Biology 102

Fall 2001

R. Brundage

A.Defining Energy

1. Potential energy is the capacity to make things happen, to do work;

it can also be called chemical energy, measured in kilocalories.

2.Kinetic energy is the energy of motion; it includes heat energy.

3.Metabolism refers to the cell’s capacity to acquire energy and use it to

build, store, break apart, and eliminate substances in controlled ways.

B.How Much Energy Is Available?

1.First law of thermodynamics states that the total amount of energy in the

universe is constant; it cannot be created nor destroyed;

it can only change form.

2. Energy cannot be produced by a cell; it can only be borrowed from

someplace else.

3.Energy can be of high quality, that is, highly concentrated and usable;

or it can be of low quality, such as heat that is released into the universe.

C.The One-Way Flow of Energy

1.Second law of thermodynamics states that the spontaneous direction

of energy flow is from high- to low-quality forms.

2.Each conversion produces energy (usually heat) that is

unavailable for work.

3.As systems lose energy they become more disorganized;

the measure of this disorder is called entropy.

4.The world of life (plant and animal) maintains a high degree of

organization only because it is being resupplied with energy from the sun.

A.Which Way Will a Reaction Run?

1.Chemical reactions can proceed from reactants to products, which,

if they are allowed to accumulate, will convert back to reactants.

2.The direction of reaction depends on concentrations and the

collision of molecules.

3.When a reaction approaches chemical equilibrium, the forward

and reverse reactions proceed at equal rates

a.There is no net change in concentrations.

b.Every reaction has its own ratio of products to reactants at

equilibrium.

B.No Vanishing Atoms at the End of the Run

1.The law of conservation of mass states that the total mass of all

substances entering a reaction equals the total mass of all the products.

2.This is why you must always "balance" a chemical equation by having an

equal number of atoms of each element on both sides of the arrow.

C.Energy Inputs Coupled with Outputs

1.Exergonic ("energy out") reactions release energy such that the products

have less energy than the reactants had.

2.Endergonic ("energy in") reactions require energy input resulting in

products with more energy than the reactants had.

A.The Structure of ATP

1.Before cells can use the energy of sunlight or that stored in

carbohydrates, they must transfer the energy to molecules of ATP.

2.ATP is composed of adenine, ribose, and three phosphate groups.

B.Phosphate-Group Transfers

1.Energy input links phosphate to ADP to produce ATP (phosphorylation).

2.ATP can in turn donate a phosphate group to another molecule,

which then becomes primed and energized for specific reactions.

3.ADP can be recycled to ATP very rapidly in the ATP/ADP cycle.

C.ATP Output and Metabolic Pathways

1.Metabolic pathways form series of reactions that regulate the

concentration of substances within cells by enzyme-mediated

linear and circular sequences.

2.In biosynthetic pathways, small molecules are assembled into large

molecules; for example, simple sugars are assembled into

complex carbohydrates.

3.In degradative pathways, large molecules such as carbohydrates,

lipids, and proteins are broken down to form products of lower energy.

Released energy can be used for cellular work.

4.Participants in metabolic pathways are defined as follows:

a.Substrates are substances that enter reactions (= reactants =

precursor).

b.Intermediates are the compounds formed between the start and

the end of a pathway.

c.End products are the substances present at the conclusion of a

pathway.

d.Energy carriers are mainly ATP.

e.Enzymes are proteins that catalyze (speed up) reactions.

f.Cofactors are small molecules and metal ions that help enzymes

by carrying atoms or electrons.

g.Transport proteins are membrane-bound proteins that participate

in adjusting concentration gradients that will influence the

direction of metabolic reactions.