Lecture 7 Flashcards
Human Eye: Retina
It contains photoreceptor cells which convert photons into electrical information
photoreceptors
pigments in photoreceptor cells absorb light
Rod photoreceptor cells handle light intensity detection
cone photoreceptor cells handle colourvision
Opsins
Opsins are light-sensitive protein in the photoreceptor cells. Retinal is one such protein
photoisomerization
When light is absorbed by retinal it transforms into an activated version of itself.
● This is called photoisomerization, as light (“photo”) triggers a change in
molecular configuration (“isomerization”)
Phototransduction
Phototransduction is the
process by which light
detected by photoreceptor
cells is converted to
electrical impulses before
these impulses are then
sent to the brain.
GTP and GDP are used in this process. They function similarly to ATP and ADP
Lennard-Jones Potential
The Lennard-Jones potential describes the potential energy of interaction between two nonbonding atoms or molecules based on their distance of separation
Disulfide bonding
A disulfide bond, or disulfide bridge, is a covalent bond derived from the oxidation of two thiol (S-H) groups
Intramolecular disulfide bonds stabilize the tertiary structure
Intermolecular disulfide bonds stabilize the quaternary structure
Capillary Action
Capillary action occurs due to forces of cohesion and adhesion
Capillary action only occuyrs when adhesive forces are stronger than cohesive forces
This occurs in tubes of small diameter, against gravity
Surface tension
Surface tension is the result of cohesive forces between liquid molecules at an interface
It leads ot a surface film, it is more difficult to break an object thought thus film than to move that object in the liquid once it is beneath the surface
Surfactants
Surfactants are compunds which lower surface tension by disrupting intermolecular forces at the interface
Self Assembly
Forces that drive self-assembly:
○ Electrostatic intramolecular and intermolecular interactions, though mostly
hydrogen bonding
○ External forces such as electric, magnetic, flow, osmotic and gravitational forces
○ Interface forces, both electrostatic and entropic
Thermodynamics of self-assembly
Spontaneous process, Gibbs free energy must be less than zero, there must be a net gain in entropy
Hydrophobic effect
Hydrophobicity a result of entropy and is often a major contributor to biological self assembly
The nonpolar groups aggregate; the
hydrogen bonds are reoriented to
minimize disruption
● This orientational change causes an
increase in entropy due to the
restricted mobility which is favoured
Q2: What systems utilize the
hydrophobic effect (natural and
artificial)?
A few examples are as follows:
● Amphiphiles
○ Molecules that contain both hydrophobic and hydrophilic sections
○ Detergents, cellular membrane, etc.
● Protein folding
○ Hydrophobic regions fold inward
● Protein purification
○ Proteins can be separated based on their hydrophobicity
