Biology Example Question #5 Outline the effects of a base substitution mutation in the case of sickle-cell anaemia

Thank you again to my biology teacher for teaching me everything I know about biology (far too many repeated words in this sentence...).

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• DNA is made up of a series of nucleotides. Each nucleotide has a nitrogenous base attached to it, either adenine, guanine, thymine, or cytosine. 
• Different combinations of these nitrogenous bases code for different proteins
• The DNA is transcribed by RNA polymerase, into mRNA (messenger RNA) so it can leave the nucleus
• From there mRNA leaves the nucleus and makes it way to a ribosome which can then translate the mRNA strand into a protein 
• The ribosome "reads" the mRNA three nucleotides at a time, called codons, each codon codes for an amino acid, which is then attached to a growing chain of amino acids, which ultimately make a protein
• There are some cases where a codon can be altered due to a base substitution, whereby one of the bases is replaced by one that should not be there, this is the case in sickle-cell anaemia
• Usually the DNA codon is CTC, which then gets translated to the mRNA strand as GAG, this codon then codes for the amino acid glutamic acid in the ribosome, which ultimately leads to the formation of haemogloblin which carries oxygen on the red blood cells.
• If someone has sickle-cell anemia instead of the DNA codon CTC, it is CAC, which when translated to mRNA, results in a GUG codon. Unfortunately, this does not code for the same amino acid, so instead of glutamic acid, valine is attached.
• Because the wrong amino acid is placed haemoglobin is not formed properly, and cannot form its quaternary (globular) structure, this makes is significantly worse at carrying oxygen, and thus sufferers tend to get short-winded. It also results in the characteristic sickle shaped red blood cells, which are less efficient at carrying oxygen. 
• If two copies of the mutated gene are inherited then all of the red blood cells are sickle shaped
• If only one copy of the mutated gene is inherited half of the red blood cells will be sickle shaped, and the others will be normal. 
• The sickle shaped cells make sufferers resistant to malaria. 

CTC

GAG- normal

GUG- not normal