Lecture 2 structures Flashcards
How are flagella assembled?
In a step-by-step manner using a specialized protein secretion pathway called type 3 secretion
How fast can flagella go?
Up to 100mph
Describe the use of flagella in H. Pylori
H. Pylori will create a “sheath” of flagella using synthesized sugar; the most vulnerable point of a flagella is its very tip, so they have extra proteins that create a “terminal bulb” at the ends of the flagella.
Coordinated counterclockwise motion of flagella leads to swimming, and is a(n) __________
Clockwise motion of flagella leads to tumbling, and is a(n) _________.
Counterclockwise swimming is an attractant; clockwise tumbling is a repellent
Define chemotaxis
Swimming motility; movement toward or away
Describe the structure of flagella
1) There’s a protein structure across the envelope, called the basal body or rotor.
2) Just above the basal body there’s a hook, called a universal joint
3) The filament acts as a propeller
What are flagella driven by?
Ionic potential/ proton motive force
The motor that turns the flagella rotates on average _____ rpm.
E. coli = ______rpm
Vibrio = ______rpm
500; E. coli is 5,000rpm; Vibrio is 100,000rpm
How does flagella motion activate for chemotaxis?
Chemoreceptors in envelope relay information to flagellar apparati, so the flagella turn on when the bacteria senses food
Why is adherence so important to bacteria?
Provides an advantage, prevents removal by fluids
True or false: Virtually all pathogenic bacteria having ways of attaching themselves firmly to host cells
True
Define pili (fimbriae) and what they do
Defined as filamentous appendages composed of “pilin” protein that are anchored to the outer membrane of Gram negative bacteria
-Mediate attachment to eukaryotic host cells
Pili are primarily found in Gram-________ bacteria
negative
Pili are peritrichou; define peritrichou
Hairy all over
Give an example of a specialized pili
Sex or F pilus for bacterial conjugation
What can be described as “rod-shaped protein structures extend from the bacterial surface and bind to host cell surface molecules (typically carbohydrates.)”?
Pili
True or false: Pili can be evenly distributed or located preferentially to one part of the bacterial cell.
True
Define afimbrial adhesins. What kind of bacteria are they found in?
-Defined as bacterial surface proteins that are not organized in a rodlike structure and mediate tight binding between bacteria and host cell.
-All bacteria have these
Bacteria may produce both pili and afimbrial adhesins. Why?
To lock into the surface if it’s in an area of fast flow
Define capsules
Capsules are an enormous layer of polysaccharides
(With the exception of Bacillus anthracis poly-D glutamic acid, a polypeptide capsule)
What does the capsule of bacteria do?
It’s anti-phagocytic; it’s also called the K-antigen and has thousands of serotypes
What is the K antigen?
Capsules
Define glycocalyx and what it does
-Also known as the slime layer, it’s a “loose” layer of polysaccharides
-It functions in attachment/adherence/motility and is a key feature of biofilm formation
What is a key feature of biofilm formation?
Glycocalyx
Define the S-layer and what it does
-A layer composed of a single protein species [sometimes glycosylated] that forms a crystalline array
-This layer is small; you’d need electron microscopy to observe it
-Aids in protection against environmental stress (osmotic, pH, enzymatic) and in phagocytosis
Lipopolysaccharide (LPS) is found on the surface of Gram-________ bacteria; it is not present on the other type of Gram bacteria
negative
Name and describe the 3 regions of lipopolysaccharides (LPS)
1) Lipid A domain: phosphorylated lipid with sugar backbone
2) Core region: oligosaccharide chain
3) O-antigen: polysaccharide chain
Describe the role of the lipid A domain (region I) of lipopolysaccharides (LPS)
-Hydrophobic anchor, holds LPS in the outer membrane.
-The portion of LPS responsible for endotoxicity
-Activates Toll-receptor (innate immune response)
–Changing the lengths of the acyl chains, changing the number of acyl chains, adding ethanolamine/phosphate/etc to the phosphate groups to alter its surface charge, or adding amino acids to Lipid A can prevent Lipid A from activating the Toll-receptor
-Important: Some bacteria synthesize a non-inflammatory lipid A to evade immune recognition
What is the portion of LPS responsible for endotoxicity?
The lipid A domain (region I)
What activates the Toll-receptor?
Lipid A domain
Describe the role of the core oligosaccharide region (region II) of lipopolysaccharides (LPS)
-Consists of short chain of sugars attached directly to lipid A
-Not required for growth in laboratory
-Clinical Relevance: During infection thought to be required for maintaining permeability properties of the outer membrane
Describe the role of the O-antigen/ O-polysaccharide region (region III) of lipopolysaccharides (LPS)
-Repeating unit of oligosaccharide subunits made up of 3-5 sugars attached directly to the outer core region (up to 40 units long)
-Major antigenic determinant with great variation between species and even strains
-Used as basis for determining serogroup of a bacterial strain
-Clinical Relevance: Loss of O-antigen results in loss of virulence; O-antigen provides protection from host defenses
The loss of what part of a lipopolysaccharide leads to loss of virulence?
The O-antigen; it provides protection from host defenses
Give 5 examples of internal structures found in bacteria
Gas vacuole, ribosomes, inclusions, nucleoid, endospore
What is the purpose of a gas vacuole?
Buoyancy for floating in aquatic environments
What is the purpose of ribosomes?
Protein synthesis
What is the purpose of inclusions?
Storage of carbon, phosphate, and other substances
What is the purpose of the nucleiod?
Localization of genetic material (DNA)
What is the purpose of an endospore, and in what type of bacteria are they found?
-Survival under harsh environmental conditions; only observed in bacteria
-Specifically only some gram-positive bacteria
What are the 3 main components of the bacterial cytoskeleton, and what do they do?
1) FtsZ: A division protein widely observed in bacteria; forms a disc shape in the center of the cell
2) MreB: maintains cell (rod) shape, localizes proteins
3) Crescentin: introduces crescent-shaped morphology
Name and briefly describe the density of 3 storage inclusions found in bacteria
1) Glycogen (sugar)
2) Polyhydroxyalkanoate granules: Very light
3) Polyphosphate granules: Very dense; store phosphate
What is the purpose of vacuoles?
To store gas for buoyancy in an aquatic environment
What do magnetosomes do?
Aid in orientation to seek nutrients; based on earth’s magnetic poles
What is the purpose of carboxysomes?
A specialized site for CO2 fixation (a protein coat with an enzyme inside)
There are as many as ________ ribosomes growing in a bacterial cell, whereas eukaryotes have up to ________
70K; 10 million
Why is the difference in size and composition between a prokaryote and eukaryote important?
It’s important for antibiotics; they can pick out bacterial ribosomes and keep them from synthesizing proteins
Describe bacterial nucleiods
-Most are circular
-No membrane
-Have proteins and histone-like proteins that interact and organize things
Name 3 types of bacterial plasmids and briefly describe what they do
1) Conjugative plasmids: the F factor; transfers copies of themselves into another bacteria
2) R (resistance) plasmids: can be conjugative (transfered through bacterial “sex”); delivers antibiotic resistance genes
3) Virulence plasmids: encode genes for pathogenicity
Some Gram-_________ bacteria are spore-formers
positive
What is the purpose of sporulation, and what do spores contain?
1) Spores represent a dormant state for long-term survival; formation (sporulation) is induced by harsh environmental conditions
2) Spores contain the entire chromosome enveloped by a membrane, peptidoglycan and an outer protein coat (keratin-like)
Certain conditions will cause spores to become activated; this is called _____________
germination
What aspect of sporulation is useful in diagnosis?
The location of endospores
Name 4 locations of endospores
1) Central
2) Swollen sporangium (makes cell somewhat sperm-shaped)
3) Terminal (at the end of a rod-cell)
4) Subterminal (almost at the end of a rod-cell)
Why do we typically set autoclaves to 121 degrees celcius?
That’s the temperature that can kill endospores
Briefly describe the morphology of protozoa, amoeba, and algae
Protozoa: motile due to cilia that cover their surface, heterotrophs
Amoeba: has a pseudopod and a contractile vacuole to control movement; prevents excess water inside the cell
Algae: have stored starch grains so they have carbon on-demand, use sunlight’s energy or can use organic compounds, extreme diversity, extremely abundant
Define siderophore and what it allows bacteria to do
-A molecule that binds to various forms of iron and makes it available to the cell
-This allows bacteria living in an animal to steal that creature’s iron
