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Questions and Answers
What is the primary function of the bacterial glycocalyx?
Which of the following accurately describes a capsule in bacterial cells?
What mechanism do bacteria primarily use to reproduce?
Which shape is not commonly associated with bacteria?
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What role do flagella play in bacterial cells?
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What characteristic of biofilms makes them significant in environmental and health contexts?
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What is the primary method used to identify viruses when examining their reaction with antibodies?
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Which of the following statements about the slime layer is incorrect?
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Which of the following diseases is NOT caused by prions?
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Which of the following is NOT a nutritional source utilized by bacteria?
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What percentage of human cancers are attributed to oncogenic viruses?
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Which virus is associated with cervical cancer?
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How are prions primarily transmitted?
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What causes the accumulation of plaques in the brains of individuals with prion diseases?
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Which of the following methods is NOT typically used for growing animal viruses in the laboratory?
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Which oncogenic virus is linked to Burkitt's lymphoma?
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What is the primary function of flagella in bacteria?
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What term describes the movement of bacteria toward chemical stimuli?
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What structure is primarily responsible for the shape of a bacterial cell?
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How do Gram-positive and Gram-negative bacteria primarily differ?
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What role do fimbriae play in bacterial cells?
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What function does the cell wall serve regarding internal water pressure in bacteria?
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Which component is primarily found in the cell wall of bacteria?
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What can occur in bacteria that lack fimbriae due to genetic mutation?
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What is the primary component of the Gram-positive bacterial cell wall?
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What do teichoic acids contribute to the Gram-positive cell wall?
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What is the composition of the outer membrane in Gram-negative bacteria?
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What is a significant role of Lipid A in Gram-negative bacteria?
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How does the peptidoglycan layer of Gram-negative bacteria compare to that of Gram-positive bacteria?
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What function do porins serve in Gram-negative bacteria?
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What is the primary function of the periplasm in Gram-negative bacteria?
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Which component of lipopolysaccharides is responsible for providing stability?
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Study Notes
Growing Animal Viruses in the Laboratory
- Animal viruses can be grown in living animals, embryonated eggs, or cell cultures
Viral Identification
- Viruses are too small to be seen with a light microscope, they can only be observed using an electron microscope
- Viruses can be identified using serological methods, such as Western blotting
- Serological methods use antibodies to detect and identify a virus based on its reaction with the antibodies
- Viruses can also be identified by observing their cytopathic effects
- Cytopathic effects are changes that occur in the host cell when a virus is growing inside it
- Modern molecular methods, such as Polymerase Chain Reaction (PCR), can be used to identify and characterize viruses
Viruses and Cancer
- Oncogenic viruses, or oncoviruses are viruses that cause cancer in animals
- Oncogenic viruses can cause about 10% of all human cancers
- The genetic material of oncogenic viruses integrates into the host cell’s DNA and replicates along with the host cell’s chromosome
- The Papilloma virus (HPV) can cause cervical cancer
- The Epstein-Barr virus (EBV) (HV4) can cause Burkitt’s lymphoma
- Hepatitis B and C viruses (HBV) can cause liver cancer
Prions
- Prions are Small proteinaceous infectious particles.
- Prions are very resistant to inactivation by radiations
- Prions can be inherited, or transmitted by ingestion, transplant, or surgical instruments
- Prions cause nine neurological diseases in animals called spongiform encephalopathies, they cause large vacuoles in the brain
- Prions cause mad cow disease, also known as Bovine Spongiform Encephalopathy (BSE)
- These diseases are caused by the conversion of a normal host glycoprotein called PrPC (for cellular prion protein) into an infectious form called PrPSc (for scrapie protein).
- Fragments of PrPSc molecules accumulate in the brain, forming plaques.
- Prion diseases can also result from a mutation in the normal PrPc gene called sporadic Creutzfeldt-Jakob disease or CJD
- The Creutzfeldt-Jakob disease can also be fatal familial insomnia or FFI
- Kuru is a prion disease that affects the brain and causes severe neurological damage.
Prion Animal Infections
- Sheep infected with scrapie
- Deer infected with “chronic wasting disease.”
- Bovine spongiform encephalopathy, “mad cow disease.”
Bacteria
- Bacteria are single-celled prokaryotes.
- The most common shapes of bacteria are bacillus (rod-like), coccus (spherical or ovoid), and spiral (corkscrew or curved)
- Bacteria have peptidoglycan (carbohydrate and protein complex) cell walls.
- Bacteria divide by a process called binary fission.
- Bacteria use organic chemicals, inorganic chemicals, or photosynthesis for nutrition and energy production.
- Many bacteria can swim using moving appendages called flagella.
Bacterial Cell Structure
- The bacterial glycocalyx is a viscous (sticky), gelatinous polymer that is external to the cell wall
- The glycocalyx is composed of polysaccharide, polypeptide, or both.
- The glycocalyx has two main types; the slime layer and the capsule.
- The glycocalyx protects the cell from dehydration and nutrient loss.
- The glycocalyx inhibits killing by white blood cells by phagocytosis, which contributes to pathogenicity.
- The glycocalyx is involved in attachment and formation of biofilms.
Slime Layer
- The slime layer is a glycoprotein loosely attached to the cell surface.
- The slime layer helps bacteria adhere to solid surfaces and protects the cell from drying out and loss of nutrients.
- In Streptococcus mutans, the slime layer allows accumulation on tooth enamel.
Capsule
- The capsule is composed of polysaccharides firmly attached to the cell wall.
- The capsule helps bacteria adhere to solid surfaces and nutrients in the environment.
- The capsule is important in contributing to bacterial virulence.
- The capsule can protect bacteria from destruction by white blood cells (phagocytosis).
- Capsules make bacteria more slippery, helping to escape engulfment by phagocytic cells.
- For example: Streptococcus pneumoniae.
Biofilm
- A biofilm is an aggregation of microorganisms growing on a solid substrate.
- Cells in a biofilm are stuck to each other and/or to a surface.
- The glycocalyx is a very important component of a biofilm.
- The glycocalyx that helps cells in a biofilm attach to their target environment and to each other is called an extracellular polymeric substance (EPS).
- Biofilms may form on living or non-living surfaces.
- An example of a biofilm is Streptococcus mutans which causes dental caries.
Flagella
- Flagella are long filamentous appendages responsible for movement.
- Not all prokaryotes have flagella.
- Bacterial cells can have one or more flagella.
- Flagella proteins are antigens and can be used to distinguish among strains within a species.
- Flagella enable a bacterium to move toward a favorable environment or away from an adverse one.
- The movement of a bacterium toward or away from a particular stimulus is called taxis: chemical stimuli – chemotaxis; light stimuli – phototaxis.
Fimbriae
- Fimbriae are fine sticky proteinaceous hair-like bristles from the cell surface.
- A bacterial cell can have hundreds of fimbriae.
- Fimbriae can occur at the poles of the bacterial cell or be evenly distributed over the entire surface of the cell.
- Fimbriae are involved in adhesion to one another, to hosts, and to substances in the environment.
- Fimbriae are used to attach the bacteria to target cells in infection and to surfaces where they form a biofilm.
- When fimbriae are absent, colonization cannot happen, and no disease takes place.
Pili
- Pili are rigid tubular structures longer than fimbriae but shorter than flagella.
- Bacteria typically only have one or two pili per cell.
- Pili are involved in motility and DNA transfer by conjugation.
The Bacterial Cell Wall
- The cell wall is a complex semirigid structure responsible for the shape of the cell.
- Almost all prokaryotes have a cell wall that surrounds the underlying, fragile plasma (cytoplasmic) membrane.
- The cell wall protects the plasma membrane and the interior of the cell from adverse changes in the outside environment.
Functions of the Cell Wall
- The cell wall prevents rupturing when the water pressure inside the cell is greater than the outside pressure.
- The cell wall helps maintain the shape of a bacterium.
- The cell wall serves as a point of anchorage for flagella.
- The cell wall contributes to the ability of some species to cause disease.
- The cell wall is the site of action of some antibiotics.
- Some eukaryotes have cell walls, but they differ in composition from those of prokaryotes.
Gram-positive and Gram-negative Bacteria
- Bacteria are divided into two major groups: Gram-positive and Gram-negative, based on their reaction to Gram staining.
- Gram-positive bacteria have a thick cell wall : they have a thick peptidoglycan layer and a cell membrane.
- Gram-negative bacteria have a thinner cell wall : they have an outer membrane, a thin peptidoglycan layer, and a cell membrane.
Cell Wall Composition
- The cell wall is mainly composed of Peptidoglycan (also known as murein).
- Peptidoglycan is composed of repeating units of disaccharides cross-linked by polypeptides.
- The disaccharide backbone (glycan portion of peptidoglycan) is made up of alternating monosaccharides derivatives of glucose: N-acetylglucosamine (NAG) and N-acetlymuramic acid (NAM).
- The penicillins interfere with the last step of bacterial cell wall synthesis (transpeptidation or cross-linkage) and expose the osmotically less stable membrane .
Cell Wall of Gram-positive Bacteria
- The cell wall of gram-positive bacteria consists of several layers of peptidoglycan forming a thick rigid structure.
- A group of molecules called teichoic acids and lipoteichoic acids run perpendicular to the peptidoglycan sheets.
- Teichoic acid gives the wall antigenic specificity allowing laboratory identification of Gram positive bacteria.
Cell Wall of Gram-negative Bacteria
- The cell wall of gram-negative bacteria is composed of an outer membrane and a thin peptidoglycan layer.
- Peptidoglycan makes up only 5 – 20% of the cell wall.
- The peptidoglycan layer is not the outermost layer, but lies between the plasma membrane and an outer membrane.
Periplasm
- The periplasm is the region between the outer membrane and the plasma membrane.
- The periplasm is a gel-like fluid that contains a high concentration of degradative enzymes and transport proteins.
Outer Membrane of Gram-negative Bacteria
- The outer membrane of the gram-negative cell consists of lipopolysaccharides (LPS), lipoproteins, and phospholipids.
Lipopolysaccharide (LPS)
- LPS is a large, complex molecule that contains lipids and carbohydrates.
- LPS consists of three components: Lipid A - Core polysaccharide - O polysaccharide.
Lipid A
- Lipid A is responsible for the symptoms associated with infections by gram-negative bacteria, such as fever, dilation of blood vessels, shock, and blood clotting.
- Lipid A functions as an endotoxin when gram-negative bacteria die.
Core Polysaccharide
- The core polysaccharide is attached to lipid A and contains unusual sugars.
- The core polysaccharide provides stability.
O Polysaccharide
- The O polysaccharide is composed of sugar molecules.
- The O polysaccharide is antigenic and useful for distinguishing species.
Porins in Gram-negative bacteria
- Porins are found in the outer membranes of Gram-negative bacteria.
- Porins are proteins that form channels across the outer membrane of Gram-negative bacteria.
- Porins allow small molecules to pass through the outer membrane.
- Porins are involved in the transport of nutrients and the excretion of waste products.
- Porins can also serve as receptors for viruses and other molecules.
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Description
This quiz covers key concepts in animal virology, including methods for growing viruses, identification techniques, and their association with cancer. Explore how viruses interact with host cells and the role of serological and molecular methods in viral research.
