Structure Of Dna And Rna

The question pertains to the association of ribosomes with a single mRNA strand to synthesize polypeptides. When multiple ribosomes concurrently translate a single mRNA molecule, they form a structure known as a "polysome" or "polyribosome."

1. Understanding the term 'Polysome':
   • A polysome is a complex of an mRNA molecule with two or more ribosomes that are translating it.
   • This allows multiple copies of a polypeptide to be synthesized simultaneously from the same mRNA strand, significantly enhancing the efficiency of protein synthesis.
2. Explanation of Options:
   • Polysome: As explained, it refers to a group of ribosomes reading a single mRNA strand.
   • Plastidome: Refers to a group of plastids within a cell. It is unrelated to mRNA and ribosomes.
   • Polyhedral bodies: These are protein bodies found in certain cells, not related to ribosomes or mRNA.
   • Nucleosome: It is a segment of DNA wound around histone cores, integral to chromatin structure—not related to the translation process involving ribosomes.
3. Conclusion: By understanding the definitions and functions of these terms, we identify "Polysome" as the correct answer because it directly describes the structure made by the group of ribosomes translating a single mRNA strand.

To answer the question about which factor induces mutations in plant cells among the given options, we need to understand the effects of each option:

1. Kinetin: It is a type of cytokinin, which is a class of plant hormones involved in regulating cell division and growth, but not known for inducing mutations.
2. Infrared rays: These are part of the electromagnetic spectrum with longer wavelengths. They are not involved in causing mutations since they primarily produce heat and do not have high energy to alter DNA structures.
3. Gamma rays: These are high-energy electromagnetic waves capable of penetrating materials and have the ability to cause damage to biological tissues, including altering DNA sequence leading to mutations. Therefore, gamma rays are often used in genetics and agriculture to induce mutations in plants for increased variation.
4. Zeatin: Similar to kinetin, zeatin is a naturally occurring cytokinin involved in promoting cell division, growth, and development in plants, not in inducing mutations.

Given the explanations above, it's clear that Gamma rays are used to induce mutations in plant cells due to their high energy, capable of altering DNA. Therefore, the correct answer is Gamma rays.

The central dogma of molecular biology explains the flow of genetic information within a biological system. It is a framework for understanding the transfer of sequence information between biopolymers in the cells. The flow typically follows this sequence:

• a) Replication: This is the process by which DNA is copied to produce identical DNA molecules. It ensures that the same genetic information is passed on through generations.
• b) Transcription: This is the process in which a particular segment of DNA is converted into RNA, especially messenger RNA (mRNA), which then serves as a template for protein synthesis.
• c) Translation: In this step, the mRNA is read by ribosomes to synthesize proteins. Transfer RNA (tRNA) brings the requisite amino acids in sequence to form a polypeptide chain.
• d) Protein: This is the final product of gene expression, performing various functions like catalyzing reactions, structural roles, and signaling.

Now, let's match the options provided with the correct steps of the central dogma:

The correct answer is:

• (a) - Replication
• (b) - Transcription
• (c) - Translation
• (d) - Protein

The other options are incorrect due to the inclusion of unrelated terms like Transduction, which is not a part of the central dogma. Transduction is a process related to gene transfer in bacterial cells, usually involving viruses, and is not part of the typical flow of genetic information depicted in the central dogma of molecular biology.