Transcription

• Function of DNA


  • The function of DNA is to code for proteins.
  • Not all of the DNA molecule codes for proteins
  • The functional part of DNA that can is known as a gene
• RNA


  • Genes are instructions to build a protein
  • unfortunately the DNA that contains the genes cant leave the nucleus
  • so a copy of the gene must be made
  • the copy is known as messenger RNA or mRNA
• Transcription


  • transcription is the name of the process in which a copy of DNA is made
  • the copy is known as messenger RNA
  • this process occurs in the nucleus of the cell
• Process of transcription part 1

  1. part of the DNA in the nucleus is unwound
  2. weak hydrogen bonds between the bases are broken by enzyme helicase
  3. causes the 2 strands of DNA to seperate. this exposes the gene that will be transcribed
  4. Free RNA nucleotides in the nucleoplasm find their complementary base pair on the DNA
  5. A hydrogen bond forms between the RNA nuclotide base and the complementary base on the DNA.
• Process of Transcription part 2

  1. The enzyme RNA polymerase then catalyses the formation of the phosphodiester bond between the ribose sugar and phosphate groups of adjoining RNA nucleotides, creating the sugar-phosphate backbone
  2. The mRNA molecule is formed
  3. Hydrogen bonds between the bases on mRNA and the bases on DNA break.
  4. The mRNA is ready to make it's journey out of the nucleus through the nuclear pore and into the cytoplasm.
  5. The hydrogen bonds between the complementary bases on DNA re-form and theDNA is wound back into a helix again.
• eukaryotic transcription


  the genome within eukaryotic cells contains many non-coding sections. Non-coding DNA can be found:

  • between genes, as non-coding multiple repeats
  • within genes as introns.
• eukaryotic transcription

  During transcription, eukaryotic cells transcribe the whole gene to produce pre-mRNA molecules. pre-mRNA contrains the introns and exons of a certain gene. Before the pre-mRNA exits the nucleus and splicing occurs:

  • Non-coding sections are removed
  • coding sections are joined together
  • resulting mRNA molecule carries only the coding sequences of the gene
  • mRNA contains only exons and exits the nucleus before joining a ribosome for translation
• what are the repeating units in DNA known as

  nucleotides
• what are the 3 parts that make up a nucleotide

  1. pentose sugar
  2. phosphate
  3. base
• Which bases form complementary base pairs in DNA


  A - T

  C - G
• what type of bond forms between the complementary bases on DNA


  Hydrogen bonds
• what type of bond forms between the sugar and phosphate molecules of adjoining nucleotides


  a phosphodiester bond
• What is the name of the enzyme that forms this bond during DNA replication


  DNA polymerase
• What is the DNA structure described as


  a double helix
• in the RNA the base uracil replaces which base found in DNA


  Thymine
• which sugar is found in an RNA nucleotide

  Ribose
• What molecule is formed in transcription


  Messenger RNA
• Which enzyme catalyses the formation of phosphodiester bonds between RNA nucleotides


  RNA polymerase
• Where does transcription occur


  nucleus