Top2-Ch2-P46-54 Flashcards
What are three biologically important gases that are non-polar and therefore not soluble in water.
CO2, O2, N2
Amphipathic molecules have
mixed polar and non polar character
Non-polar solvents are poor/good solvents for polar molecules, but easily dissolve/don’t dissolve non-polar molecules.
Name two non-polar solvents
poor
dissolve
chloroform and benzene,
Water as ionic solvent.
The attractive/ repulsive forces between charged compounds is partially neutralised by _____
hydration (A process in which water molecules are attracted to and form weak bonds with the soluble species.)
This occurs when hydrophilic compounds dissolve in water.
Formation of hydration spheres stabilise ions or dipoles
Name the four types of noncovalent (weak) interactions among biomolecules in aqueous solvent.
- H-bonds
- Ionic interactions
- Hydrophobic interactions
- Van der Waals interactions
Are noncovalent interactions weaker or stronger than covalent bonds?
weaker
Noncovalent (‘Weak’) interactions are continually forming and breaking, as strength of solute-solvent (water) is nearly as favorable as solute-solute.
The cumulative effect can be very significant. Give two examples.
- 3D shape of proteins are influenced by these interactions
- Binding of hormone to cellular receptor protein is the result of multiple weak interactions
Hydrophobic interactions are?
Explain a bit.
Forces that hold nonpolar regions together
Minimising ordered water molecules surrounding compound (water cage) to achieve greater thermostability (higher entropy)
Consider the behaviour of amphipathic molecules in water
See diagram below where: The hydrophobic portions of amphipathic molecules (a fatty acid here) interrupt the H-bonded molecular structure of water.
The decreased entropy (stable ordering of water at the margin) is energetically unfavourable
Watercages picture.
In order to achieve greater thermodynamic stability, and minimise the amount of hydrophobic area exposed to the polar solvent non-polar, hydrophobic regions of amphipathic compounds (e.g. fatty acids or membrane lipids) tend to
group together in water
Clusters of lipids condense into _____?
These, _____ are energetically more favourable because no ordered “water cages”. Explain how these clusters are shaped.
micelles
micelles
Micelles are shaped with the non-polar regions tending to group together leaving the polar regions on the outside
Thermodynamic stability is
a state in which a chemical system is neither consuming or releasing heat energy.
- In H-bonding between polar molecules the binding of polar molecules reduces _____.
- Non covalent interactions must provide a good _____ . give an example of this bonding.
- hydration
- “fit”, example is e.g. binding substrates to enzymes displaces water
- Ionic/electrostatic interactions are?
- The attraction decreases with
- Very simply, the attraction of opposite charges for each other.
- the cube of the radius (volume), so that distance is important in bond strength (must be a good ‘fit’)
Van der Waals interactions are also called ?
Describe these forces?
London forces
Description:
- Weak transient dipole attractions
- surrounding electron clouds influence each other
- Counter-balanced by repulsive forces of 2 electron clouds, to give final van der Waals radius
- These are extremely close proximity between atoms.
- i.e. require exact fit of surfaces
Do all the noncovalent bonds in water involve electrical charges. yes or no?
Yes
Which are the weakest of all non-covalent forces?
Van der Waals interactions
Not all water molecules are in the form ___. A small degree of ionisation occurs in water so there are some ___ and ___ as well. This is called the _____ of water.
H2O
H3O+ and OH−
ionisation
- What numbers of water molecules are ionised?
- These ions are in _____ with the water molecules
- About 1 in one ten million
- equilibrium
H+ free protons do not exist in solution even though we usually show it. Instead what type of ions exist?
Hydronium ions H3O+
Ionisation of water is measured by its?
electrical conductivity.
Pure water carries electrical current as ____ migrates toward the cathode and _____ toward the anode.
H3O+, OH-
