Vertebrate eye (C&S) Flashcards

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1
Q

Step 1

A

Retinal absorbs a photon of light and rhodopsin changes conformation to photoexcited rhodopsin

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1
Q

Step 2

A

A cascade of proteins amplifies the signal

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2
Q

Step 3

A

Photoexcited rhodopsin activates a Gprotein, called transducin, which activates the enzyme phosphodiesterase (PDE)

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3
Q

A single photoexcited rhodopsin activates

A

hundreds of molecules of G-protein

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4
Q

Each
activated G-protein activates

A

one molecule of PDE

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5
Q

Step 4

A

PDE catalyses the hydrolysis of a molecule
called cyclic GMP (cGMP)

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6
Q

Each active PDE molecule breaks down

A

thousands of cGMP molecules per second.

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7
Q

Step 5

A

This results in the closure of ion channels in the membrane of the rod cells, which triggers nerve impulses in neurons in the retina

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8
Q

What does a very high degree of amplification result in?

A

rod cells being able to respond to low
intensities of light

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