Final answer:
Genes are comprised of DNA and are found linearly on chromosomes. They encode proteins by specifying amino acid sequences through the genetic code. The human genome has about 20,000 to 25,000 genes which also include noncoding sequences, and only a small percentage codes for proteins.
Step-by-step explanation:
Genes are comprised of DNA, which is the carrier of genetic information. These genes are linearly arranged on chromosomes within the cell nucleus. Each gene is a sequence of DNA that specifies how to construct a protein, or a portion of a protein, leading to a particular trait or function. The sequence of DNA in a gene determines the sequence of amino acids that make up a protein. The human genome, which includes all the DNA in a human, contains approximately 20,000 to 25,000 genes spread across 23 pairs of chromosomes, which are further organized into tightly wound and folded structures to fit inside the nucleus. In addition to coding sequences, the human genome consists of noncoding regions, and only about 2% of the DNA actually codes for proteins. The genetic code within genes uses four nitrogen bases (adenine, cytosine, guanine, and uracil in mRNA) which are grouped into codons, each encoding for an amino acid or a start/stop signal in protein synthesis. A gene's main function is to guide the production of proteins, which carry out the essential functions of life. Proteins, such as interleukin-2 and alpha-2u-globulin, exhibit a diversity of structures and functions, all encoded by various genes in the DNA sequence.