RNA Molecules

RNA Molecules

RNA (ribonucleic acid) molecules differ from DNA molecules in several ways. For example, RNA molecules are usually single-stranded, and their nucleotides contain ribose rather than deoxyribose sugar Like DNA, RNA nucleotides each contain one of four organic bases, but while adenine, cytosine, and guanine nucleotides occur in both DNA and RNA, thymine nucleotides are found only in DNA.
 

In its place, RNA molecules contain uracil (U) nucleotides. One step in the transfer of information from the nucleus to the cytoplasm involves the synthesis of a type of RNA called messenger RNA (mRNA) As it is produced, a double-stranded section of a DNA molecule seems to unwind and pull apart At the same time, the weak bonds between the base pairs of this section are broken. 

RNA Structure 

A molecule of messenger RNA is then formed of nucleotides that are complementan, to those arranged along one of the exposed strands of DNA. (The other strand of DNA is not used in this process, but it is important in the duplication of the DNA molecule.) For example, if the sequence of DNA bases is A, T, G, C, G, T, A. A, C, then the complementar)' bases in the developing RNA molecule would be U, A, C, G, C, A, U, U, G,
. 

In this way , an RNA molecule is synthesized that contains the information for arranging the amino acids of a protein molecule in the sequence dictated by the DNA  "master information
". 

Once they arc formed, messenger RNA molecules, each of which consists of hundreds or even thousands of nucleotides, can mo\e out of the nucleus through the tin\' pores in the nuclear membrane and enter the cytoplasm. There they become associated with ribosomes and act as patterns or templates for the synthesis of protein molecules.