Which base will pair with uracil in RNA?

A. Periplasmic flagella: Spirochetes have flagella located within the periplasmic space between the inner and outer membranes. These internal flagella, also called axial filaments, rotate to produce a corkscrew-like motion, allowing the bacterium to move efficiently through viscous environments such as mucus or connective tissue. This unique mechanism is characteristic of genera like Treponema and Borrelia.

B. Pili: Pili are hair-like appendages on the surface of many bacteria used primarily for attachment to surfaces and for conjugation (gene transfer). Pili do not contribute to the corkscrew motility seen in spirochetes.

C. Capsules: Capsules are extracellular polysaccharide layers that protect bacteria from phagocytosis and desiccation. While important for virulence and immune evasion, capsules do not play a role in bacterial motility or the corkscrew movement of spirochetes.

A. Capsid: The capsid is the protein shell that encloses and protects the viral nucleic acid, which can be either DNA or RNA. It is composed of repeating protein subunits called capsomeres, which provide structural stability and facilitate attachment to host cells. The capsid plays a key role in viral infectivity and immune system recognition.

B. Cell wall: A cell wall is a rigid structure found in bacteria, fungi, and plants that provides shape and protection to the cell. Viruses do not have cell walls, as they are acellular entities and rely on host cells for replication.

C. Cytoplasm: Cytoplasm is the gel-like substance inside cells that contains organelles and metabolic machinery. Viruses lack cytoplasm entirely, as they are not true cells and cannot carry out independent metabolic processes.