Chemical Bonds

Because of the tendency of atoms to complete their outer energy shells with the stable number of electrons for each shell, atoms with incomplete shells have a tendency to gain electrons, lose electrons or share electrons. Atoms that have gained or lost electrons become ions. Oppositely charged ions form ionic bonds. Atoms that share electrons form covalent bonds. A much weaker, but very important bond in biological systems is the hydrogen bond.

Plant, Animal and Bacteria Cell Models

Living cells are divided into two types - procaryotic and eucaryotic (sometimes spelled prokaryotic and eukaryotic). This division is based on internal complexity. The following pages can provide graphic roadmaps to the organization of both of these cell types.
 

The Periodic Table

You've probably seen this table before — it kind of looks like a mess of random letters and numbers, right? Well it's actually one of the most important tools for understanding chemistry!

Mitosis / Meiosis

All new cells come from previously existing cells. New cells are formed by the process of cell division which involves replication of DNA and division of the cell’s nucleus (karyokinesis) and division of the cytoplasm (cytokinesis). There are two types of nuclear division: mitosis and meiosis.
 

Osmosis

Osmosis: the movement of water molecules from an area of high concentration to an area of low concentration. Cell membranes are completely permeable to water, therefore, the environment the cell is exposed to can have a dramatic effect on the cell.
 

RNA (ribonucleic acid)

A class of nucleic acids characterized by the presence of the sugar ribose and the organic base uracil. By contrast, DNA contains deoxyribose and thymine, respectively. Most RNA molecules, including messenger RNA and transfer RNA, act as cellular intermediaries; that is, they convert the genetic information stored in DNA into the proteins that provide cells with structure and enable them to carry out metabolism.
 

Nucleic Acids - Building Blocks

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are both polynucleotides, polymers of molecules called nucleotides. Nucleotides are composed of three components.
 

A Tutorial on Genes, Genomes, and Bioinformatics

DNA (deoxyribonucleic acid) is usually composed of two very long helical polymers of nucleotides. The nucleotides are composed of a sugar (deoxyribose), phosphate, and one of 4 nitrogenous bases, adenine (A), cytosine (C), guanine (G), or thymine (T). The two polymers are linked to each other by hydrogen bonds to form a double helix.
 

Glycolysis

Glycolysis occurs in the cytoplasm in the absence of O2.