Chapter 2.4 Revision Notes- How is the CFTR protein made?

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2.4
DNA contains the genetic code that dictates all of the characteristics of an
organism.
A gene is a sequence of bases on a DNA molecule that codes for a sequence
of amino acids in a polypeptide chain.
All of the genes in an individual are known as the genome.
DNA= deoxyribonucleic acid and is a long chain polymer of many units
called nucleotides or mononucleotides .
A mononucleotide contains three molecules linked together by condensation
reactions . They are deoxyribose , a phosphate group and an organic base
containing nitrogen .
The nitrogencontaining base is the only part of the nucleotide that is variable.
Four bases:
Adenine (A)
Cytosine (C)
Guanine (G)
Thymine (T)
The bond that forms between two nucleotides is a phosphodiester bond .
The polynucleotide strands are twisted around each other in a double helix .
The strands are held together by
hydrogen bonds and are said to be
antiparallel.
Adenine only pairs with thymine and
cytosine only pairs up with guanine .
Bases A and G have a tworing structure
and the bases C and T only have a
onering structure.
The AT pair has two hydrogen bonds
and the CG pair has three hydrogen
bonds.
These are referred to as
complementary base pairs .

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The CF gene is on chromosome 7 and is made up of around 230,000 base
pairs and it instructs the cell to make the CFTR protein. The sequences of
bases in the DNA tells the cell which amino acids to link together to make the
protein.
Protein synthesis:
First stage is called transcription which takes place in the nucleus . A
molecule that is a copy of the gene coding for the required protein is made.
This is made from RNA (ribonucleic acid ).…read more

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During transcription, every triplet code on DNA gives rise to a
complementary codon on mRNA.
A mutation in the sequence of bases in DNA could change a triplet that
makes up a gene.
Once in the cytoplasm, mRNA attaches to a ribosome where it causes
translation to take place.
Ribosomes are small organelles that are made up of ribosomal RNA
and protein . They are composed of two subunits a smaller and a
larger one.
The larger subunit contains two tRNA binding sites.…read more

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The first codon exposed on the ribosome is always the start codon
AUG which is the code for the amino acid methionine and the tRNA
molecules hydrogen bond to it.
The ribosome holds it all in place while a polypeptide bond forms
between the two amino acids.
Once the peptide bond has formed, the ribosome moves along the
mRNA to reveal a new codon at the binding site.
tRNA molecules are constantly ferrying amino acids from the
cytoplasm to the ribosome.…read more

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