Microbiology and Enzymes Flashcards

Flashcards for Microbiology Basics, Antibiotics and Resistance, and Enzymes

Cell membrane of Mycoplasma

Lacks a cell wall, instead membrane contains sterols; flexible and resistant to antibiotics targeting cell walls.

Shapes of Mycoplasma

Pleomorphic (can vary in shape).

Cell wall of Mycobacteria (Acid Fast)

Thick, waxy cell wall rich in mycolic acids, making them resistant to desiccation and disinfectants.

Nucleoid Region

Region in a prokaryotic cell containing the cell’s genetic material (DNA), not enclosed by a membrane. Contains one long bacterial chromosome

Bacterial ribosomes: Differences from eukaryotic ribosomes

Prokaryotic ribosomes 70S(50S and 30S) are smaller than eukaryotic ribosomes

Ribosome subunits: Svedberg Coefficient

Measurement of how quickly something runs to the bottom of a tube when put in a centrifuge

Inclusion bodies, granules

Storage of nutrients, wastes, gases, water, in/organic substances for later use when environment depleted; examples include glycogen, sulfur granules.

Endospores: Function, Cycle

Highly resistant metabolically inactive cells. Start as vegetative cell and turn to endospore when nutrients are depleted.

Briefly describe the endospore cycle (7 steps)

1. DNA aligns in center of cell. 2. DNA duplicates and membrane divides.  3. Membrane grows until forespore engulfed.  4. Cortex formed with peptidoglycan.  5. Calcium enters, water removed.   6. Protein coat formed outside cortex.  7. Enzymes destroy origin cell, endospore released.

Different shapes of bacteria

Coccus(round), bacillus(rod), spirillum(corkscrew), spirochete(spring), pleomorphic(varied)

Possible arrangements of bacteria

Single, pairs (diplo),chains(strepto), tetrads(coccus only), sarcina(cubes coccus only), palisades arrangement (row, bacillus)

Glycocalyx

Filamentous carb rich molecule coating

Types of Glycocalyx

Capsule: Organized, firmly attached layer; Slime: Loose, unorganized layer. Both protect against dehydration and phagocytosis.

Biofilm

A community of bacteria that adheres to surfaces, protected by a matrix they secrete. Forms in environments like teeth (plaque).

Quorum sensing

A communication process used by bacteria to coordinate behavior based on population density.

How biofilm forms and what is its function

Bacteria attach to an ideal surface and lay down sticky matrix that attracts other bacteria

Quorum sensing

When microbes in a biofilm signal each other and alter gene expression to coordinate functions and cooperate with other cells

Flagella: Different distributions

Monotrichous: One flagellum; Lophotrichous: Cluster at one end; Amphitrichous: One at each end; Peritrichous: Flagella all over the surface; Periplasmic: Internal flagella; All made of flagellin protein

Antibiotic

A substance produced by microorganisms that kills or inhibits other microbes.

When were antibiotics discovered?

1928 by Alexander Fleming, found penicillin in plate contaminated with mold

Microorganisms that make antibiotics

Mainly fungi (Penicillium) and bacteria (Streptomyces).

Synthetic and semisynthetic antibiotics

Synthetic: 100% inorganic, not secreted by microbes; Semisynthetic: Secreted by microbes and enhanced via chemical rxns

Ideal drug features (11)

Selectively toxic, microbicidal, remains potent, doesn’t cause allergies, doesn’t allow secondary infections, not broken down/excreted prematurely, not susceptible to resistance, compliments host defenses, active when diluted in body fluids, readily delivered to infection site, reasonably priced

Major Types of antibiotics (12)

Penicillins, griseofulvin, cephalosporins, gentamicin, bacitracin, polymyxin B, streptomycin, ethyromycin, tetracycline, vancomycin, chloramphenol, amphotericin B

Major targets of antibiotics (5)

Inhibit Cell wall synthesis, protein synthesis, interfere with RNA/DNA fxns, break membrane/ interfere w function, block metabolic pathways

Main parts of a Penicillin molecule

Beta-lactam ring, thiazolidine ring, and an R group (side chain).

Difference in other Penicillins

Different R groups attached to the beta-lactam ring.

Penicillin’s spectrum

Primarily targets Gram-positive bacteria (narrow spectrum)

Broad spectrum penicillins

Ampicillin and amoxicillin

Broad-spectrum definition

Active against a wide range of bacteria by targeting common pathogenic cell features

Mechanism of action of Penicillins

Inhibits peptide cross-linking in bacterial cell walls.

Cephalosporins structure

Beta-lactam ring, dihydrothiazine ring, and two variable R groups.

Vancomycin: Beta-lactam ring? Usage?

No beta-lactam ring. Used for staphylococcal infections, especially resistant strains or in instances of penicillin allergy

Antibiotic resistance acquisition

Spontaneous Mutation, conjugation(plasmid transfer), transduction(viral transfer), transformation(free DNA transfer)

Resistance definition

Bacteria can tolerate an otherwise lethal drug due to genetic changes.

Penicillinase/Beta-lactamase

Enzymes that deactivate beta-lactam rings in antibiotics.

Ways bacteria avoid antibiotic effects (6)

• Drug inactivation.

• Decreased permeability: change receptor shape

• Drug pumps: pump out drugs after cell entered

• Altered binding sites

• Alternate metabolic pathways

• Natural selection

Testing bacterial sensitivity to antibiotics (Kirby-Bauer test)

Tests various non antibiotic resistance on a plate by exposing them to many antibiotics and seeing which one is most effective

How antimicrobials can disrupt microbiota

Can kill beneficial microbes, leading to superinfections (overgrowth)

MIC (Minimum Inhibitory Concentration)

Lowest concentration of an antibiotic that inhibits bacterial growth.

Therapeutic Index (TI)

TI = Toxic dose / MIC. A high TI is safer.

Enzyme

A protein that acts as a catalyst to speed up chemical reactions. Lowers activation energy of rxns

Activation energy

Energy required to start a chemical reaction.

Cofactor vs. Coenzyme

Cofactor: Inorganic (metal ions); Coenzyme: Organic (vitamins); Enzymes can have both, many require at least one

Competitive inhibition

A molecule competes with the substrate for the active site. if normal substrate binds, rxns continue. If competitor substrate binds, rxns stop

Allosteric Inhibition

1) Enzyme-substrate rxn occurs, products released.                                   

2) Part of product binds to regulatory site and active site shape changes

3) Substrates can no longer bind to active site, rxns stop

Purpose of enzyme inhibition

To prevent excessive product formation.

Condensation reactions

Anabolic rxns form covalent bonds between substrates, releasing water.

Hydrolysis reactions

Catabolic rxns bonds using ATP and water.

Phosphorylation reaction

Transfer of a phosphate group to a molecule (regulated by kinase).

Kinase

Enzyme that catalyzes phosphorylation.

Exoenzymes

Secreted outside the cell, breaking down large molecules; amylase, cellulase, penicillinase

Endoenzymes

Function inside the cell; most enzymes are endoenzymes

Constitutive enzymes

Always present, constant rate of production regardless of substrate amount

Regulated enzymes

Not always present, production turned off if substrate concentration is too high

Enzyme sensitivity to environmental conditions

Affected by temperature, pH, and substrate concentration.