Chapter 8

p. 141-150

Metabolism: sum of all chemical rxns in the body

Metabolic Pathway: series of rxns catalyzed by specific enzymesCatabolic Pathways: energy-releasing

Usually by breaking down large molecules i.e.: cellular respiration

Anabolic Pathways: energy-consuming Usually by building macromolecules i.e.: protein synthesis

Energy: the capacity to cause change or rearrange a collection of matter

A) Kinetic Energy: energy of motion i.e. leg muscles pushing bicycle pedalsHeat/Thermal Energy: kinetic energy of

atomic movement B) Potential Energy: stored energy

i.e. water built up behind a damChemical Energy: potential energy stored

in molecules When broken down, gets released

On the platform,the diver hasmore potentialenergy.

Diving convertspotentialenergy to kinetic energy.

Climbing up convertskinetic energy ofmuscle movement topotential energy.

In the water, the diver has lesspotential energy.

The study of energy transformationsBased on open systems, or organisms that

transfer energy between self & surroundings

1st Law of Thermodynamics: Energy can be transferred and transformed but can not be created nor destroyed“Principle of Conservation”Energy is converted from 1 form to another

as it passes through open systems i.e.: chemical energy in food kinetic

energy for muscle contraction

2nd Law of Thermodynamics: Every energy transfer or transformation increases the entropy of the universeEntropy: measure of randomness or

disorder Every time energy is transformed, some of it is

converted to heat & escapes to the surroundings If a process increases entropy, it will occur

spontaneously (w/o energy input)

Chemical energy

Heat CO2

First law of thermodynamics Second law of thermodynamics

H2O

ΔG = G final state – G initial state

Final state has less free energy, then it is more stable

Systems will always try to move to more stable state

Chemical rxns at equilibrium are at their most stable state (ΔG is lowest)Can’t do any more work

Exergonic Rxns: net release of free energy ΔG is negative; rxns are

spontaneous Value of ΔG = amount of

work that can be performed Endergonic Rxns: absorb

free energy ΔG is positive; rxns are NOT

spontaneous Value of ΔG = amount of

energy required to drive the reaction

Living cells never exist at equilibrium Are “Open Systems”There is a constant flow of

materials into & out of a cellThe products of 1 rxn may

become the reactants of another rxn; wastes are expelled from the cell

Energy Coupling: the use of exergonic rxns to drive endergonic ones, using ATP i.e.: beating of cilia, pumping substances

across membranes, synthesizing polymers Adenosine Triphospahte (ATP):

ribose (sugar), adenine (nitrogenous base), 3 phosphate groups To release energy, one PO4 is removed by

hydrolysis Each PO4 is neg. charged & close together ΔG = -7.3 kcal/mol

This rxn may be coupled to endergonic ones to help them proceed

When ATP hydrolysis is coupled to another rxn, the removed PO4 is transferred to a reactant of an endergonic rxn“Phosphorylated” reactant is less stable

& thus more likely to react To regenerate ATP (replace the PO4),

use energy from exergonic rxns i.e. cellular respiration

Chapter 8

p. 150-159

Some rxns, although spontaneous, occur so slowly they can not be detected

Catalyst: a chemical compound that speeds up a rxn w/o being consumedEnzyme:

A protein catalyst Named for the rxn/substrate catalyzed Usually end in “-ase”

All chemical rxns involve breaking & forming bondsStarting molecules must contort to unstable

position; requires energy Activation Energy (EA): energy required

to start a rxn/contort the reactantsOften comes in form of heat from

surroundings (speeds up molecules, collide more often)

Transition State: point at which reactants absorb enough energy so bonds begin to break & form (“peak” of rxn)

Instead of heat, living cells use enzyme catalysts to overcome EA Heat denatures proteins & would speed up all

rxns Enzymes decrease EA, lowering amount

needed to reach transition state Substrate: reactant the enzyme acts upon

Very specific (I enzyme/substrate) Forms Enzyme-Substrate Complex w/ active

site of enzyme Active Site: region of enzyme to which

substrate binds Formed by few amino acids w/in the protein Induced Fit: brings substrate & enzyme in

perfect position to maximize catalysis

Substrates are held in place by weak interactions Hydrogen bonds, ionic bonds

Active Site & R-groups of amino acids decrease EA by: A) Holding substrate in proper position B) Contorting substrate into transition-state

conformation C) Providing microenvironment (pH, salinity, etc) D) Participating in rxn

Side chain of enzyme aa may briefly bond to substrate Rate often depends on:

1) Amount of Substrate Saturated Rxn: when all enzyme molecules are being

used 2) Amount of Enzyme

If rxn is saturated, can increase rate of reaction

Temperature: up to a point, an increase in temp will increase enzyme activity If too high, bonds are broken & protein will

denature Each enzyme has its own “optimal temp”

pH: most enzymes work best at a pH of 6-8 If too acidic/basic protein will denature Some enzymes are designed to work in extreme

pH conditions Cofactor: a non-protein “helper” bound to

an enzyme (i.e. zinc, iron, copper) Performs a variety of functions Coenzyme: an organic cofactor (i.e.vitamins)

Inhibitor: selectively inhibits the action of a specific enzyme If binds covalently, may be irreversible

Competitive Inhibitor: resembles substrate & blocks it from entering active siteCan be overcome by increasing substrate

concentration Noncompetitive Inhibitor: binds to

enzyme, causing it to change shapeSubstrate no longer fits in active siteCan be overcome by increasing enzyme

concentration

Enzyme activity has to be constantly and specifically regulated

Allosteric Regulation: activity at one site of a protein can alter the activity at another site (i.e. the active site) Enzymes are composed of 2+ polypeptides,

each with its own active site Enzymes are constantly switching from “active”

to “inactive” states Allosteric Activation: uses an “activator”

to hold the complex into the active state Allosteric Inhibition: Uses an “inhibitor”

to hold the complex into the inactive state The allosteric molecule will affect each active

site on the enzyme

When a pathway is shut off b/c the end product binds to and inhibits an enzymePrevents the cell

from wasting resources

Is a type of allosteric inhibition