CFTR Protein

CFTR Protein

  • Cystic fibrosis is caused by a mutation in the DNA that carries the instructions for making the CFTR protein


Structure of DNA:

  • James Watson and Francis Crick proposed model for DNA based on X-ray diffraction patterns
  • DNA is found in every cell nucleus
  • Contains the genetic code which dictates all inherited characteristics of an organism
  • Controls manufacture of proteins; this makes you unique


Gene and Genome:

  • Gene; a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chains
  • Each chromosome in the cell nucleus contains DNA and carries genes
  • The genes make up a fraction of the total DNA in the chromosomes
  • All the genes in an individual (or species) are known as the genome



  • DNA is one type of nucleic acid called deoxyribonucleic acid (long chain molecule made of many unites called nucleotides or mononucleotides)
  • Mononucleotide; three molecules joined together by condensation reactions
  • Deoxyribose – 5 carbon sugar; phosphate group; an organic base (contains nitrogen)


  • Link together by condensation reactions between the sugar of one nucleotide and the phosphate of the next
  • Long chain of mononucleotides = polynucleotide
  • The nitrogen containing base (organic base) is variable (adenine, cytosine, guanine, thymine)
  • In DNA two long strands of nucleotides twist around each other to form a double helix




  • The two strands which run in opposite directions are known as the antiparallel strands (held together by hydrogen bonds between base pairs)


Pairing up of bases:

  • Adenine pairs with thymine
  • (one ring structure – T & C)
  • Cytosine pairs with guanine
  • (two ring structure – A & G)
  • Creates a three ring structure which makes the molecule a uniform width along its length
  • Shape and chemical structure of the bases determines how many hydrogen bonds each has and which base they pair with (A and T = 2) (C and G = 3)


DNA coding for proteins:

  • CF gene is on chromosome seven (instructs the cell to make the CFTR protein that forms the transmembrane chloride channel)
  • However the sequence of bases in the DNA tells the cell which amino acids to link together to make the CFTR protein
  • Each gene is a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain





The triplet code:

  • One base does not code for one amino acid
  • The code carried by the DNA is a three-base, triplet code
  • Several triplets code for the same amino acid; others can be start or stop signals (chain terminators)


DNA to proteins:

  • DNA in our chromosomes carries the genetic information from one generation to the next
  • DNA carries codes which determine the structure and function of cells by telling the cells which proteins to make
  • DNA in the nucleus; proteins made in the cytoplasm
  • In order for the DNA to reach the cytoplasm, a copy is made
  • The copy is made from RNA instead of DNA, this can leave the nucleus


Difference between DNA and RNA:


·         Two polynucleotide strands

·         Deoxyribose

·         Thymine

·         One polynucleotide strand

·         Ribose sugar not deoxyribose

·         Uracil



Three types of RNA:

  • messenger RNA
  • transfer RNA
  • ribosomal RNA


Protein Synthesis:

  • two stages; one in the nucleus and the second in the cytoplasm
  • transcription and translation



  • takes place in the nucleus
  • DNA double helix unwinds and the hydrogen bonds between bases break
  • Sequence of one strand, template strand (antisense strand), is used in the production of a messenger RNA molecule
  • mRNA is built from free RNA nucleotides which line up alongside the DNA template strand
  • every triplet code on DNA creates a complimentary codon on the messenger RNA
  • template is also known as the antisense strand because once transcribed it makes an mRNA molecule with the same base sequence as the DNA coding strand
  • the coding strand is known as the sense strand
  • involves the enzyme RNA polymerase
  • the mRNA molecule leaves the nucleus through a pore in the nuclear envelope and enters the cytoplasm



  • takes place on the ribosomes (small organelles made of ribosomal RNA and protein)
  • ribosomes are found free in the cytoplasm or attached to endoplasmic reticulum
  • transfer RNA molecule, carrying an amino acid molecule, has three bases called an anticodon and these pair with complimentary bases on the mRNA codon
  • the amino acids that the tRNA carry join by means of peptide bonds




  • Sequence of amino acids, primary structure, determines its 3-D structure and properties of the protein. When even slightly altered it may substantially alter the proteins structure and properties