Module 3 - Prokaryotic Cell Structure Flashcards
(42 cards)
1
Q
cocci
A
spherical
2
Q
Bacilli
A
rods
3
Q
Vibrio
A
curved rod
4
Q
Spirilla
A
Rigid helices
5
Q
Spirochetes
A
flexible helices
6
Q
Mycelium
A
multinucleated filaments
7
Q
Pleomorphic
A
variable inshape
8
Q
diplococci
A
two spheres
9
Q
Streptococci
A
chain of spheres
10
Q
Staphylococci
A
cluster of spheres
11
Q
tetrads
A
groups of four
12
Q
sarcinae
A
groups of eight
13
Q
coccobacilli
A
short rod (spherical rods)
14
Q
Plasma membranes
A
- Requirement for all living organisms
- Plasma membrane encompasses the cytoplasm
– Separates cell from its environment
– Selectively permeable barrier - Some molecules are allowed to pass into or out
- Transport systems aid in movement of molecules
– Location of vital metabolic processes
– Detection and response to chemicals in surroundings with
the aid of receptor molecules - Some prokaryotes also have internal membrane
systems
15
Q
membrane lipids
A
- “Amphipathic”
- Polar ends
– interact with water
– hydrophilic - Nonpolar ends
– insoluble in water
– hydrophobic
16
Q
bacterial Membranes
A
- Highly organized, asymmetric, flexible,
dynamic - Differ from eukaryotic membranes in that they
lack sterols
– Contain hopanoids (sterol-like molecules)
– Stabilize the membranes
17
Q
Bacterial cell wall
A
- Rigid structure outside the plasma membrane
- Provides characteristic shape to cell
- Protects the cell from osmotic lysis
- May also contribute to pathogenicity
- Few prokaryotes lack cell walls
- Bacteria divided into two major groups based on
response to gram stain (due to cell wall structure)
– G+ bacteria stain blue-purple
– G- bacteria stain red-pink
18
Q
Peptidoglycan (Murein)
A
- Meshlike polymer
composed of identical
subunits - Contains N-acetyl
glucosamine (NAG)
and N-acetylmuramic
acid (NAM) and
several different amino
acids - Chains of linked
peptidoglycan subunits
are cross linked by
peptides
19
Q
Gram Positive cell walls
A
- Composed primarily of
peptidoglycan - May also contain large
amounts of teichoic acids
(polymers of glycerol or ribitol
joined by phosphate groups)
– Not present in Gram -
– Negatively charged
– Appear to extend the surface of
the peptidoglycan
– May play a role in maintaining the
cell wall structure
– The side chain (R) may be
glucose, D-alanine, or others
20
Q
Gram positive cell walls pt 2
A
- Some gram-positive bacteria have a layer of proteins
on the surface of the peptidoglycan - Periplasmic Space:
– Lies between plasma membrane and cell wall and is smaller
than that of Gram- bacteria
– Periplasm has relatively few proteins
– Enzymes secreted by Gram+ bacteria are called
exoenzymes
– Those that remain in the periplasmic space usually attach to
the plasma membrane
– Exoenzymes perform many of the same functions of the
periplasmic enzymes of Gram- bacteria
– Often serve to degrade nutrients for transport across the
membranes
21
Q
Gram negative cell wall
A
- Thin layer of peptidoglycan surrounded by an outer
membrane composed of lipids, lipoproteins, and
lipopolysaccharide (LPS) - No teichoic acids
- More complex than Gram+ walls
- Peptidoglycan is ~2-5% of wall weight
– Outer membrane lies outside the thin
peptidoglycan layer
– Braun’s lipoproteins connect outer membrane to
peptidoglycan - Periplasmic space differs from that in Gram+ cells
– may constitute 20-40% of cell volume
– many enzymes present in periplasm
22
Q
Role of LPS
A
- Protection from host defenses (O side chain)
– O antigen elicits immune response
– Many Gram- bacteria can rapidly change the
antigenic nature of their O side chains - Contributes to the negative charge on cell
surface (core polysaccharide) - Helps stabilize the outer membrane structure
(lipid A) - Lipid A can act as a toxin (termed endotoxin)
- May contribute to surface attachment and
biofilm formation - Aids in creating a permeability barrier
23
Q
Outer membrane
A
- More permeable than the plasma membrane due to
the presence of porin proteins and transporter
proteins
– porin proteins form channels through which small
molecules (600-700 daltons) can pass
24
Q
Gram staining mechanism
A
- Thought to involve
shrinkage of the pores of
the peptidoglycan layer
of gram-positive cells
– Constriction prevents
loss of crystal violet
during decolorization
step - Thinner peptidoglycan
layer and larger pores of
gram-negative bacteria
does not prevent loss of
crystal violet
25
Protective nature of the cell wall
* Osmotic lysis
– can occur when cells are in hypotonic solutions
– movement of water into cell causes swelling and
lysis due to osmotic pressure
* Cell wall protects against osmotic lysis
– Lysozyme breaks the bond between N-acetyl
glucosamine and N-acetylmuramic acid
– Penicillin inhibits peptidoglycan synthesis
* If cells are treated with either of the above they will
lyse if they are in a hypotonic solution
26
internal membranes
* Intracytoplasmic
membranes
– Observed in many
photosynthetic bacteria and
in prokaryotes with high
respiratory activity
* Mesosomes
* Plasma membrane infoldings
* function not agreed upon
* may be artifacts of chemical
fixation of bacteria for electron
microscopy
27
Glycocalyx
– network of polysaccharides extending from
the surface of the cell
– a capsule or slime layer composed of
polysaccharides can also be referred to as
a glycocalyx
28
S-Layer
– Regularly structured layers of protein or
glycoprotein
– In bacteria, the S layer is external to the cell wall
– Common among Archaea, where they may be
the only structure outside the plasma membrane
29
Functions of capsules, slime layer and S-layers
* Facilitate attachment to surfaces
* Protection:
– From host defenses (e.g. phagocytosis)
– From harsh environmental conditions (e.g.,
desiccation)
– From viral infection or predation by bacteria
– From chemicals in environment (e.g., detergents)
– Against osmotic stress
* Facilitate motility of gliding bacteria
30
Archaeal Membranes
* Membrane lipids
are a distinctive
feature of Archaea
* Some are
monolayer instead
of bilayer
* Contain ether
linkages instead of
ester linkages
(unique bonds)
31
Archaeal cell walls
* Lack peptidoglycan
* Varies from species to
species but usually
consists of complex
heteropolysaccharides
* Methanogens have
walls containing
pseudomurein
32
Cytoplasmic matrix
* Substance in which the nucleoid, ribosomes, and
inclusion bodies are suspended
* Lacks membrane-bound organelles (typical in
eukaryotes)
* Principally water (70% of bacterial mass is water)
* Major part of the protoplasm (plasma membrane
and everything within)
* Homologs of all 3 eukaryotic cytoskeletal elements
have recently been identified in Bacteria and one has
been found in Archaea
* Functions include roles in cell division, protein
localization and determination of cell shape
33
inclusion bodies
* Granules of organic (i.e.
glycogen, poly-B-
hydroxybutyrate (PHB), gas
vacuoles) or inorganic (i.e.
polyphosphate granules, sulphur
granules, magnetosomes)
material that are stockpiled by
the cell for future use
* Some are enclosed by a single-
layered membrane
– membranes vary in composition
(proteins, lipids)
34
ribosomes
* Complex structures consisting
of protein and RNA
* Sites of protein synthesis
* Smaller than eucaryotic
ribosomes
– prokaryotic ribosomes 70S
* 50S and 30S subunits
– eukaryotic ribosomes 80S
* 60S and 40S subunits
– S = Svedburg unit, measure of
sedimentation
35
The Nucleoid
* Irregularly shaped
region in the cytoplasm
* Not membrane-bound
* Chromosome location
– Usually 1 per cell
– Closed, circular, double-
stranded DNA molecule
– Looped and coiled
extensively
– Nucleoid proteins
(different than histones)
probably aid in folding
36
Plasmids
* Usually small, closed circular
DNA molecules
* Exist and replicate
independently of the
chromosome
* Relatively few genes present
* Genes on plasmids are not
essential to the host, but may
confer selective advantage
(e.g., drug resistance)
* Curing is the loss of a plasmid
* Classification based on mode of
existence, spread, and function
* Single copy (one per cell) or
multiple copies (eg. 40/cell)
37
Fimbraie and Pili
* Fimbriae (Fimbria)
– short, thin, hairlike,
proteinaceous appendages
* up to 1,000/cell
– mediate attachment to surfaces
– some (type IV fimbriae) required
for twitching motility or gliding
motility that occurs in some
bacteria
* Sex pili (pilus)
– similar to fimbriae except longer,
thicker, and less numerous (1-
10/cell)
– required for mating
38
Flagella
* Flagellum rotates like a propeller
– In general, counterclockwise rotation causes
forward motion (run)
– In general, clockwise rotation disrupts run
causing a tumble
39
Distribution varies: (Flagella)
* Distribution varies:
– monotrichous – one flagellum
– polar flagellum – flagellum at end of cell
– amphitrichous – one flagellum at each
end of cell
– lophotrichous – cluster of flagella at one
or both ends
– peritrichous – spread over entire surface
of cel
40
Other types of motility
* Spirochetes
– exhibit flexing and spinning movements of
axial filaments which are composed of
periplasmic flagella
* Gliding motility
– cells coast along solid surfaces
– no visible motility structure has been
identified
41
Chemotaxis
* Movement towards a chemical
attractant or away from a
chemical repellent
* Concentrations of chemical
attractants and chemical
repellents detected by
chemoreceptors on surfaces
of cells
* In the presence of an attractant,
tumbling frequency is reduced,
and runs in the direction of the
attractant are longer
* In the presence of a repellent,
the trend is opposite
42
Bacterial Endospore
* Formed by some
Gram+ bacteria
* Resistant to
numerous
environmental
conditions
– heat
– radiation
– chemicals
– desiccation
