Table of contents

1. Introduction to Biochemistry4h 34m
2. Water3h 23m
3. Amino Acids8h 10m
4. Protein Structure10h 4m
5. Protein Techniques14h 5m
6. Enzymes and Enzyme Kinetics13h 38m
7. Enzyme Inhibition and Regulation 8h 42m
8. Protein Function 9h 41m
9. Carbohydrates7h 49m
10. Lipids5h 49m
11. Biological Membranes and Transport 6h 37m
12. Biosignaling9h 45m
Review 1: Nucleic Acids, Lipids, & Membranes2h 47m
Review 2: Biosignaling, Glycolysis, Gluconeogenesis, & PP-Pathway3h 12m
Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism2h 26m
Review 4: Amino Acid Oxidation, Oxidative Phosphorylation, & Photophosphorylation1h 48m

5. Protein Techniques

FDNB

Biochemistry

5. Protein Techniques

FDNB

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Multiple Choice

A 660 mg sample of a protein with quaternary structure (MW=132,000 g/mol) was treated with excess 1-fluoro-2,4-dinitrobenzene (FDNB) under slightly alkaline conditions until the reaction was complete. After FDNB treatment, the peptide bonds of the protein were then completely hydrolyzed by heating it with concentrated 6M HCl. The resulting solution was found to contain 5.5 mg of DNP-Val (shown in the figure below):

2,4-Dinitrophenyl derivatives of the α-amino groups of the other amino acids were not detected. Assuming 100% yield for the reaction of FDNB with the protein, determine the number of subunits in this protein.

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Verified step by step guidance

First, understand the reaction process: FDNB reacts with the N-terminal amino group of each subunit in the protein, forming a DNP derivative. The protein is then hydrolyzed to release these derivatives.

Calculate the number of moles of DNP-Val produced using its molecular weight (MW = 283 g/mol) and the mass of DNP-Val obtained (5.5 mg). Use the formula: \( \text{moles} = \frac{\text{mass}}{\text{molecular weight}} \).

Calculate the number of moles of the protein using its molecular weight (MW = 132,000 g/mol) and the mass of the protein sample (660 mg). Use the formula: \( \text{moles} = \frac{\text{mass}}{\text{molecular weight}} \).

Determine the number of subunits in the protein by dividing the moles of DNP-Val by the moles of protein. This ratio gives the number of subunits, as each subunit contributes one N-terminal amino group that reacts with FDNB.

Interpret the result: The calculated number of subunits indicates how many polypeptide chains are present in the quaternary structure of the protein.