Absorption and Color Perception Quiz

Photometry is the measurement of light absorption by compounds. It uses the interaction of light with matter to analyze substances both qualitatively (identifying what's present) and quantitatively (measuring how much is present).

Lambert's Law states that light absorption is independent of the intensity of the incident light but directly proportional to the thickness of the absorbing medium (solution).

Beer's Law states that light absorption by a solution is directly proportional to the number of absorbing molecules in the light's path. This means more molecules in the solution absorb more light.

The Beer-Lambert Equation relates absorbance (A) to molar absorption coefficient (E), molar concentration (c), and path length (l): A = Ecl

Phosphatidylcholine, also known as lecithin, is a major class of phospholipids found in cell membranes. It's essential for forming cell membranes, lipid bilayers, and acting as a storage lipid.

Phosphatidylcholine consists of a glycerol backbone, two fatty acid residues (usually one saturated and one unsaturated), and a phosphorylated choline group.

TLC separates phospholipids in a mixture based on their polarity. Phosphatidylcholine, being a phospholipid, will migrate to a specific position on the TLC plate.

Saponification is a mild alkaline hydrolysis that releases fatty acids from phosphatidylcholine by breaking the ester bonds between the fatty acids and the glycerol backbone.

Methylation converts free fatty acids into fatty acid methyl esters (FAMEs), which are volatile and can be analyzed using gas chromatography (GC).

Chromatography involves two phases: a stationary phase (fixed in place) and a mobile phase (which moves through the stationary phase).

Solutes in a mixture are separated based on their differing affinities for the stationary phase and the mobile phase. Molecules with stronger affinity for the stationary phase move slower.

The retention factor (Rf) is the ratio of the distance a solute migrates to the distance traveled by the solvent. It helps compare migration of different solutes.

The four basic types of chromatography are gas-solid, gas-liquid (GC), liquid-liquid, and liquid-solid. These differ based on the combination of mobile & stationary phases.

In column chromatography, the mobile phase (liquid or gas) is passed through a column filled with stationary phase. This separates solutes as they move through the column.

TLC uses a thin layer of adsorbent on a flat surface. The mobile phase moves through by capillary action, separating solutes. It's quick and good for small amounts.

Partitioning involves distributing solutes between a stationary phase (often aqueous) and a moving organic phase. This is based on differences in solubility.

Absorption occurs when solutes bind to the surface of the stationary phase. This is a common mechanism in many forms of chromatography.

Ion exchange separates solutes based on their charge. The stationary phase has charged sites which attract solutes of the opposite charge.

Gel filtration separates solutes based on size. Larger molecules are excluded from the stationary phase and move faster than smaller molecules.

Affinity chromatography uses specific interactions between a solute and the stationary phase. For example, a protein may bind to an antibody on the stationary phase.

Proteins have four levels of structure: primary (amino acid sequence), secondary (local folding patterns like alpha helices and beta sheets), tertiary (overall 3D shape), and quaternary (arrangement of multiple polypeptide chains).

The main types of proteins based on solubility are albumins (water-soluble), globulins (soluble in dilute salt solutions), glutelins (soluble in dilute acids or bases), and scleroproteins (insoluble).

Denaturation disrupts the 3D structure of a protein, rendering it nonfunctional. This can happen due to chemical changes (pH shifts, detergents) or physical factors (heat, agitation).

Protein solubility in water depends on the interaction between protein molecules, water, and ions in the solution. This is influenced by the ionic strength, which reflects the concentration and charge of ions.

Salting-in occurs at low ionic strength, where added neutral salts like ammonium sulfate stabilize proteins by interacting with their charged groups. This increases protein solubility.

Salting-out occurs at high ionic strength, where excessive salt competes with proteins for water molecules. This reduces hydration and leads to protein aggregation and precipitation.

PAGE separates proteins based on molecular mass. Smaller proteins migrate farther in the gel than larger ones.

SDS (sodium dodecyl sulfate) is a negatively charged detergent that binds to proteins, denaturing them into linear chains and providing a uniform negative charge proportional to their size.

The Lowry assay determines the protein concentration in a solution with greater sensitivity than the biuret method. It involves a two-step reaction with copper ions and the Folin reagent.