ABSTRACT
Protein molecules are synthesized using different RNAs, according to information stored in the part of DNA, a gene. Prokaryotic cells have a single chromosome as a circular molecule of DNA, which is twisted. The aggregate of chromosomal DNA in prokaryotic cells that is microscopically visible is the nucleoid. In addition to a nucleoid, one or more small circular DNA molecules, called plasmids, may be present in the bacterial cell. The genetic information of eukaryotes is stored in several independent molecules of DNA, chromosomes. The chromosomes in eukaryotic cells are stored in the nucleus, which is separated from the cytoplasm by a membrane. Flow of genetic information is directed from the sequence of nucleotides in DNA to the sequence of amino acids in the protein using the genetic code. A protein-coding gene is copied into a molecule of messenger RNA (mRNA), which is complementary to the sequence of one strand of the gene. This process is called transcription. The transcribed mRNA transfers the portion of information from DNA to the ribosome, which is made from rRNA and proteins. The sequence of mRNA of the protein-coding gene is translated by ribosome to the sequence of amino acids, which is self-folding, forming an active enzyme protein molecule. A quiz bank is added to this chapter.
