Bacterial Cell Flashcards
Macromolecules in Each Cell
proteins, polysaccharide, phospholipid, nucleic acid
protein
amino acid
3 architectural regions of a Bacterial cell
- Appendages (attachments to the cell surface}
- Cell envelope
- Cytoplasmic region
Appendages (attachments to the cell surface}
Flagella
Pili (or Fimbriae)
Cell envelope
Capsule
Q Cell wall
Q Plasma membrane
Cytoplasmic region
Nucleoid (DNA)
Q Ribosomes
Q Inclusions
Threadlike (filamentous) protein appendages extending
outward from the plasma membrane and cell wall
» Slender, rigid structures, about 20nm across and up to
15 or 20 um long
» Allows a cell to move (swimming movement)
Flagella
Flagellar distribution
Polar — one or more flagella arising from one or both
poles of the cell
o Peritrichous — flagella are spread fairly evenly over the
whole cell surface
Short, fine, hairlike protein structures on the surfaces of
prokaryotic cells but not involved in motility
pili/fimbria
— shorter and stiffer than flagella and slightly smaller in
diameter
- Most often involved in adherence of bacteria to surfaces,
substrates and other cells or tissues in nature.
fimbria
similar to fimbriae, but not typically longer and only one or
a few pili are present on the surface of a cell
- Important in facilitating genetic exchange between cells in a
process called conjugation
- For pathogenic bacteria: important in the adhesion to
specific host tissues that leads to invasion
pili
polysaccharide layers outside of the cell
capsule and slime layer
if the layer is organized in a tight matrix that
excludes small particles, such as india ink
capsule
less organized and is more easily deformed, does
not exclude small particles and is more difficult to see
slime layer
formed when encapsulated microorganisms bind to
solid surfaces in nature (soil/water}
biofilms
- Mediate adherence of the cells to surface
- Protect bacterial cells from engulfment by predatory protozoa,
or from attack by antimicrobial agents of plant or animal origin - Protect cells from drying or desiccation
Functions of Capsule
-Essential structure that protects the cell
protoplast from mechanical damage
and from osmotic rupture or lysis
-Important site for attack by antibiotics
» Provide ligands for adherence and receptor sites for drugs
or viruses
cell wall
Species of bacteria can be divided into two major groups,
Gram-positive and Gram-negative based on gram staining
who developed gram staining?
Hans Christian Gram,
Danish bacteriologist
Differentiates bacteria by the chemical and physical
properties of their cell walls by detecting
peptidoglycan
a rigid polysaccharide layer that
is primarily responsible for the
strength of the cell wall
peptidoglycan
It is almost always the first
step in the preliminary
identification of a
bacterial organism
gram staining
steps of gram staining
- fixation
- crystal violet
- iodine treatment
- decolorisation
- counter stain with salfranin
gram positive color
violet
gram negative color
pink
layers of gram positive cell
- inner cytoplasmic membrane
2. outer thick peptidoglycan layer (60-100% peptidoglycan)
layers of gram negative cell
- inner cytoplasmic membrane
- thin peptidoglycan layer(5-10% peptidoglycan)
3,outer membrane with lipopolysaccharide
low lipid content
gram positive
high lipid content
gram negative
no endotoxin
no periplasmic space
no porin channel
gram positive
vulnerable to lysozyme and penicillin attack
gram positive
endotoxin (LPS)- lipid A
periplasmic space
porin channel
gram negative
resistant to lysozyme and penicillin attack
gram negative
The most dynamic structure of a prokaryotic cell
>» Made of 40 percent phospholipid and 60 percent protein
Main functions:
1. Acts as a selective permeability barrier
2. Anchors proteins that are important for metabolic processes
3. Major site for energy conservation in the cell
cytoplasmic membrane
The substance lying between the plasma membrane and the
nucleoid and consist of an aqueous solution (gel-like) of
three groups of molecules:
1. Macromolecules such as proteins (enzymes), MRNA and
tRNA
2. Small molecules that are energy sources, precursors of
macromolecules, metabolites or vitamins
3. Various inorganic ions and cofactors
Cytoplasmic
region
One large irregularly shaped region that contains the
chromosome or circular (some linear) double-stranded
molecule of DNA (deoxyribonucleic acid).
How large?
When a bacterium such as E.coli is gently lysed the
chromosomal DNA leaks out of the cell as a continuous
molecule that is many times longer than the length of the cell.
nucleoid
Small double-stranded circular DNA molecule within a cell
Physically separated from a chromosomal DNA and can replicate
independently
Often carry genes that give their bacterial host a selective advantage for
survival
Can render bacteria drug-resistant, give them new metabolic abilities,
make them pathogenic, or endow them with a number of other
properties
plasmid
____ are widely used as vectors in molecular cloning, serving
to drive the replication of recombinant DNA sequences within host organisms
Artificial plasmid
Made of both protein and ribonucleic acid (RNA
Site of protein synthesis; matrix ribosomes synthesize
proteins destined to remain within the cell, whereas the
plasma membrane ribosomes make proteins for transport to
the outside.
Prokaryotes: 70S ribosomes, have dimensions of about 14 to
15 nm by 20 nm, and are constructed of a 50S and a 30S
subunit
ribosome
Distinct granules of organic or inorganic material that may
occupy a substantial part of the cytoplasm
» Usually used for storage (e.g., carbon compounds, inorganic
substances, and energy}
Inclusion
bodies
-A special resistant, dormant structure
» Exhibit no sign of life
» Formed in response to environmental signals that indicate
a limiting factor for vegetative growth
» Resistant to environmental stresses such as high
temperature, irradiation, strong acids, disinfectants, etc.
endospores
Under appropriate environmental conditions, _______
germinate back into vegetative cells
endospores
