Question

Mass Experimental results describing a protein's amino acid composition are useful to estimate the molecular weight of the entire protein. A quantitative amino acid analysis reveals that bovine cytochrome \(c\) contains \(2 \%\) cysteine \(\left(M_{\mathrm{r}} 121\right)\) by weight. a. Calculate the approximate molecular weight in daltons of bovine cytochrome \(c\) if the number of cysteine residues is 2 .

Short answer

The approximate molecular weight of bovine cytochrome \(c\) is 12100 daltons.

Step-by-step solution

Understand the Given Information

The protein in question, bovine cytochrome \(c\), contains 2% cysteine by weight. We know the molecular weight of cysteine (\(\text{M}_r 121\)) and that there are 2 cysteine residues in this protein.

Calculate the Weight of Cysteine Residues

Calculate the total weight contributed by the cysteine residues in the protein using the formula: \( \text{Weight of cysteine residues} = 2 \times 121 = 242 \text{ daltons}\).

Use the Weight Percentage to Determine Protein's Molecular Weight

Since 2% of the protein's weight is from the cysteine, we can set up the equation: \( \frac{242}{\text{Molecular Weight of the Protein}} = \frac{2}{100}\).

Solve for the Total Molecular Weight

Rearrange the equation from Step 3 to find the molecular weight of the protein: \( \text{Molecular Weight of the Protein} = \frac{242 \times 100}{2} = 12100 \text{ daltons}\).

Verify and Conclude

Verify the calculation by checking if the percentage weight calculation matches. With a molecular weight of 12100 daltons, 242 daltons of cysteine indeed makes up 2% of the total weight. This confirms the solution.

Key concepts

Amino Acid Composition

Amino acids are the building blocks of proteins, and understanding their composition is crucial for analyzing a protein's characteristics. Each protein has a distinct chain of amino acids that determines its structure and function. Bovine cytochrome \( c \), like all proteins, is composed of various amino acids, each contributing differently to the protein's overall properties.

Knowing the composition helps in calculating the molecular weight and understanding the function of the protein. For instance, in bovine cytochrome \( c \), cysteine contributes to forming disulfide bonds that stabilize its structure. The amino acid composition provides insight into how these molecules interact and what roles they play in biological processes.

• Helps determine protein structure
• Assists in identifying functional roles
• Essential for studying protein-protein interactions

Molecular Weight Estimation

Estimating a protein's molecular weight is an essential step in further understanding its function and behavior in biological systems. The molecular weight can be determined by summing up the weights of all amino acids in the protein.

In the exercise, the molecular weight of bovine cytochrome \( c \) is approximated using cysteine residues, which contribute 2% to the total weight. The formula used in calculations considers the weight fraction and the known molecular weight of cysteine. This approach helps estimate the total molecular weight, providing essential data needed for biochemical analysis and experiments.

• Enables insight into the protein's structural properties
• Aids in designing purification and analytical methods
• Supports comparison with known proteins

Cysteine Residues

Cysteine is a unique amino acid due to its thiol side chain, which allows it to form disulfide bonds. This feature significantly contributes to the protein's tertiary structure and stability. In bovine cytochrome \( c \), cysteine residues play a critical role even though they form a small percentage of the total amino acids.

When analyzing proteins, identifying cysteine residues can provide valuable information about structural integrity and potential functional sites. The presence of disulfide bonds formed by cysteines can be a determinant of protein folding and function as well.

• Contributes to protein stability
• Involved in catalytic and regulatory processes
• Key in stabilizing protein conformation

Quantitative Amino Acid Analysis

Quantitative amino acid analysis involves determining the composition and concentration of amino acids in a protein. This analysis is vital for characterizing and understanding proteins fully and accurately.

In the example of bovine cytochrome \( c \), knowing that cysteine comprises 2% of the protein provides a starting point for molecular weight estimation. The accurate measurement of each amino acid aids in various biochemical applications, from protein sequencing to structural studies.

• Essential for confirming protein identity
• Provides data for nutritional analysis
• Aids in evaluating biological processes and pathways