BIochem Lecture 7 - Vision, Hearing, Touch

Vision

this sense is based on the absorption of light by photoreceptors

Visible Light

this spectrum of the electromagnetic spectrum is from 380nm-700nm

Rods

these type of photoreceptors perceive light, not color, there are 100 million of these in the retina, and fewer than 10 of them need to fire to perceive light

Cones

these types of photoreceptors perceive color vision, there are 3 million of these in the retina, and function in bright light

11-cis retinal

this ligand is synthesized with beta carotene and vitamin A, binds to opsin (GPCR) to make rhodopsin

proteins (GPCRs)

retinal is attached to ______

Opsin

this is a GPCR that binds with 11-cis retinal and when activated by light, sets off the GPCR pathway. When it binds with 11-cis retinal, it becomes rhodopsin

Rhodopsin

this is a receptor-ligand complex that is comprised of 11-cis retinal and opsin, but in this form with these two it is inactivated. It is activated when light comes in

All-trans-retinal

when light activates rhodopsin, it causes a confirmational change to turn the 11-cis retinal into this, which sets off the GPCR pathway to perceive light

Confirmational change

when light changes rhodopsin into metarhodopsin II (same as changing 11-cis-retinal into all trans retinal), it undergoes this (general term)

all-trans-retinal, transducin, GDP, GTP, alpha, GTP, phosphodiasterase, cGMP, GMP, closes, Na+, Ca2+, hyperpolarizes

When light shines onto rhodopsin, it turns 11-cis-retinal into _____-_________-__________, which puts the GPCR pathway in place, the G protein known as __________________ is activated by exchanging _______ for ______, which separates the __________ subunit from the G protein. This part of the G protein attached to ______ activates the enzyme ________________________, which converts _______ to _______, which ________ the ion channel that transports the ions ____ and ____, which __________________ the membrane and stimulates the visual signal

transducin

this is the G protein that is activated by metarhodopsin II in the vision GPCR pathway

cGMP

this molecule is converted into GMP by phosphodiasterase and opens the Na+ Ca2+ ion channel in rods, and depolarizes the membrane keeping the rods inactivated

GMP

this is what phosphodiasterase turns cGMP into when it is activated by the alpha subunit/GTP complex of transducin in the vision GPCR pathway

phosphodiasterase

this enzyme is inhibited before the alpha subunit of transducin+GTP come and remove the inhbitor to activate it, and it then converts cGMP into GMP

Depolarized

when the vision pathway is not stimulated (not activated), the membrane of the rods are _______________(depolarized/hyperpolarized)

Hyperpolarized

when the vision pathway is stimulated by light (activated), the membrane of the rods are _______________(depolarized/hyperpolarized)

Removing its inhibitor

the alpha subunit+GTP complex activates phosphodiasterase in the vision GPCR pathway by _____________ ____ _______________

Ca2+, guanylyl cyclase, cGMP, depolarizes

to deactivate the vision pathway of rods, the low amount of _____(what ion?) activates the enzyme ___________ ___________ to make the molecule _______ which opens the ion channel, which ________________ the membrane

inhibitor, transducin, phosphorylated, rhodopsin kinase, Arrestin, 11-cis-retinal

to deactivate the vision pathway, after the membrane has been depolarized once again, phosphodiasterase is binded back to its ___________, which deactivates it, which causes the subunit of the G Protein ___________ to reattach to the other subunits, deactivating it, then the activated Rhodopsin is _________________ by the enzyme _____________ ___________, which allows the protein ___________ to bind to the phosphorylation sites and deactivates rhodopsin, finally the all-trans-retinal is replaced by a new ___-_____-__________, resetting the whole cycle

Rhodopsin kinase

this enzyme phosphorylates the activated rhodopsin, which helps the protein arrestin to deactivate it

Arrestin

this protein binds to the phosphorylated rhodopsin in order to deactivate it

same

in the vision pathway for cones, it is the _________(same/different) than the vision pathway for rods

protein

in order to tell what different colors are, each cone has a different one of these on the receptor in order to lead to distinct absorption maxima

Red and Green

which two color photoreceptors are 95% identical to each other?

Recombination

the reason why red green colorblindness is so common is because the nucleotide sequence is so similar for both of the receptors, and there can be problems during this process, causing only one of the types of receptors to be expressed in a human

Ion channels

because hearing and touch must be super fast signaling in the pathways, they utilize these types of signaling pathways

Faster

the signaling for hearing is _____________(faster/slower) than the signaling for vision

Stereocilia

these are small, hairlike cells that are found on the specialized neurons in the cochlea that help transduce the signals

Mechanically Gated ion channels

when the hair cells of the cochlear neurons are moved due to a sound, the membrane is depolarized because the motion opens these types of ion channels

tip link

an elastic filament that attaches the tip of one cilium to the side of the adjacent cilium, that when moved open the mechanically gated ion channels to send a signal for hearing

Touch

the cellular mechanisms of this sense are not well understood quite yet, and detects things on the skin like pressure, vibrations, temperature, and pain

Piezo2

this receptor protein is mechanosensitive, and is an ion channel, and is very very important for the sensation of touch, however we don't know exactly how it works

Enormous

in terms of size, Piezo2 is _____________