Final answer:
DNA is the molecule that stores genetic instructions and codes for our traits, containing the genes that provide instructions for all proteins in our body. These proteins determine our cellular structure and function, and DNA controls cellular activities by turning genes 'on' or 'off'.
Step-by-step explanation:
The molecule that stores genetic instructions and codes for traits that make us who we are is DNA (deoxyribonucleic acid). DNA contains the genes that determine who you are by providing instructions for all the proteins your body makes. These proteins are crucial because they determine the structure and function of all your cells. The specific sequence of amino acids that composes a protein is directed by the genetic code found in DNA. All the cellular activities are controlled by DNA by turning genes 'on' or 'off' through processes involving RNA and protein synthesis.
Chromosomes are structures within cells that contain a long chain of DNA. In turn, DNA contains units called genes, each encoding the instructions to make proteins or RNA molecules. These proteins and RNA molecules perform various functions within the cell. The differences in genes, known as alleles, contribute to the variation in traits seen from one individual to another. The entire genetic content of a cell is referred to as its genome, which includes not only the DNA within chromosomes but also DNA contained in cellular organelles such as mitochondria, and in the case of plants, chloroplasts.
While the other options provided in the question play roles related to genetics, none of them store genetic instructions in the same way DNA does. For instance, RNA is involved in the process of protein synthesis and may carry genetic messages as mRNA, but it does not store hereditary information in the same permanent way as DNA. Proteins are the expressed products of genetic information and are thus dictated by the genetic code, but they do not contain or convey genetic instructions. Chromosomes are the structures that package DNA within cells, and though they are integral to the inheritance and expression of genetic traits, it is the DNA within them that holds the actual coded instructions.