CHAPTER 2

THE CHEMISTRY OF CELLS

SO WHAT DOES CHEMISTRY HAVE TO DO WITH

BIOLOGY????• Thomas Eisner

pioneered chemical ecology– the study of the

chemical language of nature

• He studies how insects communicate via chemical messages

BETTER LIVING THROUGH CHEMISTRY……..

• Rattlebox moths release a chemical that spiders don’t like

• This spider caught a rattlebox moth and then let it go

ATOMS AND MOLECULES

• 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.

Molecules and ecosystems are at opposite ends of the biological hierarchy

–Each level of organization in the biological hierarchy builds on the one below it

–At each level, new properties emerge…in other words-the higher up the ladder..the more complicated

A biological hierarchyD. Organ: Flight muscle of a moth

C. Cell and tissue: Muscle cell within muscle tissue

Myofibril (organelle

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

A. Molecule: Actin Atom

• Organ• Tissue• Cell• Organelle• Molecule• Atom

Actin

LIFE REQUIRES ABOUT 25 CHEMICAL ELEMENTS

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

• About 25 different chemical elements are essential to life

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

IODINE IS A REQUIREMENT

• Goiters are caused by iodine deficiency

ELEMENTS CAN COMBINE TO FORM COMPOUNDS

• Chemical elements combine in fixed ratios to form compounds

• Example: sodium + chlorine sodium chloride

Atoms consist of protons, neutrons, and electrons

• The smallest particle of an element is an atom

• Different elements have different types of atoms

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

nucleus• The nucleus is surrounded by electrons

Protons

Neutrons

Electrons

Nucleus

A. Helium atom

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

charged electrons• Neutrons are electrically neutral

Protons

Neutrons

Electrons

B. Carbon atom

Nucleus666

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 isotopes

– Some isotopes are radioactive

Connection: Radioactive isotopes can help or harm us

• Radioactive isotopes can be useful tracers for studying biological processes

• PET scanners use radioactive isotopes to create anatomical images

Electron arrangement determines the chemical properties of an

atom• Electrons are arranged in shells

– The outermost shell determines the chemical properties of an atom

– In most atoms, a full outer shell holds eight electrons

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

First electron shell (can hold 2 electrons)Electron

Outermost electron shell (can

hold 8 electrons)

HYDROGEN (H)Atomic number = 1

CARBON (C)Atomic number = 6

NITROGEN (N)Atomic number = 7

OXYGEN (O)Atomic number = 8

Ionic bonds are attractions between ions of opposite charge

• 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

NaSodium atom Cl

Chlorine atom

Na+

Sodium ionCl–

Chloride ion

Sodium chloride (NaCl)

Sodium and chloride ions bond to form sodium chloride, common

table salt

Na+

Cl–

Covalent bonds, the sharing of electrons, join atoms into

molecules• Some atoms share outer shell electrons

with other atoms, forming covalent bonds– Atoms joined together by covalent bonds form

molecules

• Molecules can be represented in many ways