2) Photoreceptor Protein Systems

Question 1

Where are the Photoreceptor systems found

Answer 1

Across the 3 domains of life:

• archaea
• eukaryotes (animals and plants)

Question 2

What is a Photoreceptor protein

Answer 2

Light sensitive protein, which is capable of sensing and responding to light

Question 3

What is the Photoreceptor used by archaea and how does it bring about the production of ATP

Answer 3

bacteriorhodopsin:

• generate potential differences by absorbing light to pump protons across the membrane
• the protons return through the enzyme ATP synthase, generating ATP
• Therefore this allows archaea to convert light energy to chemical energy

Question 4

what drives ATP synthase to work

Answer 4

the resting potential of hydrogen ions across the membrane

Question 5

how do plants convert light energy to chemical energy

Answer 5

by using a photosynthetic pigment called chlorophyll

Question 6

describe the process that plants use to convert light energy to chemical energy

Answer 6

• the light absorbed by photosynthetic pigments within protein systems drives an electron flow that pumps hydrogen ions across the thylakoid membrane of the chloroplast.
• The resulting diffusion of hydrogen ions back across the membrane drives ATP synthase

Question 7

what is the thylakoid

Answer 7

the membrane surrounding the grana

Question 8

name the two types of photoreceptor cells in animals

Answer 8

rods and cones

Question 9

what is the function of rods and cones

Answer 9

• rods - light sensitive and allows vision in low light intensities
• cones - wavelength (colour) sensitive, and allow colour vision

Question 10

rhodopsin - how is it made?

Answer 10

binding of:

retinal (light absorbing molecule)
opsin (membrane protein)

Question 11

what is rhodopsin

Answer 11

a visual pigment

Question 12

how is rhodopsin used in rods

Answer 12

• rhodopsin absorbs a wide range of wavelengths, and can amplify light from a single photon.
• results in vision in low light intensities

Question 13

how is rhodopsin used in cones

Answer 13

different forms of opsin combine with retinal to give photoreceptor proteins, each with maximal sensitivity to specific wavelengths (red, green, blue or UV).

Question 14

describe the nerve transmission process of rhodopsin

Answer 14

1) A photon of light excites rhodopsin.
2) Excited rhodopsin activates G-proteins.
3) G-proteins activate enzyme molecules.
4) The enzyme removes the ligand from Na+ channels.
5) The Na+ channels close so the membrane potential increases; this hyperpolarisation stimulates a nerve impulse.