Chapter 2 part 1 microbial cell structure and function PDF

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Chapter 2, part 1

Microbial Cell Structure and Function

I. II. III.

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Cells of Bacteria and Archaea 2.1 Cell Morphology 2.2 The Small World

2.1 Cell Morphology – REVIEW ON OWN Morphology refers to cell shape Major morphologies of prokaryotic cells (Figure 2.1) coccus (pl. cocci): spherical or ovoid rod/bacillus: cylindrical spirillum: curved or spiral Some stay grouped/clustered after cell division in characteristic arrangements (e.g., chains of Streptococcus, cubes of Sarcina, grapelike clusters of Staphylococcus). Cells with unusual shapes spirochetes (tightly coiled), appendaged bacteria, and filamentous bacteria Many variations on basic morphological types known

2.1 Cell Morphology • Morphology typically does not predict physiology, ecology, phylogeny, or other properties of a prokaryotic cell. • May be selective forces involved in setting the morphology

• optimization for nutrient uptake (small cells and high surface-to-volume ratio, such as appendaged cells) • swimming motility in viscous environments or near surfaces (helical or spiral-shaped cells) gliding motility (filamentous bacteria) The Small World • Size range for prokaryotes: 0.2 µm to >700 µm in diameter, most cultured rod-shaped bacteria are between 0.5 and 4.0 µm wide and 600 µm in diameter • examples of very large prokaryotes:

Epulopiscium fishelsoni

Thiomargarita namibiensis

The Small World • Surface-to-volume ratios

Prokaryotes do not have a well defined cytoskeletal system to traffic things through the cell. What this means is that they are constrained by the rates of diffusion to get things to where they are needed in the cell. As such, having a higher surface to volume ratio is advantageous as substances have much smaller distances to diffuse once in the cell. We can see that by increasing the radius of a cell by 1 um decreases the surface area to volume ration by half. As such most prokaryotic cells have remained small.

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Advantages to being small…… more surface area relative to cell volume than large cells ( i.e., higher S/V ratio). support greater nutrient and waste product exchange per unit cell volume tend to grow faster than larger cells Mutations lead to faster evolution. Eukaryotic cells adapt slower.

Adaptations to being a big prokaryote. Epulopiscium has many genomes arrayed around periphery of cell. Allows organisms to make proteins right where they are needed so can overcome constraints of diffusion

Thiomargarita has a huge sulfur vacuole which pushes the cytoplasm close to the surface of the cell so things never have to diffuse far.

2.2 The Small World • • • • •

Lower limits of cell size Cellular organisms...