Proteins PDF - Biochemistry Notes

Classification based on function ❖ Catalytic proteins – enzymes Brewed Coffee Notes ❖ Defense protei...

Classification based on function ❖ Catalytic proteins – enzymes Brewed Coffee Notes ❖ Defense proteins – immunoglobulins or antibodies Biochemistry Notes | PROTEINS ❖ Transport proteins – hemoglobin, HDL, LDL ❖ Messenger proteins – insulin, glucagon, human growth Clarisse Kim C. Felisco, RMT factor ❖ Contractile proteins – actin and myosin ❖ Structural proteins – collagen and α keratin ❖ Transmembrane proteins – protein channels ❖ Storage proteins – ferritin, myoglobin PROTEINS ❖ Regulatory proteins – sites where messenger molecules bind Widest array of functions among the 4 major biological ❖ Nutrient proteins – casein, ovalbumin molecules Contain many amide bonds – connects amino acids Amino acids Not stored unlike lipids and carbohydrates Functions of proteins 1. STRUCTURE: collagen and keratin are the chief constituents of skin, bone, hair, and nails. 2. CATALYSTS: virtually all reactions in living systems are catalyzed by proteins called enzymes. ✓ Contains 2 functional groups: amino group (NH2) & 3. MOVEMENT: muscles are made up of proteins called carboxyl group (COOH) myosin and actin. ✓ Amino acids with an additional COOH group – acidic amino 4. TRANSPORT: hemoglobin transports oxygen from the lungs acids to cells; other proteins transport molecules across cell ✓ Amino acids with an additional N atom – basic amino acids membranes. ✓ All others are neutral amino acids 5. HORMONES: many hormones are proteins, among them ✓ Have commons (3-letter or 1-letter abbreviation) insulin, oxytocin, and human growth hormone. 6. PROTECTION: blood clotting involves the protein 20 NATURALLY OCCURRING AMINO ACIDS fibrinogen; the body used proteins called antibodies to fight disease. 7. STORAGE: casein in milk and ovalbumin in eggs store nutrients for newborn infants and birds; ferritin, a protein in the liver, stores iron. 8. REGULATION: certain proteins not only control the expression of genes, but also control when gene expression takes place. Classification based on shape Fibrous Protein Elongated shape with one dimension much longer than the others are long, thread-like proteins that are typically Ckcfrmt | brewed coffee (ProteinS) structural in nature. They are insoluble in water and provide support and strength to tissues, like collagen in skin and keratin in hair. Globular Protein Peptide chains that are folded into spherical or globular shapes Folding Water-soluble are more compact, spherical proteins that are usually involved in metabolic functions. They are generally soluble in water and include enzymes, antibodies, and hormones like hemoglobin and insulin. 1 Basic Amidic Aromatic ESSENTIAL Hydroxylic Aliphatic Acidic Sulfur-containing  9 Essential Amino Acids Phenylalanine ❖ precursor for the neurotransmitter’s tyrosine, dopamine, epinephrine and norepinephrine ❖ Plays an integral role in the structure and function of proteins and enzymes and the production of other amino acids Valine ❖ Helps stimulate muscle growth and regeneration and is involved in energy production Threonine ❖ A principal part of structural proteins such as collagen and elastin which are important components of the skin and connective tissue ❖ Plays a role in fat metabolism and immune function Tryptophan ❖ Often associated with causing drowsiness ❖ Needed to maintain proper nitrogen balance ❖ A precursor to serotonin, a neurotransmitter that regulates appetite, sleep and mood Isoleucine ❖ Involved in muscle metabolism and is heavily concentrated in muscle tissue. ❖ Important for immune function, hemoglobin production and energy regulation Methionine ❖ Plays an important ZWITTERION role in metabolism and Amino acids never exist as neutral molecules with all detoxification ❖ Necessary for tissue uncharged atoms in nature growth and the absorption of zinc and selenium, minerals that are vital to health Ckcfrmt | brewed coffee (ProteinS) Histidine ❖ Used to produce histamine, a neurotransmitter that is vital to immune response, digestion, sexual function and sleep-wake cycles ❖ Critical for maintaining ESSENTIAL AMINO ACIDS the myelin sheath, a protective barrier that ✓ Humans can only synthesize 10 of the 20 amino acids surrounds the nerve ✓ Essential amino acids – obtained from diet and cells. consumed on a daily basis Leucine ❖ critical for protein synthesis and muscle repair. 2  ❖ Helps regulate blood SECONDARY STRUCTURE sugar levels, stimulates wound healing and conformations of amino acids in localized regions of a produces growth polypeptide chain; examples are α -helix, β -pleated sheet, hormones and random coil. These regions arise due to hydrogen bonding between the Lysine ❖ Plays major roles in N—H group of one amide with the C═O group of another protein synthesis, hormone and enzyme α-helix production and the absorption of calcium ✓ 3.6 amino acids per turn of the helix ❖ Important for energy ✓ 6 atoms of each peptide bond lie in the same plane. production, immune ✓ The C=O group of each peptide bond is hydrogen function and the bonded to the N-H group of the peptide bond four production of collagen amino acid units away from it. and elastin. ✓ All R- groups point outward from the helix Stereochemistry of amino acids ✓ All amino acids have a chirality center except glycine ✓ L amino acids – NH3 group on the left side of the Fischer projection o Naturally occurring ✓ D amino acids - NH3 group on the right side of the Fischer projection o Occur infrequently Biologically active peptides Neuropeptides: Enkephalins and Endorphins ❖ Enkephalins – synthesized in the brain that act as pain killers and sedatives by binding to pain receptors ❖ Endorphins – blocks pain, produce feeling of well-being experienced by athletes after strenuous exercise Oxytocin β-pleated Sheet ❖ Stimulates contraction of uterine muscles, initiates ✓ 6 atoms of each peptide bond lie in the same plane. flow of milk in nursing mother, induces labor in ✓ The C=O and N-H groups of peptide bonds from pregnant women adjacent chains point toward each other and are in the same plane so that hydrogen bonding is possible Vasopressin between them. ✓ All R- groups on any one chain alternate, first above, ❖ Also known as ADH then below the plane of the sheet, etc. ❖ Keeps electrolytes in body fluids, secreted when dehydrated Proteins: structure Ckcfrmt | brewed coffee (ProteinS) PRIMARY STRUCTURE Sequence of amino acids in a polypeptide chain; read from the N-terminal amino acid to the C- terminal amino acid. The primary structure of a protein is the sequence of amino acids joined together by peptide bonds. All bond angles are 120o, giving the protein a zigzag arrangement (in 3D models) 3 TERTIARY STRUCTURE HEMOGLOBIN and MYOGLOBIN The complete three-dimensional arrangement of atoms of a Myoglobin – 153 amino acid residues in a single polypeptide chain. polypeptide chain, gives the cardiac muscle its red color Hemoglobin - 4 polypeptide chains (two α and two β subunits) each carrying a heme unit Both hemoglobin and myoglobin are globular and conjugated proteins, meaning they contain both a protein and non-protein component. Their non-protein unit is a heme, an organic complex surrounding a Fe+2 ion. The Fe+2 ion binds to O2 gas in the bloodstream. Hemoglobin protein transports the O2 to wherever it is needed in the body. Or, if needed, the myoglobin stores O2 in tissues QUATERNARY STRUCTURE The spatial relationship and interactions between subunits in a protein that has more than one polypeptide chain. COMMON PROTEINS COLLAGEN Ckcfrmt | brewed coffee (ProteinS) Most abundant protein in vertebrates Found in connective tissues such as bone, cartilage, tendons, teeth, and blood vessels With age, collagen helices become cross-linked by covalent bonds 4