Question

19. For Huntington’s disease, expansion of trinucleotide repeat occurs within the ORF causing the HTT protein to have many repeats of the amino acid glutamine, which in turn, causes the mutant protein to be toxic to neurons. Fragile X syndrome is also a trinucleotide repeat disease. How is the FMR1gene (or its gene product) affected in the case of fragile X syndrome?

20. Classify the mutation that causes sickle cell anemia three different ways.

21. Describe a cellular process that can lead to the conversion of a cytosine in a CpG sequence in the DNA to thymine.

Answer 1

19. For Huntington’s disease, expansion of trinucleotide repeat occurs within the ORF causing the HTT protein to have many repeats of the amino acid glutamine, which in turn, causes the mutant protein to be toxic to neurons. Fragile X syndrome is also a trinucleotide repeat disease. How is the FMR1gene (or its gene product) affected in the case of fragile X syndrome?

One region of the FMR1 gene has DNA segment called as CGG trinucleotide repeat and this segment is repeated multiple times within the gene.

The FMR1 make protein called FMRP that play a role in the development of connections between nerve cells, where cell-to-cell communication occurs.

In case of fragile X syndrome, caused by an expansion of the CGG trinucleotide repeat in the FMR1 gene. CGG is repeated from 200 to 1,000 times, that makes FMR1 gene unstable. So, FMR1 gene is turned off and makes very little or no protein that disrupts normal functions of nervous system and causes fragile X syndrome.


20. Classify the mutation that causes sickle cell anemia three different ways.

The mutation that causes sickle cell anemia three different ways are :

1) Hemoglobin SS disease:

Hemoglobin SS disease occurs when patient inherit copies of the hemoglobin S gene from both parents and called as Hb SS.

2) Hemoglobin SC disease:

Hemoglobin SC disease occurs when patient inherit the Hb C gene from one parent and the Hb S gene from the other

3) Hemoglobin SB+ (beta) thalassemia:

In this size of the red blood cell is reduced as less beta protein is produced.


21. Describe a cellular process that can lead to the conversion of a cytosine in a CpG sequence in the DNA to thymine.

DNA methylation can lead to the conversion of a cytosine in a CpG sequence in the DNA to thymine. DNA methylation is the process of addition of a methyl (CH3) group to the DNA strand (to the fifth carbon atom of a cytosine ring).

DNA methylation is located at CpG sites and lead to the conversion of methylated cytosine to thymine by deamination.

Methylated cytosines are deaminated and converted to thymine.