Biology 102Biology 102

Lecture 10: Energy Flow in Cells Lecture 10: Energy Flow in Cells (Part 1)(Part 1)

Alternate title: “How life on earth Alternate title: “How life on earth can exist despite the fact that the can exist despite the fact that the

universe is falling apart”universe is falling apart”

Lecture outlineLecture outline

1.1. Some perspective: “Where we’ve Some perspective: “Where we’ve been and where we are going…”been and where we are going…”

2.2. Energy and the Universe: The two Energy and the Universe: The two basic laws of thermodynamicsbasic laws of thermodynamics

3.3. How does energy flow in chemical How does energy flow in chemical reactions?reactions?

4.4. How is energy “carried” between How is energy “carried” between coupled reactions?coupled reactions?

1. Some perspective…1. Some perspective…

Last few lectures have focused on the Last few lectures have focused on the puzzle piecespuzzle piecesAtoms and bondsAtoms and bondsOrganic molecules (structure and function)Organic molecules (structure and function)Parts of a cell (structure and function)Parts of a cell (structure and function)

Remaining lectures build towards Remaining lectures build towards understanding of how these pieces fit understanding of how these pieces fit together...together...For example…For example…

2. Energy and the Universe2. Energy and the Universe Life on earth is basically a little pocket of Life on earth is basically a little pocket of

order in a universe tending toward disorder.order in a universe tending toward disorder.

The two basic laws of The two basic laws of thermodynamicsthermodynamics

Law 1: QUANTITY of energyLaw 1: QUANTITY of energyThe Universe (or any The Universe (or any closedclosed system) has a system) has a

constant amount of energy. Energy cannot constant amount of energy. Energy cannot be created or destroyed, but only changed in be created or destroyed, but only changed in form.form.

So, what is “energy”?So, what is “energy”?So, what is “work”?So, what is “work”?

The two basic laws of The two basic laws of thermodynamics (cont.)thermodynamics (cont.)

Forms of energyForms of energyPotential energyPotential energy

Stored energyStored energy Examples…Examples…

Kinetic energyKinetic energy Energy in motionEnergy in motion Examples,,,Examples,,,

Recap: Law 1Recap: Law 1

The two basic laws of The two basic laws of thermodynamicsthermodynamics

Law 2: QUALITY of energyLaw 2: QUALITY of energyLeft to itselfLeft to itself, any system spontaneously , any system spontaneously

undergoes conversion to less organized formsundergoes conversion to less organized forms Energy becomes more randomly dispersed in form Energy becomes more randomly dispersed in form

(often dissipating as heat) and less able to do work.(often dissipating as heat) and less able to do work. Heat: Increased random movement of moleculesHeat: Increased random movement of molecules

The entire universe is proceeding The entire universe is proceeding irrevocably toward complete disorderirrevocably toward complete disorder

So how is it that life can exist on earth?So how is it that life can exist on earth?

3. How does energy flow in 3. How does energy flow in chemical reactions?chemical reactions?

What is a chemical reaction?What is a chemical reaction?Making and breaking of chemical bondsMaking and breaking of chemical bonds

Implications of the second law:Implications of the second law:Orderly reactants to less ordered products Orderly reactants to less ordered products

releasesreleases energy (EXERGONIC) energy (EXERGONIC)Examples…Examples…

Implications of the second law (cont.)Implications of the second law (cont.)Less ordered reactants to more orderly Less ordered reactants to more orderly

products products requiresrequires energy (ENDERGONIC) energy (ENDERGONIC)

Examples…Examples…

Two key reactions important in Two key reactions important in living systemsliving systems

PhotosynthesisPhotosynthesis THE major way THE major way

energy from the sun is energy from the sun is incorporated into incorporated into organismsorganisms

ENDERGONICENDERGONIC

Cellular respirationCellular respiration THE major way cells THE major way cells

of most organisms of most organisms obtain energy for obtain energy for chemical reactionschemical reactions

EXERGONICEXERGONIC

Activation energyActivation energy

Initial input of energy required to start Initial input of energy required to start reactions (both exergonic and reactions (both exergonic and endergonic)endergonic)

4. How is energy carried 4. How is energy carried between “coupled” reactions?between “coupled” reactions?

What are coupled reactions?What are coupled reactions?ExamplesExamples

ATP is the principle energy carrier that ATP is the principle energy carrier that allows coupling of reactionsallows coupling of reactionsThe basics: ATP produced during an The basics: ATP produced during an

exergonic reaction provides energy to for exergonic reaction provides energy to for endergonic reactions endergonic reactions

What’s so great about ATP?What’s so great about ATP?1.1. High energy phosphate bonds!High energy phosphate bonds!

2.2. Convenient size unitConvenient size unit

What’s so great about ATP?What’s so great about ATP?

Bonds easily formed for Bonds easily formed for easy energy transfer easy energy transfer from a high energy from a high energy compound to ATPcompound to ATP

Bonds are unstable to Bonds are unstable to easily give up energy in easily give up energy in a reactiona reaction

Coupled reactions within living cellsCoupled reactions within living cells

Glucose breakdown (cellular respiration) Glucose breakdown (cellular respiration) produces ATPproduces ATP

Protein synthesis requires ATP breakdownProtein synthesis requires ATP breakdown

Electron carriersElectron carriers