Organic compounds

1. Protein: come in a variety of structures and serve many functions. Protein is the major component of a cell's dry mass (i.e. next to water, cells are mostly protein). Some proteins serve a structural function (e.g. cytoskeleton), control chemical reactions (enzymes), provide motion (e.g. cilia, flagella), facilitate intracellular transport (e.g. motor proteins), and may play a role in intercellular communication (e.g. hormones, gap junctions, ligand-receptor binding, ion channels, etc.). Proteins are produced by ribosomes from mRNA templates, either in the cytosol or at the surface of the RER (for cytosolic or secreted proteins, respectively). 
2. Fat: (dehydrated carbs) is major part of the cell membrane, also provides energy storage and insulation in animals. Lipids are produced in the SER.
3. Nucleic acid: DNA stores our genetic information (cookbook for proteins, etc.); DNA is found in the nucleus of eukaryotes, hence the name nucleic acids. DNA is by far the largest molecule in a cell. RNA comes in a few varieties, including mRNA and tRNA which are involved in protein production. mRNA and tRNA are found in the cytosol, not the nucleus. 
4. Carbohydrate: (sugars) provide readily available energy. While ATP is the energy carrier in the cell, in animals, glucose carries energy between cells by way of the blood. In plants, starch is the main energy-storing carb, not glucose.