Chapter 5 Gases - Mr. Doyle SUIS...

Chapter 5

Ground Rules of

Metabolism Sections 1-5

5.1 A Toast to Alcohol Dehydrogenase

• In the liver, the enzyme alcohol dehydrogenase breaks down

toxic ethanol to acetaldehyde, an organic molecule even more

toxic than ethanol

• Ethanol breakdown interferes with normal processes of

metabolism – as a result, fats tend to accumulate as large

globules in the tissues of heavy drinkers

• Ethanol breakdown damages liver cells and can lead to

alcoholic hepatitis and cirrhosis of the liver

Binge Drinking

alcohol

dehydrogenase

Alcoholic Liver Disease

3D ANIMATION: Process of Secretion

videos_animations/Secretion/Secretion.html

5.2 Energy in the World of Life

• Sustaining life’s organization requires ongoing energy inputs

• Assembly of the molecules of life starts with energy input into

living cells

Energy

• We define energy as the capacity to do work

• One form of energy can be converted to another

• Familiar forms of energy include light, heat, electricity, and

motion (kinetic energy)

• The energy in chemical bonds is a type of potential energy,

because it can be stored

Energy Disperses

• First law of thermodynamics

• Energy is neither created nor destroyed, but can be

transferred from one form to another

• Second law of thermodynamics

• Entropy (a measure of dispersal of energy in a system)

increases spontaneously

• The entropy of two atoms decreases when a bond forms

between them (endergonic reaction)

En

tro

py

Time

heat

energy

Stepped Art

Figure 5-2 p78

Energy Conversion

• Only about 10% of the

energy in food goes

toward building body

mass, most is lost in

energy conversions

Energy’s One Way Flow

• The total amount of energy available in the universe to do

work is always decreasing

• Each time energy is transferred, some energy escapes as

heat (not useful for doing work)

• On Earth, energy flows from the sun, through producers, then

consumers

• Living things need a constant input of energy

Figure 5-4 p79

sunlight

energy

A Energy In. Sunlight energy reaches

environments on Earth. Producers in

those environments capture some of

the energy and convert it to other

forms that can drive cellular work.

Producers

B Some of the

energy captured by

producers ends up

in the tissues of

consumers.

Nutrient

Cycling

Consumers

C Energy Out. With each energy transfer,

some energy escapes into the environment,

mainly as heat. Living things do not use

heat to drive cellular work, so energy flows

through the world of life in one direction

overall.

ANIMATED FIGURE: One-way energy flow

and materials cycling

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videos_animations/energy_flow.html

Potential Energy

Take-Home Message:

What is energy?

• Energy is the capacity to do work; it can be transferred

between systems or converted from one form to another, but

it cannot be created or destroyed

• Energy disperses spontaneously

• Some energy is lost during every transfer or conversion

• Organisms can maintain their complex organization only as

long as they replenish themselves with energy they harvest

from someplace else

ANIMATION: Total energy remains constant




videos_animations/energy_constant.html

5.3 Energy in the Molecules of Life

• All cells store and retrieve energy in chemical bonds of the

molecules of life

Chemical Bond Energy

• Reaction

• A chemical change that occurs when atoms, ions, or

molecules interact

• Reactant

• Atoms, ions, or molecules that enter a reaction

• Product

• Atoms, ions, or molecules remaining at the end of a

reaction

Equations Represent Chemical Reactions

ANIMATED FIGURE: Chemical

bookkeeping




videos_animations/chem_equation.html

Reactions Require or Release Energy

• We can predict whether a reaction requires or releases

energy by comparing the bond energies of reactants with

those of products

• Endergonic (“energy in”) • Reactions that require a net input of energy

• Exergonic (“energy out”) • Reactions that end with a net release of energy

Endergonic and Exergonic Reactions

Why the Earth Doesn’t Go Up in

Flames

• Activation energy

• The minimum amount of energy needed to get a reaction

started

• Some reactions require a lot of activation energy, others

do not

Activation Energy

Reactants:

2H2 O2

Activation energy

Difference between free energy

of reactants and products

Products: 2H2O

Time

Fre

e e

nerg

y

ANIMATED FIGURE: Activation energy




videos_animations/energy_hill_v2.html

Energy In, Energy Out

• Cells store free energy by running endergonic reactions that

build organic compounds

• Example: photosynthesis

• Cells harvest free energy by running exergonic reactions that

break the bonds of organic compounds

• Example: aerobic respiration

Energy In

Energy Out

Take-Home Message:

How do cells use energy?

• Activation energy is the minimum amount of energy required

to start a chemical reaction

• Endergonic reactions cannot run without a net input of energy

• Exergonic reactions end with a net release of energy

• Cells store energy in chemical bonds by running endergonic

reactions that build organic compounds; they harvest energy

by breaking the bonds

ANIMATION: Energy changes in chemical

work




videos_animations/energy_changes.html

5.4 How Enzymes Work

• Enzyme

• In a process called catalysis, an enzyme makes a specific

reaction occur much faster than it would on its own

• Enzymes are not consumed or changed by participating in

a reaction

• Most are proteins, some are RNA

• Substrate

• The specific reactant acted upon by an enzyme

The Transition State

• Enzymes lower the activation energy required to bring on the

transition state, when substrate bonds break and reactions

run spontaneously

• Active sites

• Locations on the enzyme molecule where substrates bind

and reactions proceed

• Complementary in shape, size, polarity and charge to the

substrate

Active Site of an Enzyme

Figure 5-10a p82

active site

enzyme

A Like other enzymes, hexokinase

has active sites that bind and alter

specific substrates. A model of the

whole enzyme is shown to the left.

Figure 5-10b p82

reactant(s)

B A close-up shows glucose and

phosphate meeting in the active

site. The microenvironment of the

site favors a reaction between the

two molecules.

Figure 5-10c p82

product(s)

c Here, the glucose has bonded with

the phosphate. The product of this

reaction, glucose-6-phosphate, is

shown leaving the active site.

Mechanisms of

Enzyme-Mediated Reactions

• Binding at enzyme active sites may bring on the transition

state by four mechanisms

• Helping substrates get together

• Orienting substrates in positions that favor reaction

• Inducing a fit between enzyme and substrate (induced-fit

model)

• Shutting out water molecules

Effects of Temperature, pH, and Salinity

• Raising the temperature boosts reaction rates by increasing a

substrate’s energy

• But very high temperatures denature enzymes

• Each enzyme has an optimum pH range

• In humans, most enzymes work at ph 6 to 8

• Salt levels affect the hydrogen bonds that hold enzymes in

their three-dimensional shape

Figure 5-12 p83

rate of

enzyme

activity

increases

activity rate

decreases as

enzyme

denatures

Figure 5-13 p83

glycogen

phosphorylase

trypsin

pepsin

Take-Home Message:

How do enzymes work?

• Enzymes greatly enhance the rate of specific reactions.

• Binding at an enzyme’s active site causes a substrate to

reach its transition state. In this state, the substrate’s bonds

are at the breaking point

• Each enzyme works best at certain temperatures, pH, and

salt concentration

ANIMATED FIGURE: Enzymes and their

role in lowering activation energy




videos_animations/enzyme_role_m.html

5.5 Metabolism:

Organized, Enzyme-Mediated Reactions

• ATP, enzymes, and other molecules interact in organized

pathways of metabolism (activities by which cells acquire and

use energy)

Types of Metabolic Pathways

• A metabolic pathway is any series of enzyme-mediated

reactions by which a cell builds, rearranges, or breaks down

an organic substance

• Anabolic pathways build molecules

• Catabolic pathways break apart molecules

• Cyclic pathways regenerate a molecule from the first step

Controls Over Metabolism

• Concentrations of reactants or products can make reactions

proceed forward or backward

• Feedback mechanisms can adjust enzyme production, or

activate or inhibit enzymes

• Regulatory molecules can bind to an allosteric site to

activate or inhibit enzymes

• Feedback inhibition

intermediate

reactant

enzyme 1

enzyme 2

intermediate

enzyme 3

product

X

Stepped Art

Figure 5-14 p84

Figure 5-15 p84

active site substrate in

active site

A Inactive form. B Active form.

regulatory

molecules

ANIMATED FIGURE: Allosteric activation




videos_animations/allosteric_control.html

Redox Reactions

• Oxidation-reduction reactions (paired reactions)

• A molecule that gives up electrons is oxidized

• A molecule that accepts electrons is reduced

• Coenzymes can accept molecules in redox reactions (also

called electron transfers)

Figure 5-16 p85

glucose

+

oxygen carbon

dioxide

+

water

Figure 5-16 p85

glucose

1

carbon

dioxide

+

water

oxygen

+

2

3

e–

e–

H+

ANIMATED FIGURE: Controlling energy

release




videos_animations/energy_staircase.html

Take-Home Message:

What are metabolic pathways?

• Metabolic pathways are sequences of enzyme-mediated

reactions; some are biosynthetic; others are degradative

• Control mechanisms enhance or inhibit the activity of many

enzymes; the adjustments help cells produce only what they

require in any given interval

• Many metabolic pathways involve electron transfers, or redox

reactions.

• Redox reactions occur in electron transfer chains; the chains

are important sites of energy exchange in photosynthesis and

aerobic respiration

ANIMATION: Types of reaction sequences




videos_animations/reaction_sequences.html

Chapter 5 Gases - Mr. Doyle SUIS...

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