Sickle cell anemia is caused by a single amino acid substitution at the 6th amin

Question

Sickle cell anemia is caused by a single amino acid substitution at the 6th amino acid residue in the beta chains of hemoglobin where in a glutamate is replaced by a valine due to a point mutation in the beta globin gene. This amino acid substitution results in an altered hemoglobin structure that causes aggregation/crystallization of hemoglobin molecules in red blood cells, which leads to red blood cell deformation. From the list ( Arginine, serine, glycine, proline, aspartate, tryptophan) suggest two amino acid substitutions that would be less likely than valine to cause impairment of hemoglobin function if substituted for glutamate at position 6 of the beta globin peptide. Explain your choices.

Explanation / Answer

A point mutation, or single base substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide of the genetic material, DNA or RNA. The term point mutation also includes insertions or deletions of a single base pair. A point mutant is an individual that is affected by a point mutation. Point mutation is a random mutation in the deoxyribonucleic acid (DNA) that occurs at one point. This mutation may be a deletion, transition, insertion, or transversion. Point mutations usually take place during DNA replication. DNA replication occurs when one double-stranded DNA molecule creates two single strands of DNA that is a template for the creation of the coinciding strand. A single point mutation can change the whole DNA sequence. Changing one purine or pyrimidine may change the amino acid that the nucleotides code for. Point mutations may arise from spontaneous mutations that occur during DNA replication. The rate of mutation may be increased by mutagens. Mutagens can be physical, such as radiation from UV rays, X-rays or extreme heat, or chemical (molecules that misplace base pairs or disrupt the helical shape of DNA). Mutagens associated with cancers are often studied to learn about cancer and its prevention. There are multiple ways for point mutations to occur. First, ultraviolet(UV) light and higher-frequency light are capable ionizing electrons and in turn impacting DNA. Also, one of the cell metabolic byproducts, reactive oxygen molecules with free radicals, can also be very harmful to DNA. These reactants can lead to both single-stranded DNA breaks and double-stranded DNA breaks. Third, bonds in DNA eventually degrade, which creates another problem to keep the integrity of DNA to a high standard. There can also be replication errors that lead to substitution, insertion, or deletion mutations. It was previously believed that these mutations happened completely by chance, with no regard for their effects on the organisms. Recently, there have been studies suggesting that these mutations occur in response to environmental challenges. That is to say, they are more likely to occur when they are advantageous to the organism, rather than when they are neutral or disadvantageous. When cells were deprived of a certain amino acid, tryptophan, for prolonged periods of time, point mutations in trp operon reverted to tryptophan, leading to an advantageous result, more frequently than under normal conditions when the mutations were neutral. In addition, the tryptophan mutation rate was unaffected when the cells were deprived of another amino acid, cysteine, further suggesting that the mutation rate was specific to situations in which the mutation was advantageous

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