BCH 261 Lecture Notes - Lecture 1: Chemical Polarity, Intermolecular Force, Semipermeable Membrane

406 views5 pages

For unlimited access to Class Notes, a Class+ subscription is required.

Biochemistry Notes:
Unit 1: water, pKa, buffering systems
Water:
By mass water makes up 60-70% of a cell
4 major factors:
i) Acts as a universal solvent
ii) Allows proteins to fold into their correct conformation (polar molecules
on the outside, non-polar on the inside)
iii) Involved directly in many biochemical reactions
iv) Proton donator or acceptor (undergoes dissociation)
The properties of water:
Water molecules are polar:
They have an uneven sharing of electrons between both hydrogens and the
oxygen molecules, whereby the oxygen (which has a strong affinity for water)
attracts the electrons more closely than the hydrogen molecules.
Hydrogen Bonding
Because the hydrogens are both partially positive they are attracted to other
oxygen molecules, which are partially negative
*Weaker than covalent bonds (>0.1x the association chemical energy)
*Non-stable interaction, very short lived (1pico-second)
*Polarity interaction: like dissolves like
Not all hydrogen bonds are equal strength, configuration of the molecule (and
the atoms involved in the molecule) play a role in the strength of the
intermolecular bond
Covalent Bond is about 300-500 Kj/mol
Hydrogen bonding is about 23 KJ/mol – usually occur in large amounts which
make it strong
Van der Waals are about 4 KJ/mol
Water is tetrahedral molecule (meaning it has 4 possible bonding domains, or
sides)
As a result of this it can hydrogen bond to 4 other molecules (as a crystalized solid)
Liquid water (at 25°C) on average makes 3.4 H-bonds per molecule
(Note it must make a full bond, you cant have 0.4 of a bond)
At 0°C water molecules form a lattice of H-bonds and is stable enough to have all 4
bonding domains hydrogen bonding (act like a stiff arm)
The ability to hydrogen bond gives it three unique abilities:
1) High boiling and melting points
Polarity & Hydrogen are among the strongest intermolecular forces
In comparison to other molecules with similar size or shape to water, water takes
more energy (higher temperature) to break the molecules apart (to go from solid
to liquid, or liquid to gas)
find more resources at oneclass.com
find more resources at oneclass.com
Unlock document

This preview shows pages 1-2 of the document.
Unlock all 5 pages and 3 million more documents.

Already have an account? Log in
This is very conducive to our way of life, with most interacting occurring in
liquid water
2) Water is a good solvent of polar solutes
Water can act as both donor and acceptor of H-bonds with polar groups in other
molecules, such as oxygen, nitrogen and fluorine (H-bonds are not exclusive
domain to water, meaning Hydrogen bonds can form between other polar
substances)
Water molecules are attracted to polar or charged molecules
Salt on ice disrupts the normal 4 hydrogen bonds to each molecule, therefore it
disrupts the lattice and melts the ice, creating water.
3) Water is a poor solvent of nonpolar solutes
Non-polar molecules also interfere with Hydrogen bonds, because non-polar
molecules are hydrophobic which are not energetically favorable.
In terms of entropy (ΔS is negative and overall ΔG is positive not favorable.)
water molecules close to a non-polar molecule make less than 3.4 on average
bonds, therefore it is more efficient to reduce the surface area by putting all non-
polar molecules together. *This is known as hydrophobic affect
*Phospholipid bilayer works on this premise, by lining up the non polar ends
together. (Micelles, which are balls of phospholipid bilayers, have all the polar
heads facing the outside)
Hydrogen bonds which drive interactions between biomolecules:
Membrane bilayer Notes these are week bonds
Protein Folding driving biological interactions
Substrate-Enzyme interactions
Protein-Protein binding
DNA double-helix
A shell of water almost always coats biological molecules: known as a hydration shell
Water also acts as the glue to fit substrate in the correct position to allow the enzyme to
be a catalyst
Osmosis: The bulk movement of water across a semi-permeable membrane from area of
high water concentration (low solute concentration) to areas of low water concentration
(high solute concentration)
Osmotic pressure: measures as the force that must be applied to return the solution in
the tube to the level of that in the beaker. (force that holds water down)
Π = i c R T
i- ionization energy
c- concentration of solute
R- gas constant
T- temperature
Isotonic: osmolarity inside and outside the cell is equal
Hypertonic: cell shrivels and shrinks due to low concentration in the cell
find more resources at oneclass.com
find more resources at oneclass.com
Unlock document

This preview shows pages 1-2 of the document.
Unlock all 5 pages and 3 million more documents.

Already have an account? Log in

Get access

Grade+
$10 USD/m
Billed $120 USD annually
Homework Help
Class Notes
Textbook Notes
40 Verified Answers
Study Guides
1 Booster Class
Class+
$8 USD/m
Billed $96 USD annually
Homework Help
Class Notes
Textbook Notes
30 Verified Answers
Study Guides
1 Booster Class