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.
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