BIO 10 BIO 10 Lecture 6Lecture 6BIO 10 BIO 10 Lecture 6Lecture 6

THE VITAL FORCE: THE VITAL FORCE:

AN INTRODUCTION TO ENERGYAN INTRODUCTION TO ENERGY

WHAT IS ENERGY?

• Energy = the capacity to do work• Energy is a tricky subject to understand

because it can be measured but not seen.• Two main forms:

– Potential energy: stored energy • a rock on a hill • a lump of coal

– Kinetic energy: energy in motion • a rolling rock • heat from a burning lump of coal

Energy is the “Vital Force”• Vital = “of or concerned with life”• Life needs energy to work against entropy• Where does the energy come from?

– The whole Universe was wound up like a giant music box by the Big Bang

– The “winding up” is the potential energy created when matter was first separated in space and time

– This potential energy is converted to kinetic energy as matter falls together by gravity and stars “shine”

• Life on Earth sucks energy from the radiation emitted by the Sun, Earth’s nearest star– A few organisms suck energy from thermal processes

created by the heat of Earth’s own gravitational collapse

Life harvests the energy of high energy (short wavelength) photons from the Sun to work against entropy to create highly ordered systems.

The leftover energy is then re-radiated back into space at a longer (less energetic) wavelength.

Thermodynamics: The Study of Energy

• First law of thermodynamics: energy is neither lost nor gained, but only transformed. – Examples: solar energy (kinetic) used to

create carbohydrates (potential) in plants, and steam engine burning coal (potential) to generate heat to move pistons (kinetic).

• Second law of thermodynamics: explains what is observed when energy is transferred, and why certain reactions occur spontaneously (e.g. coal will burn, but ashes will not)– Start with coal (potential energy), add a flame, and a

reaction occurs spontaneously to produce ashes and hot air (kinetic energy)

– Transfer always goes spontaneously from an ordered, concentrated form (e.g. chemical bonds between carbons in coal) to a disordered, dispersed form (e.g. heat and gases).

• Coal does not spontaneously reform from ashes and hot air. Why? Because energy transformation occurs spontaneously only when it goes from greater to lesser order

• The second law of thermodynamics describes how energy is transferred, and it states that when energy is transferred it always results in a greater amount of disorder in the universe.

Entropy is a measure of the amount of disorder in a system.

Transformation of energy

The less energy is lost in an unusable form during the transformation of from one form to another, the most efficient the process is at generating WORK

Living organisms need energy in order to maintain the order (fight entropy) and do the work required to preserve and perpetuate the DNA molecules they contain.

They suck this energy from the Sun or Earth (either directly or indirectly), which sucks it from the Universe (via gravitational collapse)

Energy Reactions and Cycles in Living Organisms

• Synthesis reactions (like making carbohydrates—more ordered and complex than carbon dioxide gas) takes energy– These are “uphill” reactions because

they fight against the second law of thermodynamics

– Also called endergonic reactions• “energy in” because they require energy to

go

• Degradation Reactions (like breaking down carbohydrates into carbon dioxide again) release energy

These are “downhill” reactions because they increase entropy

Are also called exergonic reactions: “energy out” because they go spontaneously without the input of energy from the surroundings

Coupling of Reactions

• Since both endergonic and exergonic reactions take place in living organisms, they are often chemically linked.

• Example: The creation of the complex molecule glycogen is endergonic (requires the input of energy)

• The energy is provided by breaking down another molecule to release energy. That molecule is ATP.

ATP: Life’s Energy Currency

• The ATP molecule stores energy, much like your bank account stores dollars until you need to use them. – Negatively charged phosphates repel each other, ATP

(three phosphates), ADP (two phosphates).– Linking them requires overcoming this repulsion using

energy (jack-in-the-box analogy), so making ATP from ADP and a third phosphate requires energy (endergonic), but releasing the third phosphate from ATP to make ADP generates energy (exergonic).

– ATP has more energy than ADP.

• Example of how ATP can be used to perform cellular work:– Cell needs to move

calcium ions up their concentration gradient into a muscle cell.

– ATP splits into ADP and phosphate, a downhill reaction that releases energy.

– The energy is used to transfer a phosphate molecule onto a protein, causing a shape change that drives calcium across the membrane.

The Need for Enzymes

– Exergonic reactions may not happen very quickly, even though they are spontaneous

• In living organisms the reactions are hastened by enzymes.

– Many different enzymes may be needed to accomplish one task. Series of steps and the enzymes that hasten them are called metabolic pathways.

– Substrate = substance being worked on by each specific enzyme.

• Enzymes hasten reactions by lowering the amount of energy needed to get chemical reactions going (activation energy).

• Enzymes are catalysts (retain their original chemical composition while bringing about a change in a specific substrate).

• Almost all enzymes are proteins. • Have complex 3-D structures

– Active site = place that binds substrate– “Lock and key” model – highly specific

Example: • Chymotrypsin

breaks down proteins in the small intestine

• A shape change caused by the binding of the substrate leads to the breakage

Short Review of Lecture 6• What is energy and why is it so important to

living things?• What two forms does energy come in?• What do the two Laws of Thermodynamics

state?• Plants breathe in CO2 and then harvest

radiation energy from the sun to turn it into carbohydrates– Is this an endergonic or exergonic reaction?– Are carbohydrates more or less ordered than CO2?

• How are carbohydrates and ATP molecules functionally similar?