ATP and the light dependant reaction

The flow of energy through living cells occurs in three stages:

1. Light energy from the sun is converted by plants into chemical energy during photosynthesis

2. The chemical energy from photosynthesis, in the form of organic molecules, is converted into ATP during respiration in cells

3. ATP is used by cells to perform useful work

Adenosine Triphosphate (ATP) has three phosphate groups as the name suggests.. THIS IS THE KEY TO HOW ATP STORES ENERGY!!!!

• The bonds between these phosphate groups are unstable and so have a low activation energy which ultimately means the bonds ARE EASILY BROKEN DOWN
• When the bonds are broken the enrgy that is released is a considerable amount
• Usually in living cells it is only the terminal phosphate that is removed ACCORDING TO THE EQUATION!!!

ATP + H20 >>>>>>>  ADP  +  Pi    + ENERGY

The conversion of ATP to ADP is a reversible reaction 

• So energy can be used to add an inorganic phosphate to ADP to therefore reform ATP according to the reverse of the equation above
• As water is removed in the process,the reaction is known as the condensation reaction

The synethesis of ATP from ADP involves the addition of a phosphate molecule to the ADP.. it occurs in 3 ways:

1. Photophosphorlation- takes place in plant cells that contain chlorophyll during photosynthesis

2.Oxidative Phosphorylation which occurs in the mitochondria of plant and animal cells during the process of electron transport

3. Substrate-level phosphorlation, which occurs in plant and animal cells when phosphate groups are transferred from donor molecules to ADP to make ATP

The instability of ATP's phosphate bonds is also a good reason it is not a good long term energy store

FAT CARBS AND GLYCOGEN SERVE THIS PURPOSE FAR BETTER^^^^^

• ATP IS USED AS AN IMMEDIATE SOURCE OF ENERGY OF A CELL THEREFORE CELLS DO NOT STORE LARGE QUANTITIES OF ATP BUT RATHER JUST MAINTAIN A FEW SECONDS SUPPLY
• THIS IS NOT A PROBLEM AS ATP IS RAPIDLY REFORMED FROM ADP AND INORGANIC PHOSPHATE AND SO A LITTLE GOES A LONG WAY
• ATP IS A BETTER IMMEDIATE SOURCE THAN GLUCOSE BECAUSE
•  EACH ATP MOLECULE RELEASES LESS ENERGY THAN GLUCOSE MOLECULE
• THE ENERGY FOR REACTIONS IS THEREFORE RELEASED IN SMALLER MORE MANAGEABLE AMOUNTS

The hydrolysis of ATP to ADP is a single reaction that releases immediate energy. The breakdown of glucose is a long series of reactions and therefore the energy release takes longer:

ATP CANNOT BE STORED AND SO HAS TO BE CONTINUOUSLY MADE WITHIN THE MITOCHONDRIA OF THE CELLS THAT NEED IT

CELLS SUCH AS MUSCLE FIBRES AND THE EPITHELIUM  OF THE SMALL INTESTINE (REQUIRE LOTS OF ENERGY) POSSES MANY LARGE MITOCHONDRIA

ATP IS A SOURCE OF ENERGY FOR:

Metabolic processes, movement, activer transport, secretion, activation and molecules