rhodpsin and phytochromes Flashcards

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1
Q

components of a rod cell

A

inner segment with the nucleus and mitochondria and outer segment with membranes containing the purple pigment rhodopsin

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2
Q

benefits of having membranes in the outer segment

A

increases surface area for light to be absorbed

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3
Q

which direction does light travel through a rod cell

A

from the inner segment to outer segment

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4
Q

how do Na+ move in and out of the rod cell in total darkness

A
  1. Na+ diffuse into the outer segment through open cation channels
  2. and then move down the concentration gradient
  3. Na+ move out the inner segment by being actively pumped out causing the membrane to become slightly depolarised
  4. this triggers neurotransmitters to be released
  5. the inhibitory synapses between the rod cell and bipolar cell allows the neurotransmitters to bind to the bipolar cell preventing in depolarising
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5
Q

how do Na+ move in and out of the rod cell when light is present

A
  1. rhodopsin in the outer segment absorbs light and breaks in down into retinal and opsin
  2. opsin closes the cation channels so no Na+ enter the cell
  3. Na+ are actively pumped out causing the membrane to become hyperpolorised so no transmitter is released
  4. bipolar nerone is depooriesed and relaseases neortransmitter
    1. this depoliriesed the ganglion cell which sends an action potential to the occiptial lobe of the brain
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6
Q

what happens when rhodopsin absorbs light

A

rhodopsin spilts into opsin and retinal so light can no longer be absorbed which is known as bleaching as the products of colourless. this process then leads to a nerve impulse

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7
Q

what happens after rhodopsin absorbs light

A

re-synthesis of rhodopsin occurs before the rod cell can be activated again, it requires ATP and it takes longer than splitting the rhodopsin

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8
Q

what speeds up re-synthesis of rhodopsin

A

the lower the light intensity

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9
Q

what happens to the eye in bright light

A

nearly all the rhodopsin has been bleached and the eye is light adapted

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10
Q

what happens to the eye when moving from bright light to dim light

A

very little can be seen as there is not enough rhodopsin present as opsin and retinal are still recombining , after 5 min half of the rhodopsin is regenerated and after 30 mins the eye can see very well ad is dark adapted

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11
Q

benefits to flowering at the right time of the year

A
  • flowers produced when insects available to pollinate
  • day lengths reflect the seasons which is more reliable than the temperature
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12
Q

similarities between phytochromes (plants) and rhodopsin (eye)

A
  • both light sensitive
  • both made up of a protein and non protein component
  • they change shape in response to light
  • both allow the organisms to detect light
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