Lecture 1 (8/21/13) Flashcards
Describe the following pathogenic microbial agents by cellularity and determine if they are prokaryotic, eukaryotic, or particles: Bacteria, Fungi, Viruses, Protozoa, Algae, Other.
Bacteria: cellular, prokaryotes Fungi: cellular, eukaryotes Viruses: acellular, particles Protozoa: cellular, eukaryotic Algae: cellular, eukaryotic Other (eg. Pythium): cellular, eukaryotic
Explain the differences between Prokaryotic and Eukaryotic organisms.
Prokaryotic: less than 5 micrometers in length, membrane-bound organelles are absent, 70S ribosomes, nucleic acids occur as single molecules and are usually circular, nuclear membrane and nucleolus are absent, and they replicate by binary fission Eukaryotic: more than 10 micrometers in diameter, membrane-bound organelles are present, 80S ribosomes are in the cytoplasm, 70S ribosomes are located in the mitochondria and chloroplasts, nucleic acids are distributed in chromosomes, contains and nuclear membrane and a nucleolus, and they replicate by mitosis
How are prokaryotes classified?
They can be classified into Archaea and Bacteria and further classified into phenotypic groups such as: Gram-positive and Gram-negative bacteria, endospore-forming rods, spiral-shaped bacteria and spirochaetes, acid-fast bacteria, obligate anaerobes, aerobic actinomycetes, bacteria that lack cell walls, and obligate intracellular bacteria.
Explain the common international rules of nomenclature for bacteria.
You must have sufficient phenotypic and genotypic descriptions in order to compare it to related, well-described taxa. In addition, you must have a properly latinized Genus and species name. Finally, publication is given first priority in the International Journal of Systematic and Evolutionary Microbiology.
Describe the basic structure of bacteria.
Bacteria tend to have a length of 2.5 micrometers and a typical width of 1 micrometer. The outer layer of bacteria is known as the bacterial wall and is composed of peptidoglycan. The bacterial wall surrounds another cellular layer known as the cytoplasmic membrane, which surrounds the cytoplasm. Inside the cytoplasm are ribosomes and DNA.
What is another name for peptidoglycan?
Murein
What is murein and what is it responsible for?
It is a cross-linked polymer with repeating subunits of N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM). It is responsible for greater than 80% of the cell’s mass, the cell shape, staining qualities, and osmotic stability.
Explain the importance of the terminal D-Ala in the precursor subunit monomer of murein.
When the D-Ala is cleaved, it makes energy for synthesis and is therefore used as an energy source. It is also used in cross-linking between other murein units at the D-Lys amino acid.
Why is cross-linking important?
After a reaction known as transpeptidination (one of the steps of cross-linking) a resulting mesh-like matrix is formed that gives the bacterial wall its strength. This reaction occurs outside the cell membrane by enyzmes that insert a precursor to both strands by peptidases that mediate the cross-linking.
What protein is known to prevent cross-linking of strands of murein?
Pencillin-binding protein
What is the function of 16S rRNA?
It codes for RNA and is the basic gene found in all microorganisms. It can be used to classify organelles (since they are classified based on genetics).
What are the cell wall lytic enzymes?
Glucosiminidase, Muramidase, Amidase, Endopeptidase
Explain the Gram-stain reaction for both the Gram-positive and Gram-negative bacteria.
Step 1: Add aqueous solution of crystal violet dye Step 2: Add aqueous Grams iodine which interacts with peptides that fixes the stain in the cell wall. Step 3: Add decolorizer (alcohol or acetone) to keep Gram-positive stained purple and Gram-negative bacteria loses color. Step 4: Add safarin red which won’t affect the Gram-positive bacteria but will dye the Gram-negative bacteria red.
Explain the differences between the Gram-positive and Gram-negative cell walls.
Gram-positive: has more peptidoglycan and polymers made of phosphate groups (teichoic acids), some of which are covalently bound to the cell membrane; has a peptidoglycan layer as well as an inner membrane Gram-negative: has an outer membrane, cytoplasmic membrane, and a peptidoglycan layer; the outer layer contains macromolcules (endotoxin: LPS) and Porin
What are the three main functions of the teichoic acids located in the cell walls of Gram-positive bacteria?
1) Regulate surface cations 2) Surface attachment receptor 3) Major surface antigen
What are the cellular inclusions of the above bacterial cell?
No nucleus; rod-shaped; Gram-negative because of the 2 membranes; unevenly stained
What is the morphological component seen in this image? Why is this significant?
These bacteria have been positively tested for capsules. Capsules are substances secreted from cells that are polymerized. They represent a halo-like area around the bacterium. The bacterium releases hydrophilic secretions that give it its shiny, wet-looking appearance (mucoid) and most capsules are composed of simple sugars.
What is being pictured in this image? What is its significance?
Fimbriae: there are two types (sex pilus and somatic pili); there is flagella present in the fimbriae that is used for locomotion, can use their location to identify bacteria, and have a variety of flagella proteins that are used to anchor the flagella to the cell wall; the major structure is filamentous protein
What is seen in this image?
flagella
Name the five layers of bacteria endospores and describe their function.
Core: contains all components needed to create an viable cell; DNA is complexed with small acid soluble
proteins that protect from heat and UV; dipicolinic acid, a unique derivative of lysine,
is present in high concentrations as calcium chelates; low water content (28-55) accounts for
wet heat resistance [Summary: metabolically inert and contains all ingredients for life of the cell, low water content, DNA is protected against heat and UV, and derivative of lysine]
Inner membrane: semi crystalline, not fluid until germination; surrounded by thin peptidoglycan wall
Cortex: modified peptidoglycan; glycosidic bonds resistant to lysozyme; lack teichoic acid and carbohydrates
Coat: multiple layers of protein arrays; impermeable to enzymes
Exosporium: thin, complex membrane layer found in some bacteria; gives cell its distinctive structure; highly condensed; no synthesis; highly resistant
Understand this table. I don’t believe you have to necessarily memorize it.
What is sporulation and what are the steps required for it? How much time is required?
Definiton: asexual reproduction by the production and release of spores
- Changes in intracellular solute concentration
- Nuclear division and end to end formation
of a dense chromatin thread - Spore septum formation
- Engulfment of forespore
- Cortex synthesis
- Early coat synthesis
- Maturation
- Lysis and spore liberation
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