Friday 28 March 2014

DI-DCO Solved Exam Paper with Explanation (RAJASTHAN) . 2012 Part-8



Q.81 10-11 epoxide is metabolic product of
a) Phenytoin         b) Carbamezapine       c) Valproic acid       d) Ethusuximide
Ans 81. B, Carbamazepine (CBZ) (Tegretol, Equetro) is an anticonvulsant and mood-stabilizing drug used primarily in the treatment of epilepsy and bipolar disorder, as well as trigeminal neuralgia. It is also used off-label for a variety of indications, including attention-deficit hyperactivity disorder (ADHD), schizophrenia, phantom limb syndrome, complex regional pain syndrome, paroxysmal extreme pain disorder, neuromyotonia, intermittent explosive disorder, borderline personality disorder, Myotonia congenita and post-traumatic stress disorder.

The major metabolic pathway of carbamazepine (CBZ) is the formation of the stable 10,11-CBZ epoxide by cytochrome P-450 isozyme CYP3A4. This reactive metabolite is further deactivated by the action of epoxide hydrolase to give inactive 10,11-CBZ-diol that is excreted as glucuronides.




Several other minor metabolites have also been identified with CBZ. These are derived from the reactive intermediate, arene oxide by CYP2C9/19. Further metabolic conversions of this intermediate lead to the formations of 2(3)-hydroxy-CBZ, CBZ-2, 3-diol, CBZ-catechol, and CBZ-o-quinone in a similar manner as in phenytoin. [You should practice drawing the chemical structures for each of these metabolites].
   It should be pointed out that carbamazepine, similar to phenobarbital and phenytoin, is a potent liver enzyme inducers.  Furthermore, it will also induce its own metabolic biotransformations.

Q.82 Dissociation constant of acid is written as
a) Ka                             b) pKa                           c) pH                             d) Kb
Ans 82. A, An acid dissociation constant, Ka, (also known as acidity constant, or acid-ionization constant) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid-base reactions. The larger the Ka value, the more dissociation of the molecules in solution and thus the stronger the acid.
The equilibrium of acid dissociation can be written symbolically as:
 
where HA is a generic acid that dissociates by splitting into A, known as the conjugate base of the acid, and the hydrogen ion or proton, H+, which, in the case of aqueous solutions, exists as the hydronium ion—in other words, a solvated proton. In the example shown in the figure, HA represents acetic acid, and A represents the acetate ion, the conjugate base. The chemical species HA, A and H+ are said to be in equilibrium when their concentrations do not change with the passing of time. The dissociation constant is usually written as a quotient of the equilibrium concentrations (in mol/L), denoted by [HA], [A] and [H+]:






Due to the many orders of magnitude spanned by Ka values, a logarithmic measure of the acid dissociation constant is more commonly used in practice. The logarithmic constant, pKa, which is equal to −log10 Ka, is sometimes also (but incorrectly) referred to as an acid dissociation constant:
 


The larger the value of pKa, the smaller the extent of dissociation at any given pH (see Henderson–Hasselbalch equation)—that is, the weaker the acid. A weak acid has a pKa value in the approximate range −2 to 12 in water. Acids with a pKa value of less than about −2 are said to be strong acids; a strong acid is almost completely dissociated in aqueous solution, to the extent that the concentration of the undissociated acid becomes undetectable. pKa values for strong acids can, however, be estimated by theoretical means or by extrapolating from measurements in non-aqueous solvents in which the dissociation constant is smaller, such as acetonitrile and dimethylsulfoxide.


Q.83 Noyes witteny equation is used for study of
a) Dissolution rate       b) Disintegration rate c) Dissociation rate      d) Difusion rate
Ans 83. A, The rate of dissolution can be often expressed by the Noyes-Whitney Equation or the Nernst and Brunner equation  of the form:




where:
m, mass of dissolved material
t, time
A, surface area of the interface between the dissolving substance and the solvent
D, diffusion coefficient
d, thickness of the boundary layer of the solvent at the surface of the dissolving substance
Cs, mass concentration of the substance on the surface
Cb, mass concentration of the substance in the bulk of the solvent
For dissolution limited by diffusion, Cs is equal to the solubility of the substance.
When the dissolution rate of a pure substance is normalized to the surface area of the solid (which usually changes with time during the dissolution process), then it is expressed in kg/m2s and referred to as "intrinsic dissolution rate".

Q.84 Enzyme Trypsin is used as
a) D            b) E            c) Nourshing the cell   d) Deattachment of cell
Ans 84. D, Trypsin is a serine protease from the PA clan superfamily, found in the digestive system of many vertebrates, where it hydrolyses proteins. Trypsin is produced in the pancreas as the inactive proenzyme trypsinogen. Trypsin cleaves peptide chains mainly at the carboxyl side of the amino acids lysine or arginine, except when either is followed by proline. It is used for numerous biotechnological processes. The process is commonly referred to as trypsin proteolysis or trypsinisation, and proteins that have been digested/treated with trypsin are said to have been trypsinized.

Function
In the duodenum, trypsin catalyzes the hydrolysis of peptide bonds, breaking down proteins into smaller peptides. The peptide products are then further hydrolyzed into amino acids via other proteases, rendering them available for absorption into the blood stream. Tryptic digestion is a necessary step in protein absorption as proteins are generally too large to be absorbed through the lining of the small intestine.

Trypsin is produced in the pancreas, in the form of the inactive zymogen trypsinogen. When the pancreas is stimulated by cholecystokinin, it is then secreted into the first part of the small intestine (the duodenum) via the pancreatic duct. Once in the small intestine, the enzyme enteropeptidase activates it into trypsin by proteolytic cleavage. Auto catalysis can happen with trypsin with trypsinogen as the substrate. This activation mechanism is common for most serine proteases, and serves to prevent autodegradation of the pancreas.

Trypsin is available in high quantity in pancreases, and can be purified rather easily. Hence it has been used widely in various biotechnological processes.
In a tissue culture lab, trypsins are used to re-suspend cells adherent to the cell culture dish wall during the process of harvesting cells. Some cell types have a tendency to "stick" - or adhere - to the sides and bottom of a dish when cultivated in vitro. Trypsin is used to cleave proteins bonding the cultured cells to the dish, so that the cells can be suspended in fresh solution and transferred to fresh dishes.

Trypsin can also be used to dissociate dissected cells (for example, prior to cell fixing and sorting).

Trypsins can be used to break down casein in breast milk. If trypsin is added to a solution of milk powder, the breakdown of casein will cause the milk to become translucent. The rate of reaction can be measured by using the amount of time it takes for the milk to turn translucent.

Trypsin is commonly used in biological research during proteomics experiments to digest proteins into peptides for mass spectrometry analysis, e.g. in-gel digestion. Trypsin is particularly suited for this, since it has a very well defined specificity, as it hydrolyzes only the peptide bonds in which the carbonyl group is contributed either by an Arg or Lys residue.
Trypsin can also be used to dissolve blood clots in its microbial form and treat inflammation in its pancreatic form.

In food

Commercial protease preparations usually consist of a mixture of various protease enzymes that often includes trypsin. These preparations are widely utilized in food processing:
  • as a baking enzyme to improve the workability of dough;
  • in the extraction of seasonings and flavourings from vegetable or animal proteins and in the manufacture of sauces;
  • to control aroma formation in cheese and milk products;
  • to improve the texture of fish products;
  • to tenderize meat;
  • during cold stabilization of beer;
  • in the production of hypoallergenic food where proteases break down specific allergenic proteins into nonallergenic peptides. For example, proteases are used to produce hypoallergenic baby food from cow’s milk thereby diminishing the risk of babies developing milk allergies.

Q.85 Human Immuno Virus (HIV) is
a) Enveloped DNA b) Non enveloped DNA c) Enveloped RNA d) non enveloped RNA
Ans 85. C, The human immunodeficiency virus (HIV) is a lentivirus (slowly replicating retrovirus) that causes the acquired immunodeficiency syndrome (AIDS),  a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive. Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate, or breast milk. Within these bodily fluids, HIV is present as both free virus particles and virus within infected immune cells.

HIV infects vital cells in the human immune system such as helper T cells (specifically CD4+ T cells), macrophages, and dendritic cells. HIV infection leads to low levels of CD4+ T cells through a number of mechanisms including: apoptosis of uninfected bystander cells, direct viral killing of infected cells, and killing of infected CD4+ T cells by CD8 cytotoxic lymphocytes that recognize infected cells. When CD4+ T cell numbers decline below a critical level, cell-mediated immunity is lost, and the body becomes progressively more susceptible to opportunistic infections.

HIV is a member of the genus Lentivirus, part of the family Retroviridae. Lentiviruses have many morphologies and biological properties in common. Many species are infected by lentiviruses, which are characteristically responsible for long-duration illnesses with a long incubation period. Lentiviruses are transmitted as single-stranded, positive-sense, enveloped RNA viruses. Upon entry into the target cell, the viral RNA genome is converted (reverse transcribed) into double-stranded DNA by a virally encoded reverse transcriptase that is transported along with the viral genome in the virus particle. The resulting viral DNA is then imported into the cell nucleus and integrated into the cellular DNA by a virally encoded integrase and host co-factors. Once integrated, the virus may become latent, allowing the virus and its host cell to avoid detection by the immune system. Alternatively, the virus may be transcribed, producing new RNA genomes and viral proteins that are packaged and released from the cell as new virus particles that begin the replication cycle anew.
 

No comments:

Post a Comment