Biochemical Laboratory Experiments and Principles

Comprehensive vocabulary flashcards covering biochemical principles, qualitative and quantitative reagents, spectroscopy laws, and enzymatic test protocols.

Visible Light Spectrum

The narrow range of electromagnetic wavelengths visually perceived by humans between $400\,nm$ and $750\,nm$ ($1\,nm = 10^{-9}\,m$).

Chromophore

A chemical substance that absorbs visible light; the specific wavelength at which it exhibits maximum light absorption is termed its $\lambda_{max}$.

Transmittance ($T$)

The ratio of the intensity of transmitted light ($I$) through an absorbing medium to the intensity of incident light ($I_0$), expressed as $I/I_0$ (or percent transmittance as $\frac{I}{I_0} \times 100$).

Beer-Lambert Law

A physical law stating that the absorbance of monochromatic light passing through a solution is directly proportional to the concentration of the absorbing substance and path length: $A = \varepsilon C L$.

Molar Extinction Coefficient ($\varepsilon_M$)

The constant absorbance value of a $1\,mol\,dm^{-3}$ solution of a chromophore measured within a cuvette having a path length of $1\,cm$.

Colorimeter

An analytical instrument designed to quantify the intensity and wavelength of light passing through an absorbing medium, consisting of a light source, focusing lenses, a filter to select monochromatic light, and a photocell detector.

DNSA Reagent

A quantitative assay solution prepared by dissolving $1\,g$ of 3,5-dinitrosalicylic acid, $30\,g$ of sodium potassium tartrate, and $1.6\,g$ of $NaOH$ in water and adjusting the total volume to $100\,ml$.

DNSA Reaction Principle

The reduction of 3,5-dinitrosalicylic acid (DNSA) to 3-amino-5-nitrosalicylic acid by reducing sugars in alkaline conditions, yielding an orange-red color measured at $540\,nm$.

Diphenylamine Reaction for DNA

A chemical reaction where 2-deoxyribose of DNA is converted under acidic boiling conditions to $\omega$-hydroxylevulinic aldehyde, which condenses with diphenylamine to yield a blue colored complex with an absorbance maximum at $595\,nm$.

$\omega$-Hydroxylevulinic Aldehyde

The intermediate aldehyde formed by the acid-catalyzed dehydration of 2-deoxyribose during the Dische diphenylamine reaction for DNA estimation.

Biuret Reagent

A reagent composed of $1.5\,g\,CuSO_4 \cdot 5H_2O$, $4.5\,g$ sodium potassium tartrate, and $2.5\,g$ potassium iodide dissolved in $0.2\,M\,NaOH$ and brought to a total volume of $500\,ml$.

Biuret Test Principle

The reaction of alkaline cupric ions ($Cu^{2+}$) with compounds containing two or more peptide bonds to form a pinkish-violet coordination complex involving the unshared electron pairs of peptide nitrogen and water oxygen.

Orcinol Reagent

A reagent system for pentose estimation consisting of Solution A ($300\,mg$ orcinol in $5\,ml$ ethanol) added to Solution B ($0.1\%$ $FeCl_3 \cdot 6H_2O$ in concentrated $HCl$) in a ratio of $3.5\,ml$ of A per $100\,ml$ of B.

Orcinol Reaction Principle

A pentose-specific reaction in which boiling with concentrated $HCl$ converts pentose to furfural, which reacts with orcinol in the presence of $FeCl_3$ catalyst to yield a green product with a $\lambda_{max}$ of $660\,nm$.

Amylose and Amylopectin

The two structural polysaccharides that constitute starch; amylose forms linear chains of $\alpha$-glucopyranose, whereas amylopectin contains branched chains and makes up roughly $70\%$ of potato starch.

Starch

A plant reserve homopolysaccharide composed of $\alpha$-glucopyranose repeating units that occurs as white, tasteless, and odorless granules insoluble in cold water or alcohol.

Ninhydrin Reagent

A $0.2\%$ ninhydrin solution prepared in acetone, used for the qualitative colorimetric detection of amino acids and proteins.

Benedict's Reagent

A qualitative reducing sugar reagent prepared by dissolving $173\,g$ sodium citrate and $100\,g$ anhydrous $Na_2CO_3$ in hot water, combined with $7.3\,g\,CuSO_4 \cdot 5H_2O$ in water and made up to $1\,L$.

Iodine Test

A qualitative carbohydrate test where adding iodine in potassium iodide ($KI$) yields a positive colored reaction with starch, but remains negative with sucrose.

Sudan Black Test

A qualitative lipid assay where adding Sudan black dye to a melted sample produces a characteristic blue coloration indicating the presence of lipids.

Urease Assay System

An enzyme assay utilizing $1\,ml$ soybean extract as the enzyme source, $10\%$ urea solution, incubation at $60^\circ\text{C}$, and phenolphthalein indicator to monitor enzymatic activity.

Catalase Assay System

An enzymatic assay identifying catalase activity through the decomposition reaction occurring when yeast granules are introduced into a $3\%$ hydrogen peroxide ($H_2O_2$) solution.