Gene Expression

The following links offer some useful revision on Cell Structure to support your learning:

BBC Bitesize Learner Guide

BBC Bitesize Questions

Biology Coach Video Lesson

Gene Expression Quiz

Gene Expression Mindmap

Online Flashcards

At Higher, you will need to know the following:

  • Phenotype is determined by the proteins produced as the result of gene expression.
  • Only a fraction of the genes in a cell are expressed.
  • Gene expression is influenced by intra- and extra-cellular environmental factors
  • Gene expression is controlled by the regulation of both transcription and translation.
  • Structure and functions of RNA. RNA is single stranded, contains uracil instead of thymine and ribose instead of deoxyribose sugar.
  • Messenger RNA (mRNA) carries a copy of the DNA code from the nucleus to the ribosome.
  • Ribosomal RNA (rRNA) and proteins form the ribosome.
  • Each transfer RNA (tRNA) carries a specific amino acid.
  • Transcription of DNA into primary and mature RNA transcripts in the nucleus. This should include the role of RNA polymerase and complementary base pairing.
  • mRNA is transcribed from DNA in the nucleus and translated into proteins by ribosomes in the cytoplasm. RNA polymerase moves along DNA unwinding and unzipping the double helix and synthesising a primary transcript of RNA by complementary base pairing. Genes have introns (non -coding regions of genes) and exons (coding regions of genes).
  • The introns of the primary transcript of mRNA are non -coding and are removed in RNA splicing. The exons are coding regions and are joined together to form mature transcript. This process is called RNA splicing.
  • Translation of mRNA into a polypeptide by tRNA at the ribosome. tRNA folds due to base pairing to form a triplet anticodon site and an attachment site for a specific amino acid
  • Triplet codons on mRNA and anticodons translate the genetic code into a sequence of amino acids.
  • Start and stop codons exist.
  • Codon recognition of incoming tRNA, peptide bond formation and exit of tRNA from the ribosome as polypeptide is formed.
  • Different proteins can be expressed from one gene as a result of alternative RNA splicing and post -translational modification.
  • Different mRNA molecules are produced from the same primary transcript depending on which RNA segments are treated as exons and introns.
  • Post -translation protein structure modification by cutting and combining polypeptide chains or by adding phosphate or carbohydrate groups to the protein.

 

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