Child has a disease that is causing severe growth delays and rapid aging. His cells are assayed, and it is noticed that there is a severe decrease in DNA synthesis compared to normal cells. When DNA from his cells was gently heated to separate the double helix, numerous, small, single-stranded fragments of about 1000 base pairs were found. Which enzyme is likely to be defective in this child

DNA ligase

Explanation:

DNA ligase is an enzyme that responsible for the joining of two DNA strands by the formation of a bond between the deoxyribose group of one DNA strand and the phosphate group of the other DNA strand. DNA ligase is responsible for sealing recombination fragments, connects okazaki fragments formed during DNA replication and also sealing DNA during repairs.

DNA ligase deficiency also referred to as ligas 4 syndrome is characterized by  severe growth delays, combined immunodeficiences and abnormal facial structure.

Therefore, in the case of this child with this disease, the enzyme likely to be defective is DNA ligase.

1. amino acid refers to the fundamental building block of proteins, comprising of an amino group and a carboxyl group.

2. catalyst refers to any substance, which increases the rate of chemical reaction without being used up in the reaction.

3. a complex molecule containing he genetic code is dna or deoxyribonucleic acid.

4. an enzyme refers to a molecule of protein, which is unique in accelerating up a particular chemical reaction in the biological systems.

5. nucleic acid refers to an sequence of sugars, phosphates, and nitrogenous bases, for example, dna and rna.

6. a protein refers to a large, composite organic molecule comprising of a huge number of amino acids associated together with the of peptide bonds.

7. rna refers to a nucleic acid that takes part in the production of proteins.

8. substrate refers to a compound, which takes part in a chemical reaction, and is chemically modified by the reaction.