Cell Theory

Cell Theory

• All known living things are composed of one or more cells.
• All new cells are created by pre-existing cells dividing.
• The cell is the most basic unit of structure and function in all living organisms.

Cell Structure

• Cells have a cell membrane, which acts as the boundary or edge of the cell and controls what goes in and out.
• Cells contain cytoplasm, the substance inside the cell.
• Cells have DNA, the genetic material needed to provide instructions for building the cell's machinery.
• Cells have ribosomes, the structures that facilitate the building of proteins.

Cell Function

• All functions essential to life occur within the cell.
• During cell division, the cell transmits to the next generation the information necessary to conduct and regulate cell functioning.

Cell Variation

• Cells can vary widely in appearance and function.
• Many cells also contain more structures, in addition to the basic cell membrane, cytoplasm, DNA, and ribosomes.

Cell Characteristics

• Despite diversity in structure and function, all cells share certain characteristics.

Cell Types

• There are two main types of cells: prokaryotes and eukaryotes.
• Prokaryotes are small, simple cells that make up single-celled organisms, with bacteria being the most prevalent type.
• Eukaryotes are larger, more complex cells that are often multicellular organisms, including plants, animals, and fungi.

Common Cell Features

• All cells have a cell membrane that provides a barrier between the interior and exterior of the cell and regulates the flow of substances in and out of the cell.
• All cells have cytoplasm, the fluid that occupies the space inside the cell, where chemical reactions that enable life take place.
• All cells have a cytoskeleton, a network of filaments that provide support and a framework for the cell to move things around in the cytoplasm.
• All cells contain DNA, which contains the instructions for synthesizing all the cell's proteins, at some point in their life cycle.
• All cells contain ribosomes, the molecular machines that use the instructions contained in the DNA to build all the proteins needed by the cell.

Eukaryotic Cell Features

• Eukaryotic cells are more complex and have specialized structures called organelles.
• Organelles have their own membrane to partition them off from the rest of the cell and to allow them to specialize in a certain function.
• An important example of an organelle is a nucleus, a specialized compartment found in eukaryotic cells for holding DNA.

Prokaryotic Cell Features

• Prokaryotic cells have DNA, but it is localized to one area of the cell, the nucleoid region.
• The nucleoid region is not surrounded by a membrane and is therefore not a nucleus.
• Only eukaryotic cells have a nucleus.