Proteins PDF

Proteins Are the most abundant organic compounds found in any living organisms Chemically, a protein consists of one or more polypeptide chains. Each polypeptide chain is a polymer consisting of many units of amino acids linked together through a condensation reaction. There are 20 essential amin...

Proteins Are the most abundant organic compounds found in any living organisms Chemically, a protein consists of one or more polypeptide chains. Each polypeptide chain is a polymer consisting of many units of amino acids linked together through a condensation reaction. There are 20 essential amino acids occurring naturally (Definition) Amino Acids 1. All amino acids share the same basic structure but differ in their side chains. 2. Amino acids are amphoteric. This is because each amino acid consists of both the acidic carboxyl group -COOH) and the basic amino group (-NH) 3 These amino acids are classified into four groups based on the properties of their side chains polar non-polar positively charge (BASIC R GROUP) negatively charge (ACIDIC R GROUP) 4 Amino acids that have hydrocarbons as side chains are non-polar Protein molecules that consist of a large amount of such amino acids are insoluble and non-reactive. Such proteins usually form a structural protein, for example, collagen Struture of Amino Acids ⮚ Each amino acid has a central carbon atom with four covalent bonds ⮚ Central carbon atom is also known as alpha carbon ⮚ The name of amino acid is represented by a single uppercase letter or a three letter abbreviation Types Of Amino Acids Amino acids with Amino acids with Amino acids with Amino acids with NON-POLAR R group POLAR R group Basic R group Acidic R group (POSITIVELY CHARGED) (NEGATIVELY CHARGED) Example glycine (Gly) Example: serine (Ser) Example: lysine (Lys) Example: aspartic acid (Asp) Other amino acids in this Other amino acids in this Other amino acids in this Another amino acid in this group are group are group are group is alanine (Ala) asparagine (Asn) arginine (Arg) glutamic acid (Glu) valine (Val) glutamine (Gln histidine (His) leucine (Leu) tyrosine (Tyr) isoleucine (lle) cysteine (Cys)  tryptophan (Trp) threonine (Thr) proline (Pro) methionine (Met) phenylalanine (Phe) Polar R group amino acids create partial charges but do not receive or donate electrons. The presence of such amino acids increases protein solubility and facilitates hydrogen bonding. Basic and Acidic amino acids generate positively and negatively charged ions, These ions are strongly hydrophilic Proteins. In water, amino acids form zwitterions, which carry positive and negative charges due to the ionization of the amino (-NH) and carboxyl (-COO) groups. Proteins Protein is classified by the number of amino acids in a chain ❖ Peptides is a short string of 2 to 50 amino acids, formed by a condensation reaction, joining together through a covalent bond Dipeptides: 2 amino acids linked together Tripeptides: 3 amino acids linked together Polypeptides: involving 50 to a few thousand amino acid molecule ❖ Proteins: more than 50 amino acids 100 to 10, 000 amino acids linked together Proteins may differ in the following ways. (a) The total number of amino acids (b) The relative quantity of each type of amino acid (c) The sequences of amino acids in the polypeptide chain (Definiton) Essential and Non-Essential Amino Acids 1. Plants and microorganisims can synthesize all of the 20 standard amino acids 2. Mammals, however, cannot synthesize all 20 and must obtain some of them from their diet 3. Amino acids that must be supplied in the diet are referred to as essential amino acids whereas the remainder that can be synthesized by the organism are termed non-essential amino acids 4 In humans, the non-essential amino acids are Ala, Arg, Asn, Asp, Cys, Glu, Gln, Gly, Pro, Ser and Tyr while the essential ones are His, Ile, Leu, Lys, Met, Phe, Thr, Trp and Val. Protein Struture A polypeptide is not yet a protein; proteins require a stable, three-dimensional shape to be biologically active.\ Monomeric proteins consist of a single polypeptide chain that folds. Multimeric proteins consist of two or more polypeptide chains. Levels of Protein Structure ⮚ Primary Structure Is the unique sequence of amino acid in a polypeptide chain  Amino acids are attached together by covalent bond or peptide bond and this is done through the process called protein biosynthesis The linear sequence of amino acids in a polypeptide chain, determined by the genetic code in DNA, unique to each protein. ⮚ Secondary Structure Formed from local folding of polypeptide chain from protein Refers to coiling patterns of the polypeptide chain, including ❖ Alpha helix structure Helix is held in shape by hydrogen bond resembling a telephone wire ❖ Double/Triple Helix: -two or three polypeptide chains are coiled together to form fiber A. Keratin: Double helix structure found in hair, nails, and feathers. B. Collagen: Triple helix structure found in tendons and cartilage ❖ Beta pleated structure Are formed between hydrogen bonding atoms on the backbone of the polypeptide chain Parallel polypeptide chains held together by hydrogen bonds, providing strength and flexibility, common in insect and spider proteins. ⮚ Tertiary Structure Pertains to the overall 3D shape of a polypeptide by a pattern of folding of the α-helix, stabilized by hydrogen bonds, ionic bonds, and disulfide bridges. Examples include enzymes, hormones, antibodies, and myoglobin. ⮚ Quaternary Structure Is the arrangement of multiple polypeptide chains in proteins like hemoglobin, which consist of more than one polypeptide unit (Structure of Protein) Classification of Proteins Major Classes of Proteins ⮚ Structural Protein -Found in the hair of mammals; tendons and ligaments ⮚ Contractile Proteins -Proteins that provide muscular movement ⮚ Storage Protein  -Specialized for storing amino acids Proteins are classified by structure: ⮚ Fibrous Proteins: Involved in body structure formation in animals. Typically have secondary structures. Insoluble in water. Examples: Collagen, myosin, fibrin, keratin. ⮚ Globular Proteins: Have tertiary structures; some have quaternary structures. Polypeptide chains are tightly coiled and folded into a sphere. Examples: Globulin (in blood serum), enzymes, antibodies, hormones Classification of Proteins by Composition: ⮚ Simple Proteins: Pure proteins with no other substances. Examples: Fibrous proteins, globular proteins. ⮚ Conjugated Proteins: Composed of a protein portion and a non-protein component (prosthetic group). Further classified based on the properties of prosthetic group.