ATP, water and inorganic ions

Structure of ATP

• Nucleotide derivative

• Adenine, bonded to ribose, bonded to three phosphate groups

Enzyme that catalyses hydrolysis of ATP to ADP + Pi

ATP hydrolase

How is ATP formed

The enzyme ATP synthase catalyses the synthesis of ATP from ADP and Pi during photosynthesis and respiration

Purpose of hydrolysis of ATP

Provides energy to energy-requiring cellular reactions - ATP is an immediate energy source, or phosphorylates compounds, making them more reactive and therefore lowering the activation energy needed for a reaction to take place

Why is ATP useful

• It is an immediate energy source - energy is released from one hydrolysis reaction

• The bonds between phosphate groups are unstable and therefore have a low activation energy required to break them, and they release a considerable amount of energy when broken

Apart from being an immediate source of energy, why is ATP better than glucose as an energy source

The energy released from the hydrolysis of ATP is smaller than the energy released from a molecule of glucose, and therefore is more manageable and easily controlled

5 properties of water and explanations

• Metabolite - used to hydrolyse compounds, reactions all take place in an aqueous medium (water is also released in condensation). Reactant in photosynthesis, and product of aerobic respiration.

• Universal solvent - dissolves substances such as gases (oxygen and carbon dioxide), waste products (urea), small hydrophilic molecules (amino acids, monosaccharides, ATP), enzymes

• High specific heat capacity - because there are hydrogen bonds between the molecules of water - buffers changes in temperature (in organisms as well as they are mostly water)

• Large latent heat of vaporisation - large amount of energy required to evaporate water - this is useful for cooling the body using sweat

• Strong cohesion between molecules - the transpiration stream in the xylem, and surface tension. Adhesion is sticking to other surfaces

Role of hydrogen ions

They determine the pH - the higher the concentration of hydrogen ions, the more acidic the substance is. This affects the functioning of enzymes, as pH values outside the optimum pH can denature enzymes, by distrusting the tertiary structure of the protein, by breaking hydrogen and ionic bonds.

Role of iron ions

Used to form haemoglobin (a conjugated protein because it has prosthetic groups)

Role of sodium ions

Co-transport of glucose and amino acids

Role of phosphate ions

Components of DNA and ATP