Review of Last Class

Four Classes of Building Blocks

• Lipids

• Sugars – polysaccharides

• Nucleotides – nucleic acids

• Amino acids – proteins

WHAT DO MEMBRANES DO?

– Membranes are essential boundaries that separate the inside from the outside;

– Membranes regulate the contents of the spaces they enclose;

– Membranes serve as a “workbench” for a variety of biochemical reactions;

– Membranes participate in energy conversions.

Why Are All Organisms Made of Cells?

Directions and Rates of Biochemical Processes

Directions and Rates of Biochemical Processes

• How Does Thermodynamics Predict the Direction of a Reaction?– The First Law of Thermodynamics

• The total amount of energy in any process stays constant. Energy cannot be created or destroyed, only converted from one form to another.

• So, energy may switch from potential to kinetic and back again, but it is neither created nor destroyed.

» For example, the potential energy stored in the chemical bonds of ATP is converted into kinetic energy when it is split to allow a muscle contraction to occur.

Directions and Rates of Biochemical Processes

• How Does Thermodynamics Predict the Direction of a Reaction?– The Second Law of Thermodynamics

• In any process, the energy available to do work decreases.

– For example, when ATP is split to allow a muscle contraction, only a fraction of the energy from ATP is converted into useful work.The rest of the energy becomes heat which is largely wasted energy.

∆G = Gproducts – Greactants

Exergonic ∆G < 0 spontaneous rx.

Endergonic ∆G > 0

Copyright 2001 by Harcourt, Inc.

Directions and Rates of Directions and Rates of Biochemical ProcessesBiochemical Processes

How Do Concentration (and Entropy) How Do Concentration (and Entropy) Affect Equilibrium?Affect Equilibrium?

reactant Areactant A product Bproduct B

more free energymore free energy less free energyless free energy

If the reaction isIf the reaction is exergonicexergonic (energy releasing), product B will begin to (energy releasing), product B will begin to accumulate.accumulate.As the amount of B increases, so does BAs the amount of B increases, so does B’’s free energy.s free energy.

Gradually, the difference in energy between the reactants and prGradually, the difference in energy between the reactants and products oducts decreases. When the free energy of B = the free energy of A, nodecreases. When the free energy of B = the free energy of A, no further further net movement occurs and the reaction is said to be in equilibriunet movement occurs and the reaction is said to be in equilibrium.m.

Chapter Six: How Do Organisms Supply

Themselves with Energy

習題p.120, 如果你專心唸書， 24h 要用掉 1025 個 ATP 分子， 約重 40kg ，這個數字是怎麼得來的？

有化學背景的同學 ，一定要做對

沒有化學背景的同學，做對會加分