Medical Genetics - V. M. Zaporozhan 2005

Introduction to Medical Genetics
Molecular Basis of Heredity
Structure and Functions of RNA

Like DNA, RNA is a polymer composed of NUCLEOTIDES (Fig. 1.4). Unlike DNA, RNA consists of a single polynucleotide chain containing ribose within its nucleotides, and it features the nitrogenous base uracil (U) instead of thymine. All types of RNA are synthesized in The Nucleus using a DNA template.

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Fig. 1.3. Semiconservative Replication of DNA

Fig. 1.4. Cytology/cytology/92.html">SCHEMATIC Structure OF an RNA fragment

RNAs play a key role in executing the hereditary information encoded in DNA at the Protein Synthesis level. Depending on their function and structural features, several types of RNA are distinguished, the most prominent being messenger (or mRNA), transfer, and ribosomal RNA, along with small nuclear and nucleolar RNAs, and microcytoplasmic RNA (Table 1.1).

Messenger (or mRNA) RNA (mRNA) is synthesized on a DNA template via THE PRINCIPLE OF complementarity. It carries Genetic information regarding Cell/13.html">Protein Structure from the nucleus to the Cytoplasm and serves as a template for protein synthesis by Ribosomes.

Transfer RNA (tRNA) binds to its specific amino acid, transports it to the ribosome, and ensures its incorporation into the protein molecule strictly in accordance with METABOLISM/28.html">The Genetic Code. At the ribosome, tRNA attaches via its anticodon (a codon triplet) through Hydrogen Bonds to one of the mRNA triplets (codons). The complementarity between the tRNA anticodon and the mRNA codon is the specific mechanism that translates The sequence of mRNA codons—and thereby the Gene itself—into an Amino Acid Sequence in the polypeptide. Thus, the tRNA molecule holds a central position in Protein Biosynthesis, acting as an adaptor molecule responsible for translating mRNA nucleotide triplets into Amino acid sequences in the polypeptide.

Table 1.1. Functions of Nucleic Acids

Ribosomal RNA (rRNA), together with ribosomal Proteins, forms ribosomes. It performs a structural function and also assists in binding mRNA and tRNA to the ribosome.

Small nuclear RNAs take part in mRNA splicing, while small nucleolar RNAs are involved in the Processing and modification of rRNA nitrogenous bases.

Microcytoplasmic RNAs are small molecules (20–25 nucleotides) that regulate gene activity during cell development and differentiation. They are capable of silencing the expression of vital genes by interacting with their mRNA.