Chapter 3: Microscopy and Cell Structure

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Typical Bacterial Shapes Also Pleomorphic Bacteria, which vary in their shape (e.g., Corynebacterium).

Typical Bacterial Arrangements streptococci sarcina staphylococci

Prokaryotic Cell Structures

Typical Prokaryotic Cell

Movement across membrane for many substances is controlled by membrane proteins. Escherichia coli has >200 membrane proteins. Many of these proteins are involved in transport across membranes. Others of these proteins allow a bacterium to sense its surrounding environments (e.g., as in chemotaxis). Movement is via: Simple Diffusion (including osmosis) Facilitated Diffusion (with concentration gradient & no energy expended) Active Transport (against concentration gradient & energy expended) Cytoplasmic Membrane

Simple Diffusion -- Osmosis solute molecules/ions Simple Diffusion -- Osmosis

Cytoplasmic Membrane

Protein-Mediated Transport

Active Transport

The Prokaryotic Cell Wall

The Prokaryotic Cell Wall Determines cell shape. In some cases recognized by host immune system. Prevents osmotic lysis. Target for antibiotics. In Bacteria, composed of Peptidoglycan. Part of cell envelope.

Gram-Pos vs. Gram-Neg.

Gram-Positive Cell Envelope

Gram-Negative Cell Envelope endotoxin Gram-Negative Cell Envelope cell wall

Gram-Negative Cell Envelope LPS: Protection from antibiotics such as penicillin plus against certain toxins. Periplasm: Site of preliminary nutrient degradation.

Lipopolysaccharide (LPS) Carbohydrate has negative charge and provides protection against some antibiotics & some toxins (e.g., detergents). Lipopolysaccharide (LPS) Lipid A = Endotoxin

Mycoplasma lack Cell Walls Note: Pleomorphic Mycoplasma lack Cell Walls Mycoplasma pneumoniae causes “Walking Pneumonia”

Protection (e.g., Streptococcus pneumoniae from phagocytosis) Glycocalyx Attachment (e.g., Streptococcus mutans causing dental plaques)

Capsule Staining Capsules are more regular and gelatinous. Slime Layers are less regular and more diffuse.

Bacteria Flagella (plural)

Flagellar Arrangements Polar Flagellum Flagellar Arrangements e.g., E. coli also “atrichous”

Also Phototaxis, etc. Chemotaxis

Pili (sing. Pillus)

Fimbriae (a kind of pilli) Tips are Adhesins, used to adhere, e.g., to animal tissues

Closed Circular Chromosome Also Plasmids, which are smaller, circular pieces of DNA. Plasmids usually encode expendable functions, e.g., antibiotic resistance.

Ribosomes: Sites of Translation On order of 10,000 per cell!

Endospores Form inside of vegetative cells (hence “endo”). Characteristic of many soil bacteria, e.g., Bacillus spp. & Clostridium spp. Endospores Highly resistant to heat, U.V., desiccation, etc.

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