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

SDS-PAGE Strategies

Biochemistry

5. Protein Techniques

SDS-PAGE Strategies

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Multiple Choice

'Protein X' has a molecular mass of 400 kDa when measured by size-exclusion chromatography. When subjected to SDS-PAGE, Protein X gives 3 bands with molecular masses of 180, 160, & 60 kDa. When SDS-PAGE is conducted a second time but in the presence of β-mercaptoethanol (β-ME), 3 bands form again, but this time with molecular masses of 160, 90, and 60 kDa. What is the subunit composition of Protein X? (Hint: draw both SDS-PAGE gels).

Protein X has 3 subunits with masses of 160, 90 & 60 kDa.

Protein X has 4 subunits with masses of 160, 90, 90 & 60 kDa.

Protein X has 3 subunits with masses of 180, 160, & 60 kDa.

Protein X has 4 subunits with masses of 180, 160, 90 & 60 kDa.

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Verified step by step guidance

Analyze the size-exclusion chromatography data: Protein X has a molecular mass of 400 kDa, suggesting it is a multimeric protein composed of several subunits.

Examine the SDS-PAGE results without β-mercaptoethanol: The presence of bands at 180, 160, and 60 kDa indicates that Protein X is composed of at least three different subunits or combinations of subunits.

Consider the effect of β-mercaptoethanol: This reducing agent breaks disulfide bonds, which can alter the apparent molecular weight of proteins on SDS-PAGE. The new bands at 160, 90, and 60 kDa suggest that disulfide bonds were present in the original structure.

Determine the subunit composition: The change in band pattern with β-mercaptoethanol indicates that the 180 kDa band likely consisted of two subunits linked by disulfide bonds, which separate into 160 and 90 kDa subunits upon reduction.

Conclude the subunit composition: Based on the data, Protein X is composed of four subunits with masses of 160, 90, 90, and 60 kDa, as the 180 kDa band splits into 160 and 90 kDa subunits in the presence of β-mercaptoethanol.