All Exams  >   MCAT  >   MCAT Biological and Biochemical Foundations  >   All Questions

All questions of Evidence That DNA Is Genetic Material (BIO) for MCAT Exam

DNA contains nucleobases, sugar and phosphate. Removal of which among these from a DNA sample will not significantly affect the length of DNA?
  • a)
    Nucleobases
  • b)
    Sugar
  • c)
    Phosphate
  • d)
    None of the above
Correct answer is option 'A'. Can you explain this answer?

Shreya Singh answered
Nucleobases, also known as nitrogenous bases  are nitrogen-containing biological compounds that form nucleosides, which in turn are components of nucleotides, with all of these monomersconstituting the basic building blocks of nucleic acids. The ability of nucleobases to form base pairs and to stack one upon another leads directly to long-chain helical structures such as ribonucleic acid (RNA) and deoxyribonucleic acid (DNA)....

DNA has genetic properties was revealed for the first time by
  • a)
    Chargaff
  • b)
    Griffith
  • c)
    Avery
  • d)
    Wilkins
Correct answer is option 'C'. Can you explain this answer?

The discovery that DNA has genetic properties was first revealed by Oswald Avery and his team of scientists in 1944. Avery was a molecular biologist who worked at the Rockefeller Institute for Medical Research in New York City.

Experiment
Avery and his team conducted a series of experiments to determine whether DNA was the genetic material responsible for the transformation of bacteria. They used two strains of Streptococcus pneumoniae, one that was virulent (able to cause disease) and one that was non-virulent. The virulent strain had a capsule made of a complex sugar that protected it from the immune system, while the non-virulent strain lacked this capsule and was easily destroyed by the immune system.

Results
Avery and his team extracted various biochemical components from the virulent strain of bacteria, including proteins, lipids, RNA, and DNA. They then mixed each of these components with the non-virulent strain to see if they could induce transformation. Only the DNA extract was able to transform the non-virulent strain into a virulent one, proving that DNA was the genetic material responsible for the transformation.

Conclusion
Avery's discovery was groundbreaking because it showed that DNA, which was previously thought to be a simple molecule with no biological significance, was in fact the carrier of genetic information. This discovery paved the way for the development of the field of molecular biology and our current understanding of genetics.

According to Chargaff’s rule, which one is correct?​
  • a)
    [A] + [T] = [G] + [C]
  • b)
    [A] + [C] = [G] + [T]
  • c)
    [A] + [G] = [T] + [C]
  • d)
    All of these
Correct answer is option 'C'. Can you explain this answer?

Geetika Shah answered
According to Chargaff’s rule in all cellular DNA, regardless of the species, number of adenosine residues is equal to the number of thymidine residues which means that A = T and the number of guanosine residues is equal to the number of cytidine residues; G = C . Hence, that the sum of the purine residues equals the sum of the pyrimidine residues; i.e., A + G = T + C.

Whose experiments cracked the DNA and discovered unequivocally that a genetic code is a triplet?
  • a)
    Nirenberg and Matthaei
  • b)
    Hershey and Chase
  • c)
    Beadle and Tatum
  • d)
    Morgan and Sturtevant
Correct answer is option 'A'. Can you explain this answer?

Rajat Kapoor answered
The existence of a triplet code was simply an assumption till 1961 when Nirenberg and Methaei proved its existence by experiment. They were able to synthesise artificial mRNA, which contained only one nitrogenous base, ie, uracil. This synthetic poly-U sequence was then placed in a cell-free system containing protein synthesizing enzymes (extracted from bacterium E. coil) and 20 amino acids together with necessary ATP. During the process, a small polypeptide molecule was produced, which was formed by the linking of phenylalanine. This issuggested that UUU is code for phenylalanine. Nirenberg got Nobel Prize for his contributions.

A typical nucleosome contains
  • a)
    100 bp of DNA helix
  • b)
    400 bp of DNA helix
  • c)
    200 bp of DNA helix
  • d)
    300 bp of DNA helix
Correct answer is option 'C'. Can you explain this answer?

Suresh Kumar answered
A typical nucleosome contains 200 bp of DNA double helix wrapped(2 turns) around a core of histone octamer having two copies of each of four types of histone proteins ..H2A,H2B,H3,&H4.....H1 histone molecule lies outside the nucleosome core & seals the two turns of DNA by binding at the point where DNA enters and leaves the core..

In Hershey and Chase experiments, radioactive 32P was used to culture bacteriophages which resulted in radioactive
  • a)
    Protein capsule of bacteriophage
  • b)
    Viral DNA
  • c)
    Bacterial capsule
  • d)
    Viral proteins
Correct answer is option 'B'. Can you explain this answer?

Sanjana Sharma answered
The Hershey and Chase Experiment

The Hershey and Chase experiment, conducted in 1952 by Alfred Hershey and Martha Chase, provided important evidence supporting the concept that DNA, rather than protein, is the genetic material. This experiment was crucial in the development of the field of molecular biology and helped solidify the understanding of DNA as the molecule responsible for transmitting hereditary information.

Experimental Setup

In the Hershey and Chase experiment, the researchers used bacteriophages, which are viruses that infect bacteria. Bacteriophages consist of a protein coat, called the capsid, that encapsulates their genetic material, either DNA or RNA. The researchers wanted to determine whether the genetic material of the bacteriophage was DNA or protein.

To accomplish this, Hershey and Chase used two separate batches of bacteriophage T2. In one batch, they labeled the DNA of the bacteriophage with radioactive phosphorus-32 (32P), while in the other batch, they labeled the protein coat with radioactive sulfur-35 (35S).

Infection and Blending

The labeled bacteriophages were then used to infect separate cultures of E. coli bacteria. The infection process allowed the bacteriophage to inject its genetic material into the bacterial cell. To separate the bacteriophages from the bacterial cells, Hershey and Chase used a blender to shear off the protein coats that remained on the outside of the bacteria.

Centrifugation

After blending, the mixture was subjected to centrifugation, a process that separates particles based on their density. The heavy bacterial cells settled at the bottom of the centrifuge tube, forming a pellet, while the lighter bacteriophages remained in the liquid portion, called the supernatant.

Results

The researchers observed that the pellet in the 32P-labeled experiment was radioactive, indicating that the bacteriophage's genetic material had entered the bacterial cells. Conversely, the supernatant in the 32P-labeled experiment was not radioactive, suggesting that the protein coats remained outside the bacterial cells.

In the 35S-labeled experiment, the opposite pattern was observed. The pellet was not radioactive, indicating that the protein coats did not enter the bacterial cells, while the supernatant was radioactive, suggesting that the labeled protein coats had remained outside the bacterial cells.

Conclusion

Based on these results, Hershey and Chase concluded that the genetic material of the bacteriophage is DNA, not protein. The radioactive 32P-labeled DNA had entered the bacterial cells and was responsible for transmitting the genetic information, while the 35S-labeled protein coats remained outside the bacterial cells.

This experiment provided strong evidence supporting the role of DNA as the genetic material and laid the foundation for future research and discoveries in molecular biology.

Nitrogenous bases present in DNA:
  • a)
    Adenine, guanine, cytosine, thymine
  • b)
    Guanine, uracil
  • c)
    Adenine, guanine, cytosine, uracil
  • d)
    Adenine, thymine, uracil
Correct answer is option 'A'. Can you explain this answer?

Four different types of nitrogenous bases are found in DNA: two purines adenine (A) and guanine (G) & two pyrimidines cytosine (C) and thymine (T). In RNA, the thymine is replaced by uracil (U).

While analysing the DNA of an organism, a total number of 5386 nucleotides were found out of which the proportion of different bases were Adenine = 29%, Guanine = 17%, Cytosine = 32% and Thymine = 17%. Considering the Chargaff’s rule, it can be concluded that
  • a)
    It is a double-stranded linear DNA.
  • b)
    It is single-stranded DNA.
  • c)
    No conclusion can be drawn.
  • d)
    It is a double-stranded circular DNA.
Correct answer is option 'D'. Can you explain this answer?

Anjana Sharma answered
The correct answer is b.
According to Chargaff's rules of base pairing, 
(i) The amount of adenine is always equal to the amount of thymine and the amount of guanine is always equal to the amount of cytosine. (ii) Adenine is joined to thymine with two hydrogen bonds and guanine is joined to cytosine by three hydrogen bonds. 
(iii) The ratio of adenine to thymine and that of guanine to cytosine is always equal to one, i.e., A/T = G/C =1      
In the given organism, the DNA is not following the Chargaff's rule, hence it can be concluded that it is a single-stranded DNA, not double-stranded. 

Which of the following phenomena was experimentally proved by Meselson and Stahl?
  • a)
    Transformation
  • b)
    Transduction
  • c)
    Semi-conservative DNA replication
  • d)
    Central dogma
Correct answer is option 'C'. Can you explain this answer?

Anjali Sharma answered
The Meselson and Stahl experiment was an experiment to prove that DNA replication was semi-subsequently and it was first shown in Escherichia coli and subsequently in higher organisms, such as plants and human cells. Semi-conservative replication means that when the double stranded DNA helix was replicated, each pf the two double stranded DNA helices consisted of one strand coming from the parental helix and one is newly synthesised.

To prove that DNA is the genetic material, which radioactive isotopes were used by Hershey and Chase(1952) in their experiments?
  • a)
    35S and 15N
  • b)
    32P and 35S
  • c)
    32P and 15N
  • d)
    14N and 5N
Correct answer is option 'B'. Can you explain this answer?

Vivek Patel answered
Hershey and Chase experiment is based on the fact that DNA contains phosphorus and similarly, sulphur is present in proteins but not in DNA. They incorporated radioactive isotope of phosphorus (32P) into phage DNA and that of sulphur (35S) into proteins of a separate phage culture. Viruses grown in the presence of radioactive phosphorus contained radioactive DNA but not radioactive protein because DNA contains phosphorus but proteins do not, Similarly, viruses grown on radioactive sulphur contain radioactive- protein but not-radioactive DNA because DNA does not contain sulphur.

Choose the correct answer from the alternatives given:
Watson and Crick (1953) proposed DNA double helix model and won the Nobel Prize; their model of DNA was based on
(i) X-ray diffraction studies of DNA done by Wilkins and Franklin.
(ii) Chargaffs base equivalence rule.
(iii) Griffiths transformation experiment.
(iv) Meselson and Stahls experiment.
  • a)
    (i), (ii) and (iv)
  • b)
    (i) and (ii)
  • c)
    (iii) and (iv)
  • d)
    (i), (ii), (iii) and (iv)
Correct answer is option 'B'. Can you explain this answer?

Anjali Sharma answered
In 1953, James Watson and Francis Crick based on the X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin, proposed double helix model for the structure of DNA. One of the hallmarks of their proposition was base pairing between two strands of polynucleotide chains. However, this proportion was also based on the observation of Erwin Chargaff (1950) that for a double stranded DNA, the ratios between Adenine and Thymine and Guanine and Cytosine are constant and equals one.

Which of the following are the functions of RNA?
  • a)
    It is a carrier of genetic information from DNA to ribosomes synthesising polypeptides.
  • b)
    It carries amino acids to ribosomes.
  • c)
    It is a constituent component of ribosomes.
  • d)
    All of the above.
Correct answer is option 'D'. Can you explain this answer?

Nidhi Banerjee answered
Functions of RNA:
RNA, or ribonucleic acid, plays a crucial role in various cellular processes. It is involved in genetic information transfer, protein synthesis, and is a constituent component of ribosomes.

1. RNA as a carrier of genetic information from DNA to ribosomes synthesizing polypeptides:
One of the primary functions of RNA is to act as an intermediary between DNA and protein synthesis. This process involves three types of RNA: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).

- mRNA: mRNA carries the genetic information encoded in DNA to the ribosomes, where it serves as a template for protein synthesis. It carries the instructions for the order of amino acids in a polypeptide chain.

- tRNA: tRNA plays a crucial role in protein synthesis by transporting amino acids to the ribosomes. It binds to specific amino acids and carries them to the ribosome, where they are added to the growing polypeptide chain according to the instructions provided by mRNA.

- rRNA: rRNA is a major component of ribosomes, which are the cellular organelles responsible for protein synthesis. rRNA combines with proteins to form ribosomes, providing the structural framework for protein synthesis.

2. RNA carrying amino acids to ribosomes:
As mentioned above, tRNA molecules are responsible for carrying amino acids to the ribosomes during protein synthesis. Each tRNA molecule has a specific anticodon sequence that matches with the codon on mRNA, ensuring the correct amino acid is added to the growing polypeptide chain.

3. RNA as a constituent component of ribosomes:
rRNA, along with proteins, forms the structure of ribosomes. Ribosomes consist of a large subunit and a small subunit, both of which contain rRNA molecules. These ribosomal subunits work together to catalyze the process of protein synthesis.

Conclusion:
In summary, RNA serves multiple functions in the cell, including carrying genetic information from DNA to ribosomes, transporting amino acids to ribosomes, and being a constituent component of ribosomes. These functions are essential for the synthesis of proteins, which are vital for various cellular processes and functions.

Q. The process of transformation is not affected by which of the following enzymes?
A. DNase
B. RNase
C. Peptidase
D. Lipase
  • a)
    A, B
  • b)
    A, B, C, D
  • c)
    B, C, D
  • d)
    A, B, C
Correct answer is option 'C'. Can you explain this answer?

Vivek Patel answered
Transformation is a phenomenon by which DNA isolated from one type of cell when introduced into another type is able to give some of its properties to the latter. In 1944, Avery, McCarty and MacLeod discovered that protein- digesting enzymes (proteases) and RNA-digesting enzymes (RNases) did not affect transformation, so the transforming substance was not a protein or RNA. Digestion with DNase did inhibit transformation, suggesting that the DNA caused the transformation. They concluded that DNA is the hereditary material.

On which medium were the viruses cultivated by Alfred Hershey and Martha Chase?
  • a)
    A medium containing radioactive potassium (K)
  • b)
    A medium containing radioactive Uranium (U)
  • c)
    A medium containing radioactive phosphorous (P)
  • d)
    A medium containing potassium (K)
Correct answer is option 'C'. Can you explain this answer?

EduRev NEET answered
  • Alfred Hershey and Martha Chase wanted to figure out whether it was the protein from the bacteriophage that was entering into the bacteria or if it was the DNA.
  • So, they cultured the bacteriophage in a medium containing radioactive phosphorous.
  • In this medium they observed that the radioactive DNA was present in the virus but not the radioactive protein.
  • This is because, protein doesn’t contain phosphorous but on the contrary, the DNA does.

Choose the correct answer from the alternatives given:
Which of the following criteria should be fulfilled by a molecule to act as a genetic material?
(i) It should be able to replicate.
(ii) It should be structurally and chemically stable.
(iii) It should be able to undergo slow mutations.
(iv) It should be able to express itself in the form of Mendelian characters.
  • a)
    (i) and (ii)
  • b)
    (ii) and (iii)
  • c)
    (i), (ii) and (iii)
  • d)
    (i), (ii), (iii) and (iv)
Correct answer is option 'D'. Can you explain this answer?

Criteria for a molecule to act as a genetic material

A molecule that acts as genetic material must fulfill certain criteria to ensure the proper transmission of genetic information from one generation to the next. The criteria are:

1. It should be able to replicate:
The molecule must be able to replicate itself accurately and efficiently so that the genetic information can be passed on to the next generation without any errors.

2. It should be structurally and chemically stable:
The molecule must be chemically and structurally stable so that it can withstand the various chemical and physical processes that occur during replication and cell division.

3. It should be able to undergo slow mutations:
The molecule must be able to undergo slow mutations, which are necessary for the generation of genetic diversity and evolution.

4. It should be able to express itself in the form of Mendelian characters:
The molecule must be able to express itself in the form of Mendelian characters, which are the observable traits that are inherited from one generation to the next.

Correct answer:

The correct answer is option D, which includes all the above criteria. A molecule that acts as genetic material must be able to replicate accurately, be structurally and chemically stable, undergo slow mutations, and express itself in the form of Mendelian characters.

Chapter doubts & questions for Evidence That DNA Is Genetic Material (BIO) - MCAT Biological and Biochemical Foundations 2025 is part of MCAT exam preparation. The chapters have been prepared according to the MCAT exam syllabus. The Chapter doubts & questions, notes, tests & MCQs are made for MCAT 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests here.

Chapter doubts & questions of Evidence That DNA Is Genetic Material (BIO) - MCAT Biological and Biochemical Foundations in English & Hindi are available as part of MCAT exam. Download more important topics, notes, lectures and mock test series for MCAT Exam by signing up for free.

Top Courses MCAT