Cell Theory

Study Notes

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.

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.

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.

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.

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

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.

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 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 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.