Introduction to Proteins

Peptides and Proteins Peptides Peptides are chains of amino acids. If the chain contains 2-10 amino acids, it is called an oligopeptide. If the chain contains 11-50 amino acids, it is called a polypeptide. Polypeptides: If the chain contains 50 or more amino acids, it is called a polypeptide. Polypeptides are the building blocks of proteins. Proteins Proteins are large biomolecules consisting of one or more chains of amino acids. Amino acids are linked by peptide bonds. Proteins are essential for life and perform a variety of functions, including: Structural support Transport of substances Catalysis of biochemical reactions Immune response Cell signaling Peptide Bonds A peptide bond is a covalent bond formed between two amino acids. The bond forms between the carboxyl group of one amino acid and the amino group of another amino acid. This bond is formed through a dehydration synthesis reaction.   Dipeptides, Tripeptides, and Polypeptides Dipeptide: A peptide containing two amino acids. Tripeptide: A peptide containing three amino acids. Polypeptide: A peptide containing many amino acids. Protein Structure Proteins have a complex structure that determines their function. The four levels of protein structure are: Primary structure: The sequence of amino acids in the polypeptide chain. Secondary structure: The local folding of the polypeptide chain into alpha helices or beta sheets. Tertiary structure: The overall three-dimensional shape of the polypeptide chain.   Quaternary structure: The arrangement of multiple polypeptide chains to form a functional protein. Protein Functions Proteins play a vital role in many biological processes. Some of the major functions of proteins include: Enzymes: Catalyze biochemical reactions. Hormones: Regulate bodily functions. Antibodies: Protect the body from infection. Structural proteins: Provide support and structure to cells and tissues. Transport proteins: Carry molecules across cell membranes. Storage proteins: Store nutrients. Protein Synthesis Protein synthesis is the process by which cells make proteins. It involves two main steps: transcription and translation. Transcription is the process of copying the DNA sequence of a gene into mRNA. Translation is the process of decoding the mRNA sequence to produce a polypeptide chain. Protein Folding Protein folding is the process by which a polypeptide chain folds into its three-dimensional structure. The folding process is influenced by a variety of factors, including the amino acid sequence, the environment, and the presence of chaperone proteins. Misfolded proteins can lead to a variety of diseases, including Alzheimer's disease and Parkinson's disease. Protein amino acid The amino acids that are joined to form the proteins are called protein amino acids. Proteins are two types: a) Primary protein b) Secondary protein Primary protein The primary protein contains amino acids. Secondary protein The secondary protein contains amino acids. Amino acids that are joined to form the proteins are called protein amino acids. Amino acids that are joined together to form the chains of proteins are called protein amino acids. Classes of protein amino acids One class of protein amino acids are called essential amino acids. Essential amino acids: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine Post-translational modifications Post-translational modifications are modifications of amino acids. The modified amino acids are called secondary proteins. The types of protein amino acids are framed based on the chemical properties of the side chain. Polar amino acids Non-polar amino acids Positively charged amino acids Negatively charged amino acids The arrangement of amino acids is post-translational modification.