ATP and its role in living organisms

ATP is energy currency not energy storage

ATP is a nucleotide that contains a large amount of chemical energy stored in its high-energy phosphate bonds. It releases energy when it is broken down (hydrolyzed) into ADP. The energy is used for many metabolic processes. Hence, ATP is considered as the universal energy currency for metabolism.

ATP is produced via cellular respiration in the mitochondria and photosynthesis in chloroplasts.

Its functions are for intracellular energy transport for various metabolic processes including cell division.

A glucose molecule has high energy content. If all the energy was released at once then there would be severe temperature problems in a cell. It is important that energy liberation is in small bursts. This is achieved by using adenosine triphosphate (ATP) molecules. Substrates such as glucose are broken down in enzyme-catalysed stages to produce a number of ATP molecules.

ADP (adenosine diphosphate) + P (phosphate) = ATP (adenosine triphosphate)

ATP is a molecule which is needed in all energy-requiring processes.

The ATP needs to be broken down to liberate its energy. This is done by an enzyme, ATPase.

ATP is a phosphorylated nucleotide. Each nucleotide consists of an organic base, ribose sugar and phosphate group. ATP is a nucleotide with two extra phosphate groups! This is the reason for the term ‘phosphorylated nucleotide’.

Adenine –––––– ribose –––––– phosphate –––––– phosphate –––––– phosphate

Uses of ATP

muscle contraction active transport synthesis of macromolecules Stimulates the breakdown of substrates to make even more ATP for other uses.

ATP (adenosine triphosphate) is required in all living cells as a continual supply of energy, to be used in processes, which keep the organism alive such as muscle contraction. ATP is made up of three main components, the base (adenine), a phosphate chain (made of three phosphate groups) and a ribose sugar backbone. The first step in the production of ATP and the store of energy is Glycolysis, which

occurs in both aerobic and anaerobic respiration. In both cases Glycolysis takes place in the cytoplasm of the cell, because glucose is too big to get in to the mitochondria.

ATP is constantly and rapidly recycled There is only about 5g of ATP in the entire human body Up to 40kg equivalent of ATP is used in 24 hours In hard exercise 500g of ATP is broken down per minute to fulfill energy requirementsThis means that each molecule of ATP is built up and broken down up to 100 times per minute.

ATP in muscle contraction

ATP is the immediate source of energy for muscle contraction. Although a muscle fiber contains only enough ATP to power a few twitches, its ATP "pool" is replenished as needed. There are three sources of high-energy phosphate to keep the ATP pool filled.

creatine phosphate glycogen Cellular respiration in the mitochondria of the fibers.

Creatine phosphate - The phosphate group in creatine phosphate is attached by a "high-energy" bond like that in ATP.

During contraction, ATP is continually regenerated using creatine phosphate, which provides a phosphate group to ATP, allowing it to become ATP and creatine. The limited supply of creatine phosphate must be replenished via ATP from respiration. The muscle may not be able to keep up with it and a lactate pathway is used to allow continued formation of ATP, but the cells incur an oxygen debt.

ATP in active transport

Active Transport is the movement of molecules defined as the energy-consuming transport of molecules or ions across a membrane against a concentration gradient, made possible by transferring energy from ATP. Most cells have sodium/potassium pumps and these are maintained by ATP.

Active transport is vital in regulating concentrations in cells, that would otherwise be non-apparent due to ions/solutes diffusing down an electrochemical or concentration gradient. To go against a concentration gradient, proteins that provide this function require energy, and that energy is in the form of ATP. ATP is released during respiration, and without it, the human body would not survive.

Synthesis of macromolecules

ATP is the main energy source for the majority of cellular functions. This includes the synthesis of macromolecules, including DNA, RNA and proteins. ATP also plays a critical role in the transport of these macromolecules across cell membranes.