How is ATP produced and used in living organisms?

Mammals who need to respire anaerobically produce lactic acid. This process occurs by the three carbonic sugar Pyruvate being reduced into Lactic acid by the addition of the hydrogen ion from reduced NAD. One molecule of lactic acid is made for every pyruvate and there are two pyruvates per glucose put in. This build up of acid in the muscles causes a fall in pH, which in turn causes cramps and pains to occur. The lactic acid may be removed quickly when oxygen levels are restored.

However if the organism is not anaerobic then further processes takes place and produce more ATP molecules. These processes take place in the mitochondria but the pyruvate molecule is too big and is broken down into acetyl coenzyme (Acetyl CoA, a two carbon molecule). Enzyme CoA catalyses the link reaction. The extra hydrogen is used to reduce NAD to form, reduced NAD. Oxidative Decarboxylation occurs as the extra carbon and two oxygen atoms are removed to form carbon dioxide, which is exhaled through the lungs and removed from the body. The molecule is then small enough to travel through the membrane into the matrix, where Krebs cycle takes place.

At the Krebs cycle the CoA enzyme enters the Acetyl into the Krebs cycle, then returns to the cytoplasm to transport another Acetyl. Each time the cycle is completed one ATP molecule is produced by substrate level phosphorolation (see diagram below - Krebs Cycle)

The Last process takes place on the Cristi of the mitochondria and is called the Electron Transport Chain. This is the most efficient stage of respiration where around 32 molecules of ATP may be produced via a series of redox (oxidation and reduction) reactions. The hydrogen ions are brought by the reduced NAD and reduced FAD; this replenishes the cells supply of hydrogen carriers. The hydrogen atoms are brought at different energy levels depending on the carrier (NAD at the higher energy level). Once these hydrogen ions(+)are on the electron transport chain they are moved along the chain, this happens because each successive carrier on the chain has a higher electro negativity than the carrier one before it, therefore the positive hydrogen ions are pulled along down the chain. While they are being pulled along they also participate in a series of redox reactions, which join the free phosphorous groups to ADP molecules to form the end ATP. (below diagram of Electron Transport Chain)

ATP is only produced, as it is required. It releases energy by breaking off the last phosphate group on the phosphate chain, attached with a very unstable covalent bond; the bond is broken by hydrolysis (the addition of water) releasing around 30 kJ of energy This leaves adenosine diphosphate (ADP).

However if the organism does not require energy, a reverse reaction may occur where a phosphate group may be bonded back to the ADP by condensation (removal of a water molecule), using energy supplied from food or sun light (depending on organism). This stores energy until it is needed when it may be easily.

This is caused and controlled by an enzyme called ATPase. ATP production is regulated by end product inhibition, this means that when the concentration gets to high because not enough is being produced, the ATP itself acts as an end-point inhibitor. Until the concentration falls (ATP is being used at a higher rate than production) and the energy release carries on as before.

ATP is produced in 2 ways in aerobic respiration

Substrate phosphorylation - during glycolysis 4moles of ATP per glucose molecule is made. And in the Krebs cycle 1 mole is produced per circuit.

Oxidative Phosphorylation occurs when electrons from reduced NAD and FAD flow along the electron transport chain and 3 moles ATP for every mole of electron pairs transferred from NAD into the chain. 2moles of ATP produced from FAD into electron transport chain.

Below shows the amount of ATP produced by aerobic respirations

In plants ATP is produced by photosynthesis. The plants contain pigments, which allows it to capture the energy from the sunlight. This energy is used to split water, to create ATP. The light dependant reaction, which produces ATP, occurs in the thylakoids of the chloroplasts. The products of photosynthesis are rapidly removed from the chloroplast. Chlorophyll is made up of chlorophyll a and b and carotenoids . Energy captured by all of these pigments is transferred to chlorophyll s. The energy is used to boost the energy of electrons and Hydrogen in water. The excited electrons that it then contains are used to power important redox reactions called Phosphorylation. Energy from excited electrons is also used to produce ATP. ADP + Pi (+energy) --> ATP

Living Organisms need ATP for many different things. Muscles need ATP in order for humans and animals to move around, and hunt for food. The cells in our muscles contain a lot more mitochondria, than other cells due to the fact that the muscles require lots of energy to contract and therefore they need lots of mitochondria to help keep up the ATP production to its high demand. ATP is also vital in homeostasis in helping to maintain constant body temperatures e.g. mammals such as polar bears require lots of ATP to help store the heat and prevent it from being lost to the surroundings.

Anabolic Reactions also requires ATP. Such as the production of proteins from amino acids (Protein Synthesis), the production of glycogen from glucose and the production of lipids, all require ATP to be formed. Active transport is a process that requires a lot of ATP, as it's the movement of substances against a concentration gradient. An example of this- energy from ATP may be used by carrier proteins to move molecules into the cell against the gradient. The Na / K pump is a carrier protein bringing K into cell and removing Na . In plants, root cells minerals also travel from a low concentration in the soil to a higher concentration within the cell, which requires energy.

In conclusion, ATP is the most important energy source in living organisms. Obtained in different ways and amounts.