Atoms and Molecules
Atoms
Smallest particle of matter non-divisible by chemical means.
Composed of protons (+) and neutrons (neutral) in the nucleus and electrons (-)
outside the nucleus.
The smallest unit of an element to enter into chemical reactions.
All atoms of an element have a particular number of protons (atomic number).
Electrically neutral because the umber of protons equals the number of electrons.
Atomic weight depends on the number of protons and neutrons in the nucleus.
Chemical properties depend on the number of electrons in the outer shell.
Molecules
Form when two or more atoms of the same element react with one another or
combine with atoms of another element.
The smallest part of a compound that still has the properties of that compound.
Could be inorganic or organic molecules.
Chemical Bonding
Interactions involving atoms of elements combining with one another.
Determined by the electrons that surrounds the nucleus.
An atom may bond with another atom by either gaining, losing or sharing
electrons.
Types of Chemical Bonds
1. Covalent Bond
Electrons are shared; characteristic of most chemicals in living things; smallest
particle formed are called molecules.
2. Ionic Bond
An electron is transferred from one atom to another; ions (charge particles) are
formed; cations, when electron is lost; anions, when electron is gained.
3. Hydrogen Bond
When hydrogen combines with oxygen or with another electronegative atom;
weak and can easily be formed or broken; very important in biological system;
important in determining the structure of DNA, and proteins.
INORGANIC MOLECULES
Usually contain positive and negative ions.
Atoms are usually held together by ionic bond.
Usually composed of short chains.
Often associated with non-living things.
Includes water, acids and bases, salt, and gases.
Water
The most abundant component of the protoplasm.
Inorganic compound composed of two atoms of hydrogen and an atom of
oxygen.
Physical Properties of Water
Universal solvent
High degree of thermal conductivity
Immiscible with lipids
Neutral pH
Liquid in form at room temperature
High surface tension
Physiological Properties of Water
Dissolves or holds in suspension the materials of the protoplasm.
Furnishes a medium for some vital processes.
Moistens surfaces for gas diffusion.
Regulates body temperature.
Helps in the functions of the sense organs.
Serves as lubricant for movable surfaces.
Serves as cushion for the brain and spinal cord.
Acids and Bases
Acids are molecules that raise the hydrogen ion concentration (H+) when added
to a solution, such as HCl.
Bases are molecules that lower the hydrogen ion concentration (H+) when added
to a solution, such as NaOH.
pH scale is used to measure the acidity and alkalinity of a solution.
As the pH number decreases, acidity increases.
As the pH number increases, alkalinity increases.
Most organisms maintain a neutral pH (pH 7).
A much higher or lower pH may cause illness.
Salts
Formed from the neutralization of an acid and a base.
Occur in the form of soluble chlorides, sulfates, phosphates, and carbonates of
sodium, calcium, potassium, and magnesium.
Important in vital processes such as irritability of muscles and nerves, growth and
repair of tissues, etc.
Act as buffers or regulators of acid-base balance.
Gases
Important in oxidation of food molecule in order to release energy; two important
gases are oxygen and carbon dioxide.
ORGANIC MOLECULES
Always contain carbon and hydrogen
Atoms are usually held together by covalent bond
Usually composed of long chains
Usually associated with living things
Includes carbohydrates, lipids, proteins, and nucleic acids.
A. Carbohydrates
Composed of carbon, hydrogen, and oxygen in definite ratio, 1:2:1, with a
general formula of CH2O
The main source of energy in the body; building blocks are glucose molecules.
Types of Carbohydrates
1. Monosaccharide
Simple sugar
Important source of energy for the cells.
Glucose – blood sugar or dextrose
Fructose – fruit sugar
Galactose – milk sugar
2. Disaccharide
Double sugar
Two monosaccharides bonded together
Principal sugar transported throughout the bodies of land plants.
Lactose – milk sugar (glucose + galactose)
Maltose – malt sugar (glucose + glucose)
Sucrose – table sugar (glucose + fructose)
3. Polysaccharide
Complex sugar
Manny monosaccharides (usually glucose) bonded together
Starch – energy storage in plants
Glycogen – energy storage in animals
Cellulose – structural material in plants
B. Lipids
Composed of carbon, hydrogen, and oxygen with no definite ratio, the number of
oxygen atoms is very much less compared to hydrogen atoms.
Storage of energy and important component of the cell membrane.
Building blocks are fatty acids and glycerol
Types of Lipids
1. Simple Lipids
Composed of three fatty acids bonded to glycerol
Also called triglyceride (ex. Oils and fats)
Include stearin, palmitin, olein and waxes.
2. Compound Lipids
Composed of lipids found in combination with other compounds.
Lipoproteins – with protein
Glycolipids – with carbohydrates
Phospholipids – with phosphoric acid
3. Steroids
Composed of four fused rings of carbon atoms with functional groups attached.
Include cholesterol, a common component of membranes of eukaryotic cells.
C. Proteins
Composed of carbon, hydrogen, oxygen, and nitrogen plus other elements such
as sulfur, iron, iodine, etc.
For growth and repair of tissues, component of the cell membrane, acts as
organic buffer, and lay a major role in chemical reactions as enzymes, in
protection of the body as antibodies.
Building blocks of amino acids, which are united by means of peptide linkage to
form polypeptide chains.
Types of Proteins
1. Fibrous Protein
The polypeptides are arranged parallel along a single axis to produce long fibers
or sheets.
Keratin – principal component of hair, skin and nails;
Silk – pleated sheet protein produced by silk moths and spiders.
2. Globular Protein
The polypeptides are so tightly folded into spherical or globular shapes, such as
hemoglobin, the component of vertebrate blood used to transport oxygen.
3. Conjugated Protein
Simple proteins in union with other substances.
Nucleoprotein – with nucleic acids (ex. histones)
Glycoprotein – with carbohydrates (ex. mucin)
Lipoprotein – with fatty acids (ex. serum and brain tissue)
Chromoprotein – with pigments (ex. cytochrome)
D. Nucleic Acids
Composed of carbon, hydrogen, oxygen, and nitrogen and phosphorus
Important in protein synthesis as RNA, and in heredity as DNA.
Building blocks are the nucleotides, which are made up of a pentose sugar
(ribose or deoxyribose), a nitrogen base (pyrimidine or purine), and phosphoric
acid.
In DNA, purines are adenine and guanine; pyrimidines are cytosine and thymine.
In RNA, thymine is replaced by uracil.
