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