1.3 Gene Expression

• What determines a phenotype?


  The proteins that are synthesised when genes are expressed.
• What determines a genotype?


  The sequence of bases in its genes.
• The phenotype of an organism describes it's...


  physical appearance.
• State the two stages of protein synthesis.

  Transcription

  Translation
• What occurs during transcription?

  mRNA synthesis
• What is transcription the process of? 


  Creating an mRNA transcript from the DNA molecule in the nucleus and carrying it to the ribosome.
• Describe the basic structure of all RNA molecules.


  Composed of a single strand of nucleotides.

  Each nucleotide contains a ribose sugar, phosphate and a base.
• State the four RNA bases.


  Guanine and Cytosine, Adenine and Uracil.
• What is the role of mRNA?


  Carries a complementary copy of the DNA from the nucleus to the ribosome.
• What is the role of tRNA?

  Transfer RNA folds due to complementary base pairings. Each tRNA molecule picks up a specific amino acid in the cytoplasm and carries it to the ribosome.

  A tRNA molecule has an anticodon (exposed triplet of three bases) at one end and an attachment site for a specific amino acid at the other.
• What is the role of rRNA

  Combine with proteins to make the ribosome.
• Transcription involves the use of RNA polymerase, what does RNA polymerase do?


  -Unwind the DNA double helix and break hydrogen bonds between bases

  -Synthesise a primary transcript of mRNA from RNA nucleotides by complementary base pairing.
• What is RNA splicing?


  RNA splicing occurs where Introns are removed from the primary transcript and Exons are joined together. This forms the mature transcript.
• What is alternative RNA splicing?


  Process of removing introns and joining exons in different combinations to produce multiple sequences of amino acids and therefore different proteins. The order of Exons cannot change.
• What occurs during translation?


  the mRNA arrives at the ribosome and is 'read' to create a polypeptide chain.