Chapter 3:Microscopy andCell Structure

Important Point:

Typical Bacterial Shapes

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

Typical Bacterial Arrangements

streptococci

sarcina

staphylococci

ProkaryoticCell Structures

Typical Prokaryotic Cell

Cyt

opla

smic

Mem

bran

e 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)

Sim

ple

Diff

usio

n --

Osm

osis

solute molecules/ions

Cyt

opla

smic

Mem

bran

e

Pro

tein

-Med

iate

d T

rans

port

Act

ive

Tra

nspo

rt

The Prokaryotic Cell Wall

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.

Gram-Pos vs. Gram-Neg.

Gram-Positive Cell Envelope

Gra

m-N

egat

ive

Cel

l Env

elop

e

cell wall

endotoxin

Gram-Negative Cell Envelope

Periplasm: Site of preliminary

nutrient degradation.

LPS: Protection from antibiotics such as

penicillin plus against certain toxins.

Lipo

poly

sacc

harid

e (L

PS

)

Lipid A = Endotoxin

Carbohydrate has negative charge and provides protection

against some antibiotics & some

toxins (e.g., detergents).

Mycoplasma

lack

Cel

l Wal

lsNote:

Pleomorphic

Mycoplasma pneumoniae causes “Walking Pneumonia”

Gly

coca

lyx

Protection (e.g., Streptococcus

pneumoniae from phagocytosis)

Attachment (e.g., Streptococcus

mutans causing dental plaques)

Cap

sule

Sta

inin

gCapsules are more

regular and gelatinous.

Slime Layers are less regular and

more diffuse.

Bacteria Flagella (plural)

Fla

gella

r A

rran

gem

ents

also “atrichous”

e.g., E. coli

Polar Flagellum

Che

mot

axis

Also Phototaxis,

etc.

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!

End

ospo

res

Form inside of vegetative cells (hence “endo”).

Highly resistant to heat, U.V.,

desiccation, etc.

Characteristic of many soil bacteria, e.g., Bacillus spp. & Clostridium spp.

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