The genetic code

• What is the genetic code?

  A sequence of nucleotides in DNA forms a code that determines the sequence of amino acids in proteins.
• What is mRNA?

  RNA that transfers DNA code from the nucleus to the cytoplasm
• Why is mRNA useful?

  It is small enough to leave the nucleus through the nuclear pores and enter the cytoplasm
• Describe mRNA.

  Single helix and is a copy of the coding strand of DNA except T is replaced with U. mRNA acts as a template on which proteins are built. It is easily broken down and associates with proteins in the cytoplasm
• What is DNA made up of?

  Triplets
• What is a triplet?

  A sequence of 3 DNA bases that codes for a single amino acid
• What do codons code for?

  An amino acid
• What does degenerate code mean?

  Most amino acids have more than one codon
• What are stop codons and how many are there?

  There are 3 stop codons that mark the end of the polypeptide chain
• What does the genetic code being described as universal mean?

  All organisms use the same genetic code
• What does the genetic code being non-overlapping mean?

  Each base is only read once in the code
• What are exons?

  Sections of DNA that code for proteins
• What are introns?

  Sections of DNA that do not code for proteins
• What is splicing?

  The non-functional introns are removed and functional exons are joined together in a process called splicing.
• Why does prokaryotic DNA not go through splicing?

  Prokaryotic DNA does not usually contain introns
• What is a start codon?

  3 bases at the start of an mRNA sequence which help to initiate translation.
• State 3 characteristics of the genetic code.

  • universal
  • non-overlapping
  • degenerate