Friday 19 March 2021

Q. Which of the following phytohormone is responsible for regulating the opening and closing of stomata ?

... Answer is B). ABA

Abscisic acid (also called ABA), was discovered and researched under two different names before its chemical properties were fully known, it was called dormin and abscicin II. Once it was determined that the two compounds are the same, it was named abscisic acid. The name "abscisic acid" was given beceuse it was found in high concentrations in newly abscissed or freshly fallen leaves

In plants under water stress, ABA plays a role in closing the stomata. Soon after plants are water-stressed and the roots are deficient in water, a signal moves up to the leaves, causing the formation of ABA precursors there, which then move to the roots. The roots then release ABA, which is translocated to the foliage through the vascular system and modulates the potassium and sodium uptake within the guard cells, which then lose turgidity, closing the stomata.

Q. The amount of water to be added to 10 ml of 10 N HCL solution to make it decinormal solution is

... Answer is B). 990 ml

      N1V1 = N2V2

So 10x10 = 0.1 x V. 

or V = 1000 ml

So extra water addes will be 990 ml 

Thursday 18 March 2021

Q. At which stage of mitosis do you find chromosomes being first visible under the microscope ?

... Answer is C). Prophase

Prophase is a stage of mitosis in which the chromatin condenses (it becomes shorter and fatter) into a highly ordered structure called a chromosome, which becomes visible under a light microscope.

Q. Which one of the following is not a water soluble vitamin ?

... Answer is C). Retinol

Retinol is one of the most usable forms of Vitamin A. a fat-soluble vitamin and diterpenoid. Retinoids include the compounds retinoic acid, retinal (aldehyde) and retinyl ester. These compounds are available from plant and animal sources. Vitamin, A is essential for proper epithelial function, and available retinoic acid is procured by hyaluronic acid in the keratogenous zone to increase dermal moisture.

While retinol is insoluble in water, its bioavailábility in the dermal layers is hydrolyzed to retinoic acid, which is subsequently sequestered by hyaluronic acid- in the extracellular matrix to increase water content in cells. These mechanisms effect normal, hydrated dermal development.

Thursday 11 March 2021

Q. Histamine is released by which of these cells ?

... Answer is C). Mast cells

A mast cell is a resident cell of several types of tissues and contains many granules rich in histamine and heparin. Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being intimately involved in wound healing and defense against pathogens.

Q. An allosteric inhibitor of an enzyme usually

... Answer is B). participates in feedback regulation

Allosteric enzymes are those that have more than one activation center and to which other substances, called allosteric regulators, bind. Allosteric regulators can be allosteric inhibitors or allosteric activators. The interaction between an allosteric enzyme and the allosteric inhibitor disallows the binding of the substrate to the enzyme. The interactión between the allosteric enzyme and the allosteric activator allows the binding of the substrate to the enzyme and sometimes increases the affinity of the enzyme for the substrate. This regulatory phenomenon of the enzyme activity is called allosterism.

Q. Which of the following group represents pro-inflammatory cytokines ?

... Answer is C). IL-1, IL-6, IL-12

Proinflammatory cytosines can be generally defined as small chemicals that are created by or help produce inflammation. These include IL-1, IL-6 and IL-12.

Q. Which one of the following, oxygenic photosynthesis does not occur in the specialized organelles ?

... Answer is A). Auto-heterotrophic bacteria

The sun is the primary source of energy for all life. Plants, algae and some bacteria utilize the light energy from the sun during photosynthesis. Photosynthesis is the physico- chemical process by which plants use this light energy to synthesize (or produce) organic compounds. There are two types of photosynthesis: oxygenic photosynthesis and anoxygenic photosynthesis.

  Oxygenic photosynthesis is the process used by plants, algae aknd some photosynthetic bacteria. During this process carbon dioxide is reduced to a carbohydrate and electrons are removed from water, releasing oxygen into the air.

 Anoxygenic photosynthesis is performed by specialized bacteria. During this process the light energy is used to remove electrons from other sources, not water. These sources include hydrogen gas, hydrogen sulphide and iron compounds. Therefore, instead of releasing oxygen, other compounds such as sulphur are released during this process.

Friday 5 March 2021

Q. The enzymes which do not conform to Michaelis-Menten kinetics such as aspartate transcarbamoylase are called

... Answer is A). allosteric enzymes

Explanation :

Although the Michaelis-Menten model provides a very good model of the experimental data for many enzymes, a few enzymes do not conform to Michaelis-Menten kinetics. These enzymes, such as aspartate transcarbamoylase are called allosteric enzymes.

Q. If lysosomes in a cell are ruptured, what would be the most likely effect ?

... Answer is C). The macromolecules in the cytoplasm would begin to break down

Explanation :

The rapture of lysosomal membranes releases powerful digestive substances into the cytoplasmic matrix. If sufficient lysosomes are ruptured the whole cell is broken down in the process of autolysis.

Q. What is the role of DNA ligase in DNA replication ?

... Answer is C). join Okazaki fragments to one another

Explanation :

DNA ligases play essential roles in replication, recombination and repair since they join broken DNA strands by catalysing the formation of a phosphodiester bond between the 3' hydroxyl end of one stand and the 5' phosphate end of another.

Q. When tryptophan accumulates in a bacterial cell

... Answer is C). it binds to the repressor, causing it to bind to the operon

Explanation :

If free tryptophan accumulates within a bacterial cell, it binds to the allosteric site in the Tryptophan repressor, inducing a conformational charge that permits the tryptophan repressor complex to bind to at least three 21-bp operator sites.

Q. Which of the following statement about the structure of skeletal muscle is true ?

... Answer is C).When the muscle contracts, the H zone of the sarcomere shortens

According to the sliding filament theory of muscle contraction, individually linked sarcomeres shorten (contract), a condition that results when the filaments slide past each other. The movement of the actin filaments towards the middle of the sarcomere occurs as the myosin cross-bridges attach themselves to the actin sites. Muscle contraction (shortening) is reflected in the sarcomere as a decrease in the I band as the Z lines (which are located at the ends of the actin filaments) move closer together. The width of the A band (the myosin filament) remains unchanged.

Thursday 4 March 2021

Q. For an enzyme assay, it was observed based on the change of the product thus formed that 100 μ moles of the substrate is converted to product per minute per milligram of the enzyme used. The specific activity of the enzyme would be

... Answer is A). 100 units

Specific activity in biochemistry is defined as the amount of product formed by an enzyme in a given amount of time. Specific activity is often reported in units (U) per mg of enzyme, where 1 unit is equal to 1 kg mol of product formed per minute.

Wednesday 3 March 2021

Q. Identify the prochiral molecule in the citric acid cycle

... Answer is B). Citrate

The citric acid cycle is the central metabolic hub of the cell. It is the gateway to the aerobic metabolism of any molecule that can be transformed into an acetyl group or dicarboxylic acid. The cycle is also an important source of precursors, not only for the storage forms of fuels, but also for the building blocks of many other molecules such as amino acids, nucleotide bases, cholesterol and porphyrin.