Medical Biochemistry

Structure of the Heme Prosthetic Group Heme is the O2 – binding molecule common to Mb and Hb protophorphyrin IX is the backbone of heme when iron is complexed with protophorphyrin IX it is called Heme. So heme is the prosthetic group in Hemoglobin, Myoglobin and Cytochrome b, c, and c1. The Fe – porphyrin prosthetic group is, with the exception of two propionate groups, hydrophobic and planar. Heme become an integral part of the globin proteins during poly peptide synthesis. It is the heme molecule that give globin proteins their characteristic red brown colour. Once the Fe2+ (Ferrious) is incorporated, the protein is called hemoglobin. Such structural coordination creates an environment essential for Globin to bind and release O2. If the iron atom were to become oxidized to Fe3+(Ferric), the Globin would get changed to metmyoglobin or (Met hemoglobin) where heme can no longer interact with O2 and O2 transport is compromised. Fig 5.21: Structure of the heme pr...

Factors that Affect Denaturation Proteins

Factors that Affect Denaturation Proteins Denaturing agents 1. physical factors Temperature, pressure, mechanical shear force, ultrasonic vibration and ionizing radiation causes the protein to lose its biological activity. 2. chemical factors Acids and alkalis, organic solvents (actone, ethanol), detergents (cleaning agents), certain amides urea, guandidine hydrochloride, alkaloids, and heavy metal salts (Hg, Cu, Ba, Zn, Cd…) Cause the denaturation. Properties of a Denatured Protein A. an increase in number of reactive and functional group in the composition of the native protein molecule ( side chain group of amino acids, COOH, NH2, SH, OH … etc) B. Reduced solubility and pronounced propensity for precipitation this occurs due to loss of the hydration shell and the unfolding of protein molecules with concomitant exposure of hydrophobic radicals and neutralization of charged polar groups. C. Configurational ...

Lipoproteins

Lipoproteins Plasma lipids contain triacylglycerols, cholesterol and other polar lipids.Lipids combined with apolipoproteins to form Lipoproteins. Based on their density they are classified into four subgroups: Chylomicrons: These are derived from intestinal absorption of triacylglycerols and other lipids and have a very short lifespan. They have the least density and richly consist TAG. Chylomicrons transport dietary triacylglycerols and cholesterol from the intestine to the liver for metabolism. VLDL (very low density lipoproteins): These are synthesized in the liver and used to transport triacylglycerols from the liver to extrahepatic tissues. LDL (Low density lipoproteins): These are produced from the final stage in the catabolism of VLDL. They transport cholesterol synthesized in the liver to peripheral tissues. LDL is metabolized via the LDLreceptorApproximately 30% of the LDL is degraded in extra hepatic tissues, rest is degrade...

Enzymes

Enzymes Body proteins perform a large number of functions. One such unique function is, they act as biological catalysts (Enzymes) .They are responsible for highly complex reactions. They direct the metabolic events and exhibit specificity toward substrates, regulate the entire metabolism. Thus, they play key role in the degradation and synthesis of nutrients, biomolecules etc. The most important diagnostic procedures involves assay of enzymes. They assist to know damaged tissues, the extent of tissue damage, helps to monitor the course of the disease and used as a therapeutic means of diagnosing a vast array of diseases.

Classification of Enzymes

Classification of Enzymes Enzymes are classified on the basis of the reactions they catalyze- Each enzyme is assigned a four-digit classification number and a systematic name, which identifies the reaction catalyzed. The international union of Biochemistry and Molecular Biology developed a system of nomenclature on which enzymes are divided in to six major classes, each with numerous sub groups. Enzymes are classified based on the reactions they catalyze. Each enzyme is characterized by a code number comprising four digits separated by points. The four digits characterize class, sub-class, sub-sub-class, and serial number of a particular enzyme. Class I. Oxidoreducatases Enzymes catalyzing oxidation reduction reactions. Example: Lactate-dehydrogenase 1- Lactic acid + NAD+ Pyruvic acid + NADH+H+ Class II. Transferases: Enzymes catalyzing a transfer of a group other than hydrogen (methyl, acyl, amino or phosphate groups) Example: Enzymes catal...

Lipids

Lipids The bulk of the living matter is made up of Lipids, carbohydrates and proteins. Lipids are water insoluble, but can be extracted with non-polar solvents like Benzene, methanol, or ether. Some lipids act as storage molecules for example triglycerides stored in adipose tissue. Transport forms of lipids (Lipoproteins),are present in combination with proteins Building blocks of lipids are fatty acids. Some lipids like cholesterol lack fatty acids but are potentially related to them. Lipids are constituents of cell membrane and act as hydrophobic barrier that permits the entry/exit of certain molecules. Lipids carry fat soluble vitamins and form special biomolecules. Lipid imbalance can lead to serious diseases like obesity and atherosclerosis. Break down of fatty acid produce energy, excessive breakdown cause ketosis, ketoacidosis, coma and death. Cholesterol level in blood is controlled by several regulatory mechanisms. Such information is applied in the treatment ...

Regulation of Oxidation of Fatty Acids

Regulation of Oxidation of Fatty Acids Hormones regulate lipolysis, in adipose tissue.More free fatty acids are available for the βoxidation. Insulin inhibits lipolysis. Acylcarnitine transferase-1 is inhibited by malonyl CoA , one of the intermediates of fattyacid synthesis. High level of NADHH inhibits acyl CoA dehydrogenase. Increased concentration of acetyl CoA inhibits Thiolase. When the animal is well fed by carbohydrate, fatty acid oxidation is lowered. The metabolism of Ketone Bodies When the level of acetyl CoA from β-oxidation increases in excess of that required for entry into the citric acid cycle, It undergoes ketogenesis in the mitochondria of liver (ketone body synthesis). The three compounds viz., acetoacetate, β-hydroxybutyrate, and acetone are collectively known as ketone bodies. The synthesis of ketone bodies takes place during severe starvation or severe diabetes mellitus. During...

Amino acids and Proteins

Amino acids and Proteins Living systems are made up of Proteins .They are the dehydration polymers of amino acids. Each amino acid residue is joined by a peptide linkage to form proteins. Proteins are the molecular instruments in which genetic information is expressed, Hormones, Antibodies, transporters, the lens protein, the architectural framework of our tissues and a myriad of substances having distinct biological activities are derived. The type, nature and number of amino acids impart characteristic properties to the proteins. There are about 300 amino acids, but only 20 are coded by DNA of higher organisms. Acid base properties of amino acids are important to the individual physical and chemical nature of the protein. The structural organization of proteins could be primary, secondary, tertiary and quaternary. The three dimensional structure is the most biologically active one. The unfolding and disorganization of the proteins results in denaturation, the process is most...

Proteins

Proteins The word protein is derived from Greek word, proteious meaning primary. So, proteins are the major components of any living organism. Proteins are natural substances with high molecular weights ranging from 5,000 to many millions. Besides Carbon, Hydrogen and Oxygen, they also contain Nitrogen, and sometimes, Sulfur and Phosphorous. Proteins are most important constituent of cell membranes and cytoplasm. Muscle and blood plasma also contain certain specific proteins. Protein containing foods are essential for living organism, because protein is the most important biological molecules in building up and maintenances of the structure of body, giving as much energy as carbohydrates in the course of metabolism in the body. Many of the body proteins perform innumerable chemical reactions constantly taking place inside the body. Proteins are the molecular instruments in which genetic information is expressed; hormones, antibodies, transporters, muscle, the lense protein, antib...

Denaturation of Proteins

Denaturation of Proteins Proteins have finite lifetimes. They are also subject to environmental damages like oxidation proteolysis, denaturation and other irreversible modifications. Denaturation involves the destruction of the higher level structural organization (20 , 30 and 40 ) of protein with the retention of the primary structure by denaturing agents. A denatured protein loses its native physico-chemical and biological properties since the bonds that stabilize the protein are broken down. Thus the polypeptide chain unfolds itself and remain in solution in the unfolded state. The denatured protein may retain its biological activity by refolding (renaturing) when the denaturing agent is removed. Fig 5.20: Denaturation of proteins

Post History

March 202036