Frequently Asked Technical Questions During Biotech PhD Interviews
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Frequently Asked Technical Questions During Biotech PhD Interviews

Cleared the Biotech PhD Entrance Exam? Hold On it’s not over yet! Once you clear the PhD Interview you are through the finish line. PhD Interviews are very crucial. It is one of the vital steps after clearing competitive PhD entrance exams is the selection of a proper guide and project. The selection process is usually bi-directional, where first a panelist would select a candidate and then the candidate would select their guide/project based on interest. During the interview, the panelist would generally look for logical reasoning ability of the candidate along with their subject knowledge. The candidate may face questions that seem very difficult but are very simple when thought upon. The trick is to stay calm. Few examples of Frequently Asked Technical Questions During Biotech PhD Interviews have been listed below;

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Question 1: How can you differentiate between a cancer cell line and a normal cell line by just looking at it?
Answer: A transformed cell can be differentiated from a non-transformed cell by looking at a cell culture. If the cells form colonies, piling up on one another, it indicates loss of contact inhibition. This is a characteristic of transformed tumor producing cells. If the growth appears normal, they are mostly normal cell cultures. Now, tumor-forming ability can be seen by this method but whether they are benign or malignant needs to be checked by various cytological or genetic tests.


Question 2: If you have a drawer full of black and white socks, in how many chances will you be able to select a correct pair, by pulling out one sock at a time?
Answer: This is a probability type question, however, has a very simple and logical solution to it. This shows the interviewer your ability to think quickly and analyze logically. It will take a maximum on 3 chances. You will pull either a black/white sock at the first chance. You may pull out the same color in the next chance. Even if you do not, by the third chance you will have a pair of either black or white socks at hand !!


Question 3: If you have three samples with DNA, RNA, and protein, what is the easiest way to differentiate between them and identify?
Answer: The easiest way to differentiate the solution is to do a spectrometry test. The three have different absorption properties. Another way is to look at the solution tubes. Protein solution will give froth on shaking. DNA solution appears whitish with strands and spools. RNA solution is transparent and may sediment on cooling. Other biochemical tests can differentiate the three along with electrophoretic techniques. !!


Question 4: Name one GPCR ligand which is neither a protein nor a lipid nor a sugar?
Answer: Light is a GPCR ligand and is neither of the above. The receptor is Rhodopsin and is the reason we can visualize an image in dim light. Rhodopsin, a visual pigment found in the rod photoreceptor cells of the retina, is responsible for converting photons into chemical signals that stimulate biological processes in the nervous systems of humans and other vertebrate animals, allowing them to sense light !!


Question 5: If DNA is the key source of everything, why do we need to spend time and energy in preparing RNA?
Answer: At a high-stress period like an interview, a candidate may easily forget simple questions like this. This allows the interviewer to judge your basic knowledge and confidence level. RNA allows the formation of proteins only transiently. It balances the requirement. If RNA was not produced DNA would always produce proteins and keep all cellular processes on. RNA also allows different types of splice variant proteins to form from one DNA (gene). In some cases, RNA may also work as inhibitors of production processes !! Ideally the DNA in a neuron and the DNA in a macrophage is identical, however, their structure and function differ. This is attributed to the fact that we have RNA.


Question 6: Do bacteria survive in blood?
Answer: This is a very basic question which we may fail to ponder upon and hence can be asked in the interview. Bacteremia is the presence of bacteria in the blood. Bacteria may spread through the bloodstream, however, blood is normally sterile. Presence of bacteria in the blood can only be caused by severe infection or tissue harm. They are quickly removed by the body’s immune system. It can be treated with antibiotics.


Question 7: When an antibiotic medicine that dissolves in the mouth is consumed, how does it remove infection?
Answer: There are four basic stages of a medicine’s life in the body: absorption, distribution, metabolism, and excretion. This process may be abbreviated as ADME. Usually, an antibiotic releases the drug either on dilution in the mouth or stomach. Once the drug component is released it gets absorbed in the tissues and enters the organ system through which they enter the bloodstream. Usually the medicine is carried through the bloodstream throughout the body. Side effects usually occur when a drug has effect on an organ other than the target organ. Antibiotics may combat the bacterial infection by either inhibiting their DNA replication, cell wall formation etc. This slows down the infection and eventually kills the bacteria.


Question 8: If there is a linear DNA that has 3 RE sites, 2 bp, 100 bp, 4500 bp apart from the start site, how many bands will you get on digesting this fragment.
Answer: This is a practical based question, and the answer proves that you have worked with blotting techniques. Assuming that there is no overlapping fragment size (since the last length till endpoint has not been mentioned) there should ideally be 4 fragments in this linear DNA. But if we look at the western blot markers we will find ladders usually up to 100 bp or maximum till 50 bp. This is because fragments below this length are usually not obtained in the blot – it runs outside the gel.

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These questions judge both the subject knowledge and the analytical capability of a student. They are merely examples to help you understand the level or type of questions that one may face. However, questions from one’s project/work may be asked as well. It is important to convey your interest to the panelists for them to judge better.


Question 9: Name some plant and animal disease-causing gram-negative pathogens?
Answer: In Plants, Xanthomonas oryzae pv. oryzae a Gram‐negative bacterium is of rod shape and produces a yellow soluble pigment, called xanthomonadin which is an extracellular polysaccharide (EPS). EPS sheaths the bacteria from desiccating and for the attenuation of wind‐ and rain‐borne dispersal. This bacteria infects rice at multiple locations like a leaf through hydathodes at the leaf tip, broken trichomes, leaf margins and wounds in the leaves or roots, multiplies in the intercellular spaces and enters into xylem vessels. Erwinia amylovora causes fire blight disease of apple, pear, quince, blackberry, raspberry and many wild and cultivated rosaceous ornamentals. In animals: Vibrio cholerae– Cholera—is a waterborne pathogen. Yersinia pestis – Plague


Question 10: What is standard error and how is it different from standard deviation?
Answer: Standard deviation(SD)- measures the amount of variability or dispersion for each data in the sample from the mean. It gives us an information about how much is the distance between each data in the sample from the mean.

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The standard error of the mean(SEM)- Measures how far the sample mean of the data is likely to be from the true population mean. The difference between sample mean and that of a population mean. More the sample error it is more likely that the sample is not a good representation of the population.The SEM will be smaller than the SD.


About the Author:

Rashmi Sanyal is one of the most experienced team members of Biotecnika. Coming from a research background in cancer, she specializes in Cancer Genetics, Immunology & Developmental Biology. Her experience in the PhD Exam & Selection field is vast. She has a keen interest in understanding the latest developments in Biotech & Pharma Industry and is very passionate about educating the same to her students.

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