1 energy and metabolism chapter 6. section 6.1 learning objectives –the flow of energy in living...

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Energy and Metabolism

Chapter 6

Section 6.1 Learning Objectives

– The Flow of Energy in Living Systems

• Differentiate between kinetic and potential energy.

• Identify the source of energy for the biosphere (Earth).

• Contrast oxidation and reduction reactions.

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Flow of Energy

• Thermodynamics– Branch of chemistry concerned with energy

changes– Study of energy flow or transformations

• Kinetic energy potential energy• Potential energy kinetic energy

• Cells are governed by the laws of physics and chemistry

What is Energy?

• Energy – capacity to do work– 2 states

1. Kinetic – energy of motion

2. Potential – stored energy

– Many forms – mechanical, heat, sound, electric current, light, or radioactivity

– Heat the most convenient way of measuring energy

• 1 calorie = heat required to raise 1 gram of water 1ºC

• calorie or Calorie?– Calorie (1000 calories) how food energy measured

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a. Potential energy b. Kinetic energy

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Stored energy based on her position (also think of a bolder on top of a hill)

Energy in motion (she is able to slide down based on her

previous position)

The Source of Energy on Earth

• Energy flows into the biological world from the sun

• Photosynthetic organisms (plants/algae) capture this energy

• Stored as potential energy in chemical bonds (in sugars made from photosynthesis)

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photosynthesiscell respiration

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Redox reactions (how energy is transferred at molecular level)

• Oxidation– Atom or molecule loses an electron

• Reduction– Atom or molecule gains an electron– Higher level of energy than oxidized form

• Oxidation-reduction reactions (redox)– Reactions always paired– LEO says GER (leo is a lion)

• Loss of e- is oxidation• Gain of e- is reduction

To follow the energy, follow the e-

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e–

A BA + B +A+ B–

Loss of electron (oxidation) LEO

Gain of electron (reduction) GER

Lower energy Higher energy

e-

Question

Oxidation is the ____________ and reduction is the ________.

a. loss of electrons, gain of electrons

b. gain of protons, loss of protons

c. loss of protons, gain of protons

d. loss of electrons, gain of protons

Section 6.2 Learning Objectives

– The Laws of Thermodynamics and Free Energy

• Explain the laws of thermodynamics.

• Relate free energy changes to the outcome of chemical reactions.

• Contrast the course of a reaction with and without an enzyme catalyst.

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Laws of thermodynamics

• First law of thermodynamics– Energy cannot be created or destroyed– Energy can only change from one form to

another– Total amount of energy in the universe

remains constant– During each conversion, some energy is lost

as heat

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• Second law of thermodynamics– Entropy (disorder) is continuously

increasing– Energy transformations proceed

spontaneously to convert matter from a more ordered/less stable form to a less ordered/ more stable form

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Disorder happensspontaneously

Organizationrequires energy

© Jill Braaten

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Free energy• G = Energy available to do work

• G = H – TS H = enthalpy, energy in a molecule’s chemical

bonds T = absolute temperature S = entropy, unavailable energy

G

ΔG = ΔH – TS• ΔG = change in free energy• Positive ΔG

– Products have more free energy than reactants– Not spontaneous, requires input of energy– Endergonic (photosynthesis)

• Negative ΔG – Products have less free energy than reactants– Spontaneous (may not be instantaneous)– Exergonic (cell respiration)

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a.

b.

0

0

Course of Reaction

Products

G > 0

G < 0

Reactants

Reactants

Course of Reaction

Products

Fre

e E

ne

rgy

(G

)E

ne

rgy

Re

lea

se

d E

ne

rgy

Su

pp

lie

dF

ree

En

erg

y (

G)

En

erg

y R

ele

as

ed

En

erg

y S

up

pli

ed

Energy isreleased

Energy mustbe supplied

Exergonic

Endergonic

photosynthesis

cell respiration

Activation Energy: How to Start a Reaction

• Extra energy required to destabilize existing bonds and initiate a chemical reaction

• Exergonic reaction’s rate depends on the activation energy required– Larger activation energy proceeds more slowly

• Rate can be increased 2 ways1. Increasing energy of reacting molecules (heating)

2.Lowering activation energy

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ΔG

En

erg

y R

ele

as

ed E

ner

gy

Su

pp

lied

Fre

e E

ne

rgy

(G

) Activationenergy

Activationenergy0

uncatalyzed

catalyzed

Course of Reaction

Product

Reactant

Catalysts

• Substances that influence chemical bonds in a way that lowers activation energy

• Cannot violate laws of thermodynamics– Cannot make an endergonic reaction

spontaneous

• Do not alter the proportion of reactant turned into product

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ΔG

En

erg

y R

ele

as

ed E

ner

gy

Su

pp

lied

Fre

e E

ne

rgy

(G

) Activationenergy

Activationenergy0

uncatalyzed

catalyzed

Course of Reaction

Product

Reactant

Question

The energy in a system that is able to do work is called

a. Enthalpy

b. Entropy

c. Free energy

d. Kinetic energy

e. Potential energy

Question

A reaction with a positive ∆G is –

a. Exergonic

b. Entropic

c. Endergonic

d. Enthalpic

e. Energertic

Question

A ball sitting atop a hill begins to roll down after getting a slight tap. This is analogous to an endergonic reaction.

a. This is true

b. This is false

Section 6.3-6.4 Learning Objectives

– ATP: The Energy Currency of Cells

• Describe the role of ATP in short-term energy storage.

• Distinguish which bonds in ATP are “high energy.”

– Enzymes: Biological Catalysts

• Discuss the specificity of enzymes.

• Explain how enzymes bind to their substrates.

• List the factors that influence the rate of enzyme-catalyzed reactions.

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ATP: Cell Energy

• Adenosine triphosphate• Chief “currency” all cells use• Composed of

– Ribose – 5 carbon sugar– Adenine– Chain of 3 phosphates

• Key to energy storage• Bonds are unstable• ADP – 2 phosphates• AMP – 1 phosphate – lowest energy form

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AM

P C

OR

E

O

O–

O

O

O

HH H

H

O

CC

NN

N

C

N

C

CHH

P O–

O P

O P O

AD

PA

TP

Triphosphategroup

O–

CH2

High-energybonds

a.

Adenine NH2

Ribose

OHOH

b.

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ATP cycle

• ATP hydrolysis drives endergonic reactions– Coupled reaction results in net –ΔG

(exergonic and spontaneous)

• ATP not suitable for long-term energy storage– Fats and carbohydrates better– Cells store only a few seconds worth of ATP

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+

+

Pi

Energy fromexergoniccellularreactions

ATP H2O

ADP

Energy forendergoniccellularprocesses

cell respirationphotosynthesis

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Enzymes: Biological Catalysts• Most enzymes are protein

– Some are RNA

• Shape of enzyme stabilizes a temporary association between substrates

• Enzyme not changed or consumed in reaction

• Carbonic anhydrase (enzyme used to maintain blood pH)– 200 molecules of carbonic acid per hour made without

enzyme– 600,000 molecules formed per second with enzyme

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Active site

a. b.

Enzyme Enzyme–substrate complex

Substrate

Active site

• Pockets or clefts for substrate binding

• Forms enzyme–substrate complex

• Precise fit of substrate into active site

• Applies stress to distort particular bond to lower activation energy– Induced fit

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1. The substrate, sucrose, consists of glucose and fructose bonded together.

2. The substrate binds to the active site of the enzyme, forming an enzyme– substrate complex.

3. The binding of the substrate and enzyme places stress on the glucose– fructose bond, and the bond breaks.

4. Products arereleased, andthe enzyme isfree to bind othersubstrates.

BondGlucose

Fructose

Active site

Enzymesucrase

H2O

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Nonprotein enzymes

• Ribozymes• 1981 discovery that certain reactions

catalyzed in cells by RNA molecule itself1. 2 kinds

1. Intramolecular catalysis – catalyze reaction on RNA molecule itself

2. Intermolecular catalysis – RNA acts on another molecule

Enzyme function

• Small molecules can affect function– Coenzymes– Cofactors

• Rate of enzyme-catalyzed reaction depends on concentrations of substrate and enzyme

• Any chemical or physical condition that affects the enzyme’s three-dimensional shape can change rate

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a.

b.

Rat

e o

f R

eact

ion

Optimum pH for pepsin

Rat

e o

f R

eact

ion

pH of Reaction

Optimum pH for trypsin

1 2 3 4 5 6 7 8 9

30 40 50 60 70 80

Temperature of Reaction (˚C)

Optimum temperaturefor human enzyme

Optimum temperature for enzymefrom hotsprings prokaryote

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Inhibitors

• Inhibitor – substance that binds to enzyme and decreases its activity

• Competitive inhibitor– Competes with substrate for active site

• Noncompetitive inhibitor– Binds to enzyme at a site other than active

site– Causes shape change that makes enzyme

unable to bind substrate

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a. Competitive inhibition b. Noncompetitive inhibition

Enzyme Enzyme

Allosteric site

Activesite

Competitive inhibitor interfereswith active site of enzyme sosubstrate cannot bind

Allosteric inhibitor changesshape of enzyme so it cannotbind to substrate

Activesite

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Substrate Substrate

Inhibitor Inhibitor

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Allosteric Enzymes

• Allosteric enzymes – enzymes exist in active and inactive forms

• Most noncompetitive inhibitors bind to allosteric site – chemical on/off switch

• Allosteric inhibitor – binds to allosteric site and reduces enzyme activity

• Allosteric activator – binds to allosteric site and increases enzyme activity

Question

If inhibition is to be competitive, which of the following must be true?

a. There must be more than one binding site

b. The substrate and the inhibitor must be similar

c. The reaction can not require a cofactor

d. The reaction must be endergonic

e. The allosteric and active sites must be near each other

Question

Carbon monoxide (CO) binds to the hemoglobin protein at the oxygen binding site. Once the CO binds, the oxygen can no longer be transported. What does this describe?

a. Non-competitive inhibition

b. Feedback inhibition

c. Substrate inhibition

d. Allosteric inhibition

e. Competitive inhibition

Question

Increasing the temperature increases the rate of an enzyme-catalyzed reaction. Once a critical temperature is reached, the reaction stops. Why does this happen?

a. The concentration of reactants drop

b. The enzymes have all been consumed in the reaction

c. The increase in temperature alters the pH

d. The polypeptide chains in the enzyme denature

Section 6.5 Learning Objectives

– Metabolism: The Chemical Description of Cell Function

• Explain the kinds of reactions that make up metabolism.

• Discuss what is meant by a metabolic pathway.

• Describe mechanisms to control a metabolic pathway

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Metabolism• Total of all chemical reactions carried out by an

organism

• Anabolic reactions/anabolism

– Expend energy to build up molecules

– Anabolic Steroids=build muscle

• Catabolic reactions/catabolism

– Harvest energy by breaking down molecules

– Starvation=breakdown muscle

Large molecules

Small molecules

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Biochemical pathways

• Chemical reactions that create/store or produce other chemical products for daily function.

• Reactions occur in a sequence• Product of one reaction is the substrate for

the next reaction

Enzyme 1 Enzyme 2 Enzyme 3A B C D

Basic metabolic pathway chart

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http://upload.wikimedia.org/wikipedia/commons/1/11/Metabolism_wip.png

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Initial substrate

Intermediatesubstrate A

Intermediatesubstrate B

Intermediatesubstrate C

End product

Enzyme1

Enzyme2

Enzyme3

Enzyme4

Feedback inhibition

• End-product of pathway binds to an allosteric site on enzyme that catalyzes first reaction in pathway

• Shuts down pathway so raw materials and energy are not wasted

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a. b.

Enzyme 1

Enzyme 2

Enzyme 3

Enzyme 1

Enzyme 2

Enzyme 3End product End product

Initialsubstrate

Intermediatesubstrate A

Intermediatesubstrate B

Initialsubstrate

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Question

Feedback inhibition occurs when the final product acts as an inhibitor to the first enzyme in the pathway.

a. This is true

b. This is false

Question

Catabolic reactions expend energy to form or transform chemical bonds.

a. This is true

b. This is false

Final Review

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Question

The First Law of Thermodynamics states that energy can be –

a. Created

b. Destroyed

c. Converted

d. Lost

e. None of the above

Question

Small organic molecules that assist in enzymatic functions are –

a. Coprolites

b. Cofactors

c. Activators

d. Coenzymes

e. Intermediates

Question

Spending ATP involves hydrolyzing it into ADP and inorganic P. The energy released can drive other chemical reactions.

a. This is true

b. This is false

Question

Enzymes are consumed by reactions.

a. This is true

b. This is false

Question

A catalyst speeds up chemical reactions. How do catalysts do this?

a. Decreasing entropy

b. Altering ∆G

c. Consuming reactants

d. Lowering activation energy

e. Making different products

Question

A muscle contraction is ________, but as the muscle contracts heat is released which is ___________.

a. Exergonic, endergonic

b. Exergonic, exergonic

c. Endergonic, endergonic

d. Endergonic, exergonic

Question

Study this metabolic pathway: A -E1 B -E2 C -E3 D. Which of the following statements is NOT correct? (E represents enzymes)

a. C is the substrate for enzyme E1 and D is the product

b. A is the substrate for enzyme E1 and B is the product

c. Enzyme E2 can catalyze the substrate B but not A, C and D

d. B is the product formed by enzyme E1 but the substrate for enzyme E2

Question

When muscles contract, chemical energy is converted to mechanical energy with the loss of heat. This conversion of energy is an example of the ______ Law of Thermodynamics.

a. First

b. Second

c. Third

d. Fourth

Question

Which of the following is defined as the amount of heat required to raise one gram of water one degree Celsius?

a. Tesla

b. Joule

c. Newton

d. Calorie

e. calorie