polypeptide synthesis

• proteins are created on ribosomes in two man stages called?

  transcription and translation
• transcription is where the gene on the dna is copied onto mrna
• translation is where the mrna joins with a ribosome and corresponding trna molecules bring the specific amino acids the codon codes for
• transcription

  • happens inside the nucleus
  • a complimentary mrna copy of one gene on the dna is created in the nucleus
  • mrna is much shorter than dna so it is able to carry the genetic code to the ribosome in the cytoplasm to enable protiens to be made
  • dna is too big to leave the nucleus pores and enzymes in the cytoplasm will damage the dna
• process of transcription

  1. the DNA HELIX UNWINDS to expose bases to act as a template
  2. only ONE CHAIN OF DNA ACTS AS A TEMPLATE
  3. like dna replication, the unwinding is catalysed by DNA HELICASE
  4. dna helicase BREAKS HYDROGEN BONDS between bases
  5. free floating MRNA NUCLEOTIDES in the nucleus align oppposite exposed complimentary dna bases
  6. the enzyme RNA POLYMERASE bonds together the rna nucleotides to copy an entire gene
  7. once completed, mrna is modified and leaves the nucleus through the pores
• pre-mrna and mrna

  • following transcription, pre-mrna has to be modified to become mrna that is ready to leave the nucleus and take part in translation
  • the introns are SPLICED out by a protein called SPLICESOME. this leaves behind just the exons coding region
• introns are a sequence of dna that do not code for amino acids
• during translation, describe how an Amino acid is added to a polypeptide:

  1. tRNA molecules binds to a specific amino acids
  2. the anticodon binds to the codon
  3. the amino acid is joined with a peptide bond
• describe how mRNA is produced (3 marker)

  1. free nucleotides form complimentary based pairs
  2. phosphodiester bonds form
  3. by RNA polymerase
• how is mRNA formed (5 marker)

  1. hydrogen bonds break
  2. one DNA strand is used as a template
  3. free nucleotides align by complimentary based pairings
  4. usrasil is used in place of thymine
  5. rna polymerase joints nucleotides
  6. by phosphodiester bonds
  7. pre-mrna is spliced
• how is a peptide formed during translations

  1. tRNA molecules bring specific amino acids
  2. the anti-codon is complimentary to the codons
  3. a peptide bond is produced using ATP
  4. tRNA Is released
  5. ribosome moves along the mRNA to form the polypeptide