Medical Chemistry Proteins PDF

Medical Chemistry Almaaqal University Collage of Dentistry Proteins Dr/ Wael Sobhy Darwish 1ST stage&2024  Proteins Proteins are macromolecules formed...

Medical Chemistry Almaaqal University Collage of Dentistry Proteins Dr/ Wael Sobhy Darwish 1ST stage&2024  Proteins Proteins are macromolecules formed of polymer of amino acids linked together by peptide bonds. Proteins account for more than 50% of the dry mass of most cells. There are 20 amino acids from which all protein molecules are made. Some proteins contain just a few amino acids in a chain, other proteins are chains of thousands of amino acids. Polymers of proteins are called polypeptides. A protein consists of one or more polypeptide chain. The largest known protein is titin. It's made of a chain of 33,000 amino acids  Structure of amino acid - The word "acid" means that there is a carboxyl group (-COOH) on the molecule. - The word "amino" means that there is an amino group(-NH2) on the molecule. SO, Amino acid describes a compound that contains both amino groups (NH2) and carboxyl group (COOH) " except proline and hydroxyl proline "  Structure of amino acid Amino acids are organic molecules at the center of an amino acid is an asymmetric carbon atom called the alpha (α) carbon. 1- Amino group: (NH2). 2- Carboxyl group: (COOH). 3- Hydrogen atom (H). 4- Side chain or radical group (R) The 20 amino acids are distinguished by their R-group.  Amino Acid Polymers Amino acids are joined together when a dehydration reaction removes a hydroxyl group from the carboxyl end of one amino acid and a hydrogen atom from the amino group of another. The resulting covalent bond is called a peptide bond. Repeating the process over and over creates a polypeptide chain. At one end is an amino acid with a free amino group (the N-terminus), and at the other end is an amino acid with a free carboxyl group (the C-terminus).  Amino Acid Polymers Peptide bond OH SH CH2 CH2 CH2 H H H H C C N C C OH H N C C OH H O H O H O (a) H2O OH ES OH SH Side chains Peptide CH2 CH2 bond CH2 H H H H N C C N C C N C C OH Backbone H O H O H O Amino end Carboxyl end (b) (N-terminus) (C-terminus)  Biological importance of proteins Proteins do not store energy; they are the workers of a cell. Eating lots of protein will not give you a burst of energy. Proteins do things. They perform and carry out the functions that enable a cell to move, use energy, respond to stimuli, and everything else that keeps a cell alive. Function of protein 1. Catalysis : (Enzymes) are proteins 2. Structure (muscle protein). 3. Movement (myosin & actin). 4. Defense (Antibodies). 5. Regulation (Enzymes & Hormones). 6. Transport (globin). 7. Storage. (Mb & Ferritin). 8  Classification of amino acids according to nutritional value Into Essential and nonessential amino acids Essential amino acids: are not synthetized by the body and must be obtained by the diet, 9 essential amino acid. Non essential amino acids : The human body can synthesize these amino acids using only the essential amino acids. 11 of the 20 amino acids are non- essential. Semi-essential amino acids (e.g. Arginine, Cysteine, and Tyrosine) because the body cannot synthesize them in sufficient quantities during (pregnancy, adolescent growth, or recovery from trauma) Classification of amino acids according to polarity Amino acids may be :- Polar or Non-polaramino acids Polar amino acids :- - Contain polar hydrophilic side chain "R” such as :- (1)OH-group: as in serine, threonine and tyrosine (2) SH-group: as in cysteine (3) Amids-group: as in glutamine & asparagine (4) COOH-group: as in glutamic & aspartic (5) NH2-group (or) nitrogen act as a base: lysine & arginine & Histidine  Classification of amino acid according to chemical structure Amino acids may be :- Acidic Two amino acids "Aspartic acid & Glutamic acid" Basic Three amino acids "Lysine & Histidine & Arginine" Neutral 15 amino acids Metabolic classification of amino acid : -Depending on the metabolic products of amino acids, They can be classified into : (a)ketogenic amino acids :- -Which give ketone bodies on metabolism (b)Mixed ketogenic & glucogenic :-- Which give both ketone bodies and glucose on metabolism (c)Glucogenic amino acids :- -Which give glucose on metabolism - They include the rest of amino acids  Structures of proteins - Proteins are formed of a large number of amino acid linked together by peptide bonds to give a polypeptide chain. - There are four orders of protein structures 12  Structures of protein There are four orders of protein structures. 1- Primary structure of protein. Referred to the number, type and sequence of amino acids in the chain. The main bond in this structure is peptide bond.  Secondary structure Is the folding or coiling of the polypeptide into a repeating configuration Secondary structure result from hydrogen bonds between the repeating constituents of the polypeptide backbone Includes the  helix and the  pleated sheet.  Tertiary structure Secondary structures are arranged to form final functional 3D structure called domain. Is the overall three-dimensional shape of a polypeptide Results from interactions between amino acids and R groups  Forces Controlling Tertiary Protein Structure a. Hydrogen bond: between polar side chains of amino acids b. Hydrophobic forces: between the non-polar (R) groups of the amino acids c. Electrostatic forces (ionic bonds, salt bridges): between oppositely charged (R) of amino acids d. Disulfide bonds: (Strong covalent bonds) between sulfur amino acids (cysteine)  Quaternary structure Is the overall protein structure that results from the aggregation of two or more polypeptide subunits Polypeptide chain Collagen  Chains Iron Heme  Chains Hemoglobin The four level of protein structure  Protein Folding Definition Def :- Protein folding is the physical process by which a linear polypeptide folds into its characteristic and functional three-dimensional structure. It is essential for proper function of proteins. Protein mis-folding leads to loss of function and causes a wide range of diseases. such as :- Alzheimer’s disease and Parkinson’s disease.  Classification of proteins 1- Classification based on protein function i) Catalytic proteins, e.g. enzymes. ii) Structural proteins, e.g. collagen, elastin, keratin. iii) Contractile proteins, e.g. myosin, actin. iv) Transport proteins, e.g. hemoglobin, myoglobin, albumin, transferrin. v) Regulatory proteins or hormones, e.g. ACTH, insulin, growth hormone. vi) Genetic proteins, e.g. histones. vii) Protective proteins, e.g. immunoglobulins, clotting factors.  Classification Based on Composition Classification of Protein Simple Protein Derived Protein Contains amino acids only. Conjugated Protein Ex: albumin, globulins Derived from simple and conjugated proteins ex: peptones & peptides Have some non-protein moiety in its structure along with protein part Ex: lipoprotein, glycoprotein.  Classification of protein based on structure Fibrous Globular Shape Long, narrow fiber Rounded (spherical) Water solubility Insoluble Soluble Stability More stable Less stable Examples Actin, Myosin, collagen Albumin, hemoglobin, insulin Protein denaturation Protein denaturation results in the unfolding and disorganization of the protein’s secondary and tertiary structures, which are not accompanied by hydrolysis of peptide bonds. Denaturing agents include: a)Physical agents: 1- Heat 2- UV light 3- Violent shaking 4-High pressure a)Chemical agents: 1- Strong acids. 2. Strong alkalis 3- Heavy metal salts 4- Organic solvents. Denaturation may be reversible or, more commonly, irreversible. Denatured proteins are often insoluble and, therefore, precipitate from solution.  Protein and oral Health Protein acts as a building block for teeth, so it helps promote steady growth and plays a role in the protection and repair of the periodontal tissue. Protein is important for children, especially those who are still growing their permanent teeth. Protein is responsible for the growth of your teeth, whilst calcium is responsible for their strength. Consuming protein at the recommended or higher than recommended intake level is associated with better periodontal health.  Plant-Based Protein and Periodontal Health Fruits and vegetables, whole grains, nuts and seeds contain polyphenols and fibers, which can play a role in reducing oxidative stress and inflammation. Protein also helps to increase absorption of calcium, which support the mineralization of jaw bone. Dietary protein also increases the production of insulin-like growth factor-1, which stimulates bone cell activity and increases collagen and other bone matrix proteins..  Amelogenins Def :- are tissue-specific proteins, rich in proline, leucine, histidine and glutamyl residues Synthesized by the ameloblast cells of the inner enamel epithelium. Ameloblasts are cells which secrete the enamel proteins enamelin, ameloblastins, and amelogenin which will later mineralize to form enamel, the hardest substance in the human body) These proteins comprise the bulk of the extracellular matrix that becomes mineralized with a hydroxyapatite phase to become the mature enamel. Amelogenin constitute about 90% of the total enamel matrix proteins and play a major role in the mineralization and morphological changes in enamel.