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FDSN 507 Midterm 2

Protein Analysis

Give two reasons why protein analysis is important in nutrition labeling. Can give total protein content, gives protein correction in total dietary fiber determination.
What are the five characteristics of proteins which allow for analysis methods? Nitrogen content, peptide bonds, aromatic amino acids, dye binding capacity, ultraviolet absorptivity
______ method measures the presence of N and utilizes digestion, neutralization, distillation, and titration. Kjeldahl
T or F: The Kjeldahl methods measures inorganic nitrogen. False
____ methods utilizes combustion and gas chromatography to measure nitrogen. Dumas
T or F: The dumas method measures inorganic nitrogen. True
_____ method measures the absorbance of radiation by specific functional groups. IR
In the BCA method, proteins reduce _____ ions to _____ ions under alkaline conditions and these ions react with BCA to give a purple color. cupric, cuprous
What four amino acids does BCA depend on? Cysteine, cystine, tryptophan, tyrosine
What three amino acids absorb UV light at 280 nm? Tyrosine, tryptophan, phenylalanine
T or F: Heating of a food can reduce its extractabilty of protein. True
T or F: Methods other than Kjeldahl, Dumas, and UV require the use of a standard solution. True
How is non-protein nitrogen not included in protein analysis? Extraction under alkaline conditions and then precipitation.
T or F: Nonprotein nitrogen can cause overestimation of protein efficiency ratio. False
What three ways do proteins differ? Biochemical characteristics, nutritional quality, functional properties
Name three biochemical differences among proteins. Solubility, thermal stability, adsorption characteristics, charge, size
Describe salting out. Proteins are precipitates from solution as the ionic strength increases, as salt competes with the protein for water.
Describe isoelectric precipitation. Proteins precipitate at their isoelectric point because there is no electrostatic repulsion.
Describe solvent fractionation. Addition of ethanol or acetone decreases the solubility of proteins.
Describe protein denaturation. Heat or extremes in pH cause precipitation.
What are the four methods of differential solubility? Salting out, isoelectric precipitation, solvent fractionation, protein denaturation
In ____ chromatography, adsorption occurs between charged solid molecules in solution and the charged matrix. ion-exchange
In ____ chromatography, ligands bind to the support so that proteins can bind to the ligands; changing the pH allows for elution. affinity
_____ involves a semipermeable membrane which concentrates the sample with PEG. Dialysis
Name three types of membrane processes which separate based on size under pressure. Microfiltration, ultrafiltration, nanofiltration, reverse osmosis
T or F: In size-exclusion chromatography, larger molecules travel through the column fastest. True
Name three methods of electrophoresis. SDS-PAGE, isoelectric focusing, 2D electrophoresis
Describe SDS-PAGE. SDS is used to denature proteins and then is run through a polyacrylamide gel; separates charged molecules by their molar mass.
_____ can be used to determine the molecular weight of a protein. SDS-PAGE
Describe isoelectric focusing. A pH gradient is established and a sample is loaded and voltage is applied; proteins migrate to pI, where they have no net charge.
Describe 2D electrophoresis. Proteins are separated first by pI and second by molecular weight.
_____ are used to determine nutritional quality, identify a new protein, or determine molecular weight. Amino acid analysis
Describe amino acid analysis. A protein sample is acid hydrolyzed and then separated using chromatography.
T or F: Chromatography does not require the use of an internal standard or standard curves. False
What three items determine protein nutritional quality? Amino acid composition, digestability, anti-nutritional factors (eg. enzyme inhibitors/tannins)
How is protein efficiency ratio determined? Use a rat feeding test where PER = total weight gain of group/total protein consumed; compared to a casein control.
Name three tests which can be used to assess nutritional quality of protein. Essential amino acid index, in vitro protein digestability, lysine availability
Name four protein functional properties. Solubility, emulsification, foaming, gelation, dough formation
Created by: goberoi



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