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

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)....

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.

Meselson and Stahl prove experimentally semi conservation of DNA replication not say but structure of DNA.

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 1928 Griffith experiment on streptococcus pneumonia and mice

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.

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).

Option A is correct becose, the nucleic acid (DNA or RNA) is consists of polymers of nucleo tides..

The correct answer is b.

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.

Beadle and Tatum proposed one gene one enzyme hypothesis and gene is present on DNA..

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.