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Chapter 3: Microscopy and Cell Structure

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1 Chapter 3: Microscopy and Cell Structure

2 Important Point: If you are having trouble
understanding lecture material: Try reading your text before attending lectures. And take the time to read it well!

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

4 Typical Bacterial Arrangements
streptococci sarcina staphylococci

5 Prokaryotic Cell Structures

6 Typical Prokaryotic Cell

7 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

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

9 Cytoplasmic Membrane

10 Protein-Mediated Transport

11 Active Transport

12 The Prokaryotic Cell Wall

13 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.

14 Gram-Pos vs. Gram-Neg.

15 Gram-Positive Cell Envelope

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

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

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

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

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

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

22 Bacteria Flagella (plural)

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

24 Also Phototaxis, etc. Chemotaxis

25 Pili (sing. Pillus)

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

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

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

29 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.

30 Link to Next Presentation

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