In addition, the tail protects mRNA from enzymes that might break it down. It is also involved in exporting mRNA from the nucleus. The tail consists of a string of As (adenine bases). Polyadenylation adds a “tail” to the mRNA.One form is smaller than the other because editing adds a premature stop signal in the mRNA. For example, the human protein called APOB, which helps transport lipids in the blood, has two different forms because of editing. Editing changes some of the nucleotides in mRNA.Small nuclear ribonuclearproteins are involved in pre-mRNA splicing. Ribonucleoproteins are nucleoproteins that contains RNA. You can watch a video showing splicing in more detail at this link. The remaining mRNA consists only of regions that do code for proteins, which are called exons. Introns are regions that do not code for proteins. Splicing removes introns from mRNA (see Figure below).Such modifications allow a single gene to be used to make more than one protein. These processes modify the mRNA in various ways. This may include splicing, editing, and polyadenylation. It must go through additional processing before it leaves the nucleus. In eukaryotes, the new mRNA is not yet ready for translation. Transcription occurs in the three steps - initiation, elongation, and termination - shown here. The mRNA strand is complete, and it detaches from DNA. Termination is the ending of transcription, and occurs when RNA polymerase crosses a stop (termination) sequence in the gene.During this process, an adenine (A) in the DNA binds to an uracil (U) in the RNA. There is a brief time during this process when the newly formed RNA is bound to the unwound DNA. RNA polymerase reads the unwound DNA strand and builds the mRNA molecule, using complementary base pairs. Elongation is the addition of nucleotides to the mRNA strand.The enzyme is now ready to make a strand of mRNA with a complementary sequence of bases. This signals the DNA to unwind so the enzyme can ‘‘read’’ the bases in one of the DNA strands. It occurs when the enzyme RNA polymerase binds to a region of a gene called the promoter. Initiation is the beginning of transcription.The steps are illustrated in Figure below. Transcription takes place in three steps: initiation, elongation, and termination. Codons are complementary groups of bases in mRNA. Triplets are groups of three successive nucleotide bases in DNA. Transcription uses the sequence of bases in a strand of DNA to make a complementary strand of mRNA. A detailed video about transcription is available at this link.You can watch an animation of the process at this link: During transcription, a strand of mRNA is made that is complementary to a strand of DNA. It is the transfer of genetic instructions in DNA to messenger RNA (mRNA). Transcription is the first part of the central dogma of molecular biology: DNA → RNA. Translation reads the genetic code in mRNA and makes a protein. RNA then leaves the nucleus and goes to a ribosome in the cytoplasm, where translation occurs. It uses DNA as a template to make an RNA molecule. Transcription takes place in the nucleus. It actually consists of two processes: transcription and translation. The process in which cells make proteins is called protein synthesis.
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