[latexpage]
Water in Biochemistry
Water is essential in biochemistry
- Nearly all biochemical reactions occur in water
- Reactants, products, nutrients, waste depend on water
- Water itself participates in chemical reactions:
- Biomolecules adjust their shape (and therefore function) in response to physical and chemcial properties of water
Hydrogen bond = attractive force between hydrogen bonded to an electronegative atom (e.g., O, N, F) and an unshared electron pair on another electronegative atom
- In general, a hydrogen bond can be represented as D-H—-A
- DH = weaky acidic donor group (e.g., OH, NH, sometimes SH)
- A = weakly basic acceptor group (e.g., O, N, or sometimes S)
- The energy of an individual hydrogen bond is only approximately
BUT the number of hydrogen bonds in a given system can accumulate so that the overall effect of hydrogen bonds is very significant
- Note: hydrogen bonds are constantly forming and breaking in solution
- Water “networks” break up and reform every
- Thus, liquid water can be seen as a rapidly chaning 3D network of hydrogen bonds
- Water “networks” break up and reform every
- Importantly, weak molecular interactions dictate the structure of biomolecules
- This includes hydrogen bonds as well as ionic/electrostatic interactions and van der Waals interactions
Water affects solubility
- Hydrophilic = polar and ionic compounds
- Water is a good solvent for these types of molecules
- Hydrophobic = compounds that are virtually insoluble in water
- Most biomolecules will have both hydrophillic and hydrophobic groups (the technical term for these molecules is amphiphilic or amphipathic)
- Example: lipid bilayer of a cell membrane
- Hydrophobic effect = the tendency of water to minimize contacts with hydrophobic molecules
Water can participate in chemical reactions
- Water only has a slight tendency to minimize, but can form
and
ions
associates with
to form
- Thus,
is never free in solution
- Proton jumping = when the
of
jumps to other molecules
- Explains why acid-base reactions occur most quicky in aqueous solutions
- Thus,
Notes:
- high surface tension ⇒ concentrated into tiny droplets
- low surface tenson ⇒ spreads out
Sources
- Biochemistry class notes (1/9/15)\
- Water structure and science – electrolysis of water