![]() Bacterial mRNA is unstable, and thus, they are translated into proteins. In prokaryotes, mRNA is transcribed, and translated into a single cellular compartment, and occurs simultaneously. However, there are differences in the synthesis and structure of prokaryotic and eukaryotic mRNA. The function of mRNA is the same in all cells. RNA occurs as a single-stranded molecule wherein thymine is replaced by uracil. Base pairing takes place within and between RNA molecules. However, it exists as a single polynucleotide chain rather than a double helix of antiparallel strands. It is a polynucleotide chain with a 5′-3′ sugar-phosphate backbone. The primary structure of RNA is the same as that of DNA. The gaps are closed with the action of DNA Polymerase (which adds complementary nucleotides to the gaps) and DNA Ligase (which adds phosphate in the remaining phosphate-sugar backbone). In the lagging strand, the DNA Pol I -exonuclease- reads the fragments and removes the RNA Primers.The gap between two RNA primers is called “ Okazaki Fragments”. DNA polymerase reads the template and lengthens it. In the lagging strand, the RNA Primase adds more RNA Primers. The replication of this template is complicated, and the new strand is called the lagging strand. 3′-5’Template: The 3′-5′ template cannot be “read” by DNA Polymerase.5′-3′ Template: The 3′-5′ proceeding daughter strand -that uses a 5′-3′ template- is called the leading strand because DNA Polymerase can “read” the template and will continuously add nucleotides.The elongation process is different for the 5′-3′ and 3′-5′ template.RNA nucleotides are the primers (starters) for binding DNA nucleotides. RNA Primase can attract RNA nucleotides which bind to the DNA nucleotides of the 3′-5′ strand due to the hydrogen bonds between the bases. Once the DNA strands are separated, RNA Primase binds in the initiation point of the 3′-5′ parent chain.Helicase is the enzyme that separates the two strands.This is essential for a rapid replication process. Multiple replication bubbles are formed in eukaryotic DNA molecules. Two complementary strands of DNA separate at the site of replication to form a bubble.This causes the double-stranded DNA to separate. A specific protein called DNA A (20-50 monomers) binds with the site of the origin of replication. These sites consist mostly of a short sequence of A-T base pairs.In the case of prokaryotes, there is a single site in eukaryotes, there are multiple sites of origin. DNA synthesis begins at a site called the “origin of replication”. ![]() The separation of the two parental strands is the starting point of DNA replication.The first experimental evidence of semiconservative DNA replication was provided by Meselson and Stahl, 1958. DNA replication is a fundamental process of all living organisms. Each strand of DNA act as a template to copy the information to synthesize the new strands. Table of contentsĭNA replication is a semi-conservative method wherein one of each parental strand of DNA is present in each of the two daughter DNAs. mRNA sequence is thus used as a template to assemble in order the chain of amino acids that will form the protein. mRNA has a group of three bases constituting a codon, and each codon specifies a particular amino acid. It relates the DNA sequence to the amino acid sequence in proteins. This is the second major step in gene expression wherein mRNA is read according to the genetic code. mRNA molecule is then translated into its corresponding protein. This is then processed to form a mature mRNA. During transcription, DNA serves as the template for complementary base-pairing, and RNA polymerase II catalyzes the formation of a pre-mRNA molecule. In the first step, information in DNA is transferred to messenger RNA (mRNA) by a process termed transcription. It constitutes the flow of genetic information from the DNA to RNA to Protein. The organizing principle of molecular biology is termed Central Dogma. For example, enzymes metabolize nutrients and synthesize new cellular constituents, or DNA polymerases which make copies of DNA during cell division are all proteins. They carry the necessary functions for life. Genes in DNA encode protein molecules, also called the workhouses of the cell.
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