2.3 Energy and ATP 2.4 Water and Inorganic Ions (WATER (Water is dipolar…
2.3 Energy and ATP 2.4 Water and Inorganic Ions
ATP (adenosine triphosphate)
The ATP molecule is a phosphorylated macromolecule with 3 parts:
- a nitogen containing organic base
- a sugar molecule with a 5 carbon ring strucutre (pentose sugar) that acts as a backbone to which the other parts are attached
- a chain of three phosphate groups
How does it store energy?
The bonds between the phosphate groups are unstable and have a low activation energy so re easily broken. When they break they release a considerable amount of energy. (only the last phosphate is removed from the molecule)
ATP + H20 = ADP + P i + Energy
As water is used, it is a hydrolysis reaction
The conversion of ATP to ADP is a reversible reaction (energy can be used to add the phosphate back to the ADP to reform ATP). The reaction is catalysed by the enzyme
and it is a condensation reaction.
ATP synthesis occurs in:
chlorophyll containing plant cells during photosynthesis (photophosphorylation)
plant and animal cells during respiration (oxidative phophorylation)
plant and animal cells when phosphate groups are transferred from donor molecules to ADP (substrate level phosphorylation)
Roles of ATP
It is NOT a good long term energy store (fats and carbs are much better)
It is an IMMEDIATE energy source in a cell.
Large quantities of ATP are not stored in cells.
ATP is rapidly reformed from ADP and inorganic phosphate constantly in the mitochondria of the cell.
ATP releases a small manageable amount of energy that do not harm the cells
It is a single simple and immediate reaction to produce energy.
ATP is used in many processes:
provides energy for building macromolecules from their basic units eg starch and polypeptides.
provides energy for muscle contraction
provides energy to change the shape of the carrier proteins and allows molecules and ions to be moved against a concentration gradient.
energy to form lysosomes for cell secretion
activation of molecules
the inorganic phosphate released in ATP hydrolysis causes other molecules to be more reactive and lowers their activation energy eg
when phosphate joins to glucose molecules
. The oxygen atom has slight negative charge and the hydrogen atoms have slight positive charge.
This means that water can form
and these forces cause the water molecules to stick together and be really strong.
Because of this, water has a
high specific heat capacity
as it takes more energy to break the hydrogen bonds and the boiling point is higher than expected
Water can therefore act as a buffer against sudden temperature changes in both environments and inside organisms.
Hydrogen bonding means that water has a high
latent heat of vaporisation
(energy taken to evaporate 1 gram) . This helps take heat out of mammals when they sweat etc
Water has high
cohesion and surface tension
because of hydrogen bonding. This is useful in the xylem of plants so water can be pulled up through a tube. Is also strong enough to support small organisms such as pond skaters.
Water makes up large percentages of living organisms because:
it is used in metabolism - hydrolysis and condensation reactions, aqueous reactions, photosynthesis
it is a good solvent - dissolves gases such as CO2 and O2, wastes such as ammonia and urea, inorganic ions, small hydrophilic molecules, and enzymes.
evaporation cools animals
it provides support as is not easily compressed
it is transparent and light can bypass water for photosynthesis.
Inorganic ions are found in solution in the cytoplasm of cells and in body fluids and as part of larger molecules.
Iron ions found in haemoglobin play a role in the transport of oxygen
Phosphate ions provide structure in DNA and store energy in ATP.
Hydrogen ions determine the pH of solutions and affect the function of enzymes.
Sodium ions are important in the transport of glucose and animo acids across plasma membranes.