December 14, 2015

Senior Inter Zoology Important Questions - Unit IV

Q: Describe the male and female sex hormones and their actions.
A: a. Male sex hormones are called androgens (e.g., Testosterone).
They are essential for the maturation and functioning of male
accessory sex organs. They regulate the development of muscles, facial
and axillary hair, aggressiveness and low pitch (masculine) voice.

b. Female sex hormones are estrogen and progesterone. Estrogen
promotes the development and activity of the female secondary sex
organs, growth of ovarian follicles, high pitch (feminine) voice;
development of mammary glands. Progesterone prepares the uterus for
receiving and implantation of the blastocyst and inhibits
the contractions of the uterus.

Q: Explain the mechanism by which HIV multiplies and leads to AIDS.
A: a. After infection to a new person, the HIV enters the TH cells,
macrophages and dendric cells.

b. In these cells ssRNA synthesises a new DNA strand complementary to
the viral RNA in presence of reverse transcriptase.
c. Reverse transcriptase catalyses the synthesis of another strand of
DNA and thus a double strand DNA is formed.
d. Then this viral DNA gets incorporated into DNA of the host cell
with help of viral enzyme integrase.
e. Transcribed RNA from this DNA will act as the genome for the new or
it can be transcribed into viral proteins.
f. Now the infected host cells act as HIV generating factories. New
viruses are budded off from the host cell.
g. As a result, progressive decrease in number of TH cells of the
infected \ person leading to immunodeficiency.
h. Attack on certain types of cells or tissues only by viruses, such
as HIV is referred to as tissue tropism.

Q: Write short notes on immunoglobulins.
A: When antigens enter the body, B-Lymphocytes produce immunoglobulins
(antibodies), that bind to the antigens and destroy them. Antibodies
are highly specific.
a. An immunoglobulin consists of four polypeptide chains - Two light
chains (L) and two heavy chains (H). The H - chain and L - chain are
linked by disulphide bonds to form a Y - shaped molecule.
b. The ends of two arms are called variable regions.
c. The distal end of each arm of Y is known as Fab region, which binds
to the antigen.
d. The lower parts of arms are called constant regions (C).
e. The stem of Y is known as Fc region. It binds to the complement
proteins or Fc receptors of cells like phagocytes, mast cells etc.

The part of immunoglobulin that recognises and attached to an antigen
is known as paratope. The portion of antigen that binds to paratope is
known as epitope.

f. Based on the type of heavy chain, antibodies are classified into
five types, viz., IgM, IgG, IgD, IgA and IgE.
g. Antibodies (immunoglobulin) are of two types..
Membrane bound antibodies - present on cell membrane of immunocompetent cells.
Secreted antibodies - circulate in the body fluids.

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