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| Summary |
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 The molecular mechanism by which a gene shows to potential in the phenotype of an organism, is called gene expression. |
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 Every gene contains the blue print required for the function of a given polypeptide, in the form of a specific sequence of nucleotides. |
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 The transfer of a code present in the gene into a complementary base sequence in mRNA is called transcription. |
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 Transcription occurs in the nucleus during G1 and G2 phases of cell cycle. |
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 Transcription begins at a promoter/site and stops at the terminative site in the DNA. |
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 At the beginning of transcription, the histone surrounding the DNA molecule is removed exposing the nucleotides. This region of DNA is called as sense strand or master strand. |
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 The ribonucleotide phosphates found freely in the nucleus get converted into monophosphates (ribonucleotides), releasing the phosphate. |
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 Each RNA nucleotide binds with the corresponding base in the mRNA strand, as per base pairing rule. |
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 The RNA nucleotides become linked with one another, resulting in the formation of a mRNA molecule. The process is catalysed by the enzyme RNA polymerase. |
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 The mRNA subsequently detaches from the DNA template and gets released. It comes out of the nucleus and reaches the cytoplasm. |
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 The separated strands of DNA becomes linked up and coiled to regain the original shape. |
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 The RNA molecules synthesised from DNA undergo extensive changes or modifications so that they can become functional, these changes are collectively called as processing. |
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 Processing involves changes such as cleaving, splicing, joining, folding and nucleotide modification. |
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 In eukaryotic cells the genome is highly complex consisting of a large number of genes. |
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 The eukaryotic gene has stretches of coding and non-coding sequences. The coding segments are called exons and the non-coding segments called introns. |
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 The processing of mRNA in eukaryotic involves removal of introns and joining of exons. |
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