3582278557

Masaryk University

Biochemistry II

Exam Question$

Rebanil Ahmed & Khuram Ahmed

44 Retinol and its derivative.s - the hiological role, biochemistry of yjsual cxcitation (activation of transducin, conseguences in decrease of cGMP with hyperpolarization and in decreased Ca'¹ stimulating mianylate cyclase).

Retinol (Vitamin A)

Primary alcohol containing Bionone ring and unsaturated side Chain. Found in animal tissues as a retinyl ester with a long Chain fatty acid.

Retinal - component of phodopsin of rod cells in the retina

Aldehyde from retinol oxidation, both can be interconverted.

Retinoic Acid - takes part in celi regulation of gene expression

Is an acid from the oxidation of retinal. It can't be reduced in the body to give retinol or retinal.

B-carotene: is from plant food, can be oxidatively deaved to give two molecules of retinal.

Retinoids are essential for vision, reproduction, growth and maintinance of epithelial tissues. Retinoic acid mediates most of the actions of the retinoids except vision, which is mediated by retinal.

Sources of vitamin A: CARROTS, liver, kidney, egg yolk and butter.

I Rhodopsin is found in rods (photoreceptors). It is a light sensetive chromoprotein. Opsin part contains retinal. Absorption of a photon triggers isomerisation of retinal. This leads to allosteric conformational change of rhodopsin, which binds to G-protein-TRANSDUCIN. A signal Cascade follows and rods release less neurotransmitter (glutamate). Bipolar neurons register this change and transmit it to the brain for light.

In the dark, rod cells have a high concentration of cGMP (synthesized by guanylate cydase), which binds to an ion channel to open it and allow Na’ and Ca" to enter, causing depolarization and release of glutamate neurotransmitter.

General Medicine

4th semester

2009

1

Decrease of cAMP => Na’ channels closes