Normal cells die in a nutrient medium containing thymidine and methotrexate, whereas mutant cells defective in thymidylate synthase survive and grow. The mutant cells grow because the medium contains the they are unable to make normal cells, however, continue to synthesize their own and thereby convert their limited supply of to . The methotrexate inhibits , so cannot be regenerated. Without a supply of for the synthesis of nucleotides and amino acids, the cells die.

*Thymidine

*THF to DHF

*THF

Explanation:

Normal cells die in a nutrient medium containing thymidine and methotrexate, whereas mutant cells defective in thymidylate synthase survive and grow. The mutant cells grow because the medium contains theThymidine they are unable to make normal cells, however, continue to synthesize their own and thereby convert their limited supply of to__THF to DHF . The methotrexate inhibits , so cannot be regenerated. Without a supply ofTHF for the synthesis of nucleotides and amino acids, the cells die.

NOTE:

THF means Tetrahydrofolate

DHF means Dihydrofolate

Thymidine which is also reffered to as deoxythymidine, is described as a deoxynucleoside that is composed of the pyrimidine base thymine that is attached to the sugar deoxyribose. Thymidine is a nucleoside made up of pentose sugar, pyrimidine base tymine and deoxyribose, it is one of the the four nucleoside found in exclusively DNA as well as T-loop of tRNA.

Tetrahydrofolate also known as tetrahydrofolic acid can be described as part of folic acid that function as a coenzyme which aid metabolic reactions that includes nucleic acid and amino acids. It is also reffered to as one-carbon metabolism, and it's oone-carbon mechanism is associated to the histidine, serine of amino acid.

a- all cells come from pre-existing cells