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Microscopy and

Cell Structure

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Typical Bacterial Shapes

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

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Typical Bacterial Arrangements

streptococci

sarcina

staphylococci

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Prokaryotic

Cell Structures

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Typical Prokaryotic Cell

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CytoplasmicM

embra

ne

Movement across membrane for many substancesis controlled by membrane proteins.

Escherichia colihas >200 membrane proteins. Many of these proteins are involved in transport

across membranes.

Others of these proteins allow a bacterium to senseits surrounding environments(e.g., as in chemotaxis). Movement is via:

Simple Diffusion (including osmosis)

Facilitated Diffusion (with concentrationgradient & no energy expended)

Active Transport (against concentrationgradient & energy expended)

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SimpleDiffusion

--Osmosis

solute

molecules/ions

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CytoplasmicM

embra

ne

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Protein-

Mediate

dTransport

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ActiveTra

nsport

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The Prokaryotic Cell Wall

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The Prokaryotic Cell Wall

Determines cell

shape.

Prevents osmotic

lysis.

In some cases

recognized by host

immune system.

Target for

antibiotics.

Part of cell

envelope.

In Bacteria,composed of

Peptidoglycan.

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Gram-Pos vs. Gram-Neg.

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Gram-Positive Cell Envelope

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Gram-NegativeC

ellEnvelope

cell wall

endotoxin

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Gram-Negative Cell Envelope

Periplasm: Site

of preliminary

nutrientdegradation.

LPS: Protection from

antibiotics such as

penicillin plus againstcertain toxins.

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Lipopo

lysaccha

ride(LPS)

Lipid A =Endotoxin

Carbohydrate has

negative charge andprovides protection

against some

antibiotics & some

toxins (e.g.,

detergents).

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Mycoplasmalac

kCellWalls

Note:Pleomorphic

Mycoplasma pneumoniae causesWalking Pneumonia

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Glycocalyx

Protection (e.g.,

Streptococcuspneumoniae from

phagocytosis)

Attachment (e.g.,

Streptococcus

mutans causing

dental plaques)

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Ca

psuleStaining

Capsules are moreregular and

gelatinous.

Slime Layers are

less regular and

more diffuse.

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Bacteria Flagella (plural)

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Flage

llarArra

ngemen

ts

also atrichous

e.g.,E. coli

Polar

Flagellum

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Chemot

axis

Also

Phototaxis,etc.

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Pili (sing. Pillus)

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Closed Circular Chromosome

Also Plasmids, which are

smaller, circular pieces of

DNA.

Plasmids usually

encodeexpendablefunctions, e.g.,

antibiotic

resistance.

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