Detecting and Amplifying Flashcards
What do organisms use light energy for?
Generating ATP
Detect changes in their enviroment
What prosthetic group is present in bacteriorhodopsin?
Retinal
Where does retinal absorb energy from in archae?
Photons
What is the energy absorbed from photons by retinal in archae used to do?
Pump protons through the bacteriarhodopsin
What does pumping protons through the bacteriarhodospin generate
Proton gradient
What diffuses back across the membrane after retinal pump protons through bacteriarhodopson?
Hydrogen Ions
Where do the hydrogen ions diffuse back through?
ATP Synthase
What do plants do with the energy absorbed from photons?
Absorbed by photosynthetic pigments
Drives a flow of electrons along the electron transport chain
Electron flow pumps protons across the thylakoid membrane
Protons diffuse back through ATP Synthase to generate ATP
What is retinal?
Prosthetic group covalently bonded to polypeptide called opsin
What are the two classes of photoreceptor cells found in the retina of vertebrates?
Cone and Rod cells
What do cone cells contain?
Photopsins
Which class of photoreceptor cells is responsible for colour vision?
Cone cells
Why are cone cells less sensitive than rod cells?
They have about 1000x less photoreceptor molecules
How many types of photopsins are found in human cells?
3
What are the colours each type of photopsin have maximal sensitivity to?
Red, blue and green
How are different photopsins formed?
Combining retinal with different forms of opsins
What do Rod cells produce when no light has been absorbed?
Cylic GMP
Where does cGMP bind to?
Ligand gated Na+ channels
What happens when a photon of light is absorbed by a retinal molecule?
Conformational change in rhodopsin
Activates hundreds of G proteins which activates hundred of enzymes
What do the enzymes do when activated by G proteins?
Catalyse breakdown of cGMP
What does the breakdown of cGMP cause?
Na channels close
Membrane will become hyperpolarized
Nerve impulse is generated
What provides a high degree of amplification?
Protein cascade
What are the steps in the protein cascade?
Rhodopsin
G proteins
Enzymes
Channels
What is a photoreceptor?
Name given to proteins which are capable of sensing and responding to light
