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Nucleic Acid Metabolism and Genetic Information Transfer

Nucleic acids are biopolymers, or essential macromolecules, required to survive all known forms of life on the planet.

Nucleic Acid

Nucleic acids are biopolymers, or essential macromolecules, required to survive all known forms of life on the planet. DNA is a kind of macromolecule present in all organisms and viruses that belongs to the nucleic acid family. Deoxyribonucleic acid (DNA) is a nucleic acid that encodes the information that cells need to produce proteins. A similar kind of nucleic acid, known as ribonucleic acid (RNA), is found in various molecular forms and is involved in the process of protein synthesis.

Nucleic Acid Metabolism

The Nucleic acid metabolism consists of the DNA metabolism in which there are three main processes, i.e., DNA replication, repair, and recombination. DNA must be duplicated appropriately to maintain genetic code integrity. Errors that occur during or after replication must be corrected. Finally, recombination across genomes helps maintain species diversity and repair damaged DNA. Prokaryotes have been studied extensively because their mechanism is more streamlined, straightforward, and easier to examine. Eukaryotes share many of the same fundamental concepts.

DNA Replication

The primary mechanism in DNA replication is a semiconservative process, in which two strands are split, and two identical copies of the original DNA molecule are created. Each document, therefore, has one strand from the parent and one from a new synthesis. Replicated DNA starts at a particular origin, moves in both directions along the strand, and finishes differently.

Recombination

Recombination is the primary method for introducing diversity into populations. During meiosis, homologous chromosomes are paired, and recombination, or crossing-over, occurs. The two DNA molecules are broken and scrambled to form two new chromosomes, each a mosaic of the originals. Each sperm or egg gets one of the scrambled chromosomes. When sperm and egg merge, each chromosome gets two copies back.

There are two types of recombination:
  • General recombination involves cleavage and reconnecting the same or comparable sequences.
  • Cleavage occurs in site-specific recombination when DNA is usually inserted.
  • General recombination occurs during infection, bacterial conjugation, transformation (direct DNA transfer into cells), and specific repair processes. Site-specific recombination is often linked to parasite dispersion of DNA segments.
  • Many viruses and transposons rely on site-specific recombination to reproduce.

Repair

The integrity of DNA is vital for a cell's lifelong functioning and correct genetic information transmission from generation to generation. Repair mechanisms continuously scan DNA for damages and activate relevant repair enzymes. Recombination may repair severe DNA damages such as pyrimidine dimers and gaps, as discussed in General recombination, but there are numerous additional repair methods. Many malignancies have been linked to genes encoding the human mismatch repair mechanism, which has been shown. The absence of the mismatch repair mechanism enables mutations to accumulate rapidly, ultimately affecting the genes that drive cells to proliferate and finally killing them. The consequence is that cells divide in an uncontrolled way, leading to the development of cancer.

RNA Metabolism

RNA links the genetic information contained in the DNA to the actual functioning of the cell. Specific RNA molecules, such as rRNAs and Small nuclear RNAs (snRNAs), are part of complex ribonucleoprotein structures with particular cell functions. Others, like Transfer ribonucleic acid (tRNAs), play an essential role in protein synthesis, while Messenger RNA (mRNAs) drive protein synthesis via the ribosome. There are three different stages of RNA metabolism.

Transcription

The RNA polymerase enzyme copies small pieces of DNA into RNA in a regulated manner. The first step is to identify the promoter, a DNA region that marks the gene's start. RNA polymerase then starts copying from a particular place on one strand of DNA utilising a ribonucleoside 5′-triphosphate to create the expanding chain. Additional ribonucleoside triphosphates are being used as the substrate, and their high-energy phosphate link breakage forms ribonucleoside monophosphates. The complementary base pairing principles of DNA guides each ribonucleotide.
  • Transcription typically copies just one strand of DNA.
  • The template strand produces single-stranded RNA molecules.
  • The coding or sense strand of DNA corresponds to the mRNA and may vary from gene to gene.
  • Pre-mRNA is the first product of transcription in eukaryotes.
  • It is extensively spliced before maturing mRNA is ready for translation by the ribosome.

Translation

Translation utilizes the nucleotide sequence of mRNA to guide the production of a particular protein for the cell. Translation occurs on ribosomes, which are cellular RNA and protein complexes. Prokaryotes load ribosomes onto mRNA while transcription is still active. There are three STOP codons named amber (UAG), opal or umber (UGA) and ochre (UAA). The ribosome terminates translation at UAG, UAA, or UGA. These codons cause the ribosome to separate, releasing the freshly produced protein, tRNAs, and mRNA. The ribosome is now free to interact with another mRNA.
Nucleic Acid and Genetic Information Transfer

DNA and RNA are nucleic acids, long linear polymers that transmit information from generation to generation. These macromolecules comprise several corresponding nucleotides, each with sugar, phosphate, and base—the basis of a nucleic acid chain store genetic information.

Genes dictate what proteins cells make, but DNA isn't the direct blueprint for protein synthesis. Instead, RNA molecules serve as templates for protein production. Messenger RNA (mRNA) is the information-carrying intermediary in protein production. Other RNA molecules, including tRNA and rRNA, are involved in protein synthesis. RNA polymerases follow DNA template instructions to make all cellular RNA. Transcription is followed by translation, the creation of proteins based on mRNA templates.

In normal cells, the transfer of genetic information is as follows
  • This information flow is determined by the genetic code, which links DNA (or its mRNA transcript) to amino acid sequences in proteins.
  • In all species, a codon (a three-base sequence) identifies an amino acid. tRNA molecules read mRNA codons sequentially as adaptors in protein synthesis.
  • Ribosomes are complex assemblages of rRNAs and proteins that synthesise protein.
  • Finally, most eukaryotic genes are interrupted mosaics of nucleic acid sequences termed introns and exons.
  • Both are transcribed, but freshly produced RNA molecules lack introns, whereas mature RNA molecules have exons.
  • The presence of introns and exons impacts protein evolution.

Conclusion

DNA is a nucleic acid macromolecule found in all living beings, including viruses. Nucleic acids like DNA encodes information required by cells to make proteins. RNA is a nucleic acid involved in protein synthesis. DNA metabolism includes three significant processes: replication, repair, and recombination. DNA replication is a semiconservative process that splits two strands of DNA to produce two identical copies. RNA connects the genetic information in DNA to the cell's actual function, and it is a complex ribonucleoprotein structure with specialised cell activity. The genes guide protein synthesis; DNA is not the direct blueprint. Instead, RNA molecules act as protein templates.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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