Microbiology -- Chapter 3 Flashcards
What are the different possible arrangement for bacterial cells?
cocci - spheres diploccoi - pairs tetrads - 4 cocci in a square rods spirals mycelium - branching network of filaments pleomorphic - lack of single form
What is meant by “arrangement of bacterial cells” and what are the different possible arrangements?
The cell shape influences the cell arrangement
Different possible shapes for bacteria?
bacciuls (rod), coccus (oval/sphere), spiral
In what significant way do prokaryotic cells differ from eukaryotic?
lack steroils, no cholesterol, contain hopanoids, sterol-like molecules, membranes define cell boundary, do not have internal, membrane-bound organelles
What are some major feautres of plasma membrane?
separates cells form environment, selectively permeable, allows cells to acquire nutrients and eliminate waste,
Explain what is meant by phospholipid molecule being “amphipathic”?
having polar and non-polar ends, where polar ends are hydrophillic and nonpolar ends are hydrophobic
What is “fluid mosaic model”?
Singer & Nicholson, membrances – lipid bilayers in which proteins float
What are”hopanoids”?
sterol-like molecules that help stabilize the membrane
How do “peripheral proteins” differ from “integral proteins”?
peripheral proteins are associated with the membrance and easily removable and soluble. Integral proteins are embedded in the cell and not easily moveable
Describe the prokaryotic cytpolasmic matrix
substance in which nucleoid, ribosomes, and inclusion bodies are now suspended. Lacks organelles bound by unit membrane. Mostly water. Is a major part of the protoplast (plasma membrane and everything within)
In what ways is the cytoplasmic matrix similar to and/or different from eukaryotic skeleton?
Although lacking a true cytoskeleton, the cytoplasmic matrix of bacteria does have cytoskeleton-like system of proteins. In most prokarytoes, it is relatively featureless meaning there’s no large structures. In eukaryotic cells, they have mitochondria and other organelles. Prokaryotic cytoplasm is teh site of metabolic cell functions
What is the cytoplasmic matrix?
Substances within the membrance, excluding genetic material
3 eukrayotic cytoskeletal elements, homologies with bacterial components, and general functions
- microfilaments - “track” for movement. 2. intermediate filaments - “maintain cell shape. 3. Microtubules - intracellular transport, cell wall in plants, mitotic spindle.
Homologies = FtsZ, MreB & ParM, rescentin
What are inclusion bodies?
when genes from one organism are expressed in another, this results in a protein sometimes called an “inclusion body”
Examples of what might be contained in inclusion bodies:
non-unit lipid membrane, viral capsid/outershell protein
What is a nucleoid?
chromosomes within the cell which are looped coils, round & compact in nucleus of eukaryotic cells
Characteristics of bacterial chromosomes:
not bound by a membrance, can extend throughout the cytoplasm
How does the packaging of a bacterial chromosomes differ from eukaryotic chromosome packaging?
EUKARYOTIC – DNA is packaged in chromosomes. Chromosomes are single strands of DNA.
BACTERIAL – DNA is packaged into a single, continous, loop chromosome.
In bacteria, compaction involves DNA binding proteins that help to form initial loops followed by the coiling of DNA.
In eukaryotes, the DNA is wrapped around groups of histone proteins (chromatin).
What components compromise the bacterial “cell envelope”?
cell wall and outer membrance, capsule, slime layer, glycocalyx
Functions of the bacterial cell wall
protests from osmotic lysis, gives shape/rigidity to cell, may contribute to pathogenicity (ability of a pathogen to produce an infection disease), antibiotics target cell wall, very few prokaryotes lack a cell wall
How does the cell wall protect the bacteria from osmotic stress
cell wall prevents swelling and lysis of bacteria in hypotonic solutions (high concentration of solutes inside cell than outside)
What is “lysis” and “plasmolysis”?
PLASMOLYSIS - plasma membrane shrinks away in hypertonic solutions.
LYSIS – swelling up.
How does penicillin work?
attacks cell wall, cells with compromised cell wall can be easily lysed
Lysozome?
attacks cell wall
What is the gram stain?
differential stain that differentiates G+ from G- by appearance. Eukaryotes stain negative (turn pink). FIrst used to distinguish streptococcus penumoniae.
Explain how differences in cell wall structure result in the differen staining reactions in the gram stain.
Gram-negative has a thin layer of peptidoglycan, surrounded by an outer membrance. Loses the crystal-violet stain, stained by safranin
How do the Gram-positive and Gram-negative cells differ? How are they similar?
similar internal structures. – chromosome ribosomes, inclusion bodies
DIFFERENT – external structure and characteristics
Describe the structure of Gram-positive and Gram-negative cell walls.
GRAM+ — thick peptidoglycan chains, teichoic acid, lipoteichoic acid, complex polysaccharides.
GRAM- – 2 layers of cytoplasmic membrane, thin peptidogylcan layer, outer membrance, no teichoic/lipoteichoic acid
Sacculus
bacterial cell wall, made of inter-linked molecule that encloses the entire cell wall
What is peptidoglycan?
organic polymer found in cell walls of prokaryotes and consist of polysaccharides and peptide chains in a strong molecular network
Describe the molecular structure of peptidoglycan
polymer of disaccharides (glycan) cross-linked by short chains of amino acids (peptides). Consist of parallel polymers of disaccharides (called glycan) cahins cross-linked with peptides of 4 amino acids
How does the cross-linking of peptidoglycan differ in Gram-positive and Gram-negative cells?
chemical structe of G- similar to G+ because composed of disaccharide-peptide repeated coupled through glycosidic bonds to form linear glycan strands, crosslinked into mesh-like framerwork through peptide stems attached to disaccharide repeat. Major difference is the thickness of the layer surrounding the plasma membrane. G+»_space;> G- amount of cross linking.
Describe the periplasmic space of G-positive bacteria. How does it differn from Gram-negative?
smaller amount in G+ than G-, located between cell wall and plasma membrance, periplasm has few proteins because peptidoglycans are porous, proteins can pass through cell wall, enzymes secreted by G+ bacteria are called exoenzymes
What is lipopolysaccharide molecule (LPS)? Describe the 3 major components.
protection from host defenses by changing the O ANTIGEN (1), creates permeabiliy barries to prevent toxins from entering, contributes to negative charge on cell surface (CORE POLYSACCHARDIE (2)), stabilizes outer membrane structure (lipid A) (3), acts as endotoxin (3) —> toxic to host – when cells die, they release LPS that may be toxic to host
What are inclusion bodies? Examples of inclusion bodies.
gas vacuoles – found in cyanobacteria provide buoyancy to keep at surface. magnetosomes – contain iron, used to orient cells in magnetic fields.
Inclusion bodies — made of organic and inorganic granules, not always bound by a membrance
What are things stored in inclusion bodies?
glycogen, poly-B-hydroxybutyrate, carbon storage reservoirs for energy and biosynthesis, carbon compounds, energy, inorganic substances
What are ribosomes?
protein + RNA, synthesize protein (mRNA becomes protein)
How do prokaryotic ribosomes differ from eukaryotic ribosomes?
eukaryotic ribosomes are larger than prokaryotic, tetracyclin harms prokaryotic/bacterial cells but not eukaryotic because ribosomes are too big. Eukaryotes 80s. Prokaryotes 70s.
What is nucleoid?
region where porkaryote chromosome is found, contains a single, circular chromosome, not bound by membrane
How is packagin of DNA in prokaryotic cells different from situation in eukaryotic cells?
Prokaryotes lack nuclear envelope, so translation begins before mRNA transcription is over. Bacteria mRNA has transcripts for several genes to synthesize protein. Eukaryotic cells contain a nucles and must wait for mRNA to be completely formed and must pass the nuckear envelope before translation. Prokarytoic mRNA specific for many proteins while eukaryotic mRNA specific for a single protein
How is the genetic material arranged in pokaryotic cells?
single, circular chromosome of DNA
What are plasmids?
small, circular DNA that is part of the bacterial chromosomes, exist independently of the chromosome, structures that carry DNA into cell, frequently contain a gene that encodes a protein that will make the bacteria to an antiobiotic
Define episome, curing, mobilization.
EPISOME — series of genes that can exist as a plasmid or in a chromosome.
CURING – loss of a plasmid.
MOBILIZATION –???
What are the general categories of plasmids?
Bacteriocin-encoding plasmids — bacteriocins destroy other bacteria.
Col plasmids — colicins are bacteriocins directed against E.Coli.
Virulence plasmics – encode factors enhancing pathogenicity.
Metabolic plasmids – genes that code for degradative enzymes/
What are capsules, slime layers, glycocalyx, and what are the general functions of each?
CAPSULES — well organized, hard to remove, usually composed of polysaccaharides, lying outside of the cell wall. Protect from phagocytosis, dessication, viral infection, hydrophobic toxic bmaterials; aid bacterial attachment to surfaces and gliding motility.
SLIME LAYERS – similar to capsules EXCEPT diffuse and unorganized, easy to remove
GLYCOCALYX – network of polysaccharides extending from surface of the cell, capsule or slime layer can be referred to as glycocalyx
S-LAYERS – regularly structured layers of protein or glycoprotein outside of the cell wall, protect against ion and pH fluctuations, osmotic stress, hydrolytic enzymes, can help maintain cell shape and envelope rigidity, promote cell adhesion, protect against host defenses, common in Archae, only struture outside plasma membrane
General function of pili, fimbrae, flagella?
FIMBRIAE – short, thin, hair-like, 1000 per cell, mediate attachment to surfaces, twitching-gliding
PILI – longer than fimbriae, thicket 10 per cell, required from mating
FLAGELLA – slender, rigid, rotates like a propeller
Different ways flagella may be distributed on a bacterial surface
MONOTRICHUOUS — single.
AMPHITRICHOUS — single flagella at each pole
LOPHOTRICHOUS — cluster at one or both ends.
PETRICHOUS — even distribution over entire surface
What is chemotaxis?
movement towards a chemical attractant or away from chemical repellant, concentration of chemical attractants/repellents deteted by chemoreceptors on surface
What are endospores?
resistant, dormant structure formed by some Gram-positive bacteria, enabling resistance of harsh environment
Why are endospores said to provide a means of survival for bacterial cells?
calcium, acid-soluble, DNA-binding proteins, dehydrated core, spore coat, DNA repair enzyme, resistant to heat/radiation/chemical/dessication
What are 2 common bacteria that produce endospores?
bacillus and claustridium
