Mass: The majority of an atoms’ mass comes from the protons and neutrons that make up its nucleus. Electrons are the least massive of an atom’s constituent particles, with a mass of 9.11 x 10-31 kg and a size too small to be measured by current techniques.

This explains why the mass of an atom is primarily determined by the mass of the protons and neutrons in the nucleus. The electron has other intrinsic properties.

The Three Major Subatomic Particles

Atomic mass is defined as the number of protons and neutrons in an atom, where each proton and neutron has a mass of approximately 1 amu (1.0073 and 1.0087, respectively).

DNA, which contains our genetic code, is located inside the nucleus of eukaryotic organisms. DNA cannot leave the nucleus, and so to send instructions to the rest of the cell it has to be replicated, creating mRNA, which can leave the nucleus.

cytoplasm

RNA consists of four nitrogenous bases: adenine, cytosine, uracil, and guanine. Uracil is a pyrimidine that is structurally similar to the thymine, another pyrimidine that is found in DNA.

DNA or RNA are called nucleic acids because of the acidic nature of the phosphate group attached to them. The phosphodiester bond can easily lose the proton in the presence of nucleophile group subsequently masking the basic nature of nitrogenous bases.

Second, unlike the DNA polymerases involved in DNA replication, RNA polymerases can start an RNA chain without a primer. This difference may exist because transcription need not be as accurate as DNA replication (see Table 5-1, p. 243). Unlike DNA, RNA does not permanently store genetic information in cells.

The central dogma of molecular biology suggests that the primary role of RNA is to convert the information stored in DNA into proteins.