Understanding Protein Structure: Primary, Secondary, Tertiary, and Quaternary Levels, Study notes of Biology

Download Understanding Protein Structure: Primary, Secondary, Tertiary, and Quaternary Levels and more Study notes Biology in PDF only on Docsity! Protein Structure Proteins are the product of the decoding that starts with the information in cellular DNA. Proteins compose of structural and motor element in the cell, they serve as the catalyst for virtually every biochemical reaction that occurs in living organisms. Each gene in cellular DNA contains the code for a unique protein structure. These proteins are assembled with different amino acid sequences, however they are also held together by different bonds and folded into a variety of three-dimensional structures. The four levels of protein structure are distinguished from one another by the degree of complexity in the polypeptide chain. What are protein structures The building blocks of proteins are amino acids. These are small organic molecules that consist of a central carbon atom linked to an amino group, a carboxyl group, a hydrogen atom, and a variable component that are linked together by peptide bonds resulting in the formation of a long chain. (Figure 1). Peptide bonds are made by a biochemical reaction that takes a water molecule as it joins the amino group of one amino acid to the carboxyl group of a neighboring amino acid. The linear sequence of amino acids within a protein is considered the primary structure of the protein. All proteins a built from a set of 20 amino acids, each one with its own structure and property, these amino acids can be split into 7 different groups according to the characteristics of the side chains. (Figure 2). The largest group of amino acids have nonpolar side chains. Several other amino acids have side chains with positive or negative charges, while others have polar but uncharged side chains. Figure 1: When connected by multiple peptide bonds, amino acids form a polypeptide (a protein). The polypeptide will then fold into a specific conformation depending on the interactions (dashed lines) between its amino acid side chains Groups Amino acids Aliphatic Alanine, Glycine, Isoleucine, Leucine, Proline, Valine Aromatic Phenylalanine, Tryptophan, Tyrosine Acidic Aspartic Acid, Glutamic Acid Basic Arginine, Histidine, Lysine Hydroxylic Serine, Threonine Sulphur-containing Cysteine, Methionine Amidic (containing amide group) Cysteine, Methionine Proteins are polymeric chains that are built from monomers called amino acids. All structural and functional properties of proteins derive from the chemical properties of the polypeptide chain. There are four levels of protein structural organization: primary, secondary, tertiary, and quaternary. The proteins have 4 different structures and folding patterns, the different levels of protein structure are known as primary, secondary, tertiary, and quaternary structure. Primary structure of proteins The primary structure is the pattern of amino acids that make up a polypeptide chain. The 20 different amino acids are found in proteins. The primary protein sequence for a certain protein is the exact order of the amino acid in a specific protein. Secondary structure of proteins Protein secondary structure refers to regular, repeated patterns of folding of the protein backbone. The Alpha helix and beta sheet are the two most common folding patterns. The secondary structure is the first 3D structure, it’s held together by hydrogen bonds. At this stage either an alpha helix or a beta pleated sheet is formed, which depends on the hydrogen bond between – NH, which is positively charged and –C=H, which is negatively charged. The hydrogen that is used to form the hydrogen bond will make the structure either alpha or beta, this will majorly affect the physical structure of the protein, even though the same elements are present because it is an isomer. Alpha helix Figure 2: These are the 7 groups and the amino acids grouped in each one.