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Biology GS TIFR- Tata Institute of Fundamental Research Questions 1-5_ Solved





1. In a human family, the father and the mother are carriers of an autosomal recessive disease. One of their sons is phenotypically normal. What is the probability that this son is also a carrier?

(i) 1/2

(ii) 1/3

(iii) 1/4

(iv) 2/3


Answer: If both parents are carriers of an autosomal recessive disease, then each of their children has a 25% chance of inheriting two copies of the disease-causing allele and being affected by the disease, a 50% chance of inheriting one copy of the disease-causing allele and being a carrier, and a 25% chance of inheriting two copies of the normal allele and being phenotypically normal and not a carrier.


Given that one of their sons is phenotypically normal, there are two possibilities: either he inherited two copies of the normal allele (25% probability) or he inherited one normal allele and one disease-causing allele and is a carrier (50% probability).


Thus, the probability that this son is a carrier is 50% / (25% + 50%) = 2/3.


Therefore, the answer is 2/3.


2. Which of the following techniques can be used to identify a post-translational modification such as phosphorylation or methylation of a protein, and the residue where it is modified?


(i) 2-D gel electrophoresis

(ii) Size exclusion chromatography

(iii) Mass spectrometry

(iv) UV-Visible spectroscopy


Answer: Mass spectrometry is a technique that can be used to identify a post-translational modification such as phosphorylation or methylation of a protein and the residue where it is modified. This technique can provide information on the mass and structure of the modified protein, which can be used to identify the specific amino acid residue that has been modified. In contrast, 2-D gel electrophoresis, size exclusion chromatography, and UV-Visible spectroscopy are not typically used for identifying specific post-translational modifications on a protein. 2-D gel electrophoresis is a method for separating proteins based on their size and charge but does not provide information on post-translational modifications. Size exclusion chromatography separates proteins based on their size, but does not provide information on post-translational modifications. UV-Visible spectroscopy is used to measure the absorbance of light by molecules but is not typically used for identifying specific post-translational modifications on a protein.


3. Amino acids have different chemical properties that determine whether they are found on the surface of globular proteins. Which of the following series of amino acids is ordered according to how likely it will be found on the surface of a protein:


(i) Arginine > Leucine > Aspartic acid> Phenylalanine

(ii) Threonine > Arginine > Phenylalanine > Asparagine

(iii) Arginine > Phenylalanine > Threonine > Glycine

(iv) Aspartic acid > Threonine > Leucine > Phenylalanine


Answer: The correct order based on the chemical properties of these amino acids is:


Aspartic acid > Threonine > Leucine > Phenylalanine


Amino acids with polar or charged side chains, such as aspartic acid and threonine, are more likely to be found on the surface of a protein, where they can interact with the aqueous environment. Leucine, on the other hand, has a nonpolar side chain, making it more likely to be buried within the protein core. Phenylalanine also has a nonpolar side chain, but it is larger than leucine and therefore less likely to be buried within the protein core.


Arginine, asparagine, and glycine are not in the correct order based on their chemical properties and their likelihood of being found on the surface of a protein.


4. Repolarisation of membrane potential in neurons is caused by the movement of:

(i) potassium into the cell and sodium into the cell

(ii) potassium out of the cell and sodium out of the cell

(iii) potassium into the cell and sodium out of the cell

(iv) potassium out of the cell and sodium into the cell


Answer: The repolarization of the membrane potential in neurons is caused by the movement of potassium out of the cell and sodium into the cell. During an action potential, the depolarization phase is caused by the influx of sodium ions into the cell, while the repolarization phase is caused by the efflux of potassium ions out of the cell. The movement of these ions across the cell membrane is facilitated by ion channels that are regulated by the opening and closing of voltage-gated channels.


5. You synthesize a short peptide [AMxVFxGNxM], where x is any amino acid with a charged side chain. How many possible peptides can be synthesized?


(i) 15

(ii) 243

(iii) 125

(iv) 27


Answer: The peptide sequence [AMxVFxGNxM] has 3 positions with x, where x can be any amino acid with a charged side chain.


There are 2 charged amino acids: Aspartic acid (Asp or D) and Glutamic acid (Glu or E).


Therefore, there are 2 options for each of the 3 positions with x, giving a total of 2 × 2 × 2 = 8 possible peptides that can be synthesized.



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