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Big Idea #2

�Biological Systems utilize

free energy and molecular

building blocks to grow, to

reproduce and to maintain

dynamic homeostasis

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� Life runs on chemical reactions

� rearranging atoms

� transforming energy

organic molecules →→→→

ATP & organic molecules

organic molecules →→→→ ATP & organic molecules

solar energy →→→→

ATP & organic molecules

Metabolism

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Energy

�Very difficult to define

quantity

�The ability to do something

(i.e. move)

�2 general types:

� Potential energy- stored energy

� Kinetic energy – moving energy3

Types of Potential Energy

� Gravitational

� Elastic

� Nuclear

� Electrical (separation of charges)

� Chemical (energy stored in chemical bonds)

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Chemical Potential Energy

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Kinetic Energy

� Moving objects

� Radiation (movement of light particles/waves)

� Thermal (heat, movement of particles)

� Electrical (movement of electrons)

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1st Law of Thermodynamics

�Energy is never created or destroyed

�Energy is, however, transformed from

one form to another

�i.e. wind’s motion is converted to

electricity, which is converted to heat

and light energy in a light bulb7

2nd Law of Thermodynamics

�The entropy of an isolated system is

always increasing

�Entropy is the amount of energy in

an unusable form – usually heat

�Systems are always losing usable

forms of energy8

What This Means

� In every conversion of energy- a lot of energy is lost as heat

� I.e. when you burn gas in your car- you lose a lot of energy as heat

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Put Another Way

�Energy will be spread from areas of high

energy to low energy

� I.e. heat will transfer from a hot pan to the air around it

� A moving object will lose its kinetic energy to other objects and heat

� Chemicals with a lot of potential energy tend to explode – releasing heat and movement of other objects

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Why Do Biologists Care About This Physics Stuff ?

�Because living

things obey these

laws!

�Living things are

always losing

energy to their

surroundings

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We Require an Energy Input

�For living things to

remain whole they

must have an

energy input

� I.e. organisms must

get energy from

sun, deep thermal

vents or eating14

Order and Organization Require Energy

�Things naturally break down – to keep them from breaking down or to put them together requires an input of energy

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Energy Coupling� Processes that release energy are coupled to ones

that require an input of energy

� More energy must be released than is required for

the next reaction due to entropy (energy loss)

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Example

� Flexing a muscle

requires an energy input

� Breaking down food

releases energy

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Exergonic Reactions

�Release free energy

�Used in living things to provide energy for other processes

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The Most Significant Exergonic Reaction

� ATP + H2O� ADP + Pi + Energy

� This is the main molecule the body

uses to transfer energy to where it is

needed

Hydrolysis of one of its phosphate bonds releases ADP, INORGANIC PHOSPHATE, AND FREE ENERGY

ATP drives endergonic reactions by transfer of the phosphate group to specific reactants.

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Making ATP is an Endergonic Reaction

� It requires an input of energy

� Made in cellular respiration (input of chemical

energy in food)

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Energy Rxns are Coupled

catabolic/anabolic endergonic/exergonic

ATP/ADP

oxidation/reduction (redox)

ADP

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ATP

� Metabolism fuels the body’s economy

� eat high energy organic molecules� carbohydrates, lipids, proteins, nucleic acids

� break them down� digest = catabolic; exergonic

� capture released energy in a form the cell can use

� Requires an energy currency

� a way to move energy around

� need a short term energy

carrier molecule

Living Energy Economy

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� A modified nucleotide� adenine + ribose + Pi → AMP

� AMP + Pi → ADP

� ADP + Pi → ATP

� Adding phosphates – phosphorylation is endergonic

� Removing phosphates is exergonic� energy available for cell work

ATP: Adenosine Triphosphate

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� Negative PO4 makes for unstable bonds� 3rd Pi is hardest to keep bonded to molecule

� most energy stored in 3rd Pi

� Pi group “pops” off easily, releasing energy

ATP is unstable

Instability of its Pi

bonds makes ATP an

excellent energy donor

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� ATP → ADP

� releases energy • 7.3 kcal/mole ATP

� Phosphorylation

� Pi transferred to other molecules • requires kinase

PO–

O–

O

–O PO–

O–

O

–O PO–

O–

O

–O Cal+P

O–

O–

O

–O

ADPATP

ATP transfers energy

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ATP/ADP are cycled� Energy transferred as ATP ->

ATP (redox)

� ADP is recycled via

monosaccharide metabolism

(respiration)

� polysaccharides, lipids, not

ATP, for storing energy

A working muscle

recycles over 10

million ATPs per

second!

Energy

for cell

work

Energy from

catabolism

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Uses of Free Energy

�Maintain body temperature

(some organisms)

�Reproduction

�Growth

�Movement

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Fuel for Life

reproduction

movement

…and more

Bulk transport

temperature

regulation

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Body Temperature Regulation

Endothermy

� Use heat released by

metabolic reactions to

keep a stable temp

� I.e. humans

Ectothermy

� Use external sources to

try to maintain body

temperature

� I.e. snakes/reptiles

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Reproduction

� Requires a huge amount of energy!

� Many species only reproduce when energy is available

� I.e. most plants flower in the spring when sunlight energy is abundant

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Growth

� Extra free energy not

needed for cellular

processes like

movement and

reproduction can be

put to growth

� I.e. extra calories

become stored fat

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Energy Deprivation

�Mass is broken down to provide

energy

�Eventually death will occur if there is

no energy input

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Smaller Organisms Require

More Food Per Body Mass

� Smaller organisms

have more surface

area relative to

volume, so they lose

more heat

� So they must replenish

that energy loss by

eating more (relative

to their body size)

than larger animals do33

QUANTIFYING ENERGY

total energy = useable energy* + unusable energyavailable for work random atomic motion

*point of interest for biologists

useable energy = total energy - unusable energyavailable for work random atomic motion

OR

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This relationship can be used to determine the

energy change of a rxn: exergonic or endergonic?

useable = total _ unuseable

energy energy energy

GIBBS

FREE ENERGY = ENTHALPY - ENTROPY

As entropy increases, free energy decreases

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To Know

Gibbs = entHalpy - (Temp K) diSorder

If G < 0, the reaction is exergonic; occurs

spontaneously; disorder is increased G is negative

If G > 0, the reaction is endergonic;

order/complexity is increased G is positive

requires coupling with an exergonic rxn* to drive the process

* usually ATP -> ADP + P

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Energy released

Spontaneous

Exergonic

G is negative

Energy required

Non-

spontaneous

Endergonic

G is positive

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2H2O2 -> 2H2O + 02

Catabolic or anabolic?

Endergonic or exergonic?

Increasing or decreasing disorder?

Spontaneous or coupled with ATP?

Energy stored or released?

Decreasing or increasing complexity?

Change in G positive or negative?

Building or breaking down molecules?

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Catabolic or anabolic?

Endergonic or exergonic?

Increasing or decreasing disorder?

Spontaneous or coupled with ATPrxn?

Energy stored or released?

Decreasing or increasing complexity?

Change in G positive or negative?

Building or breaking down molecules?

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Gibbs Free Energy Problems

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II. ENZYMES

♦ ENZYMES SPEED UP METABOLIC

REACTIONS BY LOWERING ENERGY

BARRIERS

♦ ENZYMES: PROTEINS THAT SERVE AS

BIOLOGICAL CATALYSTS

– SPEED REACTIONS BY LOWERING

ACTIVATION ENERGY

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ENZYMES ARE SUBSTRATE-SPECIFIC

� EACH TYPE OF ENZYME HAS A UNIQUE

ACTIVE SITE THAT COMBINES

SPECIFICALLY WITH ITS SUBSTRATE

� SUBSTRATE: THE REACTANT

MOLECULE ON WHICH AN ENZYME

ACTS UPON

� MECHANISM (INDUCED FIT): THE

ENZYME CHANGES SHAPE SLIGHTLY

WHEN IT BINDS THE SUBSTRATE44

THE ACTIVE SITE IS AN ENZYME’S

CATALYTIC CENTER

♦THE ACTIVE SITE CAN LOWER

ACTIVATION ENERGY BY

ORIENTING SUBSTRATES

CORRECTLY, STRAINING THEIR

BONDS, AND PROVIDING A

SUITABLE MICRO-ENVIRONMENT

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A CELL’S PHYSICAL AND CHEMICAL

ENVIRONMENT AFFECTS ENZYME

ACTIVITY

♦AS PROTEINS, ENZYMES ARE

SENSITIVE TO CONDITIONS THAT

INFLUENCE THEIR 3-D

STRUCTURE

♦EACH ENZYME HAS AN OPTIMAL

TEMPERATURE AND PH

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NOT ALL ENZYMES FUNCTION ALONE

♦COFACTORS: IONS OR MOLECULES FOR SOME ENZYMES TO FUNCTION PROPERLY

♦COENZYMES: ORGANIC COFACTORS

♦ INHIBITORS: REDUCE ENZYME FUNCTION

–COMPETITIVE: COMPETES AND BINDS TO ACTIVE SITE

–NONCOMPETITIVE: BINDS TO A DIFFERENT SITE, BUT STILL INHIBITS

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FIGURE 6.14 ENZYME INHIBITION

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III. THE CONTROL OF METABOLISM

♦ METABOLIC CONTROL OFTEN DEPENDS ON ALLOSTERIC REGULATION

♦ SOME ENZYMES CHANGE SHAPE, WHEN REGULATORY MOLECULES, EITHER ACTIVATORS OR INHIBITORS, BIND TO SPECIFIC ALLOSTERIC SITES

♦ ALLOSTERIC SITE: A SPECIFIC RECEPTOR SITE ON AN ENZYME REMOTE FROM THE ACTIVE SITE. MOLECULES BIND TO THE ALLOSTERIC SITE AND CHANGE THE SHAPE OF THE ACTIVE SITE, MAKING IT EITHER MORE OR LESS RECEPTIVE TO THE SUBSTRATE

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FIGURE 6.15 ALLOSTERIC REGULATION

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FIGURE 6.16 FEEDBACK INHIBITION

♦ FEEDBACK INHIBITION: THE END-

PRODUCT OF A METABOLIC PATHWAY

ALLOSTERICALLY INHIBITS THE ENZYME FOR

AN EARLY STEP IN THE PATHWAY

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6.17 COOPERATIVITY

♦ COOPERATIVITY: A SUBSTRATE MOLECULE BINDING

TO ONE ACTIVE SITE OF A MULTI-SUBUNIT ENZYME

ACTIVATES THE OTHER SUBUNITS

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THE LOCATION OF ENZYMES WITHIN A

CELL HELPS ORDER METABOLISM

♦ SOME ENZYMES ARE GROUPED INTO

COMPLEXES, SOME ARE INCORPORATED INTO

MEMBRANES, AND OTHERS ARE CONTAINED

IN ORGANELLES

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