2. Huntington\'s disease (HD) is a progressive, degenerative condition causing u

Question

2. Huntington's disease (HD) is a progressive, degenerative condition causing uncontrolled movements, loss of intellectual faculties, and emotional disturbance. HD symptoms develop in middle age. HD is caused by a mutation in the huntingtin gene (HTT) located on chromosome 4. It is a dominant disease. a. What kind of macromolecule is HTT (the huntingtin gene)? b. What are the monomers that make up the macromolecule you listed in part a? c. What are the major components that make up the basic structure of the monomers you listed in part b? d. The gene for huntingtin (HTT) is 171,268 nucleotides long; the HTT mRNA that is translated in the cytoplasm is 13481nucleotides long; and the huntingtin protein is 3142 amino acids long. List the reasons why ene int

Explanation / Answer

2.

a) nucleic acid
Explanation: HTT gene codes for the huntingtin protein. The 5' end of HTT gene consists of a region called as trinucleotide repeat which has multiple CAG repeats (cytosine, adenine, and guanine).

b) nucleotides
Explanation: Nucleic acids are made up of monomers of nucleotides. Nucleotides consists of three components: a 5-carbon sugar (deoxyribose sugar in DNA and ribose sugar in RNA), a phosphate group, and a nitrogenous base [adenine, guanine, cytosine, thymine (DNA) or uracil (RNA)]

c) deoxyribose sugar, a phosphate group, and nitrogenous bases

d) The HTT mRNA translated by ribosomes is so much shorter than the HTT gene in the nucleus because gene contains introns and regulatory regions.The introns are removed by splicing mechanisms during RNA processing and the regulatory regions such as promoters, enhancers, etc are not the part of mRNA. These regulatory regions are found in the nucleus.

e) The difference in the number of nucleotides because of the untranslated regions (5' UTR and 3' UTR) that are part of the mRNA. The mRNA also has 5' CAP and 3' poly-A tail which are attached during RNA processing. Also, it has a stop codon.

f) 3' a a c g a c a c a c 5’
Explanation: The DNA-coding strand sequence of the first 10 nucleotides of the first exon is 5' t t g c t g t g t g 3'
The template DNA strand is complementary to the coding strand. You must be knowing that in DNA, thymine (t) base pairs with adenine (a) and guanine (g) base pairs with cytosine (c). The opposite is also true.
Hence,
the sequence of the first 10 nucleotides of the first exon of the template DNA strand is 3' a a c g a c a c a c 5’

g) 5' u u g c u g u g u g 3'
Explanation: In RNA, adenine (a) base pairs with uracil (u) and guanine (g) base pairs with cytosine (c).
template DNA- strand sequence: 3' a a c g a c a c a c 5’
transcribed mRNA sequence:     5' u u g c u g u g u g 3'

h) The translation initiates from the start codon (atg) which codes for the methionine aminoacid. In the given exon, the first 'atg' i.e start codon is placed at the nucleotide position #90.
The DNA sequence is 5' atg ctg gcc 3' . This sequence reads as aug cug gcc on the mRNA which will code for met-leu-ala.

i) The sequence of first three anti-codons is
3’ u a c 5' 3’ g a c 5' 3’ c g g 5’
The anti-codons are complementary to the transcribed mRNA sequence and read in the direction of opposite to the mRNA synthesis.

j) The underlined "cag" repeats codes for the glutamine amino acids. The people with HTT gene have a large quantity of glutamine amino acid in the middle of protein. This results in the formation of a different primary structure than the normal protein primary structure and alters the function of protein. As a result, it interferes with the metabolic processes of brain cells and the person will show symptoms of huntington disease.

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