Metabolism: Energy and Enzymes - Welcome to Biology! - …cherylchowbiology.weebly.com/uploads/1/7/1/7/17179396/lecture_5.pdf · •Metabolism is the sum of all the chemical reactions

1

Chapter 6 Metabolism: Energy

and Enzymes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

6.1 Life and

the Flow of Energy

• Energy is the ability to do work or bring

about change

• Cells (and organisms) need a constant

supply of energy

• Life on Earth is dependent on solar

energy

– Photosynthesis provides nutrients

6.1 Life and

the Flow of Energy

• Forms of Energy

– Kinetic energy is the energy of motion

– Potential energy is stored energy

• Food is chemical energy


heat

heat

heat

Mechanical energy

Solar

energy

Chemical

energy

6.1 Life and

the Flow of Energy

• Two Laws of Thermodynamics

1. Energy cannot be created or destroyed,

but it can be changed from one form to

another

• Law of conservation of energy

2. Energy cannot be changed from one form

to another without a loss of usable energy

• A leaf cell photosynthesizes

– Use solar energy to form carbohydrates

– Some energy is lost as heat

• Moose uses carbohydrates to power its

muscles

– Some energy is lost as heat


solar energy carbohydrate synthesis

sun

H2O

CO2

heat


carbohydrate muscle contraction

heat

6.1 Life and

the Flow of Energy

• The second law of thermodynamics can

be stated another way

• Every energy transformation makes the

universe less organized and more

disordered

• Entropy refers to the relative amount of

disorganization

6.1 Life and

the Flow of Energy

• Every process that occurs in cells

always does so in a way that increases

the total entropy of the universe

• Cellular processes obviously require an

input of energy from an outside source

• Living things depend on a constant

supply of energy from the sun

C6H12O6

H2O

CO2

energy

a.

• more organized

• more potential energy

• less stable (less entropy)

Glucose

• less organized

• less potential energy

• more stable (more entropy)

Carbon dioxide and water



channel protein

energy

b.

• more organized • more potential energy • less stable (less entropy)

• less organized • less potential energy • more stable (more entropy)

H+

H+

H+ H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

Unequal distribution

of hydrogen ions

Equal distribution

of hydrogen ions


C6H12O6

H2O

CO2

channel protein

energy

energy

a.

b.


Glucose


Carbon dioxide and water



H+

H+

H+ H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

Unequal distribution

of hydrogen ions

Equal distribution

of hydrogen ions

6.2 Energy Transformations

and Metabolism

• Metabolism is the sum of all the chemical

reactions that occur in a cell

• Catabolism – breaking down molecules

• Anabolism – building molecules


and Metabolism

A + B C + D

(reactants) (products)


and Metabolism

• Free energy (∆G) is the amount of energy

available.

– Exergonic reactions are ones where energy is

released (∆G is negative)

• Products have less free energy than reactants

– Endergonic reactions require an input of

energy (∆G is positive)

• Products have more free energy than reactants


and Metabolism

• Exergonic reactions

– Spontaneous

– Release energy

• Endergonic

– Require an input of energy to run

– Require ATP


and Metabolism

• ATP stands for adenosine triphosphate

– Energy currency for cells

– ATP is generated from ADP (adenosine diphosphate) + an inorganic phosphate molecule ( P )


a.

adenosine triphosphate

P P

P

adenosine diphosphate phosphate +

+

+ P

P P P

Energy from

exergonic reactions

(e.g., cellular

respiration)

Energy for endergonic

reactions (e.g., protein

synthesis, nerve impulse

conduction, muscle

cont r action) ADP

ATP


and Metabolism

• ATP is a nucleotide composed of:

– Adenine (a nitrogen-containing base)

– Ribose (a 5-carbon sugar)

– Three phosphate groups

• Energy stored in these chemical bonds


and Metabolism

• Coupled Reactions

– The energy released by an exergonic

reaction is used to drive an endergonic

reaction


ATP

coupling

P

A + B C + D

ADP +


b. Muscle contraction is endergonic

and cannot occur without an input

of energy.


P ADP + +

a. ATP breakdown is exergonic.

ATP energy


ADP + P

c. Muscle contraction

becomes exergonic

and can occur

when it is coupled to

ATP breakdown.

heat

ATP

muscle contraction


P

ADP + P

c. Muscle contraction

becomes exergonic

and can occur

when it is coupled to

ATP breakdown.

ADP + + heat

a. ATP breakdown is exergonic.

ATP energy

ATP

muscle contraction

b. Muscle contraction is endergonic

and cannot occur without an input

of energy.


and Metabolism

• ATP can be used for

– Chemical work

• Powers anabolism

– Transport work

• Supplies energy to pump substances across

plasma membrane

– Mechanical work

• Supplies energy to make muscles contract, cilia

and flagella beat

6.3 Enzymes

and Metabolic Pathways

• Metabolic pathways are a series of

linked reactions.

– These begin with a specific reactant and

produce an end product

6.3 Enzymes


• Enzymes

– Proteins that function to speed a chemical

reaction

– Enzymes serve as catalysts

• Participates in chemical reaction, but is not

used up by the reaction

A Metabolic Pathway

Also called substrates

6.3 Enzymes


• Energy of Activation (Ea)

– Energy that must be added to cause

molecules to react with one another

• Need a match to start wood burning

– Enzymes lower the energy of activation

• Do not change the end result of the reaction

• Increase the reaction rate

Fre

e E

ne

rgy

energy of

product

energy of

activation

(Ea)

energy of

activation

(Ea)

Progress of the Reaction

energy of

reactant

enzyme not present

enzyme present


6.3 Enzymes


• How Enzymes Function

– Enzyme binds substrate to form a complex

E + S ES E + P enzyme substrate enzyme-substrate

complex enzyme product

• Substrate binds to active site on enzyme


products

enzyme

enzyme

Degradation

The substrate is broken

down to smaller products.

enzyme-substrate

complex

substrate

active site


product

enzyme

enzyme

Synthesis

The substrates are combined

to produce a larger product.

enzyme-substrate

complex

active site

substrates

6.3 Enzymes


• Induced fit model

– Substrate and active site shapes don’t

match exactly

– Active site is induced to undergo a slight

change in shape to accommodate

substrate binding

– Change in shape facilitates reaction


a.

substrate active site

b.

6.3 Enzymes


• Reaction requires specific enzyme

• Enzymes often named for their

substrate

– Lipid – lipase

– Urea – urease

– Maltose – maltase

– Lactose – lactase

6.3 Enzymes


• Factors affecting enzymatic reaction rates

– Substrate Concentration

– Temperature and pH

– Enzyme Activation

– Enzyme Inhibition

– Enzyme Cofactors

6.3 Enzymes


• Substrate Concentration

– Enzyme activity increases as substrate

concentration increases

• More collisions between substrate and enzyme

– Maximum rate is achieved when all active

sites of an enzyme are filled continuously

with substrate

6.3 Enzymes


• Temperature

– Enzyme activity increases as temperature

rises

– Higher temperatures cause more effective

collisions between enzymes and

substrates

– Enzyme may denature at high

temperatures

• Loss of structure and function


Rate

of

Reacti

on

(pro

du

ct

per

un

it o

f ti

me)

0 10 20 30 40 50 60

Temperature °C

a. Rate of reaction as a function of

temperature.

b. Body temperature of ectothermic

animals often limits rates of reactions.

c. Body temperature of endothermic animals

promotes rates of reactions.

b: © Brand X Pictures/PunchStock RF; c: © Digital Vision/PunchStock RF

6.3 Enzymes


• pH

– Each enzyme has an optimal pH

– Enzyme structure is pH dependent

– Extremes of pH can denature an enzyme

by altering its structure


pH

Ra

te o

f R

ea

cti

on

(pro

du

ct

pe

r u

nit

of

tim

e)

0 1 2 3 4 5 6 7 8 9 10 11 12

pepsin trypsin

• Enzyme Activation

– Cell regulates metabolism by regulating

which enzymes are active

– Genes producing enzymes can be turned

on or off to regulate enzyme concentration

– Enzyme can be modified by adding or

removing phosphates – changes shape


P

kinase

P

inactive protein active protein

6.3 Enzymes


• Enzyme Inhibition

– Occurs when enzyme cannot bind its

substrate

– Activity of almost every cell enzyme is

regulated by feedback inhibition

6.3 Enzymes



– When product is abundant it binds to the

enzyme’s active site and blocks further

production

• When product is used up, it is removed from

the active site

• Enzyme begins to function again

6.3 Enzymes



– In a more complex type of inhibition,

product binds to a site other than the active

site, which changes the shape of the active

site

– Poisons are often enzyme inhibitors

• Cyanide inhibits an essential enzyme

• Penicillin blocks the active site on a bacterial

enzyme


E2 E3 E4 E5

E1

first

reactant

A

site of enzyme

where end product F

can bind

end

product

F

a. Active pathway

A E B C D


E1

E1

end

product

F

altered site of

enzyme due to

binding of F

b. Inactive pathway

Reactant A cannot bind,

and no product results.

end

product

F

first

reactant

A


E2 E3 E4 E5

A E

E1

E1

E1

first

reactant

A

site of enzyme

where end product F

can bind

end

product

F

end

product

F

altered site of

enzyme due to

binding of F

a. Active pathway

b. Inactive pathway

Reactant A cannot bind,

and no product results.

end

product

F

first

reactant

A

B C D

6.3 Enzymes


• Enzyme Cofactors

– Molecules which help enzyme function

– Copper and zinc are examples of inorganic

cofactors

– Organic non-protein cofactors are called

coenzymes

• Vitamins are often components of coenzymes

6.4 Oxidation-Reduction

and Metabolism

• Oxidation-Reduction or Redox

– Oxidation is the loss of electrons

– Reduction is the gain of electrons

– Ex: when oxygen combines with Mg

• Oxygen gains electrons – becomes reduced

• Mg loses electrons – becomes oxidized


and Metabolism

• Oxidation-Reduction

– The term oxidation is used even when

oxygen is not involved

– Ex: Na+ + Cl- NaCl

• Sodium is oxidized

• Chlorine is reduced


and Metabolism

• Oxidation-Reduction

– Also applies to covalent reactions involving

hydrogen atoms (e- + H+)

– Oxidation is the loss of hydrogen atoms

• Loss of electrons

– Reduction is the gain of hydrogen atoms

• Gain of electrons


and Metabolism

• Photosynthesis

– Energy + 6CO2+6H2O C6H12O6 + 6O2

– Hydrogen atoms are transferred from water to

carbon dioxide and glucose is formed

– Energy is required and this comes in the form

of light energy from the sun

– Chloroplasts convert solar energy to ATP

which is then used along with hydrogen to

reduce carbon dioxide to glucose


and Metabolism

• Cell Respiration

– C6H12O6 + 6O2 6CO2 + 6H2O + energy

– Glucose is oxidized (lost hydrogen atoms)

– Oxygen is reduced to form water (gained hydrogen atoms)

– Energy produced is used to form ATP

– The oxidation of glucose to form ATP is done in a series of small steps to increase efficiency


heat

heat

heat

mitochondrion chloroplast

O2

Photosynthesis Cellular respiration

CO2 + HO2

ATP for synthetic

reactions, active

transport, muscle

contraction,

nerve impulse

sun carbohydrate

(leaves): © Comstock/PunchStock RF; (runner): © PhotoDisc/Getty RF


and Metabolism

• Human beings are involved in the

cycling of molecules between

chloroplasts and mitochondria

• Our food is derived from plants or we

eat animals that have eaten plants

• Food nutrients and oxygen enter our

mitochondria to produce ATP


O2 CO2

Nutrients

Cellular respiration

Eating

O2 CO2

Breathing

ATP

Getty Images/SW Productions RF


and Metabolism

• Your diet is not all glucose

• Our food consists of carbohydrates, fats, and proteins

• Broken down into simpler molecules in digestion

• Can enter cellular respiration at various steps in the pathway to make ATP

• Excess glucose can be used to form fatty acids – Fatty acids and glycerol form lipids or fat

Documents

Metabolism: Energy and Enzymes - Welcome to Biology! - …cherylchowbiology.weebly.com/uploads/1/7/1/7/17179396/lecture_5.pdf · •Metabolism is the sum of all the chemical reactions