2: Microbial Structure

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In the 17th century, observations of microscopic life led to the development of the cell theory: the idea that the fundamental unit of life is the cell, that all organisms contain at least one cell, and that cells only come from other cells. Despite sharing certain characteristics, cells may vary significantly. The two main types of cells are prokaryotic cells (lacking a nucleus) and eukaryotic cells (containing a well-organized, membrane-bound nucleus). Each type of cell exhibits remarkable variety in structure, function, and metabolic activity.

Viruses are not cells, but are biological entities with some similarities to cells. Viruses also have a wide variety of structures and replication strategies, but unlike cells they do not metabolize and require a host cell to replicate.

Chapter 2 BSC 3271 Learning Outcomes

Compare and contrast cellular (living) microbes, viruses, and prions based on their structures, genetic material, and mechanisms of replication.
Explain the difference between the terms prokaryotic and eukaryotic.
Compare and contrast "prokaryotic" (bacterial) cell structure with eukaryotic cell structure with respect to typical size, cell boundary, and presence/absence of various intracellular compartments.
Describe the function of the following major eukaryotic intracellular structures: ribosomes, mitochondria, nucleus, Golgi apparatus.
Describe the structural similarities between bacterial and eukaryotic plasma membranes
Recognize and apply the terms for bacterial cell morphologies and arrangements
Describe in words and sketch the important chemical and structural features of the bacterial peptidolycan, murein, incluing N-acetyl-muramic acid (NAM), N-acetyl-glucosamine (NAG), amino acids, and peptide crosslinks.
Explain the importance of peptide crosslinking in murein (peptidoglycan) structure
Compare and contrast (in words and diagrammatically) Gram-positive and Gram-negative cell envelopes including: peptidoglycan structure, teichoic acid, Braun's lipoprotein, lipopolysaccharide (and its components lipid A and O-side chains), outer membrane, plasma membrane, porins
Explain at the cellular/moelcular level why Gram-positive cells stain purple and Gram-negatives pink in the Gram stain (discussed in lab)
Name a genus of bacteria that naturally lacks a cell wall
Explain how the cell wall of Mycobacterium differs from other Gram-positive bacteria
Describe structure and function bacterial appendages outside the cell wall including: flagella, pili, fimbrae, and glycocalyx (slime layer, capsule).
Explain how bacterial cellular structures aid in the pathogenicity of some organisms. Discuss specifically: LPS (a.k.a LOS), capsules, fimbrae/pili, and endospores.
Describe the generalized structure of a viral particle including location and molecular make-up of genetic material, capsid, and envelope.
Recognize and identify the most common capsid shapes.
Provide two examples of the importance of protein folding and binding specificity in the replication of certain pathogens

2.1: Foundations of Modern Cell Theory
Although cells were first observed in the 1660s by Robert Hooke, cell theory was not well accepted for another 200 years. The work of scientists such as Schleiden, Schwann, Remak, and Virchow contributed to its acceptance. Endosymbiotic theory states that mitochondria and chloroplasts, organelles found in many types of organisms, have their origins in bacteria. Significant structural and genetic information support this theory. The miasma theory was widely accepted until the 19th century.
2.2: Shared Characteristics of Cell Structure
2.3: Unique Characteristics of Prokaryotic Cells
Prokaryotic cells differ from eukaryotic cells in that their genetic material is contained in a nucleoid rather than a membrane-bound nucleus. In addition, prokaryotic cells generally lack membrane-bound organelles. Prokaryotic cells of the same species typically share a similar cell morphology and cellular arrangement. Most prokaryotic cells have a cell wall that helps the organism maintain cellular morphology and protects it against changes in osmotic pressure.
2.4: Unique Characteristics of Eukaryotic Cells
Eukaryotic cells are defined by the presence of a nucleus containing the DNA genome and bound by a nuclear membrane (or nuclear envelope) composed of two lipid bilayers that regulate transport of materials into and out of the nucleus through nuclear pores. Eukaryotic cell morphologies vary greatly and may be maintained by various structures, including the cytoskeleton, the cell membrane, and/or the cell wall The nucleolus in the nucleus of eukaryotic cells is the site of ribosomal synthesis.
2.5: Viral Structue and Prions
Viruses are acellular, meaning they are biological entities that do not have a cellular structure. Therefore, they lack most of the components of cells, such as organelles, ribosomes, and the plasma membrane. They do, however, contain genetic material, protein, and are occasionally surrounded by a lipid layer.

Thumbnail: "File:Prokaryote cell.svg" by This vector image is completely made by Ali Zifan is licensed under CC BY-SA 4.0