Lect-2 Flashcards by بدور اليزيدي

The most important structural element of the wall is

murein or peptidoglycan made up of polysaccharide

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The cell wall of Gram- negative bacteria:

2-8 nm thick .

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The cell wall of Gram-positive bacteria:

The murein may consist of as many as 40 layers (15–80 nm thick).

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a mesh-like layer outside the plasma

membrane of bacteria forming the cell wall

Peptidoglycan

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Peptidoglycan is primary component:
Which consist of
three parts back bone:

N-acetylglucosamine and N-acetylmuramic acid in alternating

chains interconnected by tri, tetra or penta peptide chains.

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Gram-positive bacteria cell
wall consisting of many
layers :

Peptidoglycan-Thicker (15 to 80 nm/40 layers) forms around 90% of the dry weight of Gram- positive bacteria.
Teichoic acids
a. Lipoteichoic acid: links to plasma membrane
b. Wall teichoic acid: links to peptidoglycan

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Lipoteichoic acid: links to

plasma membrane

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Wall teichoic acid: links to

peptidoglycan

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are fibers located in the outer
layer of the gram-positive cell wall and extend
from it.

Teichoic acids

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The medical importance of teichoic acids lies

their ability to induce inflammation and
septic shock when caused by certain gram-
positive bacteria; that is, they activate the
same pathways as does endotoxin (LPS) in
gram-negative bacteria.

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Gram-negative bacteria cell wall consist of many layers:

Outer membrane-2. Lipopolysaccharides
Lipoprotein layer 4. Periplasmic space
Peptidoglycan

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proteins-target site for

I antibiotics. is similar to cell membrane bilayer structure

Outer membrane

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proteins play a role in facilitating the passage
reaffan
of small, hydrophilic molecules into the cell.

Porin

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Porin proteins in

the outer membrane of gram-negative bacteria act as a

channel to allow the entry of essential substances

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2 . Lipopolysaccharides (endotoxin) - This layer consists of

lipid A to which is attached a Toxic

polysaccharide

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Periplasmic space

Gram-negative cell wall

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The lipopolysaccharide (LPS) of the outer membrane of the cell wall of gram-negative bacteria is

endotoxin. It is responsible for many of the features of disease, such as fever and shock (especially hypotension), caused by these organisms

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It is called endotoxin because it is

an integral part of the cell wall, in contrast to exotoxins, which are intigral
actively secreted from the bacteria.

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The constellation of symptoms caused by the endotoxinof one gram-
negative bacterium is………, but the severity of the
a
symptoms can differ greatly. In contrast, the symptoms caused by
exotoxins of different bacteria are usually………

similar to another…quite different.

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The lipopolysaccharide (LPS) is composed of three distinct units

1) A phospholipid called lipid A, which endo
is responsible for the toxic effects. (2) A core polysaccharide of five sugars linked to lipid A. link to lipid
(3) An outer polysaccharide

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An outer polysaccharide consisting of

up to 25 repeating units of three to five sugars. This outer polymer is the important somatic, or O antigen of several gram- negative bacteria that is used to identify certain organisms in the clinical laboratory.

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antigen of several gram- negative bacteria that is used to i

dentify certain organisms in the clinical laboratory.

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Cell Walls of Acid-Fast Bacteria

Mycobacterium

tuberculosis) have an unusual cell wall, air deasesepg.io

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Mycobacteria (e.g., Mycobacterium
tuberculosis) have an unusual cell wall,
resulting in their

inability to be Gram- stained

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These bacteria are said to be acid-fast (Mycobacteria)

because they resist decolorization with | acid-alcohol after being stained with “carbolfuchsin

property is related to the high | concentration of lipids, called

mycolic acids, in the cell wall of Mycobacteria.

inhibit the synthesis of peptidoglycan

penicillin , cephalosporins, and vancomycin

penicillin , cephalosporins, and vancomycin, inhibit the synthesis of peptidoglycan by

inhibiting the transpeptidase that makes the cross- links between the two adjacent tetrapeptides

Cell wall function:

1. It provides rigid support for the cell. 2. The cell wall maintains the overall shape of a bacterial cell. 3. The cell wall is an essential structure that protects the cell from to mechanical damage and from osmotic rupture or lysis

Peptidoglycan Gram-Positive Cell

Thicker; multilayer

Peptidoglycan Gram- Negative Cell

Thinner; single layer

Teichoic acids | Gram-Positive Cell

Yes

Teichoic acids | G negative cell

Outer membrane or No Lipopolysaccharide (endotoxin) In gram posative

Outer membrane or No | Lipopolysaccharide (endotoxin) Gram- Negative Cell

Yes

Periplasmic space in gram +

Periplasmic space | In gram -

Yes

Just inside the peptidoglycan layer of the cell wall lies the

cytoplasmic membrane,

cytoplasmic membrane, which is composed of

a) phospholipid bilayer and b) protein molecules. They are chemically similar, but eukaryotic membranes contain sterols, whereas prokaryotes generally do not.

The only prokaryotes that have sterols in their | membranes are

members of the genus Mycoplasma.

The plasma membrane is selectively permeable n that it helps

control what moves into and out of cell (Function)

Each phospholipid molecule contains:

Hydrophilic (a polar head) that is water- loving and soluble in water, on the surfaces of the lipid bilayer

The protein molecules can be arranged in variety | of ways.

1. peripheral proteins: which lie at the inner or We outer surface of the membrane. 2. integral proteins: Most integral proteins IET penetrate the membrane completely and are called gy transmembrane proteins

peripheral proteins function

as enzymes that support of changes in membrane shape during movement.

integral proteins: functions

channelsthat have a in p pore, or hole, through which substances enter and exit the cell.

jelly-like fluid that fills a cell is called

cytoplasm

The cytoplasm has two distinct areas when seen in the electron microscope:

An amorphous matrix that contains ribosomes, nutrient granules, metabolites, and plasmids. 2- An inner, nucleoid region composed of DNA.

Cytoplasm function

Thecytoplasm, or protoplasm, ofbacterial cellsis where | the functions for cell growth, metabolism, and replication are carried out (function).

Ribosomes

protein synthesis

Bacterial ribosomes are

70S in size

Granules function

as storage areas for nutrients and stain characteristically with certain dyes.

the area of the cytoplasm in which aI | DNA is located.

Nucleoid

Nucleoid is an irregularly-shaped region within the cell of a prokaryote that contains.

all or most of the genetic material

The DNA of prokaryotes is a

single | circular chromosome, double-stranded piece.

extrachromosomal, double-stranded, small circular DNA molecules that are capable of replicating independently of the bacterial chromosome.

Plasmids

Structures External to the Cell Wall

Capsule (Slime Layer) glycocalyx Flagella Pili and Fimbriae

is a gelatinous layer covering the entire bacterium consists of a polysaccharide

The capsule

The capsule is important for five reasons:

1. It is a determinant of virulence of many bacteria since it limits the ability of phagocytes to engulf or digest the bacteria. 2. Specific identification of an organism can be made by using antiserum against the capsular polysaccharide. 3. Capsular polysaccharides are used as the antigens in certain vaccines because they are capable of eliciting protective antibodies. 4. The capsule may play a role in the adherence of bacteria to human tissues, which is an important initial step in causing infection. 5. Protection against drought.

If the glycocalyx is organized and firmly attached to the cell wall , the if glycocalyx is described as a.

capsule

If the glycocalyx is unorganized and only loosely attached to the cell wall, it described as a

slime layer

are long, whip like appendages

Flagella

Flagella function

move the bacteria toward nutrients and other faction attractants, a process called chemotaxis.

Many gram-negativebacteria contain hair-likeappendages that are shorter, straighter, and thinner than flagella .

Pilin

They are used for attachmentand transfer of DNA rather than for motility.

Pilin

pilin, are divided | into two types

fimbriae and pili

Without………, many disease-causing bacteria lose their ability to infect because they're unable to attach to host tissue.

pili

enable cell to adhere to | surfaces, or other cells

Fimbriae

join bacterial cells in preparation for the transfer of DNA from one cell to another

Pili

Pili have two important roles

1. They mediate the attachment of bacteria to specific receptors on the human cell surface, which is a necessary step in the initiation of infection for some organisms 2. A specialized kind of pilus, the sex pilus, forms the attachment between the male (donor) and the female (recipient) bacteria during conjugation

the most important staining procedure.

Gram stain

Gram-negative bacteria, lose the purple dye when treated with acetone

because they have an outer lipid-containing membrane | thin peptidoglycan,

Not all bacteria can be visualized using Gram stain. Some important human pathogens, such as the bacteria that cause……………, cannot be seen using this stain.

tuberculosis and syphilis

Crystal violet, the primary stain, stains

both gram-positive and gram-negative cells | purple because the dye enters the cytoplasm of both types of cells.

Iodine (the mordant) is applied,

it forms large crystals with the dye that are too large to escape through the cell wall.

The application of alcohol dehydrates the peptidoglycan of gram-positive cells to make it more

impermeable to the crystal violet-iodine

The application of alcohol on gram-negative cells is

dissolves the outer membrane of gram-negative cells and even | Cell.

Safranin provides

contrasting color to the primary stain

Lect-2 Flashcards

(77 cards)