Typical Prokaryotic Cell. Prokaryotic Cell Structures.
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Transcript of Typical Prokaryotic Cell. Prokaryotic Cell Structures.
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
op
lasm
ic M
emb
ran
eC
yto
pla
smic
Mem
bra
ne
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
Dif
fusi
on
- O
smo
sis
Sim
ple
Dif
fusi
on
- O
smo
sis
Cyt
op
lasm
ic M
emb
ran
eC
yto
pla
smic
Mem
bra
ne
Pro
tein
-Med
iate
d T
ran
spo
rtP
rote
in-M
edia
ted
Tra
nsp
ort
Act
ive
Tra
nsp
ort
Act
ive
Tra
nsp
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
eg
ati
ve C
ell
Gra
m-N
eg
ati
ve C
ell
En
velo
pe
En
velo
pe
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.
Lip
op
oly
sacch
ari
de
Lip
op
oly
sacch
ari
de
(LP
S)
(LP
S) Lipid A =
Endotoxin
Carbohydrate has negative charge and provides protection
against some antibiotics & some
toxins (e.g., detergents).
Mycoplasma
Mycoplasma lack C
ell
lack C
ell
Walls
Walls
Note: 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
cocaly
Gly
cocaly
xxProtection (e.g.,
Streptococcus pneumoniae from
phagocytosis)
Attachment (e.g., Streptococcus
mutans causing dental plaques)
Cap
su
le
Cap
su
le
Sta
inin
gS
tain
ing
Capsules are more regular and gelatinous.
Slime Layers are less regular and
more diffuse.
Fla
gellar
Fla
gellar
Arr
an
gem
en
tsA
rran
gem
en
ts
also “atrichous”
e.g., E. coli
Polar Flagellu
m
Ch
em
ota
xC
hem
ota
xisis
Also 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
En
dosp
or
En
dosp
or
es
es
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.