Unit 1: Cells and Proteins 4 Flashcards
Detecting and Amplifying an Environmental Stimulus: Photoreceptor Protein Systems
Photoreceptor systems are found in:
Archaea, Prokaryota and Eukaryota
Archaea are what?
Single celled organisms with no defined nucleus
Different groups of archaea can do
different things
The haloarchae can do what?
Photosynthesise
Haloarchae relies on ___________ for activation of ATP synthase
bacterial rhodopsin
Bacterial rhodopsin consists of:
a retinal and a chromophore within a bacterial opsin
The retinal-opsin complex is known as?
Rhodopsin
Bacterial Rhodopsin Process: Stage 1, sunlight strikes a bacterial rhodopsin molecule causing the retinal to undergo?
Photoisomerisation
Bacterial Rhodopsin Process: Stage 2, Photoisomerisation of the retinal causes a?
conformational change in the opsin
Bacterial Rhodopsin Process: Stage 3, The retinal’s conformational change causes activation of which molecule?
Rhodopsin molecule
Bacterial Rhodopsin Process: Stage 4, The activated rhodopsin molecule begins to?
Pump protons out of the cell
Bacterial Rhodopsin Process: Stage 5, What force causes the protons to flow back into the cell?
The electrochemical gradient
Bacterial Rhodopsin Process: Stage 6, The protons flowing back into the cell due to the electrochemical gradient begin driving what?
ATP Synthase
Bacterial Rhodopsin Process: Stage 7, ATP synthase begins to …
Synthesise Pi with ADP
Bacterial Rhodopsin Process: Stage 8, Therefore what molecule is being generated by this whole process?
ATP
In animals, retinal is combined with a
membrane protein opsin
Retinal is a form of
Vitamin A
When stimulated by light, the retinal undergoes
photoisomerisation
During photoisomerisation the retinal goes from 11-cis-retinal into
all-trans-retinal
What is the process caused by photoisomerisation that results in retinal going from 11-cis-retinal to all-trans-retinal called?
Bleaching
What happens in the process of Bleaching?
11-cis-retinal goes to all-trans-retinal
Bleaching of a retinal induces a ________ change
conformational
Bleaching stimulates a conformational change which activates the g-protein called?
Transducin
Where is the g-protein transducin located?
On the inside of the membrane
Light Transduction: Stage 1, When stimulated by a photon, a rhodopsin molecule activates hundreds of
transducin molecules
A rhodopsin is what type of cell?
Rod cell
A photopsin is what type of cell?
Cone cell
Light Transduction: Stage 2, Transducer activates what enzyme located on the intracellular side of the membrane?
Phosphodiesterase
Light Transduction: Stage 3, The activation of phosphodiesterase leads to the breakdown of a 1000 of what molecule per second?
cGMP
Light Transduction: Stage 4, The breakdown of cGMP causes what to become very sensitive?
rhodopsin-based systems
Light Transduction: Stage 5, The decrease in cGMP levels causes what to close?
Ligand-gated Na+ channels
Light Transduction: Stage 6, The close of the ion channels prevents the release of ?
inhibitory neurotransmitters
Light Transduction: Stage 7, The prevention of the release of inhibitory neurotransmitters allows the sensory synapse to become stimulated and do what?
Transmit a nerve impulse to the visual centres of the brain
In vertebrates retina rod cells and cone cells both contain ?
opsins which contain retinal
Many rods are connected to a single
neuron
Being connected to a single neutron maximises a rode cells sensitivity to
light
Do rod cells detect colour?
No
There are three types of cone cells, but each contains a:
rhodopsin analogue and photopsin.
It is the _____ connected to the retinal that varies between the cone cells
opsin
Each type of opsin in a cone cells is sensitive to a?
narrower range of wavelengths
Each type of cone cells is sensitive to different ranges of
light wavelength
What is it that allows the detection of colour by cone cells?
The specificity of the opsins to narrower range of wavelengths
L cone cells react to
red
M cone cells react to
green
S cone cells react to
blue
Photosynthesis is the process of converting light energy into
chemical energy
One single pigment contains:
Chlorophyll a, chlorophyll b, phycobilins and carotenoids
Groups of pigments are bound together in a?
Thylakoid membrane
Groups of thylakoids band together in a geometric pattern to form?
Grana
Within a chloroplast, Groups of Grana are joined together by a road like structure called?
Lamella
The inside of a thylakoid is called the?
Lumen
Surrounding the thylakoid and lamella in the chloroplast is what aqueous fluid?
Stroma
A chloroplast has three parts to its membrane which are:
The inner membrane, the inner membrane space and the outer membrane
The light energy trapped by the pigments in the chloroplast is used to
split H2O and generate ATP & NADPH
Photolysis is the splitting of?
Water
The hydrogen and electrons produced in photolysis reduce what molecule?
NADP to NADPH
The reduced NADPH carries what to the next stage, carbon fixation
Hydrogen and Electrons
Photophosphorylation is the conversion of:
ADP + Pi —> ATP
Trapped light energy is used to pump what molecule from the stroma across into the thylakoid space?
H+
H+ is pumped from the stroma into the
thylakoid space
The diffusion of H+ back into the stroma drives what process?
ATP synthase
Chlorophyll a channels electrons to
other parts of the electron transport chain
Accessory pigments do what with their trapped energy?
Transfer it to chlorophyll a
Photosystem 2 uses the energy of electrons to split
water
The electrons generated by the splitting of water are passed onto other intermediaries such as
plastiquinones
Electrons being passed onto intermediaries results in more H+
accumulating in the thylakoid space
The large pool of thylakoid H+ leaks back across the thylakoid membrane and down the electrochemical gradient back to the
stroma
H+ leaking back into the stroma drives what
ATP synthase to generate ATP
