Advanced Placement (AP) Biology Practice Exam

Chromosomes are primarily made up of:

1. RNA and proteins

2. A single DNA molecule and proteins

3. Multiple RNA molecules

4. Sugars and lipids

The correct answer is: A single DNA molecule and proteins

Chromosomes are primarily composed of a single, long DNA molecule that carries genetic information, along with proteins that help structure and organize the DNA within the nucleus of a cell. The DNA molecule wraps around histone proteins, forming a complex known as chromatin, which condenses and organizes itself into the distinct chromosome structure that is visible during cell division. The presence of proteins is crucial for maintaining the structural integrity of chromosomes and facilitating processes such as DNA replication and repair. Each chromosome contains not only the DNA sequence but also regions that are involved in the regulation of gene expression, which are influenced by interactions with these proteins. This composition distinguishes chromosomes from other molecular structures in cells. While RNA is vital for various cellular functions, such as protein synthesis and regulation, it is not a primary structural component of chromosomes. Additionally, sugars and lipids do not form the core structure of chromosomes; rather, they play different roles in metabolism and cell membrane formation. The option that indicates chromosomes consist of a single DNA molecule and proteins accurately reflects the established understanding of chromosomal structure in biology.