MCSF Flashcards
➢ Their DNA is not enclosed within a
membrane and is usually a singular
circularly arranged chromosome.
▪ Some bacteria have two chromosomes
(Vibrio cholerae),
▪ Some have linearly arranged chromosome
➢ Their DNA is not associated with
histones (special chromosomal proteins
found in eukaryotes)
Prokaryotic Cell
➢They lack membrane-bound organelles.
➢Their cell wall almost always contain the complex polysaccharide peptidoglycan.
➢They usually divide by binary fission
Prokaryotic cells
The size, shape, and arrangement of bacterial cells
➢Vary in shape and sizes
➢ Most bacteria range from 0.2 to 2.0 μm in diameter and
from 2 to 8 μm in length.
➢They have a few basic shapes:
▪spherical = coccus (plural: cocci, meaning berries)
▪rod-shaped = bacillus (plural: bacilli, meaning little staffs)
▪ spiral
➢ usually round but can be oval,
elongated, or flattened on one
side.
➢ When cocci divide to reproduce,
the cells can remain attached to
one another
Cocci
Types of Cocci
Diplococci
Streptococci
Tetrads
Sarcinae
Staphylococci
cocci that remain in pairs after
dividing
Diplococci
those that divide and remain
attached in chainlike patterns
Streptococci
- those that divide in two planes and
remain in groups of four
Tetrads
those that divide in three planes and
remain attached in cube-like groups of eight
Sarcinae
those that divide in multiple
planes and form grape-like clusters or broad
sheets
Staphylococci
➢ divide only across their short axis, so there are fewer groupings of bacilli than of cocci.
Bacilli
Types of Bacilli
❑ Single bacilli
❑ Diplobacilli
❑ Streptobacilli
❑ Coccobacilli
- Most bacilli appear as
single rods
Single bacilli
appear in pairs after
division
Diplobacilli
- occur in chains
Streptobacilli
oval and look so much
like cocci
Coccobacilli
➢ have one or more twists
➢ they are never straight
Spiral
Types of Spiral
❑ Vibrios
❑ Spirilla
❑ Spirochetes
- Bacteria that look like
curved rods
Vibrios
- have a helical shape, like a
corkscrew, and fairly rigid bodies
Spirilla
- group of spirals which
are helical and flexible
Spirochetes
- group of spirals
which are helical and flexible
▪ Unlike the spirilla, which use propellerlike external appendages called
flagella to move, spirochetes move by
means of axial filaments, which
resemble flagella but are contained
within a flexible external sheath.
Spirochetes
Other shapes
➢ star-shaped cells (genus Stella);
➢ rectangular, flat cells (halophilic
archaea) of the genus Haloarcula; and
➢ triangular cells.
The shape of a bacterium is determined by
heredity
Generally, most bacteria are
monomorphic
However, a number of environmental conditions can
alter that shape.
‒ If the shape is altered, identification becomes difficult.
Moreover, some bacteria, such as and
Corynebacterium, are generally
pleomorphic
Structure of a Typical Prokaryotic Cell
➢ components according to the
following organization:
(1) structures external to the cell wall,
(2) the cell wall itself, and
(3) structures internal to the cell wall
Among the possible structures external to the
prokaryotic cell wall are the:
❑ Glycocalyx
❑ Flagella
❑ Axial filaments
❑ Fimbriae
❑ Pili
➢ meaning ‘sugar coat’,
➢viscous (sticky), gelatinous polymer that is external to
the cell wall and composed of polysaccharide, or
polypeptide, or both
➢ made inside the cell and secreted to the cell surface
Glycocalyx
If the substance is organized and is firmly attached to the
cell wall, the glycocalyx is described as a
capsule
If the substance is unorganized and only loosely
attached to the cell wall, the glycocalyx is described as a
slime layer
➢ Important in contributing to bacterial virulence (the
degree to which a pathogen causes disease).
➢ protect pathogenic bacteria from phagocytosis by the
cells of the host
Capsules
produces a capsule of d-glutamic acid
Bacillus anthracis
is any group of microorganisms in which cells
stick to each other on a surface.
‒These adherent cells are frequently embedded within a selfproduced matrix of extracellular polymeric substance
(EPS).
Biofilm
protects the cells within it, facilitates communication among
them, and enables the cells to survive by attaching to various
surfaces in their natural environment.
extracellular polymeric substance
(EPS).
➢long filamentous appendages that
propel bacteria
Flagella
Flagella may be:
- atrichous
- peritrichous
- polar
(lack flagella or without projections);
atrichous
distributed over the entire cell)
peritrichous (
(at one or both poles or ends of the cell)
polar
If polar, flagella may be:
- monotrichous (a single flagellum at one
pole), - lophotrichous (a tuft of flagella coming from
one pole); or - amphitrichous (flagella at both poles of the
cell).
(a single flagellum at one pole)
monotrichous
(a tuft of flagella coming from one pole)
lophotrichous
(flagella at both poles of the cell)
amphitrichous
- Spirochetes move by means
of axial filaments, or
endoflagella
– bundles of fibrils that arise at the
ends of the cell beneath an outer
sheath and spiral around the cell
– have structure similar to flagella
Axial filaments
- The rotation of the filaments
produces a movement of the
outer sheath that propels the
spirochetes in a spiral motion.
– corkscrew motion probably
enables to move effectively
through body fluids.
Axial filaments
- hair-like appendages that are
shorter, straighter, and thinner than
flagella and are used for
attachment and transfer of DNA
rather than for motility - found in Gram-negative bacteria
Fimbriae
➢Have a tendency to adhere to each other and to
surfaces.
➢Involved in forming biofilms and other aggregations on
the surfaces of liquids, glass, and rocks.
➢Can also help bacteria adhere to epithelial surfaces in
the body.
Fimbriae
- are usually longer
than fimbriae and only one or two per cell.
Pili (singular: pilus)
➢involved in motility and DNA transfer
- twitching motility
- gliding motility
a pilus extends by the
addition of subunits of pilin, makes contact with a surface or another cell, and then retracts (power stroke) as the pilin subunits are disassembled.
- twitching motility
the smooth gliding movement
of myxobacteria.
- gliding motility
is a complex, semi‐rigid structure responsible for the shape of the cell.
➢Surrounds the underlying, fragile plasma (cytoplasmic) membrane and protects it and the interior of the cell from adverse changes in the outside environment.
The Cell Wall
- The bacterial cell wall is composed of a macromolecular
network called __________.
peptidoglycan (also known as murein)
- consists of a repeating disaccharide
attached by polypeptides to form a lattice that surrounds and protects the entire cell
Peptidoglycan
The disaccharide portion is
made up of monosaccharides
called ________________and _______________, which are related to glucose.
N-acetylglucosamine
(NAG) and N-acetylmuramic
acid (NAM) (from murus,
meaning wall)
Outer membrane of Gram-negative
cell wall
* composed of :1
lipopolysaccharides (LPS),
lipoproteins,
and phospholipids
of the outer membrane is a
large complex molecule that contains lipids and
carbohydrates and consists of three components:
– (1) lipid A,
– (2) a core polysaccharide, and
– (3) an O polysaccharide
lipopolysaccharide (LPS)
is the lipid portion of the LPS and is
embedded in the top layer of the outer membrane.
–When gram-negative bacteria die, they release lipid A, which functions as an endotoxin.
–is responsible for the symptoms associated
with infections by gram-negative bacteria such as fever, dilation of blood vessels, shock, and blood clotting.
Lipid A
is attached to lipid A and contains unusual sugars.
– Its role is structural — to provide stability.
– The O polysaccharide functions as an antigen and is
useful for distinguishing species of gram‐negative
bacteria.
core polysaccharide
extends outward from the
core polysaccharide and is composed of sugar molecules.
– The O polysaccharide functions as an antigen and is
useful for distinguishing species of gram‐negative
bacteria.
O polysaccharide
Cell walls and Gram stain mechanism Developed by:
Hans Christian Gram (1884)
The mechanism is based on differences in the structure of the cell
walls of gram‐positive and gram‐negative bacteria and how each
reacts to the various reagents (substances used for producing a
chemical reaction)
Cell walls and Gram stain mechanism
– stains both gram-positive and gram-negative cells purple because the dye enters the cytoplasm of both types of cells.
Crystal violet, the primary stain,
When __________is applied, it forms large crystals with the dye that are too large to escape through the cell wall.
iodine (the mordant)
dehydrates the peptidoglycan of gram-positive cells to make it more
impermeable to the crystal violet‐iodine.
– The application of alcohol (decolorizing agent)
The effect on gram-negative cells is quite different;
– alcohol dissolves the outer membrane of gram-negative cells
and even leaves small holes in the thin peptidoglycan layer
through which crystal violet‐iodine diffuse.
– Because gram-negative bacteria are colorless after the
alcohol wash, the addition of ________
turns the cells pink or red.
safranin (the counterstain)
provides a contrasting color to the primary stain (crystal violet).
* Although gram-positive and gram-negative cells both absorb safranin, the pink or red color of safranin is masked by the darker purple dye previously absorbed by gram-positive cells.
Safranin
Structures Internal to the Cell Wall
- Plasma (cytoplasmic) membrane
- Cytoplasm
- Nucleoid
- Ribosomes
- Inclusions
is a thin structure lying inside the cell
wall and enclosing the cytoplasm of the cell.
* In prokaryotes, consists primarily of phospholipids which are the most abundant chemicals in the membrane, and proteins.
The plasma (cytoplasmic) membrane (or inner
membrane)
- serve as a selective barrier through which materials enter and exit the cell
plasma membrane
- plasma membranes have
– selective permeability
▪ (sometimes called semipermeability)
– permeability factors:
▪ size
▪ charge
▪ polarity
are also important to the breakdown of nutrients and the production of energy.
Plasma membranes
– The plasma membranes of bacteria contain
enzymes capable of catalyzing the chemical
reactions that break down nutrients and
produce ____
ATP
infoldings of the plasma membrane that
extend into the cytoplasm
Chromatophores or thylakoids -
Materials move across plasma membranes of both prokaryotic
and eukaryotic cells by two kinds of processes:
– passive and
active
- substances cross the membrane from
an area of high concentration to an area of low concentration (move with the concentration gradient, or difference), without any expenditure of energy (ATP) by the cell.
In passive processes
*the cell must use energy (ATP) to move
substances from areas of low concentration to areas of high
concentration (against the concentration gradient).
In active processes
Passive processes include :
simple diffusion,
facilitated diffusion, and
osmosis.
is the net (overall) movement of
molecules or ions from an area of high concentration to
an area of low concentration
Simple diffusion
integral membrane proteins function as channels or carriers that facilitate the movement of ions or large molecules across the plasma membrane.
In facilitated diffusion
Such integral proteins are called:
transporters or permeases.
is the net movement of solvent molecules across a selectively permeable membrane from an area with a high concentration of solvent molecules (low concentration
of solute molecules) to an area of low concentration of solvent molecules (high concentration of solute molecules)
Osmosis
- Tonicity:
– Isotonic solution
– Hypotonic solution
– Hypertonic solution
- when a bacterial cell is in an environment in which nutrients are in low concentration, the cell must use active processes, such as active transport and group translocation, to accumulate the needed substances.
- the cell uses energy in the form of ATP to move substances across the plasma membrane.
Active processes
Among the substances actively transported are ions (for
example :
Na+,
K+,
H+,
Ca2+, and
Cl–,
amino acids, and
simple sugars.
– for a prokaryotic cell it refers to the substance of the cell inside the plasma membrane
Cytoplasm
is about 80% water and contains primarily proteins (enzymes), carbohydrates, lipids, inorganic ions, and many low-molecular weight compounds. Inorganic ions are present in much higher concentrations in the cytoplasm than in most media.
- Cytoplasm
is thick, aqueous, semitransparent, and elastic
- Cytoplasm
The major structures in the cytoplasm of prokaryotes are a
nucleoid (containing DNA), particles called ribosomes, and
reserve deposits called inclusions
are most likely responsible for the rod and helical cell shapes of bacteria.
Protein filaments in the cytoplasm
- Prokaryotic cytoplasm lacks certain features of eukaryotic
cytoplasm, such as a:
cytoskeleton and
cytoplasmic streaming.
The nucleoid of a bacterial cell
usually contains a single long,
continuous, and frequently
circularly arranged thread of
double-stranded DNA called the
bacterial chromosome
- In addition to the bacterial chromosome, bacteria often contain small usually circular, double-stranded DNA molecules called
plasmids
- site of protein synthesis
Ribosomes
- Bacterial and archaea ribosome =
70S (Svedberg unit)
- Eukaryotic ribosome =
80S
- reserve deposits
- Cells may accumulate certain nutrients when they are plentiful and use them when the environment is deficient.
Inclusions
When essential nutrients are depleted, certain grampositive bacteria, such as those of the genera Clostridium and Bacillus, form specialized “resting” cells called
endospores
