Key Area 4: Photoreceptor Systems Flashcards
What type of organisms have photoreceptors?
All three domains of life
What happens with photoreceptors in archea?
Bacteriorhodopsin generates potential differences by absorbing light to pump protons across the membrane
What absorbs light in plant cells?
Chlorophyll
How do photoreceptors work in plant cells?
Light absorption gives energy to the proteins that pump hydrogen across the membrane as the light absorption causes an increase in the number of hydrogen in the chloroplast that can flow across the membrane through ATPsnthase and generate ATP. The increase in hydrogen ions increases the concentration gradient which drives the ATP synthase
What membrane protein is important for detecting light in animal photoreceptor systems?
Rhodopsin
What two molecules combine to form the rhodopsin?
Opsin and retinal
What two cell types does the retinal contain?
Cone cells and rod cells
Which molecule causes detection of different wavelengths of light (different colours)?
Different forms of opsin
What is the purpose of cone cells?
Give sensitivity to specific wavelengths of light
What is the purpose of rod cells?
Absorb a wider wavelength and amplify the signal more so are more sensitive in low light levels/intensities
Which type of cell amplifies signals more?
Rod cells
How is a signal amplified once received?
A protein cascade
How is a nerve impulse generated in photoreceptors?
- one photon is light stimulates rhodopsin
- active rhodopsin activates hundreds of G-protein molecules (transducin)
- transducin activates enzyme (phosphodiesterase)
- phosphodiesterase stimulates conversion of cyclic GMP into GMP which closes Na+ channels
- less Na+ means rod cells is hyperpolarised
- hyperpolarisation of rhodopsin molecule causes depolarisation in outside causing nerve impulse to be generated
