2.1 energy and ATP

What is energy?

Energy is defined as the ability to do work.  

- It takes a variety of forms 

- it can be changed from one form to another

- it cannot be created or destroyed

- it is measured in Joules. 

Energy is needed for:

- metabolism  - all the reactions that take place in living organisms involve energy

- movement - both within an organis and of the organism itself. 

- active transport - of ions and moleucles against a concentration gradient across plasma membranes.

- maintenance, repair and division -of cells and of organelles within the cells.

- production of substances - used within organisms, e.g. enzymes and hormones.

- maintenance of body temperature - in birds and mammals. these organisms are endothermic and need energy to replace that lost as heat to the environment.  

The flow of energy through living systems 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. 

3) ATP is used by cells to perform usefull work. 

The bonds between these phosphate groups are unstable and so have a low acivation energy, which means they are easily broke. when hey do break they release a considerable amount of energy. Usually in living cells it is only the terminal phosphate that is removed. 

Equation:

ATP + Water ---> ADP + P + energy

adenosine triphosphate + water ---> Adenosine diphostate + inorganic phosphate + energy. 

Convertion of ATP to ADP is a reversible reaction and therefore energy can be used to add an inorganic phosphate to ADP to reform ATP. As water is removed in this reaction, it is called a condensation reation.  

The synthesis of ATP to ADP involves the addition of a phosphate to ADP. 
It can happen in 3 ways:

- Photophosphorylation - which takes place in chlorophyll-containing plant cells during photosynthesis

- Oxidative phosphorylation - which occurs in the mitchondia of plant and animal cells during the process of electron transport. 

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

ATP is a better immediate energy source than glucose for the following reasons:

- Each ATP molecule releases less energy than each glucose molecule.  
The energy for reactions is released in smaller, more manageable quantities rather than much greater and less manageable, release of energy from a glucose molecule.

- 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 is a source of energy for:

Metabolic processes 
Movement - ATP provides energy for muscle filaments to slide past one another.
Active Transport - ATP provides energy to change shape of the carrier proteins in plasma membranes.  
Secretion - ATP needed to form lysosomes
Activation of Molecules