CHAPTER 2The Chemical Basis of Life

Thomas Eisner pioneered _______

__________– the study of the

chemical language of nature

He studies how insects communicate via chemical messages

Thomas Eisner and the Chemical Language of Nature

Water in three different states: 5 States of matter

Everything an organism is and does depends on chemistry

Chemistry is in turn dependent on the arrangement of atoms in molecules

In order to understand the whole, biologists study the parts (reductionism)

The emergence of biological function starts at the chemical

level

ATOMS AND MOLECULES

A _________________

A. Molecule: Actin Atom

MyosinActin

B. Organelle: Myofibril (found only in muscle cells)

Myofibril (organelle)

C. Cell and tissue: Muscle cell within muscle tissue

Rattlebox moth

D. Organ: Flight muscle of a moth

A chemical _____ is a substance that cannot be broken down to other substances by ordinary chemical means

About ____ different chemical elements are essential to _____

lead

Carbon, hydrogen, oxygen, and nitrogen make up the bulk of living matter, but there are other elements necessary for life

_________ Table 2.2

Goiters are caused by iodine deficiency

Figure 2.2

The smallest particle of an element is an _____

Different ______ have different types of atoms

2.4 Atoms consist of protons, ________, and electrons

An atom is made up of protons and neutrons located in a central nucleus

A. Helium atom

2

2

2

Protons

Neutrons

Electrons

Nucleus

The nucleus is surrounded by electrons

Each atom is held together by attractions between the positively charged protons and ________charged electrons

B. Carbon atom

6

6

6

Protons

Neutrons

Electrons

Nucleus

Neutrons are electrically _______

Atoms of each element are distinguished by a specific number of protons

– The number of neutrons may vary – Variant forms of an element are called

________– Some isotopes are ________

Radioactive isotopes can be useful tracers for studying biological processes

PET scanners use radioactive isotopes to create anatomical images

2.5 Connection: Radioactive isotopes can help or harm us

Figure 2.5BFigure 2.5A

Chemical elements combine in fixed ratios to form _________

Example: sodium + chlorine sodium chloride

2.3 Elements can combine to form compounds

Reactants Products

Electrons are arranged in _______– The outermost shell determines the

chemical properties of an atom– In most atoms, a full outer shell holds

_____ electrons

2.6 Electron arrangement determines the chemical

properties of an atom

Atoms whose shells are not full tend to interact with other atoms and ___, ____, or ______ electrons

Figure 2.6

HYDROGEN (H)Atomic number = 1

CARBON (C)Atomic number = 6

NITROGEN (N)Atomic number = 7

OXYGEN (O)Atomic number = 8

Electron

Outermost electron shell (can hold 8 electrons)

First electron shell (can hold 2 electrons)

When atoms gain or lose electrons, charged atoms called ions are created– An electrical attraction between ions with

opposite charges results in an ionic bond

2.7 Ionic bonds are attractions between ions of opposite charge

Figure 2.7A

NaSodium atom

ClChlorine atom

Na+

Sodium ionCl–

Chloride ion

Sodium chloride (NaCl)

Na Cl Na Cl

+–

Some atoms share outer shell electrons with other atoms, forming covalent bonds– Atoms joined together by covalent bonds

form molecules

2.8 Covalent bonds, the _____ of electrons, join atoms into

molecules

In a chemical reaction:– reactants interact– atoms rearrange– products result

Chemical reactions rearrange matter

REARRANGEMENTS OF ATOMS

2 H2+ O2

2 H2O

A compound that releases H+ ions in solution is an acid, and one that accepts H+ ions in solution is a base

Acidity is measured on the pH scale: – 0-6 is acidic – 8-13 is basic OH- Hydroxide Ion Alkaline– Pure water and solutions that are neither

basic nor acidic are neutral, with a pH of 7

2.15 The chemistry of life is sensitive to acidic and basic

conditions

The pH scale

pH scale

Acidic solution

Neutral solution

Basic solution

Incr

easi

ng

ly A

CID

IC(H

igh

er c

on

cen

trat

ion

of

H+)

Incr

easi

ng

ly B

AS

IC(L

ow

er

con

cen

trat

ion

of

H+)

NEUTRAL[H+] = [OH–]

Lemon juice; gastric juice

Grapefruit juice

Tomato juice

Urine

PURE WATER

Seawater

Milk of magnesia

Household ammonia

Household bleach

Oven cleaner

Human blood

H+

OH–

Cells are kept close to pH 7 by buffers

Buffers are substances that resist pH change– They accept H+ ions when they are in

excess and donate H+ ions when they are depleted

– Buffers are not foolproof