A look at the structural components of eukaryotic and prokaryotic cells and the differences between the two types of cell.
Cells are divided into two major classes, eukaryotes and prokaryotes. The difference between these two classes is that the materials making up the nucleus of eukaryotic cells are separated from the rest of the cell by the nuclear membrane, whereas in prokaryotic cells these materials are not separated. All animals and plant cells are eukaryotic and bacteria, cyanobacteria and the mycoplasmas are prokaryotic.
Eukaryotic Cells
The constituents of a typical animal eukaryotic cell are as follows:
The Plasma Membrane – the contents of the cell are separated from their surroundings by the plasma membrane, also known as the cell membrane. The plasma membrane consists of protein, lipid and carbohydrate in an arrangement known as the fluid mosaic model. The plasma membrane regulates the transfer of materials between the cell and its surroundings.
The Endoplasmic Reticulum and the Ribosomes - within the cytoplasm of most animal cells is a large network of branching channels called the endoplasmic reticulum (ER). On the surface of the ER are a large number of small particles called ribosomes. Ribosomes synthesise the cells’ proteins.
Mitochondria – found within the cytoplasm, they are responsible for energy synthesis.
The Golgi apparatus – processes, packages and dispatches proteins, within and out of the cell.
Lysosomes – found in many cells, these vesicles contain enzymes capable of digesting proteins, nucleic acid, polysaccharide and other materials. Lysosomes are involved amongst other things in the intracellular digestions of particles scavenged by some types of cell during endocytosis.
The Nucleus – is a relatively large structure, often found near the centre of the cell. The contents of the nucleus are separated from the cytoplasm by the nuclear envelope. The nucleus contains the genetic components of the cell (chromosomes etc.)
Flagella and Cilia – many free living cells (e.g. protozoa), have locomotory flagella or cilia to help them move. Cells within a multicellular animal may also have cilia, for example cells with cilia in the respiratory tract that move mucus in the lungs.
The organelles described above may also be found in similar form in many plant cells, as well as these organelles, the constituents of a typical plant eukaryotic cell are as follows:
The Cell Wall – is a thick, polysaccharide containing structure that surrounds the plasma membrane in plant cells. The cell wall provides both protection and support.
Chloroplasts – the site of photosynthesis within the cell.
Vacuoles – larger than in animal cells, they often occupy a major portion of the cell volume. Vacuoles help to expand the plant cell without diluting its cytoplasm, they are also used to store water and cell products.
Prokaryotic cells
The constituents of a typical bacterium are as follows:
Bacterial Cell Wall and Capsule – bacteria are surrounded by a cell wall, which not only contains polysaccharide but also contains protein and lipid. In some bacteria, the cell wall is surrounded by the capsule. The cell wall and capsule provide shape and form to the bacterium and also acts as a physical barrier between the bacterium and its environment.
Nucleoids – in bacteria the nuclear material is concentrated in a region called the nucleoid within the cytoplasm.
Bacterial flagella – many bacteria possess one or more flagella for locomotion.
Source:
Cell and Molecular Biology by P. Sheeler and D.E. Bianchi, Wiley
