Hydrolytic Enzyme Laboratory Tests (Week 10)

Vocabulary flashcards covering key enzymes, substrates, and interpretations for the Gelatin Stab, Starch Agar, Milk Agar, and Urea Broth tests discussed in Week 10.

Hydrolytic Exoenzyme

Complex catalytic protein secreted by cells to break down large polymers into smaller monomers outside the cell.

Gelatin

Protein derived from collagen that is solid at room temperature and can be hydrolyzed into amino acids.

Gelatin Stab Test

Assesses an organism’s ability to liquefy gelatin; liquefaction after incubation indicates a positive result.

Gelatinase

Enzyme that hydrolyzes gelatin into polypeptides and amino acids, producing a liquid medium in the Gelatin Stab Test.

Starch

Polysaccharide composed of glucose units; reacts with iodine to produce a dark purple/black color if intact.

Starch Agar Test

Detects starch hydrolysis; after iodine flooding, yellow/orange halos indicate a positive result, dark purple/black indicates negative.

Amylase

Enzyme that hydrolyzes starch into glucose monomers, producing a yellow/orange zone on starch agar after iodine addition.

Casein

Milk protein responsible for milk’s white color; substrate for the enzyme casease.

Milk Agar Test

Detects casein hydrolysis; clearing around bacterial growth indicates a positive result, no clearing is negative.

Casease

Enzyme that breaks down casein into polypeptides and amino acids, creating clear zones on milk agar.

Urea

Nitrogenous waste product that can be split into ammonia and CO₂ by certain bacteria.

Urea Broth (UB) Test

Measures urease activity via pH change; fuchsia color (basic) is positive, orange/red is negative.

Urease

Enzyme that hydrolyzes urea into ammonia and CO₂, raising pH and turning phenol red indicator fuchsia.

Phenol Red Indicator

pH indicator in Urea Broth that turns yellow in acid, red/orange at neutral, and fuchsia in basic conditions.

Common Test Organisms

Bacillus subtilis and Escherichia coli for gelatin, starch, and milk agar tests; Proteus vulgaris and E. coli for urea broth.