micro sheet #2

View previous topic View next topic Go down

micro sheet #2

Post by Ibrahim A.R Al-Omari on 22/10/2010, 2:29 pm

http://www.mediafire.com/?xhatek5v17rw05h


In this course we are concerned with the bacteria that cause human diseases so
Medically important bacteria range in size( 0.5 – 2 )micron, surface area of about 12 micron^2 ,and it's volume is only 4 micron^3 so the surface area to volume is 3:1 (it's very large compare to the ratio of the Eukaryotes cells ) this is so important because the bacteria absorb their nutrients from their surface and it's very efficient
Bacteria don’t have anything in their cytoplasm but DNA and ribosomes (the other organelles that are missing are replaced by other structures that take their place)
Now we well talk about its shape and arrangement #
Bacteria have deferent shapes , sizes , and arrangements
Now shapes of bacteria :
I. Spherical shape (cocci): because they are spherical they can be arranged : 1-adjacent to each other in a chain and then they are called streptococci (strepto=زي المسبحة),or 2-can be arranged haphazardly in a cluster form and here they are called staphylococci (staphyl=cluster). they they can be arranged in other ways but we are not concerned with here
II. Rod shape (bacilli): they can also be arranged in a chain, here they are called streptobacilli. Or they can be singles (not arranged with each other)
III. Coccobacilli: a shape that fits neither coccus nor bacillus but something in between.
IV. Dipiro shape (dipiro=شكل الفاصلة):like cholera bacteria
V. Spiral shape : are either in the form :
1- spirillium 2-spirochete
VI. And there are other arrangement like star arrangement
The palns of division determine the arrangement of the bacteria (sterpto or styphilo or …)
* If bacteria multiply in same plane of division, they form diploes or chains (chains are formed if bacteria remain attached to each other)
*If bacteria multiply in two planes of division they form tetrad
*If bacteria multiply in more than two planes of division, they form
Clusters

Now we well talk about Bacterial Structures#
It contains - starting from outside-in(this structures are not found in all bacteria) :
• Flagella : an organ for movements , for motile organisms..this organ is lacking in non-motile ones ,the number of flagella varies so the speed of motility varies between bacteria
• Pili : are smaller, utilized for attachment(fimbria ) & conjugation(pili) in microorganisms ."مو متأكد من توزيع الاسماء على الوظائف"
• Capsule :not all bacteria have capsule .
• Cell wall: its characteristic to all prokaryotes , and there is one kind of bacteria lake the cell wall which is microplasma
• Plasma membrane: a typical cytoplasmic membrane
• Cytoplasm: contains DNA(double stranded , circular , and with no membrane ) ,ribosomes ( they decrease in number in dividing bacteria "am not sure" ) , and inclusion Bodies (contain nutrient)
• spores: found in some bacteria

*Pili and flagella are known an appendages

#Now we will talk about THE CAPSULE
Capsule is better called Extracellular Polymeric Substance (EPS) (In this sheet I will write EPS instead of capsule but it is the same thing because it's better to call it like that )
It composed in all bacteria of polysaccharide excepted bacillus(exp:Bacillus anthracis that cause anthracis) it composed of protein (glutamic acid)






*Now the ESP have different names :
1-slime :
If the EPS is in huge amount and it's made of polysaccharide it's called slime (مخاط) and in this case and the bacteria appears like swimming in this slime
2- Glycocalyx:
If the EPS is in small amount of polysaccharide and it's meshfibrin surround all and loosely attached to the organism around called Glycocalyx

*EPS is an antigen , it makes an antibody aginste it , so it can be used as vaccine or make an antibodies to identify the organism in the lab(note if the capsule is not found in the organism other structure make the antigens )
*EPS is a virulence , that’s mean if the organism is capable of causing disease we call it pathogenic if it's not it called not pathogenic , the pathogenic organisms can be differentiated by virulence … the more the harm it can cause the more the virulence , and the EPS increase the virulence of the organism … why ?? because the EPS is anti phagocytic (prevent phagocytosis) and phagocytosis is a major defiance system in the body
*EPS cannot be stained by ordinary stain like gram
*EPS is not necessary for the survival of the organism so there is a bacteria without an EPS , and if we culture the bacteria for a long time it loose it's EPS so one of the way to decrease the virulence is by culturing the bacteria until it loose it's ESP
*EPS gives the smooth appearance to the colony
*there is no gene for making the EPS but there is for the enzyme the polymerize the sugar to make the EPS, this gene could be glucosyl transferases which polymerizes glucose resulting in D-glucose(dextrans) , and fructosyl transferases resulting in L-glucose (levans) . So the polysac. is either D- or L depending on the enzyme
*the capsule is important to adhere to surfaces ,like to adhere to each other and surfaces (like Streptococcus mutans adhere enamel , then replicate and
produce acid which causes destruction of the tooth enamel .)
*we don’t have an agent that prevent capsule formation in organisms

#Cell wall :
*it gives the bacteria its shape
*It's mainly made of peptidoglycan layers that gives the cell wall it's rigidity
• Peptidoglycans are known as mucopeptide & murein.

* the osmotic pressure difference between the inner intracellular membrane and the extra cellular environment is 5-20 times (so it's hyper tonic ) so without the cell-wall the cell will burst , so many medicines work on destroying this cell-wall to kill the organism >>> the bacteria they must have cell-wall or live in a hypertonic environment to survive (like the bacteria that live in the joints "a hypertonic environment")

# bacteria classified on the base of their response to gram stain into two major categories ( gram +ve and gram –ve)
*how we use it :
We put the stain on the bacteria an both gram +ve and –ve become crystal violet , then we put a depolarizing agent acid-alcohol or acetone-alcohol , now some cells loses their color (gram –ve) and some keep (gram +ve), then we add a counter stain (red stain ) now gram –ve will appear red and gram +ve will stay violet

* the different between gram positive and gram negative :
 Gram + bacteria :
1. have thicker cell wall(40 or more layers) , that makes a significant portion of the dry weight of the bacterial cell.These bacteria are stained blue or violet by Gram staining.
2. the cell wall is made up of :
 A great amount of the peptidoglycan layer.
 Teichoic acid (if phosphate is limited
teichoronic acid will be produced)
This acid is of 2 types :
• water -teichiod acid >> present in
peptidoglycan.
• lipoteichoic acid >> that attaches to the
glycolipids of the cellular membrane.
differentiate between them.
• The function of this acid is to provide the cell
with Mg.
 Polysaccharides of unknown function.
 Periplasmic space which is a limited space, it‘s the
site that contains enzymes necessary for the
survival of the organism (for metabolism) , these
are transferases to transfer solutes into cell or
synthesized to build the cell membrane.
The periplasmic space is more prominent in Gram
neg. bacteria , that’s why Gram neg. is more
resistant to antimicrobial agents.

 Gram- bacteria :
1. have thin cell wall (1-5 layers) that make an
insignificant portion of the cell weight , but still
sufficient to provide its function.
2. the layers ,that are missing , are replaced by
periplasmic space & other structures .
3. the cell wall is made up of :
• an outer membrane : is unique (only in bacteria>>
the outer leaflet is made of lipopolysac. & the
inner part is a typical phospholipids layer) . this
membrane acts as a permeable barrier, it can
extrude detrimental agents like antibiotics & bile
salts to protect the organism ,this ability varies
between Gram neg. bacteria .
• Lipoprotein : which is the most abundant protein in
Gram(-) bacteria . it anchors the peptidoglycan to
the outer membrane, so it anchors the cell
envelope.
• Periplasmic space : is a significant structure,
contains enzymes necessary for metabolism and
survival of gram(-) bacteria .

• The peptidoglycan layer : has a function similar to
that in gram+ bacteria ( integrity & poren protein
for the selective permeability and the entrance of
nutrients ).

• Peptideglycan of the cell wall has three structures :
1. the back bone structure ( the same in all bacteria)
made up by alternative amino sugars
 N- acetylglucosamine . (NAG)
 N-acetylmuramic acid. (NAM)
2. the tetra peptide ( side chain): is not the same in all
bacteria ,the difference is in a.a no. 3 (which varies
between organisms & used to connect to a second
alternative sugar by the pent peptide).
3. the cross bridges (made up by 5 a.a ”penta peptide”
that crosses one back bone to the other ) these are Dform
a.a not L- form  D- is harder to break.
5
These 3 structures connect to each other to make a
meshwork that keeps the integrity.



Micro sheet number 2
Sorry for any mistakes and being late
Good luck for all
avatar
Ibrahim A.R Al-Omari

عدد المساهمات : 72
النشاط : 1
تاريخ التسجيل : 2009-09-06
العمر : 27

Back to top Go down

View previous topic View next topic Back to top

- Similar topics

 
Permissions in this forum:
You cannot reply to topics in this forum