Abstract Gluten proteins play a key role in determining the unique baking quality of wheat by conferring water absorption capacity, cohesivity, viscosity and elasticity on dough. Publication types Review. Ab Initio Molecular Orbital Theory. Hawkesford, Peter Buchner] Molecular Analysis. Jump to Page. Search inside document. Glutathione is an important tripeptide acting as reducing agent. Documents Similar To Protein chemistry lecture 4.
Pablo Raka. Hee Ting Wong. Carlos Pezo. Danish Ahmed. Heriberto Rodriguez. Saim B. Andres Alejandro Camargo. Pankaj Sahlot. Yury Tatiana Granja. Rian Setiawan. Revision Chemical Bonding and physical properties.
Subesh Shanmugam. Nur Maulida. Explain the primary and secondary structure of protein. Explain Electrophoriesis. Wirte note on Gel filtration method for the separation of proteins. Amino acid 2. Ninhydrin solution 3. Peptide 4. Amino acid 1. They accelerate a wide variety of chemical reactions which occur in biological systems.
Thus, enzymes are biocatalysts. Pepsin has, for example, a molecular weight of 39, The number of moles of substrate converted by one mole of an enzyme per minute is termed the turnover number of the enzyme and the turnover number of enzymes range from to 3,, They may be specific for particular substrate or a particular type of reaction.
The optimum pH for most of the enzyme actions is about 7. Oxidoreductases 2. Transferases 3. Hydrolases 4. Lyases 5. Isomerases 6. Ligases Synthetases 1. Oxidoreductases These are enzymes which catalyses oxidation oxidases or reduction reductases reaction. For example, Alcohol dehydrogenase oxidises ethanol into acetaldehyde. Transferases These enzymes are concerned with the transfer of a group of atoms from one compound to another.
Example: Glutamate oxaloacetate transminase catalyses the transfer of an amino group from glutamic acid to oxaloacetic acid. It requires pyridoxal phosphate PLP as coenzyme for its activity. Hydrolases These are enzymes which catalyse hydrolysis. Lipase, for example, hydrolyses glycerides esters into glycerol and fatty acids 4. Isomerases These enzymes catalyse the interconversion of isomers. Ligases These enzymes catalyse synthesis of compounds. For example, glutamine synthetase is a ligase or synthetase which catalyses the synthesis of glutamine from glutamate and NH3 2.
Temperature The rate of enzyme catalysed reactions generally increases with temperature upto a maximum and then declines. The temperature at which the enzyme activity is maximum is called optimum temperature.
This is termed optimum pH. Above and below this pH, the enzyme activity declines. Most of the enzymes act effectively in the pH range of 5 to 9. Enzyme Optimum pH Pepsin 1. Enzyme concentration Increase in enzyme concentration has been found to increase proportionately the velocity of the reaction.
This is because of the provision of additional catalytic sites to which the substrate may bind with concomitant rate enhancement. This property is utilized in determining the level of serum enzymes for the diagnosis of diseases. Substrate concentration An increase in the substrate concentration increases the enzyme activity and velocity of the enzymatic reaction till a maximum is reached. A rectangular hyperbola is obtained when the velocity of reaction is plotted against the substrate concentration.
At low substrate concentration, the rate of the reaction is directly proportional to the substrate concentration A. At extremely high substrate concentration, the reaction rate approaches a maximum Vmax.
This is the phase C at which the reaction rate is independent of the substrate concentration. This is due to the fact that the available active sites of all the enzyme molecules are occupied by the substrate. Between the extremeties phase B the reaction follows both first and zero order kinetics.
At this phase, the substrate concentration is not directly proportional to the enzyme activity. Enzyme activators There are some inorganic ions which accelerate enzyme activity. These are called enzyme activators. The metal ions may be bound with the enzymes either loosely or tightly. When the metal ions are held loosely, the enzymes are called metal activated enzymes e.
The enzymes in which the metal ions are tightly bound are called metalloenzymes. Enzyme inhibitors Certain substances bind with the enzyme and bring about a decrease in catalytic activity of that enzyme. Such substances are called enzyme inhibitors.
For example, the activity of acetylcholine esterase is decreased by succinylcholine. The enzyme is released and can be used over and over again. This model assumes that the enzyme is a rigid three-dimensional body with specific regions on the surface.
These are called active centres or active sites which bind the substrate. Only the substrate having a matching shape will fit into the site just as a proper key can fit into a lock. Active sites : The active site of an enzyme is the region that binds the substrate to form an enzyme-substrate complex. The salient features of the active sites are : 1. The active site is very small compared of the total volume of an enzyme 2. The active site is a rigid three-dimensional body with cavity or cleft into which the substrate is bound.
The specificity of binding depends on the precisely defined arrangement of atoms in an active site. Substrates are bound to enzymes by relatively weak forces. The protein part of enzyme is known as apoenzyme. The coenzymes are linked to their apoenzymes through non-covalent forces. For example, the coenzyme ATP is attached to its apoenzyme hexokinase through noncovalent forces. When the coenzymes are tightly attached to their apoenzymes through covalent bonds, the coenzymes are termed prosthetic groups.
For example, iron protoporphyrin haem is the prosthetic group in haemoglobin apoenzyme. Example Many coenzymes are derivatives of water soluble B- complex vitamins. For example, it serves as a coenzyme for the enzyme pyruvate dehydrogenase which brings out the oxidative decarboxylation of pyruvate to give acetaldehyde.
Mechanism of action The proton at C-2 in the thiazole ring is ionised to yield a carbanion. The hydroxy ethyl group then undergoes hydrolysis to yield acetadehyde. That is, it serves as the coenzyme for many oxidoreductases. The reactive part of both molecules is the nicotinamide ring which exists in either a reduced or an oxidized form, and so acts to accept or donate electrons in an enzymatic reaction. Both of these coenzymes consists of a flavine mononucleotide unit which contains the reactive site.
FAD has an additional sugar group and an adenine base which complete its structure. ATP transports chemical energy within cells for metabolism.
It is one of the end products of photophosphorylation, cellular respiration and fermentation and used by enzymes and structural proteins One molecule of ATP contains three phophate groups and it is produceed by a wide variety of enzymes including ATP synthese from adenosine diphosphate ADP or adenosine monophosphate AMP and various phosphate group donors.
Substrate -level phosphorylation, oxidative phosphorylation in cellular respiration and photophosphorylation in photosynthesis are three major mechanisms of ATP biosynthesis. Now, the enzymes are said to be immobilished. Beaded gels and cyanogen bromide -activated sepharose are widely used for the immobilization of enzymes.
Glucose oxidase GOD and peroxidase POD are coated on a strip of paper and the immobilished enzymes are used in clinical laboratory for the detection of glucose on urine. Hence, glucose in urine may be detected and estimated by this method.
Immobilized enzymes have a variety of advantages over the free enzymes : 1. They can be stored for long periods without loss of activity.
Stability is generally increased to thermal denaturation and, in the case of proteases, to autodigestion 3. They can be recovered from the reaction mixtures in pure state and reused many times. Industrial applications of Enzymes Enzymes are widely used in food, pharmaceutical and chemical industries. Commodity produced Enzyme used Food Industry 1. Curd from milk Lactobacillus acidophilus 2.
Chees from milk Streptococcus themorphilus 3. Fermenting rice for delicious idlies Leucanostoc mesenteroides 2. Each enzyme is capable of bringing out only one or a small group of reactions. Thus, specificity is an important criterion of enzyme action. The specificity may be of various types : 1. Reaction specificity 2. Substrate specificity i Absolute specificity ii Relative specificity iii Group specificity iv Stereospecificity 1. Reaction specificity Different enzymes bring out different reactions on the same substrate e.
Substrate specificity Substrate specificity varies from enzyme to enzyme. For example, urease acts only on urea to give ammonia and carbon dioxide ii Relative specificity : some enzymes act on structurally related substrates with different speeds.
For example, D-aminoacid oxidases act on all D-amino acids, but they can bring about oxidative deamination of D-tyrosine very rapidly and less so the other D-amino acids iii Group specificity : Some enzymes act on specific bonds on different compounds.
For example, pepsin hydrolyses peptide bonds preferentially involving tryptophan, tryrosine, phenylalanine and leucine while Trypsin acts best on peptide bonds involving - COOH group of arginine and lysine. For example, L-amino acid oxidase acts on L-amino acids whereas D- amino acid oxidase acts on D-amino acids. Similarly, fumarase catalyses the interconversion of fumeric acid and L-malic acid.
It has no effect on the interconversion of maleic acid and D-malic acid. Check your progress 1. Enzymes are Coenzyme derived from pantothenic acid is Enzyme reactions are highly stereo They promote chemical reactions.
Enzymes retain their identity at the end of the reactions as in the begining. Many enzymes require the presence of certain non-protein compounds which help in accelerating the enzyme action. They are called as coenzymes or prosthetic groups. It does not affect the equilibrium of the catalysed reaction, it enhance the rate of a reaction by providing a reaction path with lower activation energy Coenzyme : An organic cofactor required for the action of certain enzymes; often contains a vitamin as a component.
NAD, NADP : Nicotinamide containing coenzymes functioning as carriers of hydrogen atoms and electrons in some oxidation-reduction reactions. Prosthetic group : A metal ion or an organic compound other than an amino acid that is convalently bound to a protein and is essential for its activity. What are coenzymes 2. Give the different classification of enzymes 3. Explain Lock and key model of enzymes action 4. Explain the different types of enzyme specificity.
Write note on immobilization of enzymes. Check Your Progress : Model answer 1. Protein 2. Acetyl coenzyme A 3. Specific 4. ATP 2. Power and G. Chatwal, Biochemistry. Neutral lipids 3. Saturated fatty acid 3. Unsaturated fatty acid 3.
Properties 3. Hydrolysis 3. Acid number 3. Saponification number 3. Auto-oxidation Rancidity 3. Addition reaction 3. Iodine value 3. Polenske number 3. Reichert-Meissl number 3. Acetyl number 3. Cholesterol 3. Biosynthesis 3. The term lipid means non-polar organic solvent.
On hydrolysis, lipids yield fatty acids which are utilised by the living organisms. Thus, they are the esters of fatty acids.
Oils, fats, steroids, waxes and related compounds are example of lipids. Lipids are widely distributed throughout the plant and animal kingdom. In plants, they occur in the seeds, nuts and fruits. In animals, they are stored in adipose tissues, bone marrows and nervous tissues. Simple lipids 2. Complex lipids 3. Derived lipids 1. Simple lipids Simple lipids are the esters of fatty acids with alcohols.
They are further classified as follows: a Oils and Fats : These are the esters of fatty acids with glycerol. Hence, they are also called triglycerides. There is no difference between an oil and a fat as far as the chemical properties are concerned. They are the triglycerides of fatty acids. The difference between an oil and a fat lies only in their melting points. Cholesteryl palmitate is the wax found in blood plasma.
Complex lipids The lipids having some additional groups besides fatty acids and alcohols are called complex or compound lipids. The additional group may be a phosphate, nitrogenous base, carbohydrate or protein. They are further classified as follows: a Phospholipids : Lipids containing a phosphoric acid residue in addition to fatty acids and alcohol are known as phospholipids.
There are two types of phospholipids. Example : Lecithin, Cephalin. Example : sphingomyelin. Examples : cerebroside, gangliosides etc.
Derived lipids These are the hydrolysis products of simple and complex lipids. They include fatty acids, glycerol, steroids e. Based on the nature of alcohol moiety, phopholipids are classified into three groups: 1.
Glycerophosphatides 42 2. Phosphospingosides 3. Glycerophophatides There are phospholipids in which the alcohol is glycerol. This includes lecithins, cephalins, phosphatidyl cerine and plasmalogens.
Composition : Lecithins contain glycerol, fatty acid, phosphoric acid and a quaternary base, choline. The structural moiety without choline is called phosphatidic acid. Hence, lecithins are also known as phosphatidyl cholines. A large number of lecithins exist differing in their fatty acid moiety. The fatty acids commonly occurring in lecithins are palmitic, stearic, oleic, linolenic and arachidonic acids.
The lecithins in human RBC membranes are reported to exist in more than 20 forms. It helps emulsification of lipid-water mixtures, a prerequisite in the digestion as well as absorption of lipids from the gastrointestinal tract. They are also present in the erythrocyte and in soyabean oil. Composition : Cephalins which are also known as phosphatidyl ethanolamines contain glycerol, fatty acid, phosphoric acid and a base ethanolamine in the place of choline of lecithins Structure : Cephalins are structurally similar to lecithins.
Composition : It has the same composition as lecithins except that the base is serine, an amino acid. Thus, it is an aid phospholipid.
Structure d Plasmalogens Occurrence : Plasmalogens occur abundantly in brain and muscles. They also occur in the seeds of higher plants. Composition : Plasmalogens contain glycerol, fatty acid, phosphoric acid and a base choline or ethanolamine. Thus, they resemble lecithins and cephalins. But, one of the fatty acids is replaced by a long chain aliphatic aldehyde. Phosphospingosides These are phospholipids in which the alcohol is sphingosine or sphingol, a complex amino alcohol.
Fatty acid, choline and phosphoric acid are the other constitutents. These are also known as sphingophospholipids or simply sphingolipids. Example : Sphingomyelin Sphingomyelin is an important constituent of myelin and present in large amounts in brain and nervous tissues. They apparently lack in plants and microorganisms.
Phosphoinositides These are phospholipids in which the base is replaced by inositol, a cyclic hexahydric alcohol. These are also known as phosphatidyl inositols, Monophosphotidyl inositols are widely distributed in animals and plants but diphosphatidyl inositols have been reported to be present in brain tissues only.
Functions of phospholipids 1 Phospholipids are present both in cytoplasm as well as cell membranes and regulate cell activity and membrane permeability. They are widely distributed in the white matter of the brain and in the myelin sheaths of nerves. Cerebrosides : These are glycosphingolipids containing ceramide sphingosine attached to fatty acid and one or more sugar residues. Similarly, galactose forms galactocerbroside. The cerebrosides occur primarily in the brain and at nerve synapses 2.
Gangliosides : These are complex glycosphingolipids derived from glucocerebroside. They contain one or more residues of sialic acid in the carbohydrate moiety. Elizabeth Howell. Chemistry of proteins 1. Chemistry of Proteins Lecture No. What are proteins? As enzymes, they are the driving force behind all the biochemical reactions which make biology work. The non-amino acid group is termed as the prosthetic group.
They are compactly folded and coiled. They are spiral and helical and are cross linked by disulfide and hydrogen bonds. Valine, Leucine, Isoleucine How many types of proteins are in our body? Blood Proteins Regulation of gene expression Regulatory proteins Neutralize trypsin that has leaked from the digestive system AlphaAntitrypsin Blood coagulation Fibrinogens Participate in immune system Immunoglobulins Create osmotic pressure and transport other molecules Albumins Vasopressin Vassopressin Chemical test for Proteins Ultracentrifugation — effects separation on the basis of molecular weight when large gravitational forces are applied in the ultracentrifuge.
Precipitation Methods — salts as sodium sulfate, ammonium sulfate, cadmium nitrate, silver nitrate and mercuric chloride at specific conc. Dialysis — is for the removal of small, crystalloidal molecules from protein solution. HPLC
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