Microfilaments differ from microtubules in that microfilaments A) are larger than microtubules. B) are found only in plants whereas microtubules are found in plants and animal cells. C) are mainly composed of actin whereas microtubules are composed of tubulin. D) anchor organelles, whereas microtubules primarily function to help cells change shape and move. E) form the inner core of cilia and flagella whereas microtubules regulate metabolism.

Cellular Energetics: Thermodynamics, ATP, and Enzyme catalysis Campbell Biology Chapter 5

Energy and Thermodynamics

Energy is the capacity to do work • There are many forms of energy: – Kinetic energy – Potential energy – Chemical energy – Electrical energy

All Living Things Require and Consume Energy • • We get our energy from food Ultimate source of energy for all life on earth is the sun

The First Law of Thermodynamics • • • Energy cannot be created or destroyed The amount of energy in the universe is constant Energy can be interconverted from one form to another: – Potential energy – Kinetic energy – Radiant energy

Potential energy • • • • Energy is the ability to do work Potential Energy of position Gravitational potential energy Chemical potential energy

Kinetic energy • • • Energy of motion KE= 1/2mv 2 Temperature is a measure of molecular kinetic energy

The 1 st Law of Thermodynamics: Energy can be interconverted from one form to another

More energy interconversions

The 2 nd Law of Thermodynamics The Law of Entropy • • • •

Interconversions of energy are never 100% efficient

Entropy!

Entropy is a measure of disorder (i.e. chaos, randomness) Each interconversion of energy involves loss of usable energy :

Entropy in Action

Biochemical reactions are inefficient

The price of minimizing entropy is the constant expenditure of free energy

Closed systems will deplete themselves of usable (free) energy • Given a finite amount of energy, each energy interconversion will result in an ever increasing amount of unusable energy (entropy)

Recognizing Entropy in the world

Which system has more entropy?

A B

Can living systems reduce entropy?

Recognizing Enthalpy Enthalpy = Energy in chemical bonds B

Which systems have more Enthalpy?

These?

 Or these?



Biochemical reactions are spontaneous only if ∆G is negative • • • • Reactions which release energy are exergonic Reactions which require energy are endergonic ∆ G = ∆H - T∆S Only exergonic processes with a negative ∆G are spontaneous Spontaneous processes can be harnessed to perform work

If ΔG < 0, the reaction is spontaneous (it will happen)

C 6 H 12 O 6(s) + 6O 2(g)



6CO 2(g) + 6H 2 O (l) Will the Reaction happen?

Well, is heat given off?

Does entropy increase?

G = ∆H - T∆S ∆H = enthalpy (heat in chemical bonds) ∆S= Degree of entropy (chaos) created by Rxn

T= Temperature at which Rxn occurs

Important: Spontanous ≠ fast

LE 5-2b

Glucose Oxygen Heat Chemical reactions ATP ATP Energy for cellular work Carbon dioxide Water

Which of these diagrams depicts an endergonic reaction?

Reactants Reactants Energy required Products Amount of energy required Energy released Products Amount of energy released

A B

LE 8-7a 

G < 0 A closed hydroelectric system



G = 0

LE 8-7c 

G < 0



G < 0



G < 0 A multistep open hydroelectric system

In living things, a state of equilibrium most often means ___________.

A) Efficiency is optimized B) The reaction is Endothermic C) Enthalpy is increased D) Entropy is minimized E) You are dead

ATP

A steer must eat over 100 pounds of grain to gain less than 10 pounds of • muscle tissue. This illustrates A) the first law of thermodynamics. B) the second law of thermodynamics. C) that some energy is destroyed in every energy conversion. D) that energy transformations are typically 100% efficient. E) None of the choices are correct.

Living cells manage to perform endergonic activities • How is this possible?

ATP hydrolysis can be coupled to endergonic reactions to power cellular work • • A cell does three main kinds of work: – Mechanical – Transport – Chemical To do work, cells manage energy resources by energy coupling, the use of an exergonic process to drive an endergonic one

• • • The Structure and Hydrolysis of ATP ATP (adenosine triphosphate) is the cell’s energy shuttle ATP provides energy for cellular functions ATP is a nucleic acid monomer

ATP is the energy currency of all living things

Adenine Phosphate groups

ATP: Adenosine Triphosphate

Ribose

LE 8-9

P P P Adenosine triphosphate (ATP) H 2 O P i Inorganic phosphate + P P Adenosine diphosphate (ADP) + Energy

Phosphorylation can change the conformation of proteins

LE 8-10 Anabolic (building up) reactions are usually endergonic

NH 2 Glu Glutamic acid + NH 3 Ammonia Glu Glutamine



G = +3.4 kcal/mol

Breakdown of ATP is exergonic

ATP + H 2 O ADP + P i



G = –7.3 kcal/mol

Coupled reactions: Overall  G is negative; together, reactions are spontaneous 

G = –3.9 kcal/mol

• • How ATP Performs Work ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to some other molecule, such as a reactant The recipient molecule is now phosphorylated

Three types of cellular work are powered by ATP hydrolysis •Mechanical •Transport •Chemical

• • • The Regeneration of ATP ATP is regenerated by addition of a phosphate group to ADP The energy to phosphorylate ADP comes from food The chemical potential energy temporarily stored in ATP drives most cellular work

LE 8-12

ATP Energy from catabolism (exergonic, energy yielding processes) ADP + P i Energy for cellular work (endergonic, energy consuming processes)

Enzymes

At which level of protein structure are interactions between R groups most important?

A) primary B) secondary C) tertiary D) quaternary E) the R groups are not related to the overall structure of a protein

Sugar is an energy-rich molecule • • Breakdown of sugar is spontaneous

C 6 H 12 O 6(s) + 6O 2(g) 6CO 2(g) + 6H 2 O (l)



• • Wood and paper are made of cellulose Cellulose is a polymer of glucose Why doesn’t our jar of sugar burst into flame?

• • • Exergonic reactions still require

activation energy

Spontaneous ≠ fast Ea is dependent on temperature At high temperatures, reactions happen faster

Jumping bean analogy • • • • • • Molecules are like jumping beans Temperature ≈ height of jump Living things cannot wait for a good jump After a long time, where will the beans be?

All of them?

Will they ever stop jumping?

• • Living things can use enzymes to speed up reactions Enzymes speed up reactions by lowering energy of activation They are catalysts

Catalysts speed up reactions • • • • Platinum is used in catalytic converters 2CO + 0 2  2CO 2 Catalysts are not consumed in a reaction They cannot add energy to a reaction

Enzymes are protein catalysts • • • • Catalysts- things added to chemical reactions which speed up those reactions Catalysts are not consumed in a reaction Catalysts cannot add energy to a reaction -ase: The enzyme suffix

Catalase

Enzymes can dramatically lower the energy of activation for a reaction

no enzyme with enzyme Energy

reactants E a E a products

Reaction Course Note that the equilibrium of the reaction is unaffected

12

How enzymes work    Structure aids function An active site naturally fits

substrate

Enzyme specificity depends on shape

Substrate Binding and Reaction

Cellulase ATP synthase

 Some important Enzymes

Nitrogenase

Catalysis in the Enzyme’s Active Site • • In an enzymatic reaction, the substrate binds to the active site The active site can lower an E A – barrier by Orienting substrates correctly – Straining substrate bonds – Providing a favorable microenvironment – Covalently bonding to the substrate

LE 5-6

Enzyme available with empty active site Active site Glucose Fructose Products are released Enzyme (sucrase) Substrate (sucrose) Substrate binds to enzyme with induced fit Substrate is converted to products H 2 O

Factors Affecting Enzyme Activity 1. Salts 2. Temperature 3. pH 4. Inhibitors and Activators

Effects of Temperature and pH

• • • Each enzyme has an optimal temperature in which it can function Each enzyme has an optimal pH in which it can function Tertiary structure can be radically altered by changes in pH

LE 8-18

Optimal temperature for typical human enzyme Optimal temperature for enzyme of thermophilic (heat-tolerant bacteria) 0 20 40 60 Temperature ( ° C) Optimal temperature for two enzymes Optimal pH for pepsin (stomach enzyme) 80 Optimal pH for trypsin (intestinal enzyme) 100 0 1 2 3 Optimal pH for two enzymes 4 pH 5 6 7 8 9 10

Enzyme Inhibition

• •

Competitive inhibitors

bind to the active site of an enzyme, competing with the substrate

Noncompetitive (allosteric) inhibitors

bind to another part of an enzyme, causing the enzyme to change shape (allostery) and making the active site less effective

Many drugs are enzyme inhibitors • Protease inhibitors fight HIV

• • Can enzymes catalyze endothermic reactions?

If so, how?

If not, why not?

Inhibition of an enzyme is irreversible when A) a competitive inhibitor is involved. B) a noncompetitive inhibitor is involved. C) the shape of the enzyme is changed. D) bonds form between inhibitor and enzyme. E) None of the choices are correct.