Bacteria are prokaryotic microorganisms found in nearly every habitat on Earth, including within and on the human body. As prokaryotes, their genetic material (DNA) is not housed within a true nucleus. Most bacterial cells feature cell walls containing peptidoglycan. While many bacteria are harmless or beneficial, some act as pathogens and cause diseases in humans and other animals.

Bacteria

Photosynthesis is the process of using the sun's light as energy and converting it to chemical energy to fix gaseous carbon dioxide and create sugars such as glucose. The first organisms with the capability to photosynthesize stemmed from prokaryotes 3.8 billion years ago. What is required for photosynthesis include a light source, carbon, electron donor, and pigments to harvest energy.

Photosynthesis

Bacteria is a very diverse domain, characterized by their prokaryotic cells and lack of ether linkages, with membranes made of phospholipid bilayers.

Bacteria (domain)

Archaea are unicellular prokaryotic organisms that have distinct evolutionary histories, genetics, metabolic pathways, and structural compositions compared to bacteria. They are found in nearly every habitat, including extreme environments that are very cold, hot, basic, or acidic. While some archaea reside in the human body, none have been identified as human pathogens.

Archaea

The cell envelope is a collective term for the structural layers that enclose the cytoplasm and internal components of a cell. In prokaryotic organisms, the precise composition of the cell envelope varies depending on the species and cell type, but it universally includes a plasma membrane and, in the vast majority of cases, a surrounding cell wall.

Cell Envelope

A prokaryotic cell is a major category of cell that lacks a nucleus surrounded by a complex nuclear membrane. Instead, its genetic material is generally a single, circular chromosome located in a nucleoid region. While prokaryotic cells generally lack complex membrane-bound organelles, they often contain inclusions that compartmentalize their cytoplasm. Microorganisms composed of these cells are classified within the domains Archaea and Bacteria.

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Classification of Pathogenic Microorganisms

Although cells share certain fundamental characteristics, they exhibit remarkable variety in their structure, function, and metabolic activity. The two primary categories of cells are prokaryotic cells, which lack a nucleus, and eukaryotic cells, which possess a well-organized, membrane-bound nucleus.

Types of Cells

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At the simplest level of construction, all cells possess a few fundamental components despite varying significantly in size, shape, structure, and function. These components include a cytoplasm (a gel-like substance composed of water and dissolved chemicals needed for growth), a plasma membrane (also called a cell membrane or cytoplasmic membrane) that contains the cytoplasm, one or more chromosomes containing the genetic blueprints of the cell, and ribosomes which are organelles used for the production of proteins.

Fundamental Components of Cells

Prokaryotic Cell

Eukaryotic cells are defined by the presence of a nucleus surrounded by a complex nuclear membrane and membrane-bound organelles in the cytoplasm, which are supported and held in place by an internal cytoskeleton. These cells, which can exist as independent, single-celled microorganisms or as part of multicellular organisms (comprising protozoans, algae, fungi, plants, and animals), feature plasma membranes structured as a bilayer consisting of ester-linked, straight-chain fatty acids and sterols, and they contain multiple, linear chromosomes associated with histones.

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