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A-Level Biology OCR A

Dna Strand Gene Sense Mrna Complementary Ribonucleotides Transcribed

This note describes transcription in bullet points, outlining the roles of DNA helicase and RNA polymerase in unwinding DNA and synthesizing mRNA, respectively, and mentioning that mRNA then leaves the nucleus.

Transcription steps: DNA unwound by helicase, RNA polymerase adds complementary ribonucleotides to template strand, mRNA leaves nucleus.

Front Describe the process of transcription in bullet points.
Back Transcription:
  • Section of DNA that contains the gene is unwound by DNA helicase at the start of the gene
  • RNA polymerase adds the free complementary ribonucleotides to the template (antisense) strand
  • Sense strand of DNA contains the triplet code in correct order but is not transcribed
  • Antisense strand of DNA is complementary to the sense strand and is transcribed to make mRNA which is a copy of the sense strand
  • Ribonucleotides are joined together by condensation (phosphodiester bonds) to form a copy of the gene in the form of mRNA
  • When the whole gene was transcribed, mRNA separates from DNA and leaves the nucleus through the nuclear pores

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