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Proteins structure amino acid composition

Protein Structure Function & Responsibilities Key Amino Acids (Examples) Bond Types Active Sites Associated Medicines
Approx. No. of Amino Acids
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Hemoglobin Quaternary (four subunits) Transports oxygen from lungs to tissues and removes carbon dioxide from tissues. Heme (contains iron), Histidine Peptide bonds (within each subunit), Hydrogen bonds (between subunits) Heme group in each subunit None directly associated with hemoglobin structure
~574 (per subunit)
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Insulin Globular Regulates blood sugar levels by facilitating glucose uptake by cells. Cysteine (forms disulfide bonds) Peptide bonds, Disulfide bonds Receptor binding site Insulin itself is a medication for diabetes ~51 Explore  in Uniprot
Collagen Fibrous Provides structural support to skin, bones, tendons, and ligaments. Glycine, Proline, Hydroxyproline Peptide bonds, Hydrogen bonds, Cross-links (e.g., covalent bonds between lysine residues) Not applicable (primarily a structural protein) Vitamin C deficiency affects collagen synthesis (Scurvy)
~1000 (varies by collagen type)
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Antibodies Y-shaped Bind to foreign substances (antigens) and neutralize them, playing a crucial role in the immune response. Variable regions with diverse amino acid sequences for antigen binding Peptide bonds, Disulfide bonds Antigen-binding sites (variable regions) Immunoglobulins (antibodies) themselves are used as therapeutic agents ~1300-1500 Explore  in Uniprot
Actin Filamentous Major component of the cytoskeleton, involved in cell movement, muscle contraction, and cell division. Actin-specific amino acids involved in polymerization Peptide bonds, Non-covalent interactions (e.g., hydrophobic interactions) Myosin binding sites Medications that target muscle contraction (e.g., muscle relaxants) may indirectly affect actin-myosin interactions ~375 Explore in Uniprot
Myosin Filamentous Interacts with actin to generate force for muscle contraction. Myosin head contains ATP-binding site and actin-binding site Peptide bonds, Non-covalent interactions Actin-binding site, ATP-binding site Medications that target muscle contraction (e.g., muscle relaxants) may indirectly affect actin-myosin interactions
Varies greatly depending on the myosin type (e.g., ~1900 for myosin II)
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Enzymes (e.g., lysozyme) Globular Catalyze biochemical reactions by speeding them up without being consumed in the process. (e.g., lysozyme breaks down bacterial cell walls) Active site contains specific amino acids for substrate binding and catalysis Peptide bonds, Hydrogen bonds, Hydrophobic interactions Active site (contains catalytic residues) Many medications target enzymes (e.g., enzyme inhibitors used to treat various diseases) ~129 Explore  in Uniprot
Membrane proteins Integral or peripheral Transport molecules across cell membranes, act as receptors for signals, and participate in cell-to-cell communication. Hydrophobic amino acids for membrane insertion, specific amino acids for ligand binding Peptide bonds, Hydrophobic interactions (for integral proteins) Ligand-binding sites (for receptor proteins), Channel pores (for transport proteins) Many medications target membrane proteins (e.g., beta-blockers, which target receptors in the heart)
Highly variable (can range from a few dozen to thousands)
Keratin Fibrous Provides strength and resilience to hair, nails, and skin. High in cysteine (forms disulfide bridges) Peptide bonds, Disulfide bonds Not applicable (primarily a structural protein) None directly associated with keratin structure
Varies greatly depending on the keratin type (e.g., ~310 for alpha-keratin)
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Elastin Fibrous Provides elasticity and flexibility to tissues such as blood vessels and lungs. Rich in glycine and proline Peptide bonds, Cross-links (desmosine) Not applicable (primarily a structural protein) None directly associated with elastin structure ~800-1000 Explore  in Uniprot
Casein Globular Major protein in milk, provides nutrition for infants. Phosphorylated amino acids Peptide bonds, Hydrogen bonds, Phosphoryl groups Not applicable (primarily a nutritional protein) None directly associated with casein structure ~200 Explore  in Uniprot
Albumin Globular Major protein in egg white, provides nutrition and protection to the developing embryo. Contains a variety of amino acids Peptide bonds, Hydrogen bonds, Hydrophobic interactions Not applicable (primarily a nutritional protein) None directly associated with albumin structure ~585 Explore  in Uniprot
Rhodopsin Globular Pigment in the retina, essential for vision by absorbing light. Contains retinal (a light-absorbing molecule) Peptide bonds, Hydrogen bonds, Hydrophobic interactions Retinal binding site Medications for eye diseases (e.g., glaucoma) may indirectly affect retinal function ~348 Explore in Uniprot
Histones Globular Package and order DNA into structural units called nucleosomes, helping to regulate gene expression. Rich in lysine and arginine (positively charged) Peptide bonds, Hydrogen bonds, Ionic interactions (between positively charged histones and negatively charged DNA) DNA binding sites Medications that affect gene expression may indirectly influence histone interactions with DNA
~102-130 (varies by histone type)
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GFP (Green Fluorescent Protein) Beta-barrel Used as a fluorescent tag in biological research to visualize specific proteins or cellular structures. Contains chromophore responsible for fluorescence Peptide bonds, Hydrogen bonds, Hydrophobic interactions Chromophore None directly associated with GFP structure ~238 Explore in Uniprot

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