Chapter 3: Bacterial Cell Structure Flashcards
• Bacteria are referred to as → prokaryotes
• Lack a membrane-bound nucleus, membrane-bound
organelles, and internal membranous structures
The problem is some bacterial groups do have their genetic material enclosed in a → membrane
• Some also have membrane-bound → organelles
Most common shapes ___ and ___:
cocci ; rods
Cocci
spherical cells, single cells or clusters
Rod (bacilli)
cylindrical shape
Less common cells shapes are
Spirilla, Spirochetes, Vibrio, and Pleomorphic.
Spirilla
rigid, spiral-shaped cells
Spirochetes
flexible, spiral-shaped cells
Vibrio
resemble rods, comma
shaped
Pleomorphic
organisms that are
variable in shape
Arrangement of cells is determined by what?
• Determined by plane of division
• Determined by whether or not there is cell →
separation
Diplococci
pairs
Streptococci
chains
Staphylococci
grape-like clusters
Tetrads
4 cocci in a square
Sarcinae
cubic configuration of 8 cocci
Common features of a bacterial cell
• Cell envelope - 3 layers: cell membrane, cell wall, capsule
• Cytoplasm – internal fluid
• External structures
Bacterial Cell Envelope
• Cell envelope – plasma membrane and all of its external
surrounding layers
Bacterial plasma membrane
encloses the cytoplasm and
defines the cell’s → shape
• It is a selectively permeable barrier
• Only allows certain ions and molecules to enter or
exit and prevents others
Fluid-mosaic model
states that membranes consists of
fluid lipids with floating proteins
Plasma Membrane Structure
• Lipids in the membrane are →
phospholipids
• Amphipathic – both polar and
nonpolar ends
• Hydrophilic – polar phosphate
ends interact with → water
• Hydrophobic – nonpolar fatty
acid ends are insoluble in water
and only associate with → one
another
Amphipathic
both polar and
nonpolar ends
Hydrophilic
polar phosphate
ends interact with → water
Hydrophobic
nonpolar fatty
acid ends are insoluble in water
and only associate with → one
another
Peripheral proteins
connected
to the membrane and are easily
removed
Integral proteins
transport
proteins that move materials into
and out of the cells
Bacterial membranes lack
the sterol cholesterol
Bacterial membranes contain hopanoids that are….
Similar to cholesterol and probably stabilizes the membrane
Plasma membrane function as a barrier but also
have to
bring nutrients into the cell
Primary function is to obtain energy and nutrients
sources for the cell
Bacteria can only take in dissolved molecules
Bacteria mainly transport nutrients into the cell ____
their concentration gradient
against
• High levels in the cells (storage) and low levels in the
environment
• Bacteria commonly live in nutrient-poor habitats
Passive diffusion
movement of molecules from an area of high concentration to one with a low concentration
• Molecules move down the concentration gradient
• A large concentration gradient is required for adequate
nutrient uptake
___
, ____
, and, ___ cross the membrane by passive diffusion
• O2
, CO2
, and, H2O
Facilitated diffusion
substances move across the plasma
membrane with the help of a carrier or channel protein
Facilitated diffusion
substances move across the plasma
membrane with the help of a carrier or channel protein
Channel protein
pore, substances pass through
Carrier protein
carry substances across the membrane
• Carrier proteins change their shape to facilitate the
movement of a substance across the membrane
• Go back to their original shape when transport is →
completed
Active transport
substance moves from an area of a low concentration to a high concentration with the help of → energy
• Movement against a concentration gradient
• Uses carrier proteins and some form of energy to drive the reaction
Primary active transport
uses ATP
energy to move substances against a concentration gradient without
modifying the substance
Uses a uniporter
uniporter
moves a single
molecule across the membrane
• Ex. ABC Transporter
Secondary active transport
moves
substances against a concentration
gradient with the use of ion gradient →potential energy
• Uses cotransporters, which move two
substances at the same time
• The ion that powers the transport and the substance being moved across the membrane
Symporter (In secondary active transport)
ion and substance move in the same direction
Antiporter (In secondary active transport)
ion and substance move in opposite directions
Group translocation
molecule is chemically modified as
it is transported into the cell
Transporters of different types of sugars _____
phosphorylate
them (add a phosphate)
Group translocation used by bacteria to _____
extract energy from organic energy
sources to generate ATP
Cell wall
layer found outside of the plasma membrane
• Helps maintain cells shape and protects it from osmoticlysis (plasmoptysis)
• Protects the cell from → toxins
Peptidoglycan
Rigid structure lying just outside the cell plasma
membrane
Two types based on Gram stain
Gram-positive (monoderms)
Gram-negative (diderms)
Gram-positive (monoderms)
stain purple; thick
peptidoglycan
Gram-negative (diderms)
stain pink or red; thin
peptidoglycan and outer membrane
Peptidoglycan
Structure
Meshlike polymer of identical
subunits forming long strands • Two alternating sugars • N-acetylglucosamine (NAG) • N- acetylmuramic acid (NAM) • Alternating → amino acids
Peptidoglycan strands have a ___
shape
helical
Peptidoglycan chains are _____ by peptides for _____
crosslinked; strength
• Called a peptide → interbridge
• Various structures occur
Gram-positive bacteria
have thick cell walls made of
peptidoglycan and other polymers like → teichoic acids
Teichoic acids
– polymers of glycerol or ribitol joined by
phospholipids (negatively charged)
• Covalently linked to → peptidoglycan
Typical Gram-Positive Cell Walls
Consist Primarily of _____
Peptidoglycan
Peptidoglycan
Create and maintain the structure of the cell envelope by
anchoring the cell wall to the plasma membrane
• Function to take-up → ions
• Help pathogenic species bind to host tissues
Gram-negative
cell walls are more
complex then gram-positive
• Consist of a thin layer of
peptidoglycan surrounded by an
outer membrane
• Outer membrane composed of
lipids, lipoproteins, and →
lipopolysaccharide (LPS)
• No teichoic acids
Gram-Negative Cell Walls
• The outer membrane of gram-negative bacteria lies outside of
the thin peptidoglycan layer
• Linked by lipoproteins
• Most abundant protein
linked to underlying
peptidoglycan and
embedded in the outer
membrane
• Outer membrane also contains
lipopolysaccharides (LPSs) – consist of both a
lipid and carbohydrates
lipopolysaccharides (LPSs)
consist of both a
lipid and carbohydrates
Functions of Gram-Negative Cell
• Contribute to the cells walls negative charge
• Stabilize the outer membrane and create a
permeability barrier
• Helps protect pathogenic bacteria from → host
defenses (O antigen)
• Acts as a toxin called endotoxin (lipid A) – causes
septic shock once it enters the bloodstream
Hypotonic environments
• Solute concentration outside cell less than inside cell
• Water moves into cell and cell swells
• Cell wall protects from → lysis (plasmoptysis)
Hypertonic environments
• Solute concentration outside cell is greater than inside
• Water leaves the cell
• Plasmolysis (plasma membrane shrinkage)occur
Lysozymes
(antimicrobial in tears, saliva, and oil) breaks
bond between → NAG and NAM
Penicillin inhibits
peptidoglycan synthesis
• If cells are treated, they lyse in a hypotonic solution
Protoplasts
bacteria that have had the → cell wall
removed
Bacteria that Lack Cell Walls
Mycoplasma
• Never produce a cell wall
• Plasma membrane more resistant to osmotic pressure
Capsules
composed of polysaccharides, well organized,
and → not easily removed
Capsules help pathogenic bacteria resist phagocytosis by
host phagocytes
• Found outside of the cell wall
• When bacterial cells that lack capsules they are
phagocytized easily and do not cause disease
• When capsulated they can quickly cause disease
Slime layer
Functions in attachment of bacteria to solid surfaces
and host tissue surfaces (biofilms)
• made of unorganized polysaccharides that
are → easily removed
• Produced by gliding bacteria to facilitate → movement
• Slime layers and capsules consist of glycocalyx – network
of polysaccharides coming off of the cell surface
Protoplast
plasma membrane and everything contained
→ within
Cytoplasm
the material contained within the plasma
membrane
(cytosol, ribosomes, and plasmids)
cytosol
the liquid component
Bacterial Cytoskeleton
Homologs of all 3 eukaryotic cytoskeletal elements have
been identified in bacteria
• Functions are similar as in eukaryotes
• Participate in → cell division
• Localize proteins
• Determine → cell shape
Inclusions
formed by the clumping of substances
• Granules, crystals, or globules of organic or inorganic
material that are stored by the cell for → future use
Storage inclusions are formed when a
nutrient has a….
good supply, and another →
does not
• End products of metabolic reactions are
commonly stored and used later used by
the microbe when it is in a harsh
environmental condition
Microcompartments enclose one or more
enzymes
Carboxysomes
present in
cyanobacteria (photosynthetic bacteria)
• Contain enzymes of photosynthesis
reactions
• Microcompartment prevents CO2
from escaping so it can be
converted into → sugars
Gas vacuoles
allow aquatic,
photosynthetic bacteria to be→
buoyant
• Made up of clumped→ gas vesicles
Microbes can adjust their depth to
reach proper
light, oxygen
concentrations, and nutrient levels
• Descend by collapsing vesicles and
ascend by forming → new ones
Magnetosomes
formed by magnetotactic
bacteria that orient along → magnetic fields
• Intracellular chains of magnetite or greigites
particles (iron ores) enclosed within
invaginations of the plasma membrane
• Act as tiny magnets to swim to nutrient-rich
sediments or locate fresh or marine water
habitats
Ribosomes
site of → proteins synthesis
• Found in the cytoplasm or attached to the plasma
membrane
• Bacterial ribosomal RNA =
70S
• 16S small subunit
• 23S and 5S in large subunit
Nucleoid
contains the cell’s chromosomes and several
proteins
• Most bacterial have a single circular chromosome of
DNA, some have a linear chromosome, and some have
more than one chromosome
Binary fission
asexual reproduction in bacteria
Single circular chromosome → replicates
Plasma membrane and cell wall separate
the cell into → two identical cells
Plasmids
extrachromosomal DNA
• Found in bacteria, archaea, some fungi
• Usually small, closed circular DNA molecules
• Exist and replicate independently of chromosome
Episomes
may integrate into chromosome
• Inherited during → cell division
Fimbriae or pili
fine, hair-like
structures that are thin and short
Fimbria
function to attach cells
to solid surfaces like host tissue or
rocks in streams
Sex pili
involved in motility and
gene transfer
• Conjugation
Flagella
used by many motile bacteria
• Threadlike appendage that extends outward from the
plasma membrane and cell wall
• Main function is → motility
Flagellar Movement
Flagellum rotates like a propeller
• Very rapid rotation up to 1100
revolutions/sec
• In general, counterclockwise (CCW)
rotation causes forward motion (run)
• In general, clockwise rotation (CW)
disrupts run causing cell to stop and
tumble
Swarming
• Occurs on moist surfaces as a type of
group behavior by bacteria
• Most swarmers have peritrichous
(uniform) flagella
• Production of molecules that aid
movement is typical
Spirochete Motility
• Multiple flagella form axial fibril
which winds around the cell
• Flagella remain in periplasmic space
inside outer sheath
• Corkscrew shape exhibits flexing and
spinning movements
Twitching
• Pili at ends of cell
• Short, intermittent, jerky motions
• Cells are in contact with each other and the surface
Gliding
• Smooth movements (slime layer)
Chemotaxis
the movement toward or away from
chemical attractants or repellants
• Move in response to temperature, light, oxygen,
osmotic pressure, and gravity
Phototaxis
movement of a motile
organism in response to light,
either toward the source of light or
away from it
• Common with → cyanobacteria
Endospores
dormant cells formed within mother cells
• Resistant to environmental stresses like heat, ultraviolet
radiation, gamma radiation, chemical disinfectants, and
desiccation
Clostridium botulinum
Example of endospore.
causes botulism toxin, food-borne disease
• Food must be prepared and stored properly
Bacillus anthracis
Example of endospore.
causes anthrax if inhaled , spores
germinate in the lungs
Endospore forming bacterial are commonly found in
soil
Sporulation
process of making endospores.
growth ceases due to a → lack of
nutrients
• Produces a dormant cells that can survive until
nutrients are available and vegetative growth will
restart
Formation of Vegetative Cell
• Activation
• Germination
• Outgrowth
Activation
• Prepares endospores
for germination
• Often results from
treatments like →
heating
Germination
• Environmental
nutrients are detected
• Spore swelling and
rupture or absorption
of spore coat
• Increased metabolic
activity
Outgrowth
• Emergence of
vegetative cell
