Cellular Structure: Function & Definition

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  • 0:00 Two Types of Cells
  • 1:12 Plasma Membrane
  • 2:09 Prokaryotes
  • 2:54 Bacteria: Cell Structure
  • 4:03 Eukaryotes
  • 6:45 Lesson Summary
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Lesson Transcript
Instructor: Vibha Jha

Vibha has doctorate in Immunology and has taught college level Microbiology

Living organisms are divided into two major types, prokaryotes and eukaryotes. This lesson describes the structure and functions of these two cell types. When you are through, you can test your understanding with a quiz.

Two Types of Cells

Cells are like small factories; they have different departments and laborers that work day and night to make life possible. In this lesson, we will study the different types of cells and different working units within a cell that carry out various functions like energy production and protein synthesis.

There are two major categories of living organisms, separated by their cellular structure: prokaryotes and eukaryotes. Prokaryotes are made up of cells that do not have a nucleus. They are single-celled microorganisms, including bacteria, archaea and photosynthetic blue green algae, commonly known as cyanobacteria. All eukaryotes contain cells that have a nucleus. This huge category includes all plants, animals, protozoa (such as the parasite that causes malaria, Plasmodium falciparum) and fungi such as mushrooms, molds, and yeast.

Plasma Membrane

Whether they're prokaryotic or eukaryotic, all cells are surrounded by a thin bilayer of plasma membrane that prevents the contents of the cells from leaking out. The plasma membrane, also called cytoplasmic membrane, is made up of phospholipids and contains integral proteins embedded in its bilayer. The plasma membrane is responsible for controlling the transport of nutrients and electrolytes in and out of the cell. It is also responsible for cell to cell communication.

Cellular life is dependent completely on various chemical process for its survival. These chemical reactions mostly take place in a watery solution inside the cell called cytoplasm, or cytosol.


A prokaryotic cell is a single unit without any compartments. It consists of a plasma membrane covering the cytoplasm. In a prokaryotic cell, the plasma membrane contains the energy-producing machinery known as an electron transport chain (ETC).

Most prokaryotic cells have a cell wall made up of peptidoglycan surrounding the plasma membrane. Archaea are an exception; they have various other compositions of cell wall. Next, let's discuss the cellular structure of bacteria as an example of a prokaryote.

Bacteria: Cell Structure

The DNA (deoxyribonucleic acid) containing the bacteria's genetic material is condensed mostly in the center of the cell. Ribosomes are the protein synthesizing units of the cell that are dispersed in the cytoplasm in the DNA free region of the cell. Bacteria have granules, or inclusion bodies, that are complex molecules made up of lipids or sugars and they act as a reservoir of energy or structural building blocks.

Like most prokaryotes, they also have flagella, which are long and thin appendages attached to the outer surface of the cell membrane that provide motility to the cells. A group of bacteria called gram negative bacteria have an outer membrane made up of lipopolysaccharide (LPS) that protects them from the harsh environment. The outer membrane surrounds the cell wall of gram negative bacteria but is absent in gram positive bacteria.


Eukaryotic cells have various membrane-bound compartments, or organelles, dispersed in the cytosol. Let us find out more about these organelles in the eukaryotic cell:

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