Microbiology Flashcards Preview

POD Test 1 > Microbiology > Flashcards

Flashcards in Microbiology Deck (33):

Gram Stain Procedure

1) stain cells with gram stain (crystal violet)
2) treat with mordant (grams iodine) to form complex with crystal violet
3) wash with alcohol to dehydrate cell wall
4) counter stain with safranin

Results- G+ are blue/ purple; G- are pink/red


Peptidoglycan Structure

glycan polymers cross-linked with peptide chains

Alternating NAM-NAG with B-1,4 glycosidic linkages with tetrapeptide covalently linked off of NAM consisting of L-alanine, D-glutamic acid, DAP, and D-alanine

D-alanines are linked by a glycine pentapeptide in gram positives only


What is muramyl dipeptide (MDP)?

A product of peptidoglycan degredation that is an adjuvant, mitten, pyrogen, and somnagen


What is the function of teichoic and lipoteichoic acids?

Teichoic Acids- polymers of ribitol phosphate or glycerol phosphate covalently linked to peptidoglycan

Lipoteichoic Acids- teichoic acids with a terminal FA that anchors the molecule in the plasma membrane

Both are virulence factors for gram positives because they permit attachment to receptors on cell surfaces



Viral structure consisting of an RNA genome without any protein

Ex- hepatitis delta


Components of LPS

Lipid A- endotoxic activity, anchors LPS to outer leaflet of outer membrane and is a disaccharide with es terrified long chain fatty acids

Core Polysaccharide- 9-12 sugars (ex- KDO 8 carbon sugar)

O Antigen- long linear polysaccharide and is basis for stereotypes of bacterial strains


Components of the Outer Membrane

1) Porins- protein channels
2) Braun Lipoprotein- anchors the outer membrane to peptidoglycan
3) Omp Proteins- stabilize outer membrane, receptor fxn


Contents of periplasmic space

Hydrolytic enzymes and components of sugar transport systems. Pathogenic gram negatives also have collagenases, hyaluronidases, and beta-lactamases (virulence factors) that are released when the outer membrane is shed


Kingdom Protista

Protozoa, Algae, Fungi and Slime Molds


Kingdom Prokaryota

All bacteria


Virulence Factors promoting adherence

Pili, adhesins, and biofilms


Virulence Factors for invasion and intracellular residence

Induced Phagocytosis (by invasins)
Surviving Phagocytosis (catalase + SOD, lysozyme resistant cell wall)
Escape from phagocytic vesicles


Virulence Factors for Iron Aquesition

Receptors for transferrin, lactoferrin, ect.
Cytotoxins which damage/kill host to release iron


Types of Exotoxins

AB Toxins
Hemolysins (pore formers and phospholipases)
Damage Host Defense (Autoimmune Activation, Septic Shock, and Superantigens)


Consequences of Sepsis

Increased Vascular Permeability
DIC Thrombosis
Acute phase proteins (inflammation)
Low Iron


Definition of Auxotroph

Organisms that require the addition of macromolecules (amino acids, nucleotides) to media because they are unable to synthesize all they need.


Definition of Prototrophs

Organisms that only require C, N and S


Reactions catalyzed by catalase, peroxidase and SOD

202 + 2H --> O2 + H2O2 (SOD)
2H2O2 --> 2H2O +O2 (Catalase)
NADH + H + H2O2 --> NAD + 2H2O (Peroxidase)


Strict Aerobes

Aerobic, Have Ox enzymes, require oxygen and cannot ferment


Strict Anaerobe

Anaerobic, No Ox enzymes, killed by oxygen, fermentative


Facultative Anaerobes

Aerobic and Anaerobic, have Ox enzymes, respire with O2 and ferment without


Aerotolerant Anaerobes

Aerobic, anaerobic, have Ox enzymes, ferments in the presence or absence of O2



Aerobic, have Ox enzymes but not great, grow best at low Oxygen


Describe the function of the PTS

PEP Sugar Phosphotransferase System (PTS) is a mechanism to transport glucose and other sugars. The PTS consists of enzymes that transfer Phosphate groups from PEP to the sugar as it crosses the cytoplasmic membrane- energy saving mechanism.

Also plays role in directing cell towards nutrients and in regulating the glucose effect


Mathematical Expression of Growth Rate Doubling Time

b = a x 2^t/g

where b is the new number of cells, a is the initial cell number, t is the growth period (how long you are waiting for the experiment) and g is the doubling time. t/g is refered to as n


Action of bacterial DNA Polymerase

5' to 3' polymerase activity, 3' to 5' exonuclease activity


Antibiotics that block the initiation step of transcription

Rifampin (binds Beta subunit and inhibits first PDE bond) and Streptovaricins


Antibiotics that block the elongation step of transcription

Streptolydigin (Beta Subunit), Actinomycin D (binds DNA and blocks holoenzyme)


Shine Dalgarno Sequence

A region in the 5' untranslated region of mRNA where the ribosome binds to start translation


Antibiotics that block translation (4)

1. Streptomycin and other aminoglycosides (block assembly of 70s ribosome and cause misreading by ribosomes)

2. Tetrayclines including doxycycline and minocycline (block tRNAs binding to the A site)

3. Chloramphenicol (blocks peptidyltransferase rxn)

4. Erythromycin (blocks translocation)


Genes of the lac operon

LacZ- Beta Galactosidase
LacY- Permease
LacA- Transacetylase


General Control of the Lac Operon

Negative Control- turns transcription of genes ON
Positive Control- turns transcription of genes OFF


Regulatory role of PTS in sugar metabolism

Low glucose conditions- PTS enzyme P-IIIalc activates adenylate cyclase to produce cAMP which binds the CAP site in lacP to facilitate RNA polymerase binding and transcription of the lac operon