ATP stands for Adenosine Triphosphate and is simply described as the “energy currency” of the cell. This very large molecule is used for cellular activities that require energy and is used by every organism. ATP is what we call a nucleotide, which is made up of a nitrogenous base, a phosphate group, and a sugar.

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  All nucleotides contain these three parts. The nucleotides you might have heard of are adenine, thymine, guanine, cytosine, and uracil. These nucleotides make up the cell’s genetic material known as DNA and RNA. However, uracil is found in RNA and not DNA. 

  The phosphate group of a nucleotide is made up of a phosphorus atom and 4 oxygen atoms (chemical formula PO_43-, the 3- means that there are 3 oxygens that are negatively charged). The sugar is usually a ribose, which is a sugar that contains 5 carbon atoms and is known as a pentose sugar because of this amount, there are also 10 hydrogens, and 5 oxygens with a chemical formula of C₅H₁₀O₅. If DNA is a ladder, the sugar and the phosphate group make up the two sides which contain the rungs, or the nitrogenous bases, in between them.  The Nitrogenous bases contain nitrogen, carbon, hydrogen, and oxygen. Adenine does not contain any oxygen however, but has 5 carbons, 5 nitrogens, and 5 hydrogens.

  The big difference between ATP and the nucleotide shown above is the number of phosphate groups in the molecule. In genetic nucleotides, as shown above, there is only one phosphate group (There is only one phosphate in polymer form, but before a genetic nucleotide is added to a polymer, it has three phosphates). In ATP however, there are three phosphate groups. These phosphate groups are joined together in “high energy” bonds and when one of those bonds is broken, a lot of energy is released. Quotations are put around the high energy because the ATP molecule is actually not very high energy despite what textbooks might mislead you to believe. The reason they are called high energy is because when ATP is used in a reaction, the products have a lower energy state than the reactants (in a chemical reaction the reactants are the input substances and products are the result of those inputs interacting), thus there is a net release of energy. The products are accompanied by 57 kilojoules of energy (joules is the metric unit for energy and kilojoules is 1000 joules) and is abbreviated kj. 

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  ATP is so important to the body because of this high energy. There are many reactions in the body that cannot happen without the help of ATP. This is why we have a digestive and a respiratory system, because when we eat food, the glucose contained in that food is used by the cell to make thirty eight ATP molecules. The process that produces this ATP is called Cellular respiration and it occurs in a cellular organelle called the mitochondrion (plural: mitochondria).

  What is GTP? GTP is another nucleotide energy source that is built like ATP with the exception of the nitrogenous base used. In ATP, Adenine is used, whereas in GTP, guanine is used. ATP is used as the main energy carrier of the cell as during a process of cellular respiration, GTP is converted to ATP. However, there are reactions where GTP must be used instead of ATP and scientists are still learning why.

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