Typical Prokaryotic CellTypical Prokaryotic Cell

ProkaryoticProkaryoticCell Cell StructuresStructures

Functions of Cell Functions of Cell MembraneMembrane

1. Selective barrier (selectively 1. Selective barrier (selectively permeable)permeable)

2. Secretes exoenzymes2. Secretes exoenzymes amylasesamylases lipaseslipases peptidasespeptidases

Functions of Cell Functions of Cell MembraneMembrane

3. E.T.S. is located here3. E.T.S. is located here 4. Enzymes for cell wall synthesis4. Enzymes for cell wall synthesis 5. If photosynthesis, enzymes are located 5. If photosynthesis, enzymes are located

on membranous structures called on membranous structures called thylakoidsthylakoids

6. Mesosomes - invagination of cell 6. Mesosomes - invagination of cell membrane attached to DNA membrane attached to DNA (Binary (Binary Fission)?Fission)?

Cyt

opla

smic

Mem

bran

eC

ytop

lasm

ic M

embr

ane

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 - O

smos

isSi

mpl

e D

iffus

ion

- Osm

osis

Cyt

opla

smic

Mem

bran

eC

ytop

lasm

ic M

embr

ane

Prot

ein-

Med

iate

d Tr

ansp

ort

Prot

ein-

Med

iate

d Tr

ansp

ort

Act

ive

Tran

spor

tA

ctiv

e Tr

ansp

ort

The Prokaryotic Cell WallThe 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.

Cell WallCell Wall Main structural component - Main structural component -

PeptidoglycanPeptidoglycan

PeptidoglycanPeptidoglycan repeating dissacharide unitsrepeating dissacharide units polypeptidespolypeptides

Gram-Pos vs. Gram-NegGram-Pos vs. Gram-Neg

Budowa mureinyBudowa mureiny

Budowa mureinyBudowa mureiny

Gram-Positive Cell Gram-Positive Cell EnvelopeEnvelope

Gra

m-N

egat

ive

Cell

Gra

m-N

egat

ive

Cell

Enve

lope

Enve

lope

cell wall

endotoxin

Gram-Negative Cell Gram-Negative Cell EnvelopeEnvelope

Periplasm: Site of preliminary

nutrient degradation.

LPS: Protection from antibiotics such as

penicillin plus against certain toxins.

Lipo

poly

sacc

hari

de

Lipo

poly

sacc

hari

de

(LPS

)(L

PS) Lipid A =

Endotoxin

Carbohydrate has negative charge and provides protection

against some antibiotics & some

toxins (e.g., detergents).

Myc

oplasm

aMyc

oplasm

a la

ck C

ell

lack

Cel

l W

alls

Wal

lsNote:

Pleomorphic

Mycoplasma pneumoniae causes “Walking Pneumonia”

Prokaryotic Cell StructureProkaryotic Cell Structure Glycocalyx - term to describe substances Glycocalyx - term to describe substances

that surround bacterial cellsthat surround bacterial cells 1. Capsule1. Capsule

if substance is organized and firmly attached if substance is organized and firmly attached to cell wallto cell wall

2. Slime Layer2. Slime Layer if substance is unorganized and loosely if substance is unorganized and loosely

attached to cell wallattached to cell wall

Function of Capsule

1. Contribute to Virulence of bacteria by preventing phagocytosis by WBC’s

A. Streptococcus pneumoniae

B. Bacillus anthracis

Functions of CapsulesFunctions of Capsules

2. Prevents drying out or dessication2. Prevents drying out or dessication

3. Allows bacteria to adhere to various 3. Allows bacteria to adhere to various surfacessurfaces Streptococcus mutans - Streptococcus mutans - enamel on teeth to enamel on teeth to

cause dental carriescause dental carries Klebseilla pneumoniaeKlebseilla pneumoniae - attaches to - attaches to

respiratory tractrespiratory tract

Gly

coca

lyG

lyco

caly

xxProtection (e.g.,

Streptococcus pneumoniae from

phagocytosis)

Attachment (e.g., Streptococcus

mutans causing dental plaques)

Caps

ule

Caps

ule

Stai

ning

Stai

ning

Capsules are more regular and gelatinous.

Slime Layers are less regular and

more diffuse.

Flag

ella

r Fl

agel

lar

Arra

ngem

ents

Arra

ngem

ents

also “atrichous”

e.g., E. coli

Polar Flagellu

m

Chem

otax

Chem

otax

isisAlso

Phototaxis, etc.

Fimbriae (a kind of Fimbriae (a kind of pilli)pilli)

Tips are Adhesins, used to adhere, e.g.,

to animal tissues

MotilityMotility Almost all Almost all SpiralSpiral bacteria arebacteria are motilemotile

About 1/2 ofAbout 1/2 of BacilliBacilli areare motilemotile

Almost allAlmost all Cocci Cocci are are non-motilenon-motile

Axial Filament - found only in spirochetes (flexible spirals)

Treponema pallidum

FimbriaeFimbriae Filamentous appendages that are Filamentous appendages that are

shorter, straighter and more numerous shorter, straighter and more numerous that flagellathat flagella

found mostly in Gram (-) Bacteriafound mostly in Gram (-) Bacteria

used for attachment not motilityused for attachment not motility

E. coli (pathogenic)

Nuclear area (nucleoid)Nuclear area (nucleoid) 1 circular chromosome (ccDNA)1 circular chromosome (ccDNA) attached to a mesosomeattached to a mesosome

segragation of DNA during Binary Fissionsegragation of DNA during Binary Fission

PlasmidsPlasmids Small circular, extra-chromosomal pieces Small circular, extra-chromosomal pieces

of DNAof DNA 5 to 100 genes 5 to 100 genes Code for auxiliary metabolic functions:Code for auxiliary metabolic functions:

antibiotic resistanceantibiotic resistance penicillasepenicillase

production of toxinsproduction of toxins E. coliE. coli 0157:H7 0157:H7

Ribosomes - Ribosomes - protein protein synthesissynthesis

Prokaryotic RibosomeProkaryotic Ribosome

70 S70 S 50 S50 S 30 S30 S

Eukaryotic Eukaryotic RibosomesRibosomes

80 S80 S 60 S60 S 40 S40 S

Selective ToxicitySelective Toxicity Some antibiotics are aimed at the 70 S Some antibiotics are aimed at the 70 S

ribosomes of bacterial cellsribosomes of bacterial cells

Streptomycin, Neomycin, Erythromycin Streptomycin, Neomycin, Erythromycin and Tetracycline work by inhibiting and Tetracycline work by inhibiting protein synthesis by disrupting the 70 S protein synthesis by disrupting the 70 S ribosomeribosome

Endospores - Endospores - formed under formed under periods of environmental periods of environmental stressstress

Only found in Gram (+) BacteriaOnly found in Gram (+) Bacteria BacillusBacillus

Bacillus cereusBacillus cereus Bacillus anthracisBacillus anthracis

ClostridiumClostridium Clostridium tetaniClostridium tetani Clostridium botulinumClostridium botulinum Clostridium perfringensClostridium perfringens

EndosporesEndospores Extremely resistant to heat, cold, Extremely resistant to heat, cold,

chemicals, lack of water, etc.chemicals, lack of water, etc.

Most vegetative bacterial cells are killed Most vegetative bacterial cells are killed at temps. above 70 C (160 F)at temps. above 70 C (160 F) Endospores can survive boiling water for several hours (some Endospores can survive boiling water for several hours (some

for as long as 20 hours)for as long as 20 hours)

EndosporesEndospores Spores can remain viable for weeks, Spores can remain viable for weeks,

months, yearsmonths, years Thermoactinomyces vulgarisThermoactinomyces vulgaris

spores found in Minnesota were 7,500 spores found in Minnesota were 7,500 years old and still germinatedyears old and still germinated

Endo

spor

Endo

spor

esesForm 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.