Adenosine TriPhosphate ATP

ATP - A universal energy currency

Adenosine Tri-Phosphate or more conveniently ATP, is a small molecule made of a 5 carbon ribose sugar, a nitrogenous base Adenine (a purine) and three phosphates.

It is known as a nucleotide derivative as it is very similar in structure to an RNA nucleotide. The main difference between the two is that ATP has three phosphates while the RNA nucleotide only has one phosphate.

ATP is a source of energy for all living organisms and is referred to as the Universal Energy Currency.

As ATP is used by all cells in an organism, it has a standardised process of releasing or storing energy. ATP is therefore a currency of energy that is universally used within organisms.

ATP stores its energy in high energy bonds between each of the inorganic phosphates. Energy can be released each time a phosphate is cleaved from the main ATP molecule. The energy that is released is done so in small manageable amounts, enough to carry out most metabolic reactions however not too much. Energy released in small quantities ensures there is no excess energy that will be wasted or that could physically damage cell components.

The total quantity of ATP in the human body is about 0.1 mole, and the majority of ATP is not usually synthesised but rather is generated from ADP. The total amount of ATP + ADP will remain fairly constant in the human body as it is constantly being converted from one form to another.

The energy used by human cells requires 100 to 150 moles of ATP daily (50 - 75 kg). This means that each ATP molecule is recycled 1000 to 1500 times during a single day.

Releasing energy

ATP can release energy by removing the outermost phosphate of the three. The removal of the phosphate releases 30.5KJ/mol of energy and as a result the ATP (Adenosine Tri-Phosphate) is converted to ADP (Adenosine Di-Phosphate) as it now only has two phosphates attached.

ATP can also be converted to AMP (Adenylic acid or Adenosine Mono-Phosphate) were two phosphates are cleaved from the main molecule releasing twice the energy (45.9KJ/mol).

AMP in some circumstances can be converted to Adenosine (a 5 carbon sugar and the nitrogenous base Adenine) by removing the final phosphate of the three. This will release energy (14.7KJ/mol) but not as much as the removal of the first two phosphates.

During respiration ATP can be created by using the energy from respiratory substrates (lipids, carbohydrates and proteins) to add a phosphate to ADP to create ATP and so creating a high energy bond between the two phosphates.

Source

A Level Exam Questions

1. All organisms require energy in order to remain alive. Plants use solar energy to combine water and carbon dioxide into complex organic molecules. Both plants and animals then break down organic molecules in respiration. Energy released in this process is used in the formation of ATP.

Describe the structure of ATP.

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[Total: 4 marks]

A level Exam Questions Mark Scheme

1. accept labelled sketch diagram for marking points below

nitrogenous base / purine;
adenine;
pentose / 5 carbon, sugar;
ribose;
three, phosphate groups / Pi; R phosphate molecule
phosphorylated nucleotide;

A adenosine as an alternative to adenine plus ribose 4 max

[4]

Answering the A-Level Exam Questions

1. All organisms require energy in order to remain alive. Plants use solar energy to combine water and carbon dioxide into complex organic molecules. Both plants and animals then break down organic molecules in respiration. Energy released in this process is used in the formation of ATP.

Describe the structure of ATP.

Your answer should focus solely on describing the structure of ATP (Adenosine Tri-Phosphate).

Firstly you should bring to your minds eye the structure of the ATP molecule. You could make a quick sketch on your paper to help settle your nerves so you can organise your thoughts before committing to writing.

It is useful to start at one side of the molecule and work across it describing each part you come across in order.

It is also important to note how many marks the question is worth. In this case it is 4 marks. In my mind there are 3 main parts to the ATP molecule so in order to access the 4th mark your answer is going to need to go into some of the detail for each of the component.

Answer:

An ATP molecule is a phosphorylated nucleotide and is made up of 3 phosphates (1)*, a pentose (5 Carbon) (2)* ribose (3)* sugar and a nitrogenous base (4)* adenine (5)*.

*The numbers in the brackets denote where a mark would be awarded

Comments 1 comment

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Spirit Whisperer 5 years ago from Isle of Man

This is an excellent hub. I would highly recommend any A-Level student to use this series of Biology study aids to achieve the success that every student deserves once the material is accessible and in a form that makes it easy to understand and outlining how it may be tested. I hope you continue to add to this series and my children will definitely be studying from your notes. I would also say that this series would also be an invaluable resource for any conscience teacher of Biology and wouldn't it be great if more teachers shared their resources like this? Thank you.

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