Dna and Protein synthesis

• Degenerate code 


  ​A feature of the genetic code; more than one triplet can code for a particular amino acid
• Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. Give two reasons why.

  The degenerate code (different codons can code for the same amino acid) or a mutation could take place in introns (Non-coding region)
• What is RNA splicing?

  When introns(Non-coding regions) are removed and exons are joint together so that translation of mRNA into a protein can take place.
• What are protein Domains?

  discrete structural and functional regions of proteins.
• What are Homologous Chromosomes?

  Two pieces of DNA that carry the same gene in the same position and are the same shape.
• What do RNA molecules use instead of Thymine?

  Uracil
• What are the two processes that take place in protein synthesis

  Transcription and then translation. Transcription is where Pre-mRNA is spliced to from mRNA and then translation uses the mRNA for protein synthesis.
• Identify three differences between transcription in eukaryotes and prokaryotes

  There are no introns within prokaryotes so no splicing is needed, In prokaryotes translation and transcription happen at the same time unlike Eukaryotes, In eukaryotes RNA splicing is needed to make functional mRNA.
• Explain why gene expression in prokaryotes can occur many times faster than in eukaryotes.

  Transcription and translation occurs at the same time and mRNA here does not need editing (In the prokaryote)
• What type of loop does tRNA have?

  An anticodon 3' AAG 5'
• What type of loop does mRNA have?

  A codon 5' UUC 3'
• Why does prokaryotic mRNA have a much shorter lifespan than eukaryotic mRNA?

  Prokaryotic mRNA are used immediately. Eukaryotic mRNA has to leave the nucleus before it is translated.
• What is a polysome and explain how they are useful?

  Polysomes are a cluster of ribosomes held together by mRNA. These are useful because multiple copies of the same polypeptide can be translated at the same time.
• Define the role of RNA polymerase in transcription

  RNA polymerase joins adjacent RNA nucleotides to phosphodiester bonds.
• A strand of mRNA has 64 codons but the protein produced from it has only 63 amino acids. Suggest a reason for this difference.

  There would be a stop codon within the sequence.
• non-overlapping code

  each base in a sequence is read once and is only part of one triplet
• What is a proteome?

  The complete set of proteins that can be produced by a cell
• Describe the structure of messenger RNA

  A long single strand with a base sequence complementary to the DNA it was transcribed for
• Advantage of mRNA over DNA

  mRNA is shorter and uses uracil which breaks down quickly. mRNA does not contain introns so will not need to be spliced (No RNA splicing)