021 chemical basis of life

7/27/2019 021 Chemical Basis of Life

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BIOLOGYCONCEPTS & CONNECTIONS

Fourth Edition

Copyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor

From PowerPoint Lectures forBiology: Concepts & Connections

CHAPTER 2The Chemical Basis of Life

Modules 2.12.8


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Thomas Eisnerpioneered chemicalecology

the study of thechemical language ofnature

He studies how insectscommunicate viachemical messages

Thomas Eisner and the Chemical Language of

Nature


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Rattlebox mothsrelease a chemical

that spiders dontlike

This spider caughta rattlebox moth

and then let it go


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Everything an organism is and does depends onchemistry

Chemistry is in turn dependent on thearrangement of atoms in molecules

In order to understand the whole, biologistsstudy the parts (reductionism)

2.1 The emergence of biological function starts atthe chemical level

ATOMS AND MOLECULES


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Molecules and ecosystems are at opposite endsof the biological hierarchy

Each level of organization in the biological

hierarchy builds on the one below it

At each level, new properties emerge


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A biologicalhierarchy

Figure 2.1 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


7/21Copyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings

A chemical element is a substance that cannotbe broken down to other substances by ordinarychemical means

About 25 different chemical elements areessential to life

2.2 Life requires about 25 chemical elements



Carbon,hydrogen,

oxygen, andnitrogen makeup the bulk ofliving matter,

but there areother elementsnecessary for

life

Table 2.2



Goiters are caused by iodine deficiency

Figure 2.2



Chemical elements combine in fixed ratios to

form compounds

Example: sodium + chlorine sodium chloride

2.3 Elements can combine to form compounds



The smallest particle of an element is an atom

Different elements have different types ofatoms

2.4 Atoms consist of protons, neutrons, andelectrons



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

Figure 2.4A A. Helium atom

2

2

2

Protons

Neutrons

Electrons

Nucleus

The nucleus is surrounded by electrons



Each atom is held together by attractionsbetween the positively charged protons and

negatively charged electrons

Figure 2.4B B. Carbon atom

6

6

6

Protons

Neutrons

Electrons

Nucleus

Neutrons are electrically neutral


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Atoms of each element are distinguished by aspecific number of protons

Table 2.4

The number of neutrons may vary

Variant forms of an element are called isotopes

Some isotopes are radioactive


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Radioactive isotopes can be useful tracers forstudying biological processes

PET scanners use radioactive isotopes to create

anatomical images

2.5 Connection: Radioactive isotopes can help orharm us

Figure 2.5BFigure 2.5A


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Electrons are arranged in shells

The outermost shell determines the chemicalproperties of an atom

In most atoms, a full outer shell holds eightelectrons

2.6 Electron arrangement determines the chemicalproperties of an atom


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Atoms whose shells are not full tend to interactwith other atoms and gain, lose, or share

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)


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When atoms gain or lose electrons, chargedatoms called ions are created

An electrical attraction between ions withopposite charges results in an ionic bond

2.7 Ionic bonds are attractions between ions ofopposite charge

Figure 2.7A

Na

Sodium atom

Cl

Chlorine atom

Na+

Sodium ion

Cl

Chloride ion

Sodium chloride (NaCl)

Na Cl Na Cl

+


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Sodium and chloride ions bond to form sodiumchloride, common table salt

Figure 2.7B

Na+

Cl


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Some atoms share outer shell electrons withother atoms, forming covalent bonds

Atoms joined together by covalent bonds form

molecules

2.8 Covalent bonds, the sharing of electrons, joinatoms into molecules


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Copyright 2003 Pearson Education Inc publishing as Benjamin Cummings

Molecules can berepresented in

many ways

Table 2.8

021 chemical basis of life

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