Introduction to Bacteria: Videos & Practice Problems

Bacteria and archaea are both prokaryotic organisms, meaning they lack a nucleus. However, they have several key differences. Bacteria typically have cell walls made of peptidoglycan, whereas archaea do not. Instead, archaea have unique cell wall compositions that can include pseudopeptidoglycan. Additionally, the lipid composition of their cell membranes differs; bacteria have ester-linked lipids, while archaea have ether-linked lipids. Genetically, archaea share more similarities with eukaryotes in terms of their replication, transcription, and translation processes. Furthermore, archaea often thrive in extreme environments, such as high temperatures or high salinity, whereas bacteria are found in a wider range of habitats.

Bacteria reproduce primarily through a process called binary fission. In binary fission, a single bacterial cell, or bacterium, duplicates its genetic material and then divides into two identical daughter cells. The process begins with the replication of the bacterial chromosome. Once the chromosome is replicated, the cell elongates, and the two chromosomes are separated to opposite ends of the cell. A septum, or dividing wall, forms in the middle of the cell, eventually splitting the cell into two separate, genetically identical cells. This method of reproduction allows bacteria to multiply rapidly under favorable conditions.

The human microbiota refers to the community of microorganisms, including bacteria, that inhabit various parts of the human body, such as the skin, mouth, gut, and other mucosal surfaces. These microorganisms play crucial roles in maintaining health by aiding in digestion, producing essential vitamins, and protecting against pathogenic microbes. The balance of the microbiota is important for immune system function and overall health. Disruptions to this balance, known as dysbiosis, can lead to various health issues, including infections, inflammatory diseases, and even metabolic disorders. Understanding the human microbiota is essential for developing new therapeutic strategies.

Bacteria exhibit a variety of shapes, which are often used to help identify and classify them. The three main shapes are: 1) Cocci: These are spherical or oval-shaped bacteria. Examples include Streptococcus and Staphylococcus. 2) Bacilli: These are rod-shaped bacteria. Examples include Escherichia coli and Bacillus anthracis. 3) Spirilla: These are spiral or corkscrew-shaped bacteria. Examples include Spirillum and Vibrio cholerae. Each shape can have variations, and some bacteria can change shape depending on environmental conditions. The shape of a bacterium can influence its mobility, how it interacts with its environment, and its ability to cause disease.

Peptidoglycan is a complex polymer that forms a mesh-like layer outside the plasma membrane of most bacteria, providing structural support and shape. It is composed of sugars and amino acids, creating a strong, rigid structure. Peptidoglycan is crucial for maintaining the integrity of the bacterial cell wall, protecting against osmotic pressure and environmental stress. It is also a target for antibiotics, such as penicillin, which inhibit peptidoglycan synthesis, leading to cell lysis and death. The presence of peptidoglycan is a key feature distinguishing bacteria from archaea, which do not have peptidoglycan in their cell walls.