All questions of DNA for Grade 9 Exam

The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O. group of the amino acid located three or four residues earlier along the protein sequence.

Because mRNA is called messanger RNA, which carries the information from DNA to synthesis of protein and other essential products in cell.

DNA TO DNA - replication
DNA TO RNA-transcription
RNA TO PROTEIN-translation

Purine is a type of nitrogenous base found in DNA and RNA molecules. The purine bases are adenine and guanine. Among the given options, the purine derivative is:

c) Guanine

Explanation:

- Purine and pyrimidine are two types of nitrogenous bases found in DNA and RNA molecules.
- Purine bases are larger and have a double-ring structure, while pyrimidine bases are smaller and have a single-ring structure.
- Adenine and guanine are purine bases, while cytosine, thymine, and uracil are pyrimidine bases.
- Therefore, among the given options, the purine derivative is guanine.

The structure of nucleotide and nucleoside units are distinguished primarily by the presence (or lack thereof) of this phosphate group. Deoxyribose in DNA differs from the ribose found in RNA in that it has only a hydrogen atom in the same position that ribose has a hydroxyl (-OH) group.

Uracil is not found in DNA , as it Uracil has more base pair affinity to adenine , guanine and cytosine. Instead thymine is present in DNA.

Introduction:
RNA cleavage is a crucial process in various cellular activities such as gene expression, RNA degradation, and RNA processing. The enzyme responsible for cleaving RNA is called ribonuclease (RNase).

Explanation:
Ribonuclease (RNase):
- Ribonuclease is an enzyme that catalyzes the cleavage of RNA molecules.
- It plays a vital role in various biological processes, including RNA degradation and turnover, RNA processing, and regulation of gene expression.
- There are different types of ribonucleases that have evolved to perform specific functions in different cellular contexts.

DNase:
- DNase is an enzyme that cleaves DNA molecules, not RNA.
- It is responsible for degrading DNA and plays a role in DNA repair, chromatin remodeling, and other DNA-related processes.

Ligase:
- Ligase is an enzyme that catalyzes the joining of two molecules by forming a covalent bond between them.
- It is involved in DNA repair, DNA replication, and other processes that require the joining of DNA or RNA fragments.

Protease:
- Protease is an enzyme that cleaves peptide bonds in proteins, not RNA.
- It is responsible for protein degradation, protein processing, and regulation of protein function.

Conclusion:
The enzyme that cleaves RNA is ribonuclease (RNase). It is specifically designed to recognize and cleave RNA molecules, playing essential roles in RNA degradation, processing, and gene expression regulation. DNase cleaves DNA, ligase joins molecules, and protease cleaves peptide bonds in proteins.

Introduction:
In recombinant DNA technology, selectable marker genes are used to distinguish transformed cells from non-transformed cells. These marker genes provide a selective advantage to the cells that have taken up the recombinant DNA, allowing for their identification and isolation.

Explanation:
Selectable marker genes, such as ampicillin resistance, are commonly used in recombinant DNA technology for the following reasons:

1. Selective advantage:
Selectable marker genes provide a selective advantage to the transformed cells that have successfully incorporated the recombinant DNA. In the case of ampicillin resistance, the gene encodes for an enzyme called β-lactamase, which confers resistance to the antibiotic ampicillin. Therefore, only the cells that have taken up the recombinant DNA containing the selectable marker gene will be able to grow and survive in the presence of ampicillin.

2. Selection of transformed cells:
By including the selectable marker gene in the recombinant DNA construct, researchers can selectively grow and isolate only those cells that have successfully taken up the desired gene or DNA fragment of interest. This allows for the identification and selection of transformed cells from a population of non-transformed cells.

3. Identification of successful transformation:
The presence of the selectable marker gene, such as ampicillin resistance, allows researchers to easily identify successful transformations. Transformed cells will be able to grow on selective media containing ampicillin, while non-transformed cells will not survive. This simplifies the screening process and confirms the presence of the desired gene or DNA fragment in the transformed cells.

Conclusion:
The purpose of using a selectable marker gene like ampicillin resistance in recombinant DNA technology is to provide a selective advantage to the transformed cells, allowing for their identification and isolation. This marker gene helps in distinguishing transformed cells from non-transformed cells and facilitates the selection of cells that have successfully taken up the desired gene or DNA fragment of interest.