1.4 DETECTING AND AMPLIFYING AN ENVIRONMENTAL STIMULUS Flashcards
Where are photoreceptor protein systems present?
Across the three domains
What are the three domains?
Bacteria, Archaea, Eukaryota
In which domain are plants, animals and fungi found?
Eukaryota
How can light energy be used to generate ATP?
It can be used to generate a proton gradient to drive ATP synthase
What molecule absorbs light energy in archaea?
Bacteriorhodopsin
How does bacteriorhodopsin absorb light energy?
Its prosthetic group, retinal, absorbs energy from photons
How does the light energy absorbed by bacteriorhodopsin generate a proton gradient?
The energy is used to pump protons through the bacteriorhodopsin so that a proton gradient is created across the membrane
What molecule absorbs light energy in plants?
Photosynthetic pigments within the chloroplast absorb energy from photons
How does the light energy absorbed in the chloroplast generate a proton gradient?
It drives an electron flow that pumps hydrogen ions across the thylakoid membrane of the chloroplast
What is the thylakoid membrane?
A compartment inside a chloroplast
How does the proton gradient generate ATP?
It results in the diffusion of hydrogen ions back across the membrane, driving ATP synthase
What is retinal?
A light-sensitive molecule
What is retinal combined with (in animals)?
It is combined with membrane protein opsin
What amplifies light signals (in animals)?
A cascade of proteins
What are the two types of cell found in the retina?
Rod cells and cone cells
What is the term given to the retinal-opsin complex in rod cells?
Rhodopsin
What happens when rhodopsin is stimulated by a photon?
Hundreds of G protein molecules are activated
What is the result of the G proteins being activated rhodopsin?
Many enzyme molecules are activated
What is the result of the enzymes being activated by the G proteins?
If the enzymes produce sufficient product then a nerve impulse may be generated
What is the benefit of rhodopsin to rod cells?
They can absorb a wide range of wavelengths
What is the benefit of rod cells absorbing a wide range of wavelengths?
They are highly sensitive even in low light
How is the retinal-opsin complex in cone cells different to rhodopsin?
Different forms of opsin combine with retinal
What is the collective term given to the various different retinal-opsin complexes?
Photopsins
How does the function of photopsins differ to rhodopsin?
Photopsins are sensitive to different colours
How are photopsins sensitive to colour?
Each has maximal sensitivity to a specific wavelength
Which colours are photopsins in humans sensitive to?
Red, green and blue
