Transcription

• does DNA leave the nucleus in transcription?

  no
• what happens during transcription?

  • its the process whereby the DNA, the gene, acts as a template for the production of mRNA, which carries information needed for protein synthesis from the nucleus to the cytoplasm
  • ribosomes in the cytoplasm provide a suitable surafce for the attachment of mRNA and the assembly of protein
• what is the sequence of events that take place during transcription?

  • DNA helicase breaks the H bonds between the bases in a specific region of the DNA molecule
  • RNA polymerase binds to the template strand of DNA to be copied
  • ribonucleotides align based on complimentary relationships between bases in DNA and the free nucleotides
  • RNA polymerase moves along DNA, forming bonds-results in synthesis of a mRNA molecule and unwound part of DNA-DNA strands reform double helix
  • RNA polymerase separates from the template strand
  • production of transcript is complete and the new RNA detaches from the DNA
• what is the 1st step of transcription?

  the enzyme DNA helicase breaks the hydrogen bonds between the bases in a specific region of the DNA molecule - this causes the 2 strands to separate and unwind, exposing nucelotide bases
• what enzyme breaks the hydrogen bonds between the bases in a specific region of the DNA molecule (transcription)?

  DNA helicase
• what does the breaking of hydrogen bonds between the bases in a specific region of the DNA molecule do (transcription)?

  it causes the 2 strands to separate and unwind, exposing nucleotide bases
• what is the 2nd step of transcription?

  the enzyme RNA polymerase binds to the template strand of the DNA at the beginning of the sequence to be copied
• what part of the template strand of the DNA does the RNA polymerase bind to (transcription)?

  at the start of the sequence
• why does the RNA polymerase bind to the template strand of the DNA (transcription)?

  to be copied
• what is the 3rd part of transcription?

  free RNA nucleotides (ribonucleotides) align opposite the template strand, based on the complimentary relationship between bases in DNA and the free nucleotides:

  • C-G
  • G-C
  • A-T
  • U-A
• what are ribonucleotides?

  free RNA nucleotides
• what do the ribonucleotides align opposite the template strand based on (transcription) ?

  based on the complimentary relationship between bases in DNA and the free nucleotides
• how would you describe the separation of the 2 strands of the double helix (transcription)?

  unwinding
• what is the 4th part of transcription?

  • RNA polymerase moves along the DNA, forming bonds that add RNA nucleotides, one at a time, to the growing RNA strand
  • this results in the synthesis of a molecule of mRNA alongside the unwound portion of DNA
  • behind the RNA polymerase, the DNA strands rewind to reform the double helix
• what happens when RNA polymerase moves along the DNA (transcription)?

  bonds are formed that add RNA nucleotides, one at a time, to the growing RNA strand
• what happens behind the RNA polymerase (transcription)?

  the DNA strands rewind to reform the double helix
• what is the 5th step of transcription?

  the RNA polymerase separates from the template strand when it reaches a ’stop’ signal
• what does RNA polymerase do when it reaches a ‘stop’ signal?

  the RNA polymerase separates from the template strand
• what is the 6th (final) step of transcription?

  the production of the transcript is complete and the newly formed RNA detaches from the DNA
• what does the RNA do when the production of transcript is complete (transcription)?

  it detaches from the DNA
• what does RNA having no thymine cause?

  a nucleotide containing uracil aligns opposite an adenine nucleotide in the DNA instead
• what is the newly formed RNA in prokaryotes?

  its mRNA and it attaches to a ribosome in the cytoplasm
• what is the newly formed RNA in eukaryotes?

  its pre-mRNA thats processed to form mRNA, which carries the information, originally held in the DNA, through a nuclear pore to a ribosome in the cytoplasm
• how is replication and transcription different?

  • replication uses both polynucleotide strands of a DNA molecule as templates
  • transcription only uses one strand, called the coding or sense strand, as a template
• what is this a diagram of?

  transcription