What Is Found in the Nucleus & Makes RNA?

What Is DNA?

• DNA is a double strand of sugar and phosphate molecules connected by amino acids called bases. It contains the manufacturing instructions for every protein in the body, even though only a portion of that information is used in any one cell. Human cells have 46 strands of DNA, coiled tightly into a double-helix, which looks like a twisted staircase, and combined with a protein that keeps it tightly coiled. These protein-DNA strands form strings of chromatin, which exist like a mass of spaghetti throughout most of the cell's life, but which condense into tightly packed bundles called chromosomes during cell reproduction.

Building Blocks of DNA

• Each DNA strand contains one deoxyribose sugar and one phosphate molecule for each base. The alternating deoxyribose and phosphate molecules form the long double strands that create the backbone of the DNA molecule. Each sugar molecule bonds with one of four nucleic acids: adenine, guanine, cytosine and thymine. These form the "rungs" of the DNA ladder. A single strand of DNA may contain millions of these bases. The base sequence that creates a single protein is called a gene.

DNA to mRNA

• DNA cannot create proteins directly. Instead, it forms an intermediary molecule called messenger ribonucleic acid, or mRNA. When the cell prepares to divide, the DNA molecule unwinds and the two rungs separate, exposing the bases. Each base can only bond to one of the other three bases; for example adenine with thymine (or urucil) and cytosine with guanine. When the strands separate, each base's complementary amino acid bonds with it. The other end of the amino acid bonds to the ribose sugar and phosphate chain that forms the backbone of the mRNA molecule. This molecule then detaches, resulting in an mRNA strand that is an exact duplicate of the opposite half of the DNA chain, except for urucil, which replaces thymine.

mRNA to tRNA

• Once the mRNA molecule is complete, it leaves the nucleus and travels to an organelle called the ribosome, where strands of transfer RNA, or tRNA, connect to it. Each piece of tRNA contains three bases, called an anticodon, and carries with it an amino acid molecule. As each anticodon attaches to the correct three-base sequence, or codon, on the strand of mRNA, the amino acids bond into a protein chain. Through creating the mRNA, which orders the tRNA into the right sequence, the DNA molecules indirectly construct all the proteins that make up the body.