Nucleoside Triphosphates

[vivatix]

My biochemistry textbook states that CTP, GTP and UTP are equivalents of ATP.

1. I am wondering why TTP is not the case? I tried to look this up and it seems that TTP doesn't exist - Can someone explain this? Is TTP not stable and thus it doesn't exist?

2. Why do biochemical pathways prefer to use ATP over the other nucleoside triphosphates? Is it becasue we have developed enzymes throughout evolution that prefer ATP over the others?

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[Lawpy]

1. ATP/CTP/GTP/UTP are all ribonucleoside triphosphates, because the 2' position of the sugar has a hydroxy group. They are RNA components. TTP is deoxygenated at the 2' position so it's a deoxyribonucleoside triphosphate and a DNA component. The 2' hydroxy position is important because it corresponds to increased reactivity of the nucleotide.

2. Yes it's evolutionary. Perhaps you can also look into the structure of ATP and realize that adenine is the only nitrogenous base with no carbonyl groups, which can correspond to its increased usage over the course of the evolution. Under anaerobic conditions in the early Earth atmosphere, the absence of oxygen means only adenine can predominate (whereas all the other nitrogenous bases use oxygen in their chemical structure). When atmospheric oxygen levels increased thanks to photosynthetic bacteria, the other nitrogenous bases arrived, but the greater amount of adenine that already existed in anaerobic conditions corresponded to greater predominance of adenosine, AMP, ADP and ATP for its usage by the early enzymes.