Typical Prokaryotic Cell
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Transcript of Typical Prokaryotic Cell
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)
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-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
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
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
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