Molecular Biology of DNA and RNA Structures

Nucleic Acid Components and Structure

Nucleic Acid Components: 269

Nucleosides: 270

Nucleotides: 270

Nucleic Acid: 270

Primary and Secondary DNA Structure

Primary structure of DNA (Nucleotide Sequence): 272. The nucleotide sequence of a single strand can present as a single filament, extended or slightly curved on itself. It consists of a skeleton of phosphodiester deoxyribose and a sequence of nitrogenous bases.

Double Helix: This is the disposition in space of two polynucleotide strands or chains in a double helix, with the nitrogenous bases facing each other and linked by hydrogen bonds (273).

Supercoiled DNA and Packaging

Supercoiled DNA: Found in bacterial or mitochondrial DNA. It consists of a 20-fiber twisted on itself, forming a sort of superhelix. This is largely due to the action of DNA polymerase II enzymes. Advantages: It reduces the length of the DNA molecule to provide stability and facilitate the process of duplication.

DNA Structural Variations

DNA Structure (276):

• Single-Stranded: A single strand. This is very rare but has been found in a linear fashion in parvoviruses.
• Double-Stranded: Two strands. It can exhibit supercoiling.
  • Circular: Found in bacteria, mitochondria, chloroplasts, and viruses.
  • Linear: Found in the DNA core of eukaryotic cells and viruses.

The Need for DNA Duplication

Hypothesis: 281. DNA duplication in bacteria: 286. DNA duplication in eukaryotes: 287.

Ribonucleic Acid (RNA) Types and Functions

Ribonucleic Acid (RNA): Composed of ribose nucleotides with the bases adenine, guanine, cytosine, and uracil. Unlike DNA, it contains no thymine. It features phosphodiester bonds in the 5' - 3' direction and is almost always single-stranded.

Transfer RNA (tRNA) Structure and Function

Soluble or Transfer RNA (tRNA) is found in the cytoplasm as a scattered molecule. Its function is to transport specific amino acids to the ribosomes where proteins are synthesized. It is single-stranded but presents areas with double-helical secondary structures and areas with linear primary structures that form loops, which give the molecule a cloverleaf shape.

It distinguishes the D arm (containing dihydrouridine) and its handle, a T arm (ribothymidine) and its handle, an arm called the anticodon (contains a triplet) and its handle, and an amino acid acceptor arm.

In fact, the molecule is much more folded, adopting a tertiary structure in the form of an L. The nucleotides in tRNAs include G, T, C, and U, as well as other methylated bases. At the 5' end, there is a guanine ribonucleotide with a free phosphate group. At the 3' end, there is the triplet C-C-A. The terminal -OH group of the nucleotide A is what binds to the carboxyl group of the amino acid.

Messenger and Ribosomal RNA

Messenger RNA (mRNA): A linear, single-stranded molecule. Its function is to transmit the information contained in DNA and carry it to the ribosomes so they can synthesize proteins from amino acids supplied by the tRNA. (Eukaryotic and prokaryotic mRNAs: 292).

Ribosomal RNA (rRNA): Found in ribosomes and nucleoli (293).