What types of cells contain no true nucleus?

In DNA (deoxyribonucleic acid), nucleotides are composed of three components: a nitrogenous base, a deoxyribose sugar, and a phosphate group. The four nitrogenous bases found in DNA are adenine (A), guanine (G), cytosine (C), and thymine (T). Adenine forms hydrogen bonds with thymine, while guanine forms hydrogen bonds with cytosine. These complementary base pairs are held together by hydrogen bonds, with adenine pairing with thymine via two hydrogen bonds, and guanine pairing with cytosine via three hydrogen bonds. This base-pairing specificity is crucial for the accurate replication of DNA during cell division and ensures the fidelity of genetic information transmission from one generation to the next. The complementary base-pairing rule, also known as Chargaff's rule, states that the amount of adenine is equal to the amount of thymine, and the amount of guanine is equal to the amount of cytosine in a DNA molecule, maintaining a balance of purines (adenine and guanine) and pyrimidines (thymine and cytosine).

Antibiotics are medications used to treat bacterial infections by inhibiting the growth and reproduction of bacteria or by killing bacteria outright. Antibiotics target specific bacterial structures or metabolic processes essential for bacterial survival and proliferation, such as cell wall synthesis, protein synthesis, nucleic acid synthesis, and metabolic pathways. By disrupting these vital processes, antibiotics can effectively eliminate bacterial pathogens responsible for various infections, including respiratory infections, urinary tract infections, skin infections, gastrointestinal infections, and sexually transmitted infections. However, antibiotics are ineffective against viral infections, as viruses are intracellular parasites that replicate using the host cell's machinery and lack the metabolic processes targeted by antibiotics. Therefore, antibiotics are not used to treat viral infections such as the common cold, influenza, or COVID-19. Overuse or misuse of antibiotics can lead to the development of antibiotic resistance in bacteria, reducing the effectiveness of antibiotics and posing a significant public health threat.

Passive transport is a type of nutrient exchange across a cell membrane that does not require the input of cellular energy (ATP). It relies on the inherent kinetic energy of molecules and the concentration gradient to drive the movement of substances across the membrane. Passive transport mechanisms include diffusion, facilitated diffusion, and osmosis. Diffusion is the spontaneous movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached. Facilitated diffusion involves the facilitated movement of specific molecules (e.g., ions, polar molecules) across the membrane through protein channels or carriers, following their concentration gradient. Osmosis is the passive diffusion of water molecules across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. Unlike passive transport, active transport requires the expenditure of energy (ATP) to transport molecules against their concentration gradient, typically using protein pumps or carriers embedded in the membrane. Passive transport plays a crucial role in nutrient uptake, waste removal, and maintaining osmotic balance in cells and tissues.

Uracil is a nitrogenous base that is unique to RNA (ribonucleic acid) and is not found in DNA (deoxyribonucleic acid). In RNA, uracil pairs with adenine through complementary base pairing during transcription, which is the process of copying genetic information from DNA to RNA. In DNA, thymine pairs with adenine, while cytosine pairs with guanine. RNA plays various roles in the cell, including serving as a messenger molecule (mRNA) that carries genetic information from the nucleus to the ribosomes for protein synthesis, as well as functioning in other types of RNA such as transfer RNA (tRNA) and ribosomal RNA (rRNA) involved in translation and protein synthesis.