All questions of DNA, RNA, and Protein for Grade 9 Exam

RNA polymerase moves along the template strand, synthesising an mRNA molecule. In prokaryotes RNA polymerase is a holoenzyme consisting of a number of subunits, including a sigma factor (transcription factor) that recognises the promoter. In eukaryotes there are three RNA polymerases: I, II and III. The process includes a proofreading mechanism.

NUCLEOBASE(it is base pairing between nitrogen bases i.e A ,T,G,C) therefore  it does not affect the length of DNA where as sugar phosphate bond is the back bone of DNA therefore they both affect the length of 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

For gene transfer into the host cell without using vector microparticles made of tungsten and gold coated with foregin DNA are bombarded into target cells at a very high velocity. This method is called biolistics or gene gun which is suitable for plants.So the correct option is 'gold or tungsten'.

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..

Restriction endonuclease is a type of enzyme that can cleave molecules of DNA at a particular site called restriction site having polindromic sequence. These enzymes are produced by many bacteria and protect the cell by cleaving and destroying the DNA of invading viruses. Now a days, restriction enzymes are widely used in the techniques of genetic engineering.Therefore, the correct answer is option 'A'.

The correct answer is b.

Overview of Restriction Endonucleases
Restriction endonucleases, also known as restriction enzymes, are crucial in molecular biology for manipulating DNA. Let's evaluate the statements provided regarding these enzymes.
Statement Analysis
- i. Hind II was the first restriction endonuclease discovered and cuts DNA at a specific sequence of six base pairs.
- This statement is incorrect. Hind II was not the first restriction enzyme discovered; that title goes to Hind II's predecessor, Hind I. Additionally, while Hind II does cut DNA at a specific site, it does not necessarily cut at a sequence of six base pairs.
- ii. The convention for naming these enzymes is the first 2 letters of the name comes from the genus and the second one letter comes from the species of the prokaryotic cell from which they were isolated.
- This statement is correct. For example, EcoRI is derived from Escherichia coli (genus: Eco, species: R).
- iii. Exonucleases and endonucleases are both types of restriction enzymes that function by cutting DNA at specific sites.
- This statement is incorrect. Exonucleases remove nucleotides from the ends of DNA, while endonucleases cut within the DNA strand. Only endonucleases are classified as restriction enzymes.
- iv. Each restriction endonuclease can only recognize and cut palindromic sequences in the DNA.
- This statement is correct. Most restriction enzymes recognize specific palindromic sequences in the DNA, which are sequences that read the same forwards and backwards.
Correct Statements
Based on the analysis, the correct statements are ii and iv. Thus, the correct answer is option 'c' (i and iv).

The Genetic Code Explained
The genetic code is a set of rules by which information encoded in genetic material is translated into proteins. Understanding its characteristics is crucial in molecular biology.
Key Characteristics of the Genetic Code
- Comma-less: The genetic code does not have gaps or punctuation between codons. This means that the codons are read continuously without any breaks.
- Overlapping: This statement is incorrect. The genetic code is not overlapping; instead, each nucleotide is part of only one codon. In an overlapping code, a single nucleotide could belong to multiple codons, which is not the case here.
- Nearly Universal: The genetic code is nearly universal across different organisms, with some minor variations. This universality allows for gene transfer between species.
- Unambiguous: Each codon specifies only one amino acid, meaning that there is no ambiguity in the translation process. This characteristic ensures that the same codon will always produce the same amino acid in virtually all organisms.
Conclusion
In summary, the correct answer is option 'B' because the genetic code is not overlapping; each nucleotide is assigned to a single codon, making the translation process straightforward and efficient. Understanding these properties helps in grasping how genetic information is expressed in living organisms.

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..

Role of tRNA in Translation
During the process of translation, tRNA (transfer RNA) plays a crucial role in protein synthesis. Here's a detailed explanation of its function:
Recognition of Codons
- tRNA molecules have a specific structure that includes an anticodon region.
- The anticodon is a sequence of three nucleotides that is complementary to the mRNA codons.
- This complementary pairing allows tRNA to accurately recognize and bind to the corresponding codon on the mRNA strand.
Bringing Specific Amino Acids
- Each tRNA molecule carries a specific amino acid attached to its 3' end.
- The amino acid corresponds to the codon that the tRNA recognizes.
- When a tRNA molecule matches with its complementary codon on the mRNA, it delivers the specific amino acid to the growing polypeptide chain.
Formation of Polypeptide Chain
- As the ribosome moves along the mRNA, tRNA molecules continue to bring in the appropriate amino acids in the sequence specified by the mRNA.
- This process continues until a stop codon is reached, completing the formation of the polypeptide chain.
Conclusion
- Thus, option 'C' accurately describes the function of tRNA during translation: it recognizes codons on mRNA through its anticodon and brings specific amino acids.
- Other options do not correctly represent the role of tRNA, highlighting the importance of understanding this key biological process.

Understanding Elution in DNA Extraction
Elution is a crucial step in molecular biology, particularly in the context of DNA manipulation and purification. Here’s a detailed explanation of the concept:
What is Elution?
- Elution refers to the process of extracting a substance that has been adsorbed or trapped in a solid medium.
- In molecular biology, this typically involves isolating DNA fragments that have been separated using gel electrophoresis.
Why is Option C Correct?
- Option C states that elution is "cutting out of the separated band of DNA from the agarose gel and extracting them from the gel piece."
- This is accurate because, after running an agarose gel electrophoresis, specific DNA fragments are visualized and can be excised from the gel.
Steps of Elution:
- Separation: DNA fragments are separated based on size during gel electrophoresis.
- Visualization: After running the gel, the DNA bands are often stained (commonly with ethidium bromide) to visualize them under UV light.
- Excising the Band: The desired band is carefully cut out from the agarose gel using a clean scalpel or razor.
- Extraction: The DNA is then extracted from the gel piece, usually by dissolving the agarose in a buffer or using a commercial gel extraction kit.
Importance in Molecular Biology:
- This elution process allows researchers to obtain pure DNA fragments for further applications, such as cloning, sequencing, or PCR amplification.
- It ensures that only the desired DNA fragments are isolated, free from other contaminants.
In summary, elution is a fundamental step in DNA purification, enabling the recovery of specific DNA fragments for downstream applications in genetic research and biotechnology.

Primary Function of the Origin of Replication (ori)
The origin of replication (ori) is a crucial component in DNA vectors used in molecular biology. Its primary function can be summarized as follows:
Initiation of DNA Replication
- The ori serves as a specific sequence where the process of DNA replication begins in a host cell.
- During replication, proteins recognize the ori and bind to it, unwinding the DNA to create a replication bubble.
- This process allows the DNA polymerase enzyme to synthesize new strands of DNA, effectively duplicating the vector and any inserted genetic material.
Importance in Cloning and Gene Expression
- The presence of a functional ori ensures that the vector can replicate independently once inside a suitable host cell, such as bacteria, yeast, or mammalian cells.
- This replication is essential for cloning genes, producing proteins, or creating genetically modified organisms.
Other Functions of DNA Vectors
While option 'B' is correct, it's worth noting that DNA vectors can also contain other elements, such as:
- Selectable Markers: Help identify successfully transformed cells.
- Promoters and Enhancers: Facilitate gene expression.
- Stability Elements: Ensure the maintenance of the vector within the host.
In summary, the primary function of the origin of replication (ori) in a DNA vector is to initiate DNA replication, allowing the vector and its genetic content to be copied and propagated within host cells. This is essential for successful cloning and gene expression studies.

Gel electrophoresis is used to separate macromolecules like DNA, RNA and proteins. DNA fragments are separated according to their size. Proteins can be separated according to their size and their charge (different proteins have different charges).

Correct Option - C

Correct Option - The correct option label i.e. C

Correct Option - B

Explanation:

Recognition sequences are specific DNA sequences that are recognized and cleaved by Type II restriction enzymes. These enzymes typically recognize palindromic sequences, which read the same forward and backward on both strands of DNA. The recognition sequence is usually 4-8 base pairs in length.

Let's analyze each option to determine if it can be a recognition sequence for a Type II restriction enzyme:

a) GAATTC: This sequence is the recognition sequence for the restriction enzyme EcoRI. It is a palindromic sequence, reading the same forward and backward on both strands: 5'-GAATTC-3' on one strand and 3'-CTTAAG-5' on the complementary strand.

b) AGCT: This sequence is not palindromic and therefore cannot be a recognition sequence for a Type II restriction enzyme. It reads 5'-AGCT-3' on one strand and 3'-TCGA-5' on the complementary strand.

c) GCGGCCGC: This sequence is the recognition sequence for the restriction enzyme NotI. It is a palindromic sequence: 5'-GCGGCCGC-3' on one strand and 3'-CGCCGGCG-5' on the complementary strand.

d) ATGCCT: This sequence is not palindromic and therefore cannot be a recognition sequence for a Type II restriction enzyme. It reads 5'-ATGCCT-3' on one strand and 3'-TACGGA-5' on the complementary strand.

Therefore, option D (ATGCCT) cannot be a recognition sequence for a Type II restriction enzyme because it is not palindromic. The correct answer is D.

Correct Option - A