Question

In living cells, chromosomes consist of a. DNA and RNA. b. DNA only. c. RNA and proteins. d. DNA and proteins. e. RNA only.

Short answer

The correct answer is option d. Chromosomes consist of DNA and proteins.

Step-by-step solution

Understanding Chromosome Composition

Chromosomes, located in the nucleus of a cell, are the structures that hold genetic information. They are composed of DNA (Deoxyribonucleic Acid), which carries the genetic instructions used in the growth, development, functioning, and reproduction of all known organisms and many viruses, and different types of proteins, which help in packaging this DNA into a compact, organized structure.

Evaluating the Options

Now study the options given. First, consider option a, chromosomes are not only made of DNA and RNA. RNA is not a core structural component of chromosomes, it is the product of DNA transcription. Hence, option a can be ruled out. Similarly, option b, c, and e can also be ruled out as chromosomes are not made up of DNA alone, RNA and proteins alone, or RNA alone respectively. Option d states that chromosomes consist of DNA and proteins, corresponding to the explanation in Step 1.

Conclusion

Based on the explanation of the composition of chromosomes, and the evaluation of the options provided, it is concluded that the correct answer is option d, chromosomes consist of DNA and proteins.

Key concepts

DNA Structure

DNA, or Deoxyribonucleic Acid, is a remarkable molecule that holds the blueprint for nearly all living organisms. It has a double-helix structure, resembling a twisted ladder. This structure was famously discovered by James Watson and Francis Crick in 1953. The sides of the ladder are composed of alternating sugar and phosphate groups, creating the backbone of the DNA.
The rungs of the ladder are made up of pairs of nitrogenous bases - Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). These bases pair in a specific way: Adenine with Thymine, and Cytosine with Guanine.

• The pairing of bases is crucial for DNA replication and ensures the genetic information is accurately passed on during cell division.
• The sequence of these bases along the DNA strand dictates the genetic information available for building and maintaining an organism.

Protein Role in Chromosomes

Proteins play a vital role in the structure and function of chromosomes. The most significant proteins associated with chromosomes are called histones. These proteins help in the packaging of DNA into a compact, well-organized form called chromatin.
Histones act like spools around which DNA strands are wound, allowing the lengthy DNA molecules to fit within the confines of the cell nucleus.

• This packaging is crucial as it affects gene expression and DNA replication.
• Histones can undergo chemical modifications, which can influence how tightly or loosely DNA is wrapped around them, consequently regulating gene accessibility.
• The ability of DNA to wrap around protein structures helps protect it from damage and facilitates its accurate distribution during cell division.

Genetic Information in Cells

Genetic information is stored in the nucleotide sequences of DNA and is essential for the proper functioning of cells. This information is used to produce proteins, which perform a myriad of functions crucial to life.
Genes, the functional units of DNA, serve as instructions to synthesize proteins through two central processes: transcription and translation.

• During transcription, a specific gene segment is copied into RNA, particularly mRNA (messenger RNA).
• The mRNA then travels to the ribosomes in the cytoplasm, where translation occurs, leading to the synthesis of a protein.
• The sequence of bases in the mRNA determines the sequence of amino acids in the resulting protein, dictating the protein's structure and function.

Understanding genetic information and its flow from DNA to protein is central to molecular biology and is often referred to as the "Central Dogma" of biology.

Chromosomal Organization

Chromosomal organization within a cell is crucial for maintaining the integrity of genetic information. This organization allows cells to manage DNA replication, gene expression, and chromosome segregation efficiently.
Chromosomes are meticulously organized structures composed of tightly coiled DNA and protein, forming the chromatin structures necessary for supporting functions in cell division and gene regulation.

• Each species has a characteristic number of chromosomes located in its nucleus; humans have 46 chromosomes.
• During cell division, chromosomes ensure that DNA is accurately copied and distributed among daughter cells.
• The structural organization helps prevent genetic information loss and protects against mutations during replication and segregation.

Understanding this organization is vital for grasping how genetic information is safeguarded and shared across generations.