Lecture 5 and 6 Flashcards
What is a flagella?
A filamentous protein structure attached to the cell surface that provides a swimming movement
How do flagella in prokaryotes differ from eukaryotes?
The lack the 9+2 arrangement of microtubules
The way they are powered
What is the diameter of a prokaryotic flagella?
20 nanometers
How are bacterial flagella powered?
By a proton motive force established on the bacterial membrane
How are eukaryotic flagella powered?
ATP hydrolysis
Why are very few cocci motile?
They are adapted to dry environments so lack hydrodynamic design
What are the several distinct proteins that make up the flagellar apparatus?
Basal body, hook structure, flagella filament
What is the structure of the basal body?
A system of rings embedded in the cell envelope
What name is given to the shape of bacterial flagella?
Helical
How is a flagella different to fimbria and pili?
They are longer and thicker
What name is given to bacteria with no flagella?
Atrichous
What name is given to bacteria with flagella distributed all over the bacterial surface?
Peritrichous
What name is given when flagella are distributed at one or both ends of the bacteria?
Polar
What are the two names given to describe the number of polar flagella?
Monotrichous- one flagellum
Lophotrichous- multiple flagella
What name is given to describe the distribution of polar flagella?
Amphitrichous- flagella at either end
What is the filament of the flagella composed of?
Flagellin (globular protein)
How is flagellin arranged?
In intertwining chains to form a hollow tube
What is the purpose of the hook?
It is a connector region between filament and basal body
What is the hook composed of?
Flagella hook protein
What does the hook act as?
A universal joint
What does the basal body consist of?
A small central rod inserted into a series of rings
What does the basal body function as?
A motor, also anchors flagella to cell wall and plasma membrane
What do gram negative bacteria have in their basal bodies?
2 pairs of rings, the outer anchored to cell wall and inner to plasma membrane
What do gram positive bacteria have in the basal bodies?
Inner pair of rings anchored to plasma membrane
In what direction do flagella rotate?
Both clockwise and anticlockwise
What is interesting about the speed a flagella can be rotated?
It can be altered (200-17,000 rpm)
What name is given to movement in one direction of a bacteria?
A run, or swim
What name is given to the change in direction that interrupts runs?
Tumbles
What is it called when cells move towards favorable or away from adverse environment?
Taxis
Name two type of taxis.
Chemotaxis
Phototaxis
What names are given to positive and negative taxis stimulus?
Attractant and repellant
When does the frequency of tumbles increase?
When bacteria are moving away from repellent stimulus
What is an axial filament?
A modified flagellum (endoflagella) that is enclosed in space between outersheath and cell wall
Name two examples of spirochete bacteria with axial filaments.
Treponema pallidum- syphilis
Borrelia burgdoferi- lyme disease
Where is one end of the axial filament attached?
Near to polar of cell
What does rotation of the axial filament cause?
Corkscrew-type movement
What is the plasma membrane?
A barrier that separates the cytoplasm from the environment
How thick is the plasma membrane?
6-8nm
Where are photosynthesis complexes found on the plasma membrane of bacteria?
Folds called thylakoids or chromatophores
Name some structures found within the bacterial cytoplasm.
Cytoskeleton, nucleoid, ribosomes, inclusion bodies, endospores
Define nucleoid.
Region containing bacterial chromosome
Describe the bacterial chromosome.
Generally a singular, circular chromosomes composed of double stranded DNA, not associated with histones
What does the shape of the bacterial nucleoid depend on?
Where the cell is within the cell cycle
Why is the chromosome attached to the cell membrane?
Cell membrane proteins responsible for DNA replication and segregation
When a cell is actively dividing, how many ribosomes may they have?
10,000+ ribosomes per cell
What structures give the cytoplasm a granular appearance?
Ribosomes
What do ribosomes consist of?
Two subunits made of proteins and rRNA
Why is the difference between the 70s ribosome and 80s ribosomes significant?
Difference can be exploited in terms of drug development to block protein production in bacteria
Give examples of the bacterial ribosome being targeted by antibiotics.
Steptomycin and gentamicin bind to 30s subunit
Erthromycin and chloramphenicol bind to 50s subunit
What is the function of inclusion bodies?
Energy reserves or resevoirs of structural building blocks
What are inclusion bodies?
Aggregates of specific material (s) that are not membrane bound
What name is given to the reserve of high energy, inorganic phosphate?
Metachromatic granules (volutin)
Give an example of a bacteria that has volutin inclusion bodies.
Corynebacterium diphtheriae
What name is given to the reserve of carbon (not lipid)?
Polysaccharide granules (starch/glycogen)
What name is given to the lipid reserve of carbon?
Polyhydroxybutyrate (PHB)
Give an example of a bacteria that has polysaccharide granule reserves.
E. coli
Give an example of types of bacteria that have polyhydroxybutyrate reserves.
Mycobacterium, Bacillus
Name another type of molecule that can be stored in inclusion bodies.
Sulphur granules
Name two types of bacteria that store sulphur granules.
Purple and green sulfur bacteria
What structures do bacteria have that compartmentalize bacterial processes?
Microcompartments
What are microcompartments?
Non-membrane, organelle like protein shell structures surrounding enzymes, proteins and gas
Give an example of microcompartments filled with enzymes.
Carboxysomes
What is the shape of carboxysomes?
Polyhendral shape
In what type of bacteria are carboxysomes commonly found?
Many autotrophic bacteria
What is the long name for rubisco?
Ribulose 1,5-diphosphate carboxylase
What do carboxysomes contain?
Rubisco
What shape are gas vacuoles?
Hollow cylinders
In what type of bacteria are gas vacuoles commonly found?
Aquatic bacteria such as cyanobacteria
Why is adjusting buoyancy important?
To be able to move up and down the bacteria column to be able to photosynthesize.
What type of intracellular structure might be found in magnetic responsive bacteria?
Magnetosomes
What type of magnetic substance is commonly found in magnetosomes?
Iron oxide (magnetite)
What is the purpose of magnetosomes?
Can be used to orientate and migrate bacteria along geomagnetic lines field lines
What is the structure of a magnetosome?
Membranous
What is the barrier between the lumen of the microcompartment and the cytosol formed of?
Conserved families of proteins assembled into a selectively permeable shell
How many structural groups of shell proteins are there that make up microcompartment shells?
3
Give an example of bacterial microcompartments being adapted for bioengineering in plants.
Enhancing CO2 fixation by installing carboxysomes in chloroplasts
What are some other potential applications for engineered microcompartments?
Serving as nano-factories for biochemical production, or as novel drug delivery devices
What type substance stored in a microcompartment may be toxic to certain insects?
Parasporal crystals
Name a bacteria that has magnetosomes.
Magnetospirillum spp and several gram negative bacteria
Name a bacteria that produces parasporal crystals.
Endospore-forming Bacillus
How can parasporal crystals be potential exploited?
As insecticides.
What is an endospore?
A dormant, tough, non-reproductive structure produced by some bacteria to ensure survival through periods of environmental stress
In what bacteria are endospores found?
Some gram positive bacteria (Bacillus, Clostridium)
How are endospores dispersed?
Wind, water, animal gut
What is the name given to endospore formation?
Sporulation
What is the name given to the return to vegetative state from endospore?
Germination
When does sporulation occur?
When key nutrients become scarce/unavailable (environmental stress)
How long does it take for sporulation to occur?
Several hours
What is the first step in sporulation?
Newly replicated chromosome and some cytoplasm become isolated by ingrowth of plasma membrane (spore septum)
What happens after the replicated chromosome has become isolated?
The mother cell engulfs the spore, double layed membrane surrounds the chromosome and cytoplasm, creating a forespore
What happens to the newly formed forespore?
A thick layer of peptidoglycan is laid down between the 2 membranes
What happens after the peptidoglycan is laid down between the two membranes?
Spore coat (made of protein) is laid down around the outermembrane, forming endospore. Cytoplasm of endospore becomes dessicated.
What is important about the shape and position of an endospore?
It varies in different species, so is useful for classification and identification purposes.
Name the three types of position of an endospore.
Terminal spores, subterminal spores, central spores.
What are the three distinct phases of endospore germination?
Activation, germination, outgrowth
rapid, takes few minutes
How can activation of endospores occur?
Heating activated spores conditioned to germinate
What occurs during germination?
In the presence of nutrients (amino acids- alanine) spore becomes metabolically active
What occurs during outgrowth of endospores?
Uptake of water, RNA, DNA protein synthesis begins, vegetative cell emerges
What 4 structures are found in all bacteria?
Cytoplasm, ribosomes, plasma membrane, nucleoid
What is a cell wall?
A complex, semi-rigid structure that maintains cell shape
How is the cell wall related to osmosis?
Prevents osmotic lysis of cell
What is another function of the cell wall?
To serve as an attachment point for appendages such as flagella, pili, fimbri etc.
What is a major component of bacterial cell walls?
Peptidoglycan
What are the two alternating sugars that peptidoglycan consists of?
N-acetyglucosamine (NAG or G)
N-acetylmuramic acid (NAM or M)
How are NAG and NAM connected?
By a Beta-1,4 glycosidic bond
What are 2 amino acids that peptidoglycan is made of?
Lysine, diaminopimelic acid (DAP)
What is attached to N-acetylmuramic acid?
A peptide chain of three to five amino acids, which can be cross-linked to the other peptide chain of another strand
What is unusual about the amino acids found in the cell wall of bacteria?
They can alternate between L- and D- forms (only L-form amino acid are used in proteins)
What enxyme can break the B1-4 linkages?
Autolysins (found in lysozome)
What aspect of cross linking varies between species?
The degree of cross linking
How does cross linking effect the cell wall?
Provides strength, more cross linking = greater rigidity
What name is given to the peptide chains linking directly between each glycan backbone?
Transpeptidation
What name is given to a bridge that can connect peptide chains indirectly?
Pentapeptide bridge
What effect does pentapeptide bridges have on the cell wall?
Makes the cell wall more flexible
What is the structure of a pentapeptide bridge?
5 gly amino acids
Give an example of a bacteria that has a pentapeptide bridge in its cell wall.
Staphylococcus aureus (gram positive)
Give an example of a bacteria that has transpeptidation.
Escherichia coli (gram negative)
What antibiotics stops the formation of cross links in bacterial cell walls?
Beta-lactam antibiotics, such as penicillin and cephalosporins
How do beta-lactam antibiotics stop cross link formation?
They inhibit transpeptidase
What does transpeptidase do?
Catalyses the formation of the final bond between two peptide chains (transpeptidation)
How thick is the peptidoglycan layer in gram negative bacteria?
2-5nm
How thick is the peptidoglycan layer in gram positive bacteria?
Up to 25nm
How much of the cell wall is made up of peptidoglycan in gram positive bacteria?
90%
What else can be found in the petidoglycan layer of many gram positive bacteria?
Teichoic acids (glycopolmers)
What are the two parts of a teichoic acid?
Disaccharide linkage unit
Main chain polymer
What is the structure of the disaccharide linkage unit in teichoic acids?
N-acetylmannosamine beta(1,4) bonded to N-acetylglucosamine-1-phosphate
How conserved is the disaccharide linkage until across bacteria species?
Highly conserved
What is the structure of the main chain polymer in teichoic acids?
Glycerophosphate or ribitol phosphate polymer which binds to sugars and D-alanine
What properties do main chain polymers of teichoic acids have?
Zwitterionic properties (+ and - electrical charge)
How conserved are main chain polymers in teichoic acids across bacterial species?
Not conserved
What are the two types of teichoic acid?
Lipoteichoic acid (LTA) Wall teichoic acid (WTA)
What is a lipoteichoic acid?
The disaccharide linkage unit attaches to diacylglycerol in the cell membrane
What does lipoteichoic acid interact with?
The main chain polymer interacts with petidoglycan
What does the linkage unit of wall teichoic acid bind with?
N-acetylmuramic acid in the petidoglycan chain
What happens to a cell without teichoic acid?
It dies
What is the function of teichoic acid?
Still unknown, could attract cations/anions (gives rigidity to cell wall or regulate their movement), could regulate blastosomes
What does the main chain of a WTA interact with?
Peptidoglycan and into the surrounding environment
What is pathogenesis?
The manner of development of a disease
How are teichoic acids involved in pathogenesis?
They promote adherence to host tissues
Give an example of teichoic acids promoting adherence to host tissues.
Mediate attachment of staphylocicci to mucosal cells
How can teichoic acid induce spetic shock?
They can promote injury/damage to organ, causing low blood pressure
What is another importance of teichoic acid in medicine?
Suspected ligands for toll-like receptors
Where are toll-like receptors found?
On cells (e.g. macrophages/dendritic cells) of the immune system
What can teichoic acid do to toll-like receptors?
Trigger innate immune response and development of antigen-specific acquired immunity
As a general rule, are gram negative or gram positive bacteria better at getting into our bodies?
Gram negative
What percentage does peptidoglycan make up of the outermembrane of gram negative bacteria?
10%
Where is the peptidoglycan layer found in gram negative bacteria?
In the periplasm- between outer and plasma membrane
How wide is the periplasm?
15nm
What is the periplasm?
Gel-like fluid containing degradative enzymes, binding proteins, chemoreceptos, detoxifying enzymes
Name three degradative enzymes found in the periplasm.
Phosphatatses (degrade phosphate containing compounds)
Proteases (degrade proteins/peptides)
Endonucleases (degrade nucliec acid)
Name a detoxifying enzyme found in the periplasm.
Beta-lactamase- degrades Beta-lactam antibiotics
What does the outermembrane of gram negative bacteria contain?
Lipopolysaccharides, lipoproteins, phospholipids
What is the role of the outermembrane in gram negative bacteria?
Aids in evading phagocytosis, acts as a barrier to antibiotics, enzymes, detergents, heavy metals, bile salts, dyes, and prevents molecules in periplasm being lost
What name is given to transporter proteins in the outermembrane of gram negative bacteria?
Porins (can be specific and non-specific)
What is embedded in the top layer of the outermembrane of gram -ve bacteria?
Lipopolysaccharides
What do lipopolysaccharides do?
Stabilise outer membrne, increase negative charge, protect from chemical attack
What three main parts do lipopolysaccharides consist of?
Lipid A
Core polysacchairde
O-polysaccharide
What does lipid A consist of?
Phosphorylated glucosamine disaccharide and fatty acids
What do the fatty acids in lipid A do?
Anchor LPS into the outermembrane
What else does lipid A function as?
An endotoxin- released when gram negative bacteria die and are degraded
What do endotoxins do?
Elicit symptoms associated with infection- fever, blood vessel dilation, vomit, diarrhoea, blood clotting
What does the core polysaccharide of LPS contain?
Sugars
What is the role of the core polysaccharide in LPS?
Structural role, provides stability, role varies between species.
What else is the O-polysaccharide known as?
O-antigen or O-chain
What is the O-polysaccharide made of?
Repetitive sugar polymer
What are the two types of O-chains found in bacteria?
Long O-chains (Smooth LPS)
Shorter O-chains (rough LPS)
What do O-chains do?
Prevent hydrophobic molecules from getting to outer membrane surface
Extend into the external environment
Function as antigens
What are some bacteria with rough LPS more susceptible to?
Hydrophobic drugs
Do O-chains vary?
Greatly between bacterial species and strains (e.g. 160 in E.coli)
How are O-chains useful in medicine?
Distinguishing between strains of the same species
Name a strain of E.coli.
E coli O157:H7
What does E coli O157:H7 cause?
Enteroheamorrhagic fever
What does H7 mean?
The strain of flagelar antigen
When was the gram stain test developed and by who?
1884
Christian Gram
What is the first step of the gram stain test?
Heat fixed cells treated with primary stain, crystal violet
What is the second step of the gram stain test?
The stain is washed off and the smear treated with a mordant (iodine)
What does mordant mean?
A substance that combines with a dye or stain and fixes it in a material
What happens to cells after the are treated with iodine?
The cells are washed with a decolourising agent (alcohol)
What happens to the cells after they are treated with alcohol?
The smear is counterstained with safranin and observed under the microscope
Name two mycobacterium.
Mycobacterium tuberculosis
Mycobacterium leprae
Describe the cell wall of mycobacterium.
Cell wall contains thin layer of peptidoglycan, surrounded by mycolic acid
What is mycolic acid?
Hydrophobic, waxy lipid (hence can’t be stained, and also repels antibiotics)
How can mycobacterium instead be stained?
With carbolfuchsin which binds to components of the cytosol after the cells are heated to make mycolic acid more pliable
Name some wall-less bacteria.
Mollicutes (mycoplasma)
How are mycoplasma bacteria protected?
Their plasma membrane contains sterols which give rigidity and protect the cell from lysis
What is a glycocalyx?
A viscous, gelatinous polymer surrounding the cell secreted by most bacteria
What is the glycocalyx composed of?
Polysaccharides and/or protein, composition varies within a species
What are the two types of glycocalyx?
Capsule, slime layer
How do capsules and slime layers vary?
Capsule is well organised and firmly attached to cell wall, slime layer is unorganised and loosely attached to cell wall
How are glycocalyx and biofilms associated?
The glycocalyx assists in the attachment to surfaces
What bacteria can adhere to teeth?
Steptococcus mutans
What bacteria can adhere to the small intestine?
Vibrio cholera
What bacteria can adhere to and colonise the respiratory tract?
Klebsiella
The glycocalyx can also help in the evasion of…
the immune system (phagocytosis)
The glycocalyx helps resist ______ (the loss of water)
desiccation
How can the glycocalyx aid nutrient supply?
It can be degraded and the sugars used as an energy source.
Viscosity can prevent loss of nutrients
What is one more function of the glycocalyx?
Facilitate cell to cell communication by acting as a medium for chemical signalling
What are fimbriae?
Short, stiff, hair-like proteinaceous appendages found predominantly in gram negative bacteria
Where are fimbriae found and how many are there?
At poles or along entire surface (rods have them at poles)
Few to several hundred
What do fimbriae do?
Stick cells to each other and to surfaces, such as during biofilm formation (colonization can occur)
Give an example of fimbriae adhering to surfaces.
In E.coli O157:H7, when fimbriated, it adheres to lining of small intestine
What are pili?
Hair-like, proteinacrous appendage, longer than fimbriae, only 1 or 2 per cell
What are 3 functions of pili?
Adherence to surfaces, motility, sex (conjugative pili)
How do type IV pili enable motility?
Synthesis of pili until it reaches surface, retraction as it is dismantled.
Twitching motility- short, jerky, intermittent motion
Gliding motility
