Question

What is true about genetic material of a prokaryotic cell (a) Lacks histones (b) Not enveloped by nuclear membrane (c) Composed of a single circular DNA molecule (d) All of these

Short answer

All of the statements about the genetic material of a prokaryotic cell – (a), (b), and (c) – are correct. Therefore, the answer is (d) All of these.

Step-by-step solution

Analyze Option (a) - Check for Histones

Prokaryotic cells typically do not have their DNA wrapped around histones (proteins found in eukaryotic cell nuclei that package and order the DNA into nucleosomes).

Analyze Option (b) - Examine Nuclear Envelope Presence

Prokaryotic cells do not possess a nucleus. Their genetic material is not enveloped by a nuclear membrane; instead, it is located in a region called the nucleoid.

Analyze Option (c) - Composition of Genetic Material

Most prokaryotic cells contain a single circular DNA molecule that constitutes their genetic material.

Conclusion - Verify All Statements

After analyzing the three options individually, we testify that all statements (a), (b), and (c) are true characteristics of the genetic material in a prokaryotic cell.

Key concepts

Histones in Prokaryotes

Unlike their eukaryotic counterparts, prokaryotic cells typically do not contain histones. Instead of being wrapped around histones, the DNA in prokaryotes is found in a less organized form within the cell. Histones are the chief protein components of chromatin, acting as spools around which DNA winds, and playing a role in gene regulation. In eukaryotes, this function is critical because it helps to package the DNA into a compact, dense structure, a necessity given the large amounts of DNA present in these cells.

However, in prokaryotes, the DNA is often a single, circular chromosome that is much smaller and requires no such compaction. While prokaryotes do not have histones, some do possess proteins that are functionally similar to histones, known as nucleoid-associated proteins (NAPs). These proteins help in structuring the chromosome and in gene regulation, somewhat analogous to eukaryotic histone functions.

Nuclear Membrane in Prokaryotes

A defining characteristic of prokaryotic cells is the absence of a true nucleus. This means there is no nuclear membrane to enclose their genetic material. Instead, the DNA in prokaryotic cells resides in a region called the nucleoid. The nucleoid is simply a part of the cytoplasm where the DNA is concentrated. This lack of a nuclear membrane has implications for how prokaryotic cells regulate their DNA replication and transcription processes, which occur in the same space as the rest of the cell’s activities.

Unlike eukaryotic cells, where transcription (the process of making RNA from DNA) occurs inside the nucleus and the resultant mRNA is then transported out into the cytoplasm to be translated into protein, prokaryotic cells carry out both processes simultaneously within the cytoplasm. This means that in prokaryotes, gene expression is more directly linked to environmental changes, as there is no nuclear compartment to delay or modulate the flow of genetic information.

Circular DNA in Prokaryotes

The genetic material of prokaryotic cells is distinct and simpler in form compared to that of eukaryotes. Prokaryotic cells typically possess a single chromosome composed of a circular DNA molecule. This circular chromosome carries all the genetic information required for the cell's functions and reproduction. The circular nature of prokaryotic DNA is important for the methods used by these cells to replicate their genetic material and divide.

During cell division, for example, the circular chromosome is duplicated, and each copy is allocated to one of the two daughter cells. Moreover, the circular DNA is not enclosed in a membrane-bound nucleus, which enables some processes like transcription and translation to be tightly coupled. Additionally, prokaryotic cells sometimes contain small, extra-chromosomal DNA molecules known as plasmids, which contain genes that can be beneficial to the cell, such as antibiotic resistance genes - allowing them to thrive in various environments.