Protein Part 2 Biochemistry PDF

S&F MODULERS BIOCHEMISTRY DR. Mohamed Hesham  Biochemistry Content Simple Proteins 2 Conjugated or Complex Proteins 11 Der...

S&F MODULERS BIOCHEMISTRY DR. Mohamed Hesham  Biochemistry Content Simple Proteins 2 Conjugated or Complex Proteins 11 Derived proteins 14 1 DR. M. Hesham / Modulers team  Biochemistry Types of Proteins Classification of Proteins:  Proteins can be classified according to chemical composition and properties. 1. Simple proteins. 2. Conjugated proteins. 3. Derived proteins  Each of these main groups is sub-divided into a number of classes. A. Simple Proteins  Simple proteins are defined as those proteins, which on hydrolysis yield only amino acids or their derivatives. 1) Albumin 2) Globulin MW  LOW (68.000)  High (150.000)  insoluble in pure water Solubility  Soluble in pure water  soluble in diluted solution of salts, alkali and acids Coagulation  Heat coagulable  The same  mainly in animal Distribution  found In animal and plant  minute amount in plant Precipitation  By full saturated ammonium sulfate  By Half saturated ammonium sulfate Types  One type  3 types, α, β, γ  Act as carrier  Act as carrier associated with Function  responsible for blood osmotic hemoglobin and essential for pressure immunity DR. M. Hesham / Modulers team 2  Biochemistry 3) Glutelins  The glutelins are soluble in very dilute acids and alkali but they are insoluble in neutral solvents.  They are plant proteins which include gluten of wheat and oryzenin of rice. 4) Prolamins or Alcohol  Soluble Proteins, The prolamins are soluble in 70 to 80% alcohol, but they are insoluble in water, neutral solvents, or absolute alcohol.  The prolamins are plant proteins found principally in seeds.  Gliadin is acidic protein as it contain high content of glutamic acid and glutamine while 5) Histones  Histones are basic proteins.  They are basic usually occur in tissues in salt combination with acidic substances such as heme of hemoglobin and nucleic acids.  They are positively charged so, bind with negatively charged nucleic acid.  An example of histones includes globin of hemoglobin that bind –ve charged oxygen. 6) Protamins  They are strongly basic and yield mainly basic amino acids on hydrolysis, particularly arginine.  They usually occur in tissues, in salt combination with acids, particularly with nucleic acid as nucleoproteins in fish. 3 DR. M. Hesham / Modulers team  Biochemistry 7) Albuminoids or Scleroproteins  The albuminoids include keratin, collagen, elastin.  They are generally insoluble in water, salt solutions, dilute acids and alkali and alcohol.  They are entirely animal proteins and are the chief constituents of the exoskeletal structures such as hair, skin, and nails as well as of supporting and connecting fibrous tissues, and of the organic material of cartilage and bone. A: Keratins  are the major proteins of hair and fingernails and skin.  They are rich in cysteine residues, forming what are called cysteine cross links.  There are different type of keratins such as α keratin and β keratin. DR. M. Hesham / Modulers team 4  Biochemistry B) Collagen Definition  is the single most abundant protein in most vertebrates - up to a third of the total protein mass.  Collagen fibers provide the matrix of bone and skin. Collagen structure  The triple-helix tropo collagen molecule is the basic unit of the collagen fiber.  Composed of about 1000 amino acids each, the individual chains of tropocollagen contain a left-handed helical structure, but are wound together with the other two chains of the fiber in a right-handed manner.  The repeating amino acid sequence is Gly-X-Y,  Where:  X is often proline  and Y is proline or hydroxyproline (a modified form of proline).  Collagen is unusual not only in having modified amino acid residues, such as hydroxyproline and hydroxylysine, but also in having so many of them.  Hydroxyproline helps to stabilize the triple helix via hydrogen bonds.  Hydroxylysine functions to form attachment sites for polysaccharides.  Hydroxylation of proline requires ascorbic acid (vitamin C). Deficiency of vitamin C  reduces hydroxyproline production, leading to weakened collagen fibers and the condition known as scurvy. 5 DR. M. Hesham / Modulers team  Biochemistry In aging  Part of collagen's toughness arises from cross-links between lysine residues of adjacent chains.  This cross-linking reaction occurs throughout life and makes bones, skin, and tendons less elastic. Collagen diseases Definition  Alterations in collagen structure arising from abnormal genes or abnormal processing of collagen proteins results in numerous diseases including: 1. Scurvy: 2. Ehlers-Danlos syndrome: 3. Osteogenic imperfecta (OI) “brittle bone disease” Causes  Collagen diseases are due to mutations in collagen genes or in genes encoding some of the enzymes involved in the post-translational modifications. DR. M. Hesham / Modulers team 6  Biochemistry 1) Scurvy a) Etiology » Vitamin C deficiency leads to impaired collagen production and defective collagen structure due to reduced activity of prolyl and lysyl hydroxylase enzymes, which causes weakening of the capillary walls, teeth and bones. b) Clinical picture » These biochemical defects are responsible for the pathophysiology of scurvy, characterized by 1. generalized weakness 2. bleeding from the gums 3. loosening of the teeth 4. poor wound healing 5. formation of red spots surrounding hair follicles and underneath the fingernails from bleeding (hemorrhage). 7 DR. M. Hesham / Modulers team  Biochemistry 2) Ehlers-Danlos syndrome a) The principal clinical picture is 1. hyper extensibility of skin 2. abnormal tissues fragility and increased joint mobility 3. These can be noticed at birth or in early childhood. b) Complications may include 1. aortic dissection 2. joint dislocations 3. scoliosis 4. chronic pain or early osteoarthritis. 3) Osteogenic imperfecta (OI) “brittle bone disease” a) Definition » It is a genetic disorder characterized by bones that break easily, often from little or no apparent cause and it is due to defect(mutations) in collagen type I. b) Etiology » The most common mutations cause the replacement of glycine (in –Gly–X–Y–) by amino acids with bulky side chains. » The resultant structurally abnormal α chains prevent the formation of the required triple-helical conformation. DR. M. Hesham / Modulers team 8  Biochemistry c) It’s characterized by » mild bone fragility » hearing loss » and blue sclerae » the most severe form, is typically lethal in the perinatal period because of pulmonary complications. It is characterized by multiple fractures at birth, short stature, spinal curvature appearance, and blue sclerae 9 DR. M. Hesham / Modulers team  Biochemistry C) Elastin a) Def: Elastin is a highly elastic fiber b) Site: present in ligaments and arterial blood vessels. c) Structure: » The polypeptide is rich in glycine, alanine, and valine. » Its secondary structure is fibrous proteins. » Like collagen, elastin contains lysine groups involved in cross-links between the chains. » In elastin, however, four lysine chains can be combined to form a desmosine cross-link. » Thus, fewer cross-links are needed to provide strength for the chains and a more elastic network is created. α 1 antitrypsin  Elastase enzyme hydrolyze elastin, it is inhibited by α 1 antitrypsin secreted by liver, lung and monocyte  deficiency of α 1 antitrypsin leads to fibrosis of liver and lose of alveolar wall elasticity (emphysema). DR. M. Hesham / Modulers team 10  Biochemistry B) Conjugated or Complex Proteins Definition  Conjugated or complex proteins are composed of simple proteins combined with some non-protein substance.  The non-protein group is referred to as the prosthetic (addition) group. 1) Nucleoproteins  The nucleoproteins are composed of simple basic proteins (protamines or histones) and nucleic acids as the prosthetic groups.  They are proteins of cell nuclei and apparently are the chief constituents of chromatin.  Examples include nucleohistone and nucleoprotamines 2) Glycoproteins and proteoglycans 11 DR. M. Hesham / Modulers team  Biochemistry 3) Chromoprotein  The chromoproteins are composed of simple proteins united with a colored prosthetic group.  Many proteins of important biological functions belong to this group.  There are two classes of chromoproteins: a) Metallochromoproteins:  The colored prosthetic group contains metal e.g. 1. Haemoglobin: respiratory proteins in which the prosthetic group is the iron- containing heme. 2. Hemocyanin (oxygen carriers of invertebrate) contains copper. 3. Chlorophyll contains magnesium. b) Non-metallochromoproteins:  The colored prosthetic group does not contain metal e.g. 1. Flavoproteins: cellular oxidation, reduction proteins in which the prosthetic group is riboflavin. 2. Visual purple of the retina: a chromoprotein in which the prosthetic group is a carotenoid pigment. 4) Phosphoproteins  Phosphoric acid is the prosthetic group of the posphoproteins.  (phosphoserine has been isolated from casein and vitellin) Casein of milk and vitellin of egg yolk are the best known phosphoproteins. 5) Lipoproteins DR. M. Hesham / Modulers team 12  Biochemistry 6) Metalloproteins  Proteins in which metal ions are bound directly to some of the side chains of histidine, cysteine, or some other amino acid are called metalloproteins.  It include: a) Protein containing iron: 1. Ferritin: Storage form of iron. 2. Transferrin: Transport form of iron. b) Proteins containing copper: 1. Ceruloplasmin: Transport form of copper. 2. Hemocuprin: In RBCs. c) Proteins containing zinc: -Inulin hormone - Carbonic anhydrase enzyme. d) Proteins containing selenium: Glutathion peroxidase enzyme 13 DR. M. Hesham / Modulers team  Biochemistry C) Derived proteins are subdivided into primary derived proteins and secondary derived proteins. 1) Primary Derived Proteins  These protein derivatives are formed by processes which cause only slight changes in the protein molecule and its properties.  There is little or no hydrolytic cleavage of peptide bonds.  The primary derived proteins are synonymous with denatured proteins. 1. Metaproteins: » The metaproteins are formed by further action of acids and alkali upon proteins » e.g. action of HCL on protein in the stomach. 2. Coagulated Proteins: » The coagulated proteins are insoluble products formed by the action of heat or alcohol upon natural proteins. » Examples include cooked egg albumin, cooked meat and other proteins, and alcohol-precipitated proteins. DR. M. Hesham / Modulers team 14  Biochemistry 2) Secondary derived proteins  These substances are formed in the progressive hydrolytic cleavage of protein molecules.  They are grouped into proteoses, peptones, and peptides. 1. Proteases: » Proteases are first hydrolytic products of proteins which are soluble in water. 2. Peptones: » Peptones are simpler in structures than the proteases. » They are soluble in water. 3. Peptides: » They are named according to the number of amino acid groups present as di-, tri-, tetra peptides or polypeptides. » The complete hydrolytic decomposition of a natural protein molecule into amino acids passes through successive stages as follows:  Protein → metaproteins →proteose → peptone → peptides → amino acids 15 DR. M. Hesham / Modulers team