Cell Structure and Function: Prokaryotes vs Eukaryotes

Concept of the Cell

A cell is a structure formed by a plasma membrane, cytoplasm, and genetic material (DNA), which has the ability to perform three vital functions: nutrition, interaction, and reproduction. Of these three functions, the most important is reproduction, which characterizes a living being. Viruses are also capable of reproducing, but they need to invade a living cell to do so.

Structure of the Cell

The Plasma Membrane

The plasma membrane is formed by a lipid double layer in which proteins are embedded. The lipid membrane acts as an insulating barrier between the internal aqueous environment and the external environment. The proteins allow the entry and exit of substances.

The Cytoplasm

The cytoplasm contains the internal liquid and cellular organelles. The genetic material is formed by one or more DNA molecules in the nucleoid. Cells with nuclei are eukaryotes, and those without are prokaryotes.

Eukaryotic Cells

Eukaryotic cells are very complex. The plasma membrane is very similar in all cells, differing only in the associated molecules. In the cytoplasmic matrix, there are three types of structures:

• Endomembrane System: This is the set of membrane structures that can occupy almost all types of cytoplasm. Each membrane performs a distinct function. This includes the endoplasmic reticulum, which is continuous with the Golgi apparatus, and is related to vacuoles and lysosomes.
• Energy Transducers: These are the organelles: mitochondria and chloroplasts. They possess a double membrane, and their function is energy production, either from the oxidation of organic matter (mitochondria) or from light energy (chloroplasts).
• Lacking Membrane Structures: Structures lacking membranes in the cytoplasm are ribosomes, centrioles, and microtubules that form the cytoskeleton.

The Nucleus of Eukaryotic Cells

The nucleus is separated from the cytoplasm by a nuclear envelope. Inside is the nucleoplasm, which contains the hereditary material and the nucleolus.

Prokaryotic Cells

Prokaryotic cells also have a plasma membrane, cytoplasm, and genetic material. They are simpler: they only contain mesosomes and ribosomes. The genetic material is condensed into the nucleoid, and there are no nucleoli.

Animal and Plant Cells

Both animal and plant cells are eukaryotic. They share:

• A plasma membrane
• An endomembrane system
• Cytoplasm
• Mitochondria, lysosomes, peroxisomes
• Vacuoles
• A nucleus with a nuclear envelope
• A cytoskeleton

In Plant Cells:

Plant cells have a thick cell wall made of cellulose secretion, a large central vacuole that displaces the nucleus to one side, and the presence of plastids that store starch.

In Animal Cells:

The secretion membrane is made of mucopolysaccharides. Vacuoles are small, and the nucleus is centrally located. Animal cells may have cilia, flagella, or pseudopods. The energy reserve polysaccharide is glycogen.