:root {
–primary-blue: #004a99;
–success-green: #28a745;
–light-background: #f8f9fa;
–white: #ffffff;
–dark-text: #333;
–border-color: #dee2e6;
}
body {
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
background-color: var(–light-background);
color: var(–dark-text);
line-height: 1.6;
margin: 0;
padding: 20px;
display: flex;
justify-content: center;
align-items: flex-start;
min-height: 100vh;
}
.loan-calc-container {
background-color: var(–white);
padding: 30px;
border-radius: 8px;
box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
max-width: 800px;
width: 100%;
}
h1 {
color: var(–primary-blue);
text-align: center;
margin-bottom: 25px;
}
h2 {
color: var(–primary-blue);
margin-top: 30px;
margin-bottom: 15px;
border-bottom: 2px solid var(–primary-blue);
padding-bottom: 5px;
}
.input-group {
margin-bottom: 20px;
padding: 15px;
border: 1px solid var(–border-color);
border-radius: 5px;
background-color: var(–light-background);
display: flex;
flex-wrap: wrap;
gap: 15px;
align-items: center;
}
.input-group label {
font-weight: 600;
margin-right: 10px;
flex-basis: 150px; /* Fixed width for labels */
text-align: right;
}
.input-group input[type="number"] {
flex-grow: 1;
padding: 10px;
border: 1px solid var(–border-color);
border-radius: 4px;
font-size: 1rem;
min-width: 120px;
}
.input-group input[type="text"] {
flex-grow: 1;
padding: 10px;
border: 1px solid var(–border-color);
border-radius: 4px;
font-size: 1rem;
min-width: 120px;
}
button {
background-color: var(–primary-blue);
color: var(–white);
border: none;
padding: 12px 25px;
border-radius: 5px;
font-size: 1.1rem;
cursor: pointer;
transition: background-color 0.3s ease, transform 0.2s ease;
display: block;
width: 100%;
margin-top: 20px;
}
button:hover {
background-color: #003366;
transform: translateY(-2px);
}
button:active {
transform: translateY(0);
}
#result {
margin-top: 30px;
padding: 20px;
background-color: var(–success-green);
color: var(–white);
text-align: center;
border-radius: 8px;
font-size: 1.5rem;
font-weight: bold;
box-shadow: 0 2px 10px rgba(40, 167, 69, 0.3);
}
#result span {
font-size: 2rem;
display: block;
margin-top: 5px;
}
.article-content {
margin-top: 40px;
border-top: 1px solid var(–border-color);
padding-top: 25px;
}
.article-content h3 {
color: var(–primary-blue);
margin-bottom: 15px;
}
.article-content p {
margin-bottom: 15px;
}
.article-content ul {
margin-left: 20px;
margin-bottom: 15px;
}
.article-content li {
margin-bottom: 8px;
}
@media (max-width: 600px) {
.input-group {
flex-direction: column;
align-items: stretch;
}
.input-group label {
text-align: left;
margin-bottom: 5px;
flex-basis: auto;
}
.input-group input[type="number"],
.input-group input[type="text"] {
width: calc(100% – 20px); /* Adjust for padding */
min-width: auto;
}
h1 {
font-size: 1.8rem;
}
#result {
font-size: 1.2rem;
}
#result span {
font-size: 1.5rem;
}
}
Understanding Protein Molecular Weight Calculation
Proteins are fundamental molecules in biology, composed of long chains of amino acids linked by peptide bonds. The molecular weight of a protein is a crucial characteristic that helps in its identification, purification, and understanding its function. This calculator assists in determining the approximate molecular weight of a protein based on its amino acid sequence and any known post-translational modifications.
The Basic Calculation: Amino Acids
Each of the 20 standard amino acids has a specific, well-defined average molecular weight (usually expressed in Daltons, Da, or Kilodaltons, kDa). When amino acids link together to form a polypeptide chain, a molecule of water (H₂O) is lost for each peptide bond formed. Therefore, the molecular weight of a polypeptide is calculated by summing the molecular weights of all constituent amino acids and subtracting the weight of water molecules lost during peptide bond formation.
The formula for a polypeptide of n amino acids is:
MW = (Σ MW_amino_acid) – (n-1) * MW_H₂O
Where:
- MW is the molecular weight of the polypeptide.
- Σ MW_amino_acid is the sum of the molecular weights of all individual amino acids in the sequence.
- n is the number of amino acids in the sequence.
- MW_H₂O is the molecular weight of water (approximately 18.015 Da).
Note: For a single amino acid (n=1), no water is lost, and the molecular weight is simply the weight of that amino acid residue.
Incorporating Post-Translational Modifications (PTMs)
Proteins often undergo modifications after synthesis, known as post-translational modifications. These modifications can significantly alter a protein's molecular weight and function. Common PTMs include phosphorylation, glycosylation, acetylation, and ubiquitination, each adding a specific mass to the amino acid residue it modifies.
Our calculator accounts for common modifications by adding their standard mass. It also allows for the input of custom modifications with their specific masses in Daltons.
How the Calculator Works
1. Amino Acid Sequence Input: You provide the sequence of amino acids using their one-letter codes (e.g., A for Alanine, R for Arginine, N for Asparagine, D for Aspartic Acid, C for Cysteine, Q for Glutamine, E for Glutamic Acid, G for Glycine, H for Histidine, I for Isoleucine, L for Leucine, K for Lysine, M for Methionine, F for Phenylalanine, P for Proline, S for Serine, T for Threonine, W for Tryptophan, Y for Tyrosine, V for Valine). The calculator looks up the average residue weight for each amino acid.
2. Standard Modifications: If you indicate common modifications (e.g., 'P' for phosphorylation of Serine, Threonine, or Tyrosine; 'A' for acetylation of Lysine or N-terminus), their associated mass is added.
3. Custom Modifications: For modifications not listed, you can enter their specific mass in Daltons.
4. Calculation: The calculator sums the residue weights of all amino acids, subtracts the appropriate number of water molecules, and then adds the masses of all specified modifications.
Typical Use Cases
- Mass Spectrometry Data Analysis: Comparing the calculated molecular weight to experimentally determined masses from MS.
- Protein Identification: Verifying if a purified protein matches a known sequence.
- Bioinformatics: Estimating protein properties for computational studies.
- Experimental Design: Planning experiments that involve protein purification or detection.
Disclaimer: This calculator provides an approximate molecular weight based on average residue masses. Actual molecular weights can vary slightly due to isotopic variations and variations in residue masses used by different databases.
var aminoAcidWeights = {
'A': 71.079, 'R': 156.188, 'N': 114.104, 'D': 115.089, 'C': 103.145,
'Q': 128.131, 'E': 129.116, 'G': 57.052, 'H': 137.141, 'I': 113.160,
'L': 113.160, 'K': 128.174, 'M': 131.193, 'F': 147.177, 'P': 97.116,
'S': 87.078, 'T': 101.105, 'W': 186.213, 'Y': 163.176, 'V': 99.133
};
var modificationMasses = {
'P': 79.96633, // Phosphorylation (Phospho group: PO3H2)
'A': 42.01056, // Acetylation
'M': 15.99491, // Oxidation of Methionine
// Add more common modifications as needed
// e.g., 'G': 75.0669 for Glycation (glucose addition)
};
var waterWeight = 18.01528; // Molecular weight of water (H2O)
function calculateMolecularWeight() {
var sequenceInput = document.getElementById("proteinSequence").value.toUpperCase();
var modificationsInput = document.getElementById("modifications").value.toUpperCase();
var customModificationsInput = document.getElementById("otherModifications").value;
var totalAminoAcidWeight = 0;
var numberOfAminoAcids = 0;
var sequenceError = false;
for (var i = 0; i 1) {
calculatedWeight -= (numberOfAminoAcids – 1) * waterWeight;
}
// Add masses for standard modifications
var modificationChars = modificationsInput.split(");
for (var j = 0; j 0) {
calculatedWeight += customModWeight;
} else if (customModificationsInput !== "") {
// Optionally warn about invalid custom modification input
// console.warn("Invalid custom modification mass entered.");
}
// Display the result
var resultElement = document.getElementById("result");
var calculatedWeightElement = document.getElementById("calculatedWeight");
calculatedWeightElement.textContent = calculatedWeight.toFixed(4) + " Da";
resultElement.style.display = 'block';
}