism

synthesis of macromolecules from monomers

catabolism

degrading energy-containing macromolecules (fats, carbohydrates, proteins) into energy-depleted, oxidized products

product of catabolic pathways

chemical energy in the form of ATP, NADH, NADPH and FADH2

chemical energy in anabolic pathways

energy carriers are used to convert small precursor molecules into cellular macromolecules

metabolites

intermediates of a metabolic pathway, most are shared by >1 pathway

amphibolic pathways

pathways that can be either anabolic or catabolic based on the energy requirements of the cell

catabolic reaction formula example

carbohydrates → CO2, H2O, useful energy

anabolic reaction formula example

useful energy + precursor → comple molecules (such as protein synthesis)

metabolic pathway

a series of consecutive enzymatic reactions that result in a product used or excreted by the cell

enzyme regulation of metabolic pathways

enzymes are regulated on multiple levels

examples of metabolic regulation/enzyme activity

• only as much that is needed can be made by the enzyme

• enzyme can be sequestered to be inactive

• enzyme can be limited by the substrate, a ligand, or by phosphorylation/dephosporylation

do catabolic pathways converge or diverge

converge

do anabolic pathways converge or diverge

diverge

free energy change

the maximum energy made available to do work when a chemical reaction occurs

ATP (in simple terms)

the universal energy currency in living organisms

how to make ATP

indirectly provided by oxidation-reduction reactions

how living organisms use energy

transform energy from one form to another

what happens as energy is transformed by organisms?

the living organisms must increase the entropy of the universe

relationship between equilibrium constants and standard free energy change

exponential

equilibrium constant (keq) in simple terms

ratio of product/reactant at equilibrium

when keq is small how much product is there?

product < reactant

when keq is large how much product is there?

product > reactant

when free energy is negative how much product is there?

product > reactant

when free energy is positive how much product is there?

product < reactant

exergonic

energy is released, spontaneous and favorable

endergonic

energy is required to proceed, NOT spontaneous or favorable

keq and ∆G when exergonic

keq > 1

-∆G

keq and ∆G when endergonic

keq < 1

+∆G

keq and ∆G when at equilibrium

keq=1

∆G=0

what does actual free energy change in the cell depend on?

• standard change in free energy

• actual concentrations of products and reactants

how do you drive an endergonic reaction forward?

coupling to a highly exergonic reaction, usually ATP hydrolysis

keq for coupled reactions

multiplicative

∆G for coupled reactions

additive

why hydrolysis of ATP is highly favorable

1. electrostatic repulsion is lost with hydolysis

2. products (ADP and Pi) have greater resonance stabilization than ATP

3. hydration, water binds more effectively to products and stabilizes them

what does ∆G of ATP hydrolysis depend on

the Mg2+ complex

purpose of MgATP2- complex

• shields the negative charges

• influences conformation of phosphate groups in nucleotides

phosphorylation potential keq (∆Gp)

the actual free energy of hydrolysis of ATP under intracellular conditions

is ∆Gp constant or variable

varies from cell to cell and over time

ATP hydrolysis in vivo

the energy released is greater than the standard free energy change due to higher concentrations than the standard tells

NTPs analogous to ATP

• UTP→ uridine triphosphate

• GTP→ guanosine triphosphate

• CTP→ cytidine triphosphate

molecules with higher ∆Gp than ATP upon hydrolysis

• phosphoenolpyruvate

• 1,3-biphosphoglycerate

• creatine phosphate