Question

ԿԱՆՉՈ» 2. Genes are made of DNA nucleotides. The gene for the beta chain of hemoglobin is 1,734 nucleotides in length and is located on the human chromosome 11. The mutation responsible for sickle-cell anemia affects a single nucleotide, which in turn changes a single amino acid. (9 pt) a. How are these nucleotides joined together to form a long polynucleotide chain? Name the relevant nucleotide constituents important for making the linkage. (see Slides 5-7 of Lecture 4b) (2 pt) b. The normal sequence of one strand of a region of this gene is 5' ACTCCTGAGGAGAAG 3. How many nucleotides are in this segment? Which nucleotide component do you find at each 5' and 3' ends? (see Slides 12 of Lecture 4b) (2 pt) c. What is the sequence of the other strand of this region of DNA? Write the sequence and polarity (5' and 3' ends) of the complementary strand it base pairs with. (1 pt) d. The mutant sequence of one strand of a region of this gene is 5' ACTCCTGTGGAGAAG 3'. What nucleotide change causes the disease? Which nucleotide component is altered by the mutation? (2 pt) e. What chemical bond allows the two strands of DNA to form a double helix? Are these bonds present in RNA? (2 pt)

Answer 1

A. Nucleotides in a polynucleotide chain are connected to each other by phosphodiester Bond. Phosphodiester bond is the type of covalent bond which is formed between 5' phosphate group of one nucleotide and 3' hydroxyl group of the other nucleotide.

B. In this sequence, there are 15 nucleotides. The number of nucleotides is equal to the number of nitrogenous bases present in a given sequence. At 5 prime end, phosphate group is present whereas at 3 prime end hydroxyl group is present.

C. The Other strand will be opposite in direction and complementary to the given strand.

3' TGAGGACTCCTCTTC 5'

D. If we compare the mutant sequence with the wild type sequence, then we can see that eight nucleotide in the wild type sequence is adenine and in the mutant it is changed to thymine. This mutation is changing the nitrogenous base of the nucleotide.

E. Hydrogen bonds present between complementary bases. These bonds are not present in RNA because it is mostly single stranded in nature. But it is double stranded sometimes, than hydrogen bonds are present.

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