ENERGY, THERMODYNAMICS and ENZYMES

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5.10 Cells transform energy as they perform work

All organisms require nutrients = raw building blocks

Most common elements: C, H, O, N, P, S

These materials are acquired by living organisms, broken down, recycled, and built back up again into new organic compounds as needed

All organisms require energy for basic life functions – any characteristic to define life ultimately requires energy!!

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5.10 Cells transform energy as they perform work

All organisms require energy for basic life functions – any characteristic to define life ultimately requires energy!!

Energy = capacity to cause change or to perform work.

Two kinds of energy:

1. Kinetic energy is the energy of motion.

2. Potential energy is energy that matter possesses as a result of its location or structure.

Heat = thermal energy

Free energy = portion of energy available to do work,

Chemical energy = potential energy available in bonds within molecules and released in a chemical reaction.

– Most relevant energy to living organisms

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Figure 5.10

Fuel Energy conversion Waste products

Gasoline

Oxygen

Oxygen

Glucose

Heatenergy

CombustionKinetic energyof movement

Energy conversion in a car

Energy conversion in a cell

Energy for cellular work

Cellular respiration

ATP ATP

Heatenergy

Carbon dioxide

Carbon dioxide

Water

Water

Thermodynamics = study of energy transformations

First law of thermodynamics = energy in the universe is constant

– Implication: Biological organisms cannot produce energy - only convert forms of energy

– Ultimate source of energy for all ecosystems = sun (solar energy)

Second law of thermodynamics = energy conversions increase the disorder (entropy) of the universe.

– No energy transformations are 100 % efficient

– With every energy transformation some sable energy lost as heat

– Energy transformations are one-way street

– Biological organisms require constant supply of energy to maintain order!!

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Metabolism = total of an organism’s chemical reactions

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Spontaneous chemical reactions are exergonic

Chemical reactions are either

– Exergonic reactions release energy.

– These reactions release the energy in covalent bonds of the reactants.

– Cellular respiration

An endergonic reaction

– requires an input of energy; products contain more chemical/potential energy

– Photosynthesis

Energy coupling = energy released from exergonic reactions drive endergonic reactions!!

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Figure 5.11A

Reactants

EnergyProducts

Amount ofenergy

released

Po

ten

tial

en

erg

y o

f m

ole

cule

s

Figure 5.11B

Reactants

Energy

Products

Amount ofenergy

required

Po

ten

tial

en

erg

y o

f m

ole

cule

s

Cells need energy to perform work!!

There are three main types of cellular work:

1. chemical

2. mechanical

3. transport

ATP drives all three of these types of work.

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ATP = Adenosine triphosphate

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AdenineP P P

Phosphategroup

ATP: Adenosine Triphosphate

Ribose

Figure 5.12A_s2

ADP: Adenosine Diphosphate

P P P Energy

H2OHydrolysis

Ribose

AdenineP P P

Phosphategroup

ATP: Adenosine Triphosphate

ATP drives cellular work

Hydrolysis of ATP releases energy by transferring phosphate from ATP to some other molecule

– Phosphorylation = transfer of a phosphate functional group from one molecule to another

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Figure 5.12B

ATP ATP ATP

ADP ADP ADPP P P

P

P

P

PP

P

Chemical work Mechanical work Transport work

Reactants

Motorprotein

Solute

Membrane protein

Product

Molecule formed Protein filament moved Solute transported

How Does Cell Regenerate ATP?

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Energy fromexergonicreactions

Energy forendergonicreactions

ATP

ADP P

ATP = renewable source of energy for the cell.

ATP cycle = energy released in an exergonic reaction is used in an endergonic reaction to generate ATP.

HOW ENZYMES FUNCTION

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Enzymes = Organic catalysts

Increase RATE of chemical reaction by decreasing activation energy (EA).

– EA = energy barrier must be overcome before any chemical reaction can begin.

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Activationenergy barrier

Reactant

Products

Without enzyme With enzyme

Reactant

Products

Enzyme

Activationenergy barrierreduced byenzyme

En

erg

y

En

erg

y

Animation: How Enzymes Work

Reactants

Products

En

erg

y

Progress of the reaction

a

b

c

Enzymes Only Increase RATE of reaction, NOT the energyLevel of reactants or products!!!

A specific enzyme catalyzes each cellular reaction

An enzyme

– Is specific in substrate(s) it binds

– And reaction it catalyzes

Substrate = reactant

A substrate binds at enzyme active site.

Enzymes are specific because their active site fits only specific substrate molecules

– Active site is result of 3D folding of protein

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4

3

2

1

Products arereleased

Fructose

Glucose

Enzyme(sucrase)

Active site

Enzyme availablewith empty activesite

Substrate(sucrose)

Substrate bindsto enzyme withinduced fit

Substrate isconverted toproducts

H2O

Catalytic cycle of an enzyme

Factors that Effect Enzyme-Catalyzed Reactions

For every enzyme, there are optimal conditions under which it is most effective.

– Temperature

– pH

– Substrate Concentration

– Enzyme Concentration

– Cofactors/coenzymes

– Inhibitors

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Factors that Affect Enzyme-Catalyzed Reactions

Many enzymes require nonprotein helpers called cofactors, which

– bind to the active site and function in catalysis.

– Inorganic molecules

Coenzymes

– Organic

molecule

that acts as

cofactor

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Enzyme Concentration

Substrate Concentration

Temperature - affects molecular motion

pH

Enzyme inhibitors can regulate enzyme activity Inhibitor = chemical that interferes with an enzyme’s activity.

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Substrate

Enzyme

Allosteric site

Active site

Normal binding of substrate

Competitiveinhibitor

Noncompetitiveinhibitor

Enzyme inhibition

Competitive inhibitors

– block substrates from entering the active site and

– reduce an enzyme’s productivity.

Noncompetitive inhibitors

– bind to the enzyme somewhere other than the active site,

– change the shape of the active site, and

– prevent the substrate from binding.

Feedback inhibition

Startingmolecule

Product

Enzyme 1 Enzyme 2 Enzyme 3

Reaction 1 Reaction 2 Reaction 3A B C D

Enzyme inhibitors are important in regulating cell metabolism.

– Feedback inhibition = product of metabolic pathway acts as an inhibitor of one of the enzymes in the pathway

1. Describe the fluid mosaic structure of cell membranes.

2. Describe the diverse functions of membrane proteins.

3. Relate the structure of phospholipid molecules to the structure and properties of cell membranes.

4. Define diffusion and describe the process of passive transport.

You should now be able to

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5. Explain how osmosis can be defined as the diffusion of water across a membrane.

6. Distinguish between hypertonic, hypotonic, and isotonic solutions.

7. Explain how transport proteins facilitate diffusion.

8. Distinguish between exocytosis, endocytosis, phagocytosis, pinocytosis, and receptor-mediated endocytosis.

You should now be able to

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9. Define and compare kinetic energy, potential energy, chemical energy, and heat.

10. Define the two laws of thermodynamics and explain how they relate to biological systems.

11. Define and compare endergonic and exergonic reactions.

12. Explain how cells use cellular respiration and energy coupling to survive.

You should now be able to

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You should now be able to

13. Explain how ATP functions as an energy shuttle.

14. Explain how enzymes speed up chemical reactions.

15. Explain how competitive and noncompetitive inhibitors alter an enzyme’s activity.

16. Explain how certain drugs, pesticides, and poisons can affect enzymes.

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Table 5.UN05

Figure 5.UN06

pH

Rat

e o

f re

acti

on

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