cell structure

A cell consists of many organelles (small units within the cell responsible for a specific function). The structure of a cell includes a cell membrane , also called a cell wall or plasma membrane, which holds the cell together. This membrane is half lipid and half protein. One end is attracted to water and the opposite end is repelled by water. Cell membranes are semipermeable, meaning they allow some substances to pass through but not others. Some molecules, like water, pass through easily, whereas other molecules, like proteins and starches, are not able to pass. The cytoplasm is the fluid part of the cell that allows the cell’s internal structure to move. The nucleus is the brain of the cell and is located in the center of the cell. (Note that red blood cells do not have a nucleus.) DNA is found in the nucleus of a cell. As the cell divides, chromosomes begin to form, and the genetic material is passed on to all daughter cells. Within the nucleus is the nucleolus , which forms genetic material. This is where RNA is produced that then forms ribosomes. The ribosomes are structures within the cell that make protein. Ribosomes are macromolecular machines, found within all living cells, that perform biological protein synthesis. Ribosomes link amino acids together in the order specified by the codons of messenger RNA molecules to form polypeptide chain. The endoplasmic reticulum is a collection of folded membranes that attach to the nucleus. Endoplasmic reticulum that is lined with ribosomes that give the appearance of bumps along the edge is called rough endoplasmic reticulum. Smooth endoplasmic reticulum has no ribosomes attached to it and occurs less often throughout the body. The Golgi apparatus , where lysosomes are produced, is formed with large amounts of folded membrane similar to smooth endoplasmic reticulum. Lysosomes are enzymes that digest food and proteins. They help break down other molecules. Cells that die within the body are removed when enzymes within the lysosomes are released into the cytoplasm. This is called autolysis and allows for room for new cells to develop. This is often how the body fights infection. The mitochondria are the part of the cell that makes energy and are often referred to as the “powerhouse of the cell.” These rod-shaped cells have a double membrane. The inner membrane is folded and forms ridges, while the outer membrane is smooth. Mitochondria convert food particles into energy.