3. Cell Walls Flashcards
All bacteria except the ______ have a cell wall
mycoplasms
Bacteria cell walls can be divided into three types: _____, _____, and _____
Gram +, Gram -, and Acid Fast
Gram + bacteria stain a _____ color
purple
Gram - bacteria stain a _____ color
pink
Acid fast + bacteria stain ____
red
non-acid fast bacteria stain ____
blue
In a gram + cell wall, there is a thick layer of peptidoglycan over the _____
cell membrane
Peptidoglycan is a peptide of _____
sugars
Peptidoglycan is composed of two sugars: ______ and ____, they are linked together in alternating units
N-acetyl glucosamine and N-acetyl muramic acid
Each N-acetylmuramic acid molecule is attached to a chain of ___ amino acids
4
In Gram - organisms, a _____ ______ is a covalent bond between the 3rd amino acid on an N-acetyl muramic acid residue on one chain and the 4th amino acid of an N-acetyl muramic acid residue of another chain
direct crosslink
Gram + organisms do not use a direct crosslink. They use an ______ which is usually composed of glycine.
interbridge
A pentaglycine interbridge is a series of __ amino acids (glycine) which link together the 3rd amino acid on an N-acetyl muramic acid residue on one chain and the 4th amino acid of an N-acetyl muramic acid residue of another chain.
5
up to 90% of a gram + cell wall is _____, they can have up to 25 layers of this substance.
peptioglycan
_____ and ____ acids are interspersed with the peptidoglycan
teichoic and lipotechoic
_______ extends all the way through the peptidoglycan layer and into the cell membrane
lipotechoic acid (LTA)
______ do not extend into the membrane.
teichoic acids
Both lipotechoic acid (LTA) and teichoic acids are usually involved in ______ to cells in the body during infection.
attachment
In a Gram - , the inner membrane is the _______
cell membrane
In a Gram -, the ______ is the space between the inner and outer membranes
periplasm
a very thin _______ layer is in the periplasmic space
peptidoglycan
Gram - peptidoglycan connects via ____
direct crosslinks
In gram- organisms only ____ of the cell wall is peptidoglycan
10%
in a gram -, there are many _____ which exist between the two membranes
periplasmic proteins
in a gram -, _______ bind to molecules from the environment allowing bacteria to detect what chemicals are nearby
receptor proteins
in a gram-, ________ carry molecules across the periplasm both into and out of the cell
transport proteins
in a gram -, the outer layer of phospholipids always contains some ____. Different bacteria have different amounts but all Gram negative bacteria have some.
lipopolysaccharide (LPS)
In a gram -, in some bacteria, _____ replaces all of the phospholipids in the outer layer of the outer membrane.
LPS
Lipid A is fatty acids linked to an ______ (not glycerol as would be found in normal membrane phospholipids)
N-acetyl glucosamine phosphate
Lipid A can insert into the membrane in place of a ____ since it has the same general structure (hydrophilic head, and hydrophobic tail made of fatty acids)
phospholipid
LPS is also called ____ because of its damaging effects on animals. the primary mechanism of release of endotoxin is autolysis; after bacterial cells die, they break open releasing endotoxin
endotoxin
living bacteria release endotoxin by ____ (releasing small portions of the outer membrane)
blebbing
the presence of large amount of released endotoxin, particularly in the blood, causes ______ (also known as Gram negative sepsis)
endotoxic shock
There are approximately ______ cases of Gram-negative sepsis in the US each year. because most patients are already debilitated in these settings, the mortality rate from Gram - sepsis is very high (about 50% of patients die)
400,000
the disease known as ______ causes fever, chills, dehydration, extremely low blood pressure, increased heart rate, inflammation, liver failure, multiple organ failure, and eventual death
Gram - sepsis
Lipid A is essentially the same in all _____ bacteria
Gram -
core polysaccharide, branched polysaccharide chain containing ______ sugar residues
9-12
a core polysaccharide contains 2-keto-3-deoxy-octonate (KDO). ). Chemical tests for LPS look for ____ since it is not present in anywhere else in nature
KDO
the KDO is linked to various sugars including ______
including heptose sugars (7 carbon sugars)
Gram negative bacteria always have some seven carbon sugars in their ____
LPS
The make-up of the core polysaccharide (number of sugars, order of sugars) is the same for all strains of a particular species but is ______ between species
different
the ______ is a long unbranched polysaccharide (50 -100 repeating units of 4 to 7 sugars each). Consists of chains of sugars with some dideoxy sugars
O antigen
The O antigen is also called the ______ or the _____
the O-specific side chain, O polysaccharide
the O side chain is very ____ (each Gram negative bacterial strain can have its own O-antigen which can be used to identify the bacteria); within the genus Salmonella there are over 1000 O-antigen types
variable
O- Antigen is used for _____, especially with Salmonella and E. coli. Reactivity of antibodies with this side chain can be used for typing bacteria. (example: E. coli strains with O antigen type O157 are responsible for the cases of food poisoning due to undercooked meat)
epidemiology
Some bacteria do not have O-antigens in their LPS. These bacteria are called ____. the lack of O antigen makes the bacteria clump in suspensions
rough
Bacteria that have an O antigen are called ____
smooth
The LPS from bacteria which are always ____ is called LOS (lipooligosaccharide) to indicate this difference in structure
rough
. The Gram stain is used to detect which type of _______ a bacterium has
cell wall
the gram stain was developed by _____ in 1882
Hans Christian Gram
Step 1 in the gram stain. Primary stain: ________ is put on the cell for 1 minute and then rinse with water. The crystal violet stains the peptidoglycan purple. Since all bacteria have peptidoglycan in their cell wall, all bacteria will turn purple after this step.
crystal violet
Step 2 in gram stain. Mordant: _____ is added to help the stain bind to the bacteria better. It is left on for 1 minute and then rinsed with water. The iodine does _____________ of the bacteria. At this point, all bacteria will still be purple.
Iodine, change the color
Step 3 in gram stain. Decolorizer: Decolorizer is added briefly and rinsed with water. Decolorizer is always an alcohol. In our lab, we use alcohol mixed with acetone. The decolorizer removes the _________ from the peptidoglycan. Since Gram positive bacteria have a thick layer of peptidoglycan it takes longer to remove all of the crystal violet from them than it does to remove it from the Gram negative bacteria which only have a thin layer of peptidoglycan. It is very important to only leave the decolorizer on for a short time. Over-decolorizing will result in all bacteria looking Gram negative. At the end of this step, the Gram positive bacteria are still purple and the Gram negative bacteria are clear.
crystal violet
Counterstain: Safranin is added for 1 minute and rinsed with water. The safranin stains cells ______. At the end of this step, the Gram positive bacteria are still purple (adding the red from the safranin to the purple from the crystal violet just makes the color a little darker– it still looks purple). Gram negative bacteria are pink (they will get a darker red the longer you leave the safranin on).
red
only ______ and _____ have acid fast cell walls
Nocardia, Mycobacteria
______ bacteria are responsible for several diseases such as tuberculosis (caused by Mycobacterium tuberculosis) and leprosy (caused by Mycobacterium leprae)
Mycobacteria
_____ causes a disease known as nocardiasis.
Nocardia
Acid fast bacteria have a thin layer of peptidoglycan with direct cross-links like Gram negative bacteria. They do not have an ______
outer membrane.
Instead of a traditional outer membrane Acid Fast cell walls they contain a thick layer of a waxy substance called ______. Up to 60% of their cell wall may be this,
mycolic acid
.Because the mycolic acid makes it hard to remove stain, when treated with _______ in an acid fast stain procedure, they do not lose their color and are called acid fast.
acid alcohol
The acid fast stain useful in a hospital lab for detecting ____ Mycobacterium tuberculosis is a very slow growing organism. It can take 3 weeks or more to grow up in the lab. If the lab technicians can perform an acid fast stain and see acid fast bacteria, this means the physician can treat the patient much sooner than waiting for the bacteria to grow.
tuberculosis
Acid fast stain step 1: Primary stain: The primary stain is _______. It contains a fuchsia colored dye and carbolic acid (which is also known as phenol). Carbolic acid is an organic chemical. Because of this, it penetrates the waxy, organic layer of mycolic acid much better than a water based dye such as crystal violet which is used in the Gram stain. The slide is heated on a steam bath for five minutes to help the dye penetrate the wax like mycolic acid layer. At this point, all bacteria will be red (technically, they are fuchsia, but most people just call it red).
carbolfuchsin
Acid fast stain step 2: _______: the slide is decolorized briefly with a mixture of acid and alcohol. This is a very strong decolorizer. It will quickly remove all the stain from non-acid fast bacteria (i.e. Gram + or Gram - bacteria). However, the thick layer of mycolic acid makes it hard to get the stain out of the acid fast bacteria. At this point, acid fast bacteria are red and non-acid fast bacteria are clear.
decolorizer
Acid fast step 3: Counterstain: ________ is added for one minute and rinsed with water. The methylene blue will stain the non-acid fast bacteria but it cannot get through the mycolic acid layer on the acid fast bacteria. At the end of this procedure, acid fast bacteria are red and non-acid fast bacteria are blue (remember, non-acid fast bacteria may be Gram positive or Gram negative; you cannot tell which one they are without doing a Gram stain).
Methylene blue
