BIO 156

Chapter 2

Atoms and Subatomic Particles

•Atoms are the fundamental unit of all matter.

•Atoms contain electrons, protons, and neutrons.

Elements are pure substance that contains only one type of atom.

•92 naturally occurring elements are known

•only about 20 are found in organisms

•Four elements in this group: carbon, oxygen, hydrogen, and nitrogen (remember: COHN) comprise 98% of the atoms of all living things

Isotopes are alternative forms of atoms, differing only in the number of neutrons additional neutrons makes some atoms a bit unstable.

•To achieve a more stable state, many isotopes release tiny energetic particles from their nuclei.

•These emissions are known as radiation

•Radioactive isotopes are called radionuclides

The Making of a Molecule

Atoms combine to form molecules.

•Compound: a substance made up of two or more atoms

•Molecule: the smallest particle of a compound that still retains the properties of that compound.

Atoms bond to form more stable configurations.

There are two types of bonds that form between atoms:

1. Ionic 2. Covalent

Electrons are responsible for creating the bonds that hold atoms together

Ionic bonds are electrostatic attractions between two oppositely charged particles.

Ionic bonds form between two atoms when one loses an electron and the other gains an electron

This reaction creates two charged particles, known as ions

Covalent bonds are formed by the sharing of electrons between atoms

Covalent Bonds Simplified

Covalent Bonds Simplified

Polar covalent bonds occur any time there is an unequal sharing of electrons by two atoms

A polar covalent bond’s atoms bear a slight charge—either positive or negative

Chemical compounds fall into two broad groups: organic and inorganic.

Organic compounds contain molecules that are made primarily of carbon atoms.

Inorganic compounds are compounds that are not organic

Water, Acids, Bases, and Buffers

Water is vital to life for many reasons.

•Water is a major component of all cells and organisms

•Water serves as a solvent, a transport medium, and a lubricant.

•Water participates in many chemical reactions.

•Water helps regulate body temperature.

Acids are substances that add hydrogen ions to solution; bases remove them.

•Acidity is measured on the pH scale

•A solution with a pH less than 7 is acidic.

•A solution with a pH greater than 7 is basic.

•On the pH scale, a change in one pH unit represents a tenfold change in acidity

•Most biochemical reactions occur at pH values between 6 and 8.

Homeostasis is ensured in part by buffers, molecules that help maintain pH within a narrow range.

•Buffers help maintain a constant pH by removing hydrogen ions from solution when levels increase.

•Buffers give back the hydrogen ions when levels fall.

Overview of Other Biologically Important Molecules

1. Carbohydrates

2. Lipids

3. Amino acids and proteins

4. Nucleic acids (DNA)

End of Chapter 2