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
Nucleotides:
- 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:
DNA | 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