Though there are many different types of cells, all cells have a plasma membrane, deoxyribonucleic acid (DNA), ribosomes and cytoplasm. The other structures found in a cell vary depending on the type of cell.
Cells are the fundamental building blocks of life and make up all living things. From microscopic bacteria to enormous blue whales, all living things are composed of these little structures. Some organisms consist of a single cell and others are made up of billions. Cells come in many shapes and sizes, and they all have different purposes. The structure and design of the cell all help it do its job. For example, nerve cells which transmit messages quickly have a much different shape than blood cells that transport oxygen throughout the body. Because cells have different jobs, they also have different components or structures within the cell that help them complete those tasks. However, there are four structures found in all cells no matter what type: plasma membrane, DNA, ribosomes and cytoplasm.
Plasma Membrane The plasma membrane, also referred to as the cell membrane, is the structure that completely surrounds the outside of the cell. It holds all of the other cell components inside while separating them from the rest of the environment. It acts as a skin that offers protection for the cell and its components. The plasma membrane is made up of a thin coating of fats, known as the phospholipid bilayer, and proteins that prevent objects from the environment from passing through. However, the plasma membrane is selectively permeable and allows small, nonpolar molecules to pass through freely.
DNA DNA is the genetic material of a cell. The DNA contains the genetic code or instructions for how to make proteins. Eukaryotic cells have a nucleus, which is like the control center for the cell. It is in this organelle that DNA resides. However, prokaryotic cells do not have a nucleus. Instead, the DNA exists in a coiled loop floating around in the cytoplasm in the nucleoid region.
Ribosomes Ribosomes are small organelles that float in the cytoplasm or are attached to other structures. Their job is to synthesize proteins by connecting amino acids together to make long chains. Proteins are necessary for several purposes. Enzymes use proteins as catalysts for biological reactions. Likewise, the cells themselves need proteins to carry out their specific functions. Although ribosomes look different in prokaryotic and eukaryotic cells, their purpose is the same.
Cytoplasm Cytoplasm is a fluid that fills the inside of the cell, except for the nucleus. It is made up of cytosol and all other organelles are suspended inside it. The cytoplasm has other purposes aside from just being a filler. however. Although this jelly-like substance is comprised of 80 percent water, it also contains dissolved enzymes that it uses to break down large molecules into usable smaller molecules. For example, the cytosol in cytoplasm can break down glucose into smaller molecules that are used to provide energy for the mitochondria. If the cell has a nucleus, the fluid inside is known as nucleoplasm. Although similar, they have very different compositions and purposes.