ATP and Water

• What is the structure of ATP?

  ATP is a phosphorylated macromolecule.

  It contains:

  .adenine - a nitrogen-containing base

  .ribose - a pentose sugar

  .phosphates - a chain of 3 phosphate groups
• How is energy stored in ATP?

  The bonds between phosphates are unstable so have a low activation energy, so are easily broken. When broken they release energy.

  Equation showing this:

  ATP+H2O→ADP+Pi+ free energy

  Pi = terminal phosphate.

  This is a hydrolysis reaction and it is catalysed by ATP hydrolase (ATPase).
• Draw a diagram of ATP. 


  As shown below.

  
• How is ATP synthesised?

  The conversion of ATP to ADP is reversible, in reverse it is a condensation reaction catalysed by ATP synthase.
• When are the 3 times ATP synthesis happens?

  1.in chlorophyll containing plant cells during photosynthesis

  2. in plant and animal cells during respiration

  3. in plant and animal cells when phosphate groups are transferred from donor molecules to ADP.
• Why is ATP not a good long term energy store?

  ATP is a better immediate energy source due to unstable phosphate bonds. Cells only maintain a few seconds supply of ATP, not a large supply. This is because ATP is rapidly reformed. ATP cannot be stored so it is continuously made in mitochondria that need it. e.g. muscle fibres
• Why is ATP a better immediate source than glucose?

  ATP releases less energy then glucose which is more manageable for chemical reactions. Hydrolysis of ATP to ADP is a single reaction, however the breakdown of glucose involves many reactions and takes longer.
• Explain the use of ATP in metabolic processes, movement and active transport.

  metabolic processes - ATP provides energy needed to build up macromolecules from basic units e.g. glucose to starch

  movement - energy for muscle contraction, energy for filaments of muscle to slide over one another, shortening the length of muscle fibre.

  active transport - energy to change shape of carrier proteins in plasma membranes, allows molecules or ions to be moved against concentration gradient.
• Explain the use of ATP in secretion and phosphorylation.

  Secretion - ATP needed to form lysosomes necessary for secretion of cell products.

  Phosphorylation - the addition of an inorganic phosphate to a molecule making them more reactive by lowering activation energy, the bond is unstable e.g. glucose + Pi at start of glycolysis.

  It is vital for cellular storage and transfer of free energy using energy carrier molecules.
• What is the structure of water?

  Water is a polar molecule - the shared H electrons pair with oxygen leaving the other ends of H atoms slightly positive. The unpaired electrons of the oxygen have a slight negative charge. Water is dipolar. Therefore it can form hydrogen bonds with other water molecules which are weak bonds but form important forces.
• How is high specific heat capacity a beneficial property of water?

  Hydrogen bonds need energy to break so boiling point is higher then would be expected, without hydrogen bonding water would be gas at earth's temperature's. Life as we know it would not exist. It acts as a buffer to sudden temperature changes, humans are 60-70% water so buffers sudden temperature changes in environment. Water is a stable temperature environment for aquatic life.
• How is high latent heat of vaporisation a beneficial property of water?

  Hydrogen bonding between water molecules means it requires lots of energy to evaporate 1g of water. In mammals, this means evaporation of water is a very effective means of cooling as heat is used to evaporate water (sweating).
• How is cohesion and surface tension a property of water?

  Cohesion - tendency of molecules to stick together, due to hydrogen bonding water has large cohesive forces, allows it to be pulled through a tube e.g. xylem vessels

  Surface tension - where water molecules meet air they are pulled back into the body of water and don't escape from it. The surface of the water acts like a skin and strong enough to support small organisms.
• How is water a metabolite?

  Water is used in hydrolysis and condensation reactions, chemical reactions take place in an aqueous medium. Water is a major raw material in photosynthesis.
• What are other important features of water?

  It is not easily compressed, provides support e.g. for hydrostatic animals such as earthworm. It is transparent and aquatic plants can photosynthesise and also light rays can penetrate the jelly-like fluid that fills the eye so reach the retina.
• What is an inorganic ion?

  Inorganic ion - an ion that does not contain carbon, found in cytoplasm of cells are in bodily fluids as well as part of larger molecules.
• What are some examples of inorganic ions?

  Iron ions - found in haemoglobin where they aid in transport of oxygen. Fe2+ when bound to oxygen and Fe3+ when not.

  Phosphate ions - form a structural role in DNA and storing energy in ATP molecules, exists as PO4$^{3-}$.

  Hydrogen ions - determine pH of solutions there fore functioning of enzymes.

  Sodium ions - transport of glucose and amino acids across the plasma membrane.