Nucleic Acids

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Nucleic acids are polymers comprised of monomers, called nucleotides. These nucleotides consist of three components:

1. A nitrogenous base.

2. A pentose sugar

3. A phosphate group

There are two types of nitrogenous bases: single ring pyrimidines, such as cytosine, thymine and uracil, and double ring purines, such as adenine and guanine.


ATP can be referred to as a 'universal energy currency', as it is involved in energy changes in all organisms. ATP is synthesised in the mitochondria when energy is made available, and broken down when energy is needed, for example, for muscle contraction. 


ATP consists of three phosphate groups, an adenine base and a ribose sugar. Collectively, it is called adenosine triphosphate. 

ATP and energy:

When energy is needed in living organisms, the enzyme ATPase hydrolyses the bond between the second and third phosphate groups, producing a phosphate ion and ADP, alongside the release of chemical energy: this reaction is exergonic. However, as this reaction is reversible, ADP can recombine with a phosphate ion to produce ATP and water. This requires an input of chemical energy, and so the reaction is endergonic. This process is called phosphorylation. 

The roles of ATP:

When a phosphate ion is released, it combines with another molecule, making it more reactive, effectively lowering the activation energy for the reaction in which it is involved. For example, ATP is involved in:

1. Metabolic processes: to build large, complex molecules from smaller ones, such as DNA synthesis from nucleotides.

2. Active transport: it is required to change the shape of the carrier proteins in the membrane.

3. Movement: for muscle contraction.

ATP transfers free energy from energy rich compounds, like glucose, to cellular reactions where it is needed. 


The use of ATP as an intermediate in providing energy has several advantages over using glucose directly:

1. The hydrolysis of ATP is one reaction and releases energy immediately.

2. Only one enzyme is involved in the hydrolysis of ATP, whereas for glucose there are several.

3. ATP releases energy in small amounts, when and where it is needed, whereas glucose releases energy in large amounts.

4. ATP provides a common source of energy for many different chemical reactions, increasing efficiency. 


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