Signal transduction 3: Sensory perception Flashcards
What are the types of receptors for the 5 senses
Vision, Taste and Smell by GPCRS
Hearing and Touch by ion channels
What are the target tissues for vision reception
Cone cells (homologs of rhodopsin) that process colour: 3 types specific for wavelengths of red, green and blue.
+
Rod cells that respond to low levels of light, not in colour but provide contrast
What is the reception pathway for Vision
Vision is based on the absorption of light by
Rod is for low levels of light and have no colour
Cones encode colour. There are 3 types specific to wavelength
Describe the signal transduction pathway of the rhodopsin receptor and its relationship to vision.
signal, target tissue, receptor, G protein type, effector enzyme , second messenger and response
- When photons hit chromophore, 11-cis-retinal goes through a 5-a turn to become all-trans-retinal.
- This conformational change of the prosthetic group causes a shape change in Opsin because they are linked.
- G protein G transducin binds to Rhodopsin, and G alpha unit goes to primary affector : Phosphodiesterase.
- Phosphodiesterase converts CGMP originally bound to CGMP gated ion (Na+ or Ca2+)
- By getting rid of CGMP, it shuts down the ion channel. Less influx of Na+ and Ca2+
- Cell becomes hyperpolarised (more negative) as photoreceptor cells have a more positive resting potential than normal) which triggers AP= flash of light
Describe the structure of Rhodopsin
Rhodopsin which is made of 7 transmembrane protein that determines the wavelength of light absorption: opsin.
+ Prosthetic group which absorbs light (chromophore) =11-cis-retinal.
What is Retinosa Pigmentosa and what part of the signalling pathway is affected
Retinosa pigmentosa: inherited disease where rod cells start degenerating, resulting in a tunnel vision: loss of peripheral.
This is the loss of reception.
What is Colour blindness and what part of the signalling pathway is affected
Colour blindess: when functional green and red opsin not made because of either
a) recombination in between X and Y genes where X given to male is the one missing the gene
b) recombination within genes where greenlike + redlike hybrid are made
This also dysfunction in reception
What is taste perception
nutritious vs poisonous
Commercial value
Health intervention. The compliance from patients increases with good tasting medicines
What are the subunits of sweet, umami and bitter taste GPCR receptors
Sweet+ Umami are T1 family with T1R1, T1R2, T1R3
Bitter is T2 family with T2R2-> T2R65
What are the signals for sweet, umami and bitter taste and How is signal for taste received
Sweet: Sugar + sweeteners
Umami: Amino acids
Bitterness: Quinine + others.
The ligand is received by taste pore surrounded by taste in the papillae of the tongue which contain tastebuds
What signal triggers Salty + sour
Ion channels
Sour : H+
Salty: Na+
What is structure of the GPCR of sweet and Umami vs GPCR of Bitter. Similarities and Differences
Similarities: 7 transmembrane protein with extracellular N terminus.
- couples to and activates G protein
T1: It has Venus fly trap motif. Heterodimer required to be functional.
T2: Monomer
What is the signal transduction pathway of the taste receptors and its relationship to taste perception.
- Signal binds to GPCR and leads to activation of G protein: Gustducin
- a-subunit of Gustducin activates Phospholipase C (1’ effector) which cleaves PLCB2 into DAG and IP3
- IP3 will release Ca2+ into cytosol
- Ca2+ causes increase voltage gated Na+ ion channel to open
- Na+ influx depolarises the cell and starts AP through afferent neurons to the brain.
What are taste disorders Phantom taste sensation, Hypogeusia and Dysgeusia
Phantom taste sensation: ligand isn’t there
Hypogeusia : ageusai : less taste/no taste
Dysgeusia: not getting the right taste
What is activated form of Rhodopsin
Metarhodopsin 2
