SUMMARY
Each of the cell structures is composed of four major groups of organic molecules: carbohydrates, proteins, nucleic acids, and lipids. These molecules contain C, H, and O. Proteins also have N (and sometimes S), and each membrane has P in the phospholipids that compose that membrane.

The nucleus directs cell functions, using the DNA instructions for protein synthesis, and the nucleolus makes ribosomes that follow the instructions contained in DNA to actually produce the proteins. The proteins produced in the rough ER are further processed and packaged by the Golgi apparatus, often for secretion from the cell.

The cytoplasm contains a variety of other membrane-bound organelles. Many of these organelles contain enzymes that carry out functions specific to the particular organelle.

The cytoskeleton and related structures also are composed of proteins. These proteins provide structural support and motility functions for cells. This is in contrast to the enzymes in the membrane-bound organelles that carry out chemical reactions.

Activity
Return to Part 1