Anatomy of the Bacterial Cell Flashcards
How would you describe a bacterial cell wall?
A complex, semi-rigid structure responsible for cell shape
The bacterial cell wall acts as an attachment point for the…
Flagella
The major component of bacterial cell walls is…
Peptidoglycan
How does the cell wall prevent the osmotic lysis of a bacterial cell?
The interior of the cell wall is at a higher pressure than it’s surrounding environment, without the cell wall the bacteria would pop. In a hypotonic solution, water moves into the cell. If the cell wall is strong, it contains the swelling. If the cell wall is weak or damaged, the cell bursts, osmotic lysis.
What two sugars is peptidoglycan composed of?
N-acetylglucosamine and N-acetylmuramic acid
What is an isotonic solution?
A medium in which the overall concentration of solutes equals that found inside the cell
What is a hypotonic solution?
A hypotonic solution outside the cell is a medium whose concentration of solutes is lower than that inside the cell
What is a hypertonic solution?
A hypertonic solution is a medium having a higher concentration of solutes than inside the cell has
How do N-acetylglucosamine and N-acetylmuramic acid make the cell wall?
The pair form repeating disaccharides which create a polymer
Name two amino acids that form cross links between the disaccharide polymer chains.
Lysine and diaminopimelic acid (DAP)
What is special with the amino acids that make up the cell wall?
They are alternating between the L- and D- forms
Why are alternating L- and D- amino acid forms unique?
Usually only the L-form of amino acids are used in proteins in nature
How are N-acetylglucosamine and N-acetylmuramic acid linked to each other?
By a beta, 1-4 linkage glycosidic bond
How does the enzyme lysozyme damage cell walls?
By breaking the beta 1-4 linkage connecting the disaccharide
How are the sugar chains cross linked?
By amino acids connecting N-acetylmuramic acid
The more cross linking, the greater the…
Rigidity
What is DAP?
An amino acid found in the peptide linkages between NAM and NAG. Stands for diaminopimelic acid
How much of the cell wall does peptidoglycan make up in gram positive bacteria?
Up to 25nm
How much of the cell wall does peptidoglycan make up in gram negative bacteria?
2-5nm
In gram negative bacteria, the NAG-NAM chains are…
Directly linked
In gram positive bacteria, the NAG-NAM peptide chains are…
Linked by a pentapeptide bridge
B lactam antibiotics inhibit…
Transpeptidase enzymes which catalyses the formation of the final bond between two peptide chains
Give two examples of B lactam antibiotics
Penicillin and cephalosporins
Staphylococcus is
Gram positive
Bacillus is
Gram positive
Clostridium is
Gram positive
Listeria is
Gram positive
Corynebacterium is
Gram positive
90% of the cell wall is made up of peptidoglycan in a…
Gram positive bacterium
Teichoic acids are found in…
Gram positive bacteria
What are the teichoic acids that span the whole cell wall and link to the plasma membrane called
Lipoteichoic acid
What are the teichoic acids associated with the peptidoglycan called
Wall teichoic acid
Teichoic acids usually bind to
Sugars and D-alanine
Teichoic acids are polymers of
Glycerophosphate or ribitol phosphate
Roles of teichoic acids include
May bind and regulate the movement of cations due to -ve charge from phosphate groups. Structural stability. Provide antigenic specificity.
Five major parts of a gram positive bacterial cell wall:
Wall associated protein, wall teichoic acid, lipoteichoic acids, peptidoglycan and cytoplasmic membrane
What is the overall structure of a gram negative cell wall?
Outer membrane, periplasm and cytoplasmic membrane
Where is the peptidoglycan located in gram negative bacteria?
In the periplasmic space between the outer membrane and cytoplasmic membrane
Are there any teichoic acids in gram negative bacteria?
No homie!
How wide is the periplasm layer?
15nm
What does the periplasm contain?
Digestive enzymes and transporter proteins
The outer membrane is a…
Bilayer
What is the complement system?
The complement system consists of a number of small proteins found in the blood. The complement system is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear pathogens from an organism.
The outer membrane aids in evading…
Phagocytosis and complement
The outer membrane acts as a barrier to…
Certain antibiotics, penicillin, digestive enzymes
The outer membrane prevents molecules from the periplasm from being…
Lost
What are porins and where are they found?
Transporter proteins found in the outer membrane
What does LPS stand for?
Lipopolysaccharide
Where are lipopolysaccharides found?
In the outer membrane of a gram negative bacterium
What do lipopolysaccharides consist of?
Lipid A, the core polysaccharide and the O-polysaccharide
Three roles of the lipopolysaccharides present?
Stabilise the outer membrane
Increase the -ve charge
Protect from chemical attack
What is lipid A made of?
Phosphorylated glucosamine disaccharides decorated with multiple fatty acids
One of the main functions of LPS?
An endotoxin
An endotoxin is released when the bacteria dies and can cause symptoms to arise, such as..
Fever and vomitting
Does the gram negative bacteria have to be pathogenic to release endotoxins?
No
What is O-polysaccharide/O-antigen made of?
It’s a sugar polymer
What is the long O-polysaccharide chains in some gram negative outer membrane of the cell wall called?
Smooth LPS
What is the short O-antigen chain called?
Rough LPS
Some bacteria with a rough LPS are ____ suseptible to hydrophobic drugs
more
The O-polysaccharide functions as an
Antigen
The O-polysaccharide is useful for distinguishing between
different bacterial species and strains
What does E.coli O157:H7 cause?
Enterohemorrphagic fever
List the main components of a gram negative cell wall?
Outer membrane including proteins, the lipopolysaccharide - O-antigen, core polysaccharide and Lipid A. The periplasm layer which has the peptidoglycan and then the cytoplasmic membrane
Escherichia is…
Gram negative
Salmonella is
Gram negative
Pseudomonas is
Gram negative
Legionella is
Gram negative
Wolbachia is
Gram negative
Serratia is
Gram negative
Helicobacter is
Gram negative
Neisseria is
Gram negative
Klebsiella is
Gram negative
Who came up with gram positive/gram negative staining method?
Christian Gram in 1884
What stain is used first to treat the heat fixed cells?
Crystal violet
The primary stain is washed off and smear treated with a mordant. The mordant stain used is
Iodine
After primary stain and the mordant stain is added, the cells are washed with a de-colourising agent. The de-colourising agent is
Alcohol
After the cells have been de-colourised. The smear is counterstained using
Safranin
Mycobacterium cell walls are different in what way?
They contain a thin layer of peptidoglycan with a layer of mycolic acid
What is a layer of mycolic acid?
Consists of a hydrophobic waxy lipid
Why does gram stain not work for mycobacterium?
The dyes can not get through the waxy myolic acid layer
What method is used to stain mycobacterium?
Acid-fast - carbonfuchsin binds to components in cystol
High affinity mycolic acids found in their cell membranes
What are wall-less bacteria called?
Mollicutes such as mycoplasma
What can mycoplasma cause?
Mycoplasma pneumonia
What do mollicutes have that is unique?
They contain sterols in their plasma membrane
What is the glycocalyx?
A viscous gelatinous polymer that surrounds the cell, secreted by most bacteria
What is the glycocalyx composed of?
Polysaccharides and/or protein
One type of glycocalyx is well organised and firmly attached to the cell. This is called
A capsule
One type of glycocalyx is unorganised and loosely attached to the cell wall. This is called
A slime layer
Capsules can be visualised. How?
By using negative staining
How can the glycocalyx assist in the formation of biofilms?
They assist with attachment
Steptococcus mutans can
adhere to teeth
Vibrio cholera can
adhere to the small intestine
Klebsiella can adhere/colonise
the respiratory tract
What does Bacillus anthracis cause?
Anthrax
What does Streptococcus pneumoniae cause?
Pneumonia
How can capsules aid in the evasion of the immune system?
Capsule prevents phagocytosis
What are fimbriae?
Short, hair like, proteinaceous appendage
What protein makes fimbriae?
Curlin protein
What type of bacteria have fimbriae?
Mostly gram negative, very few gram positive bacteria have fimbriae
Where are fimbriae found?
At poles or along the entire length
Fimbriae have a tendency to stick to…
each other as well as to surfaces
How are fimbriae involved in biofilm formation?
Help bacteria adhere to epithelial surfaces of the body.
E.coli when fimbriated adhere to the lining of the small intestine. What happens when fimbriae are absent?
Colonisation does not occur
What are pili?
Hair like, proteinaceous appendages
How do they differ from fimbriae?
Typically longer and only one/two found per cell
What do sex pili do?
Facilitate genetic exchange between cells - conjugation
What are the pili that are associated with motility called?
Type IV pili
How do motility pili work?
Involves synthesis of pili until it reaches a surface then retraction of pili as it is dismantled
There are two types of motility by the type iv pili, what are these called?
Twitching motility and gliding motility
Describe twitching motion.
Short, jerky, intermittent motion
Describe gliding motion
Smooth, continuous motion
Give an example of a bacteria that uses gliding motion from its pilus.
Myxococcus
What is the flagella?
A tail-like appendage
Where is the flagella found? Gram pos or gram negative
It is found in both
What is the main function of the flagella?
Locomotion - they are said to be motile and swim
What is the shape of the flagella?
Helical
What is the difference between flagella and fimbria/pilli?
The flagella is longer and thicker
What are bacteria without a flagella called?
Atrichous
Bacteria with flagella all over the surface are called?
Peritrichous
If the flagella has only one flagella at one pole of the bacterium, it is said to be…
Monotrichous
If there are multiple flagella at a pole it is said to be…
Lophotrichous
If a bacteria is polar and has flagella at both ends it is known to be
Amphitrichous
The flagella consists of which three parts?
The filament, the hook and the basal body
The filament of a flagellum is composed of…
Flagellin (globular protein)
The flagellin is unique to the bacteria, how is this an advantage?
Useful in identifying the bacteria
The flagellin is arranged as…
Chains, they interwine to form a hollow tube
The filament of a flagellum is not generally covered with a membrane, why is this key?
Because eukaryotic flagella are covered with a membrane
What is the hook in a flagella?
The hook is the connecting region between the filament and the basal body
The hook acts as an…
Universal joint
The basal body of the flagella serves what purpose?
Anchors the flagella to the cell wall and plasma membrane
How does the basal body allow the flagella to move?
It serves as the motor allowing the flagella to move
Describe the structure of the basal body of a flagella in a gram negative bacterium.
Gram negative bacteria have two pairs of rings. The outer pair is anchored to the cell wall. The inner pair anchored to the plasma membrane.
Describe the structure of the basal body of a flagella in a gram positive bacteria.
Gram positive bacteria only have the inner pair of rings anchored to the plasma membrane
The flagella can rotate clockwise and anticlockwise. True or false?
True
The speed of flagella rotation can be altered between?
200-17,000 rpm
Runs by flagella are interrupted by changes in directions called…
Tumbles
Flagella with a polar arrangement can have two types of flagella, one being reversible flagella, the other being…
Unidirectional flagella where they move rapidly and typically spin around
Cells can move toward a favourable or away from an adverse environment by their flagella, what is this called?
Taxis
What are two types of stimuli and what would the movement be?
Chemical and light. Chemotaxis and phototaxis
Describe the motion of a bacterium when near a positive stimulus
Many runs and few tumbles
Describe the motion of a bacterium when near a negative stimulus
Frequency of tumbles increase
What is the axial filament?
Wraps around the cells of spirochete bacteria
Two examples of spirochete bacteria
Treponema pallidum that causes syphilis and Borrelia burgdoferi that causes Lyme disease
How is Lyme disease transmitted?
Through the bites of infected ticks
How is Syphilis transmitted?
Sexually transmitted
Where is the axial filament?
Enclosed in the space between the outersheath and the cell wall
The rotation of the axial filament causes what type of movement for spirochete bacteria?
Corkscrew-type movement
What advantage do spirochete bacteria have?
Most live in bodily fluids, The axial filament can allow them to swim through mucus - propel through
Size of plasma membrane?
7nm
Function of the plasma membrane
Separate cytoplasm from the env, selective permeability enables movement
The phospholipid bilayer contains hydrophobic and hydrophilic components, what makes the hydrophobic environment?
The fatty acids - they point inwards
The glycerophosphate heads exposed to the external environment or the cytoplasm are
Hydrophilic
Proteins found on the surface of the bilayer of the plasma membrane are called
Peripheral proteins
Proteins found in the bilayer of the plasma membrane are called
Integral proteins
Proteins that go through the bilayer of the plasma membrane are called
Transmembrane proteins
The plasma membrane is described to be _________ permeable
Selectively
Is simple diffusion across a plasma membrane a passive or an active process?
Passive
Facilitated diffusion involves
Transmembrane proteins
Active transport involves movement
against a concentration gradient
Does the bacterial cytoplasm contain a cytoskeleton?
No babes
What is the nucleoid in a bacterial cell?
The region containing the bacterial chromosome
The site of protein synthesis and there are 10,000+ of these per cell…
Ribosomes
In a bacterial cell, the ribosomes are composed of two subunits, what are these
A small subunit of 30S and a large subunit of 50S to make a 70S ribosome
The function of inclusion bodies is
To act as energy reserves or reservoirs of structural building blocks
Can inclusion bodies be observed?
Yes by light microscopy after staining
What are metachromatic granules?
They contain inorganic phosphate and a reserve of high energy phosphate
Polysaccharide granules (starch/glycogen) contain
a reserve carbon and energy source
Lipid inclusions…
reserve carbon and energy source
Sulphur granules as a
energy reserve
Gas vacuoles
for buoyancy
Carboysome inclusion bodies
for co2 fixation
Magnetosomes iron oxide inclusion bodies for
orienting and migrating along geo-magnetic field lines
Endospores are
An endospore is a dormant, tough, and non-reproductive structure produced by certain bacteria
Endospores work because they are
resistant to heat, harsh chemicals and radiation
Endospores are produced in the ______ stage of a bacterial life cycle
Dormant
They are usually produced by gram negative or gram positive bacteria?
Gram positive such as bacillus and clostridium
Define sporulation
Endospore formation
Define germination
Returning to vegetative state
When does sporulation begin and how long does it take?
When a key nutrient becomes scarce, it takes several hours long
What happens in the first stage of endospore sporulation?
The newly replicated bacterial chromosome and a small portion of the cytoplasm become isolated by the ingrowth of the plasma membrane (spore septum)
What happens in the second stage of endospore sporulation?
The mother cell engulfs the spore leading to a double layered membrane that surrounds the chromosome and cytoplasm -> forespore
What happens in the third stage of endospore sporulation?
A thick layer of peptidoglycan is laid down between the two membanes
What happens in the fourth stage of endospore sporulation?
The spore coat is laid down around the outer membrane - endospore
What happens in the fifth and final stage of sporulation?
The original cell ruptures releasing the spore
There are different types of spores, what are the three?
Terminal, subterminal and central spores
What are the three distinct phases of endospore germination?
Activation, germination and outgrowth
What causes the activation of the germination stage?
Heating, for example the cytoplasm may activate at 100 degrees
What happens in the germination stage of endospore germination?
In the presence of nutrients and amino acids, the spore becomes metabolically active
What happens in the outgrowth stage of endospore germination?
Uptake of water. RNA, DNA protein synthesis begins and the vegetative cell emerges
