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Energy & MetabolismChapt. 6

• All living things require energy• One of the primary functions of

macromolecules is to provide E.• Energy is the ability to do Work• Energy exists in two forms:

– Kinetic Energy– Potential Energy

Kinetic Energy

Kinetic energy is the energy of motion. An object which has motion - whether it be vertical or horizontal motion - has kinetic energy. There are many forms of kinetic energy - vibrational (the energy due to vibrational motion), rotational (the energy due to rotational motion), and translational (the energy due to motion from one location to another).

The amount of translational kinetic energy which an object has depends upon two variables: the mass (m) of the object and the speed (v) of the object.

Kinetic energy is an expression of the fact that a moving object can do work on anything it hits; Moving objects cause other objects to move…

Movement is work

• Text pg 96

Potential Energy

• Stored energy• Objects with the capacity to

do work but not active now have PE.

• Kid on the top of a slide• Bolder perched on an edge• Chemical bonds…• Much of life relates to

converting PE to KE PE= mass x gravity x height

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Forms of Energy

• Mechanical• Sound

• Electricity• Light

• Radiation • Heat

Heat

• Useful way to study energy because all other E. forms can be converted to heat

• This is the study of Thermodynamics• Heat Energy measured in units of

calories or kilocalories

Thermodynamics

• Thermodynamics is a branch of physics which deals with the energy and work of a system…

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Energy Flow

• Ultimately, all E. for life on earth comes from the sun

• Sunlight shines 40 million billion calories/second on earth!

• Plants, algae and photosynthetic bacteria convert sun E. to sugars

Sunlight to Chemical Bonds

• Photosynthesis converts a small (~10%) amount of sun E. into covalent bonds

• Where does the rest (~90%) of sunlight E. go?

Energy from Chemical Bonds

• Chemicals may be considered from a potential energy or kinetic energy standpoint. One pound of sugar has a certain potential energy. If that pound of sugar is burned the energy is released all at once. The energy released is kinetic energy (heat). So much energy is released that organisms would burn up if all the energy was released at once.

• Organisms must release the energy a little bit at a time.

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Covalent Bonds• Sharing of electrons

between atoms• Covalent bonds are a form

of PE• Energy is stored in each

covalent bond• Breaking covalent bonds

releases E. ~98Kcal/Mole for C-H bonds

• Bond energy is the energy in each orbiting e-

Electron Energies

• In Oxidation/Reduction reactions e- are passed from one atom to another

• Oxidized atom gives e- to reduced atom

• Reduced form now has more energy than oxidized one

• The amount of E passed on by e- depends on how far it was from the nucleus Reduction is the gain of an electron. Sometimes we also have

H ions along for the ride, so reduction also becomes the gain of H. Oxidation is the loss of an electron (or hydrogen).

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Photon of Light

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Red/Ox Reaction: NADH/ NAD+

Example of the Energy in Covalent Bonds

Photosynthesis:6CO2 + 12H2O + Light E. à C6H12O6 +6O2 + 6H2O

Light Energy requirements = ~3,000-7,000 Kcal

Respiration:C6H12O6 + 6O2à 6CO2 + 6H2O + Energy

Energy released = 686 Kcal

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• Photosynthesis uses lots of energy (3000-7000 Kcal) to produce one glucose molecule…

• But, the energy released from one glucose molecule produces only 686Kcal

• Most of the excess energy is lost as Heat...but the energy is never really gone…

Energy Loss in each Energy Transfer

All Energy transfers follow certain rules…

• First Law … Energy can never be created nor destroyed.

• The total amount of Energy in the universe remains always the same, it just changes forms…

The Laws of Thermodynamics

First Law

• Energy can be exchanged…between systems and their surroundings… However, the total energy of the system plus the surroundings is constant.

That's the First Law of Thermodynamics.

The First Law is also stated as energy is conserved.

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How do we know this?This is an empirical law, which means that we know that energy is conserved

because of many repeated experiments by scientists. It's been observed that you can't get any more energy out of a system than you put into it .

James Prescott Joule did a famous experiment which demonstrated the conservation of energy and showed that heat and work were both of the same nature: energy.

His experiment involved water in a thermally insulated containerand a paddle which was connected to the outside world (surroundings). Joule found that the amount of energy could change from one form to another (work to heat); however, no net change of energy in the system plus the surroundings occurred and thus Energy is conserved.

http://www.secondlaw.com/two.html

• The first law is very simple: You can't create or destroy energy.

• You can just change it from one form to another, for example, electricity to heat, heat that will boil water and make steam, hot steam to push a piston (mechanical energy) or turn a turbine that makes electricity which can be changed to light (in a light bulb) or, using only a tiny quantity changed to sound in an audio speaker system, and so forth.

The First Law of Thermodynamics

The Second Law

• Energy spontaneously tends to flow only from being concentrated in one place to becoming diffused or dispersed and spread out.

• A blowout in a tire and lightning -- what could seem to be more unlike than those! Yet the reason for their occurring is the same, the tendency for concentrated energy not to stay localized, to disperse if it has a chance and isn't hindered somehow.

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The Second Law

• Energy is constantly being converted to random molecular motion (heat Energy)

• This random motion is less ordered (disordered) and is always increasing

• The universe is becoming more disordered all the time

• Disorder = Entropy• And Entropy is always increasing

And so…The Universe is Breaking Down

• Entropy is increasing• It takes constant E. inputs to keep a road in

good shape, your car running and your dorm room clean…

• Leave things alone… and things fall apart• Playing cards rarely form a card house without

your help… card houses, once built, usually fall apart.

So What’s This Got to do with Life?

• Metabolism….involves E. transfers• Biological Reactions follow this format:

Reactants --> Products

• Energy transfers go along with this1. Reactants --> Products + Energy2. Energy + Reactants --> Products

A B

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Energy from Food

• Some living things can convert sun E. to food E.

• Food E. transfers from Plant to Deer to Coyote…

• Each E. transfer step loses ~90% to heat (random molecular motion).

How to measure the Energy in a molecule?

• Energy in a molecule (G) equals the energy in the chemical bonds (H) minus the energy lost as heat (S)

G= H - S• Also...The heat factor increases with

Temp (T)G = H - ST

In Chemical Reactions, usually it’s the Change in E. between Reactants and

Products that matters

?G = ?H - T?S

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Energy + Reactants --> Products

• If products contain MORE energy than reactants

• Energy input is required for reaction• Reactions will NOT occur spontaneously• Termed Endergonic reactions• ?G value is positive• Text pg. 99

Endergonic Reactions

?G = ?H - T?S

Products contain MORE energy than reactants

?G value is positive

Reactants --> Products + E

• Products contain LESS energy than reactants, excess E. is released

• Energy is released to do work• Reactions will occur spontaneously• Termed Exergonic reactions• ?G value is negative• Text pg. 99

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Exergonic Reactions

?G = ?H - T?S

Products contain LESS energy than reactants

?G value is negative

Activation Energy

• If so many reactions are exergonic and release energy spontaneously, why haven’t they already all occurred?

• They all require a bit of E. input…• This is the Activation Energy• A kid on the slide needs a slight push…• Text pgs. 103

Catalysts and Enzymes

• The role of a catalyst is to lower the amount of E. to push a reaction forward

• Catalysts may be biological or chemical• Biological catalysts are termed enzymes• Catalysts (and enzymes) thus lower the

Activation E.• Text pg. 104

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Enzymes• Speed up reactions by bringing molecules together or

by putting stress on covalent bonds to break them• Enzymes can speed up reactions thousands-millions

of times faster

CO2 + H2O --> H2CO3

• Enzyme for this reaction is carbonic anhydrase

How Enzymes Work to Speed Up Reactions

• Substrate molecule binds to enzyme active site…

• This forms an enzyme-substrate complex

• Enzyme may now act on substrate to induce a change…

• Text pg. 104

Factors Affecting Enzyme Activity

TemperaturepH

– Text pg. 112

Inhibitors– Competitive– Non-competitive

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Competitive Inhibitors

• Compete with normal substrate molecule for enzyme active site

• Text pg. 109

Noncompetitive Inhibitors

• Bind to a different site on enzyme and change its conformation

• Text pg. 109

How do cells use the energy of chemical bonds for work in the

cell?

By creating an energy-rich compound for use now or stored for later use…

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ATP

• Chief energy currency of cells• Plant photosynthesis results in this

compound being produced• ATP powers many cell reactions• A nucleotide composed of sugar,

adenine and 3 PO4

• Text pg. 101