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Course: AP®︎ Biology (2018) > Unit 30
Lesson 1: Free-response questions: 2015 AP Biology exam- 1a-c, Responses to the environment
- 1d-e, Responses to the environment & natural selection
- 2a-b, Cellular respiration & common ancestry
- 2c-d, Cellular respiration & cell compartmentalization and its origins
- 3a-b, Phylogeny
- 4a-b, Meiosis and genetic diversity
- 5a-b, Responses to the environment
- 6a-c, Population ecology
- 2015 AP Biology free response 7
- 2015 AP Biology free response 8
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2015 AP Biology free response 7
Olfactory neurons.
Want to join the conversation?
- So are these odorant-receptors ion channels, or are they located near ion channels and activate those? Or something completely different?(1 vote)
- They belong to the group of GPCRs (G-protein coupled receptors). Upon activation on the outside the receptor protein activates a G-protein on the inside which then triggers further cell responses depending on the cell.(3 votes)
- So we don't have to mention anything about calcium and sodium channels in relation to the neurotransmitters?(1 vote)
- I am confused. How can one receptor bind to more than one molecule if receptors have specific sites and certain shapes to only be able to bind to one specific molecule?(1 vote)
Video transcript
- [Voiceover] Smell perception
in mammals involves the interactions of airborne odorant molecules from the environment with receptor proteins
on the olfactory neurons in the nasal cavity. The binding of odorant molecules to the receptor proteins triggers action potentials
in the olfactory neurons and results in transmission of information to the brain. Mammalian genomes typically
have approximately one thousand functional odorant-receptor genes, each encoding a unique odorant receptor. Alright, part a, describe how the signal
is transmitted across the synapse from an activated olfractory sensory neuron to the interneuron that transmits the
information to the brain. Alright, so let's draw this out. So, this is part a, so
let's, let me draw the activated olfactory sensory neuron, so, it might, so those
are its dendrites, there, so, I'm not gonna draw a perfect, so those are its dendrites
right over there, and this is its axon, it's axon, and then this is the axon terminals. The axon terminals, just like that. And I could draw other details if I want, I don't think you'd have to
draw all of these details on the actual test. But, just to get a sense of things, we could also draw the well, we could do it in a different color, we could also draw the nucleus right over there. So this is the activated
olfactory sensory neuron, so activated olfactory, olfactory sensory neuron. sensory neuron. And let me draw, let me
draw the interneuron. So, the interneuron,
so I'll draw one of its dendrites right over there. So this is the interneuron, drawing its dendrites, and then its axon. I'll draw it a little
bit better than that, its axon just like that
and it goes to the brain. And if we zoom in on the synapse, where we have to transmit
the signal between the two, so if we zoom in, if we zoom in, right over there, we would see the axon terminal of the sensory neuron. So, maybe it looks something like that. And then the, the, the interneuron right over that. Just like this. And this is the synapse. So, this is the zoomed in of the synapse. And the activated
olfactory sensory neuron, you have this activation potential that is going to go down the axon, and then when it gets to when it gets to the axon
terminal right over here, it will trigger the release
of neurotransmitters. So, these neurotransmitters are typically hanging out in, in these, these vessels right over here, but then when
the action potential comes, they will get released
into the synaptic cleft. And then, the interneuron
is going to have, is going to have proteins
that sense, that sense those neurotransmitters, and that activates that neuron. So, once again this is the interneuron, interneuron, and we could
say that interneuron, interneuron gets activated, actually
it could be inhibited as well, but activated
by, by neurotransmitters neurotransmitters released into synapse, released into synapse by the sensory neuron, by sensory neuron due to action potential, due to action, action potential. And this is probably enough, but I went through a few more
pains to draw it out a little bit, and you
could draw other details. You could draw the myelin
sheath and all of that, you could draw the nuclei
of the different cells, but the basic idea is
that the signal goes from one neuron to another
with the release of these, these chemicals, these neurotransmitters, which are actually fairly,
fairly small molecules, but then they trigger the next neuron, and then after that
signal goes they get all they get metabolized by enzymes and things and there might be a few
that just always stick around but for the most part they signal from one neuron to another. And they could activate the next neuron, or they actually could inhibit it as well, but in this case, they
would probably activate. Alright, let's do part b. Let's do part b. Explain how the expression
of a limited number of odorant receptor genes,
you see there's thousands, receptor genes, can lead
to the perception of thousands of odors. Use the evidence about
the number of odorant receptor genes to support your answer. So, one way to think
about it is, and this is this is kind of a theory, here, is that you don't necessarily have a one-to-one mapping between odorant, odorant receptors and odorant molecules, so don't, don't necessarily, necessarily have one-to-one relationship between, between odorant molecules odorant molecules and receptor proteins. And receptor proteins. Maybe, maybe one protein can, can detect multiple molecules, maybe one, maybe a given protein can detect multiple molecules. Or vice versa, or vice versa, whoops I keep having trouble with my little pen here. or vice versa, or vice, vice versa. And so then, you could have this could lead to many combinations, combinations being detected. So even though you could
have, maybe these one thousand odorant genes, they code for one thousand
receptor proteins, and so you might say well, well those'll only be able
to detect one thousand different molecules, well, no, each of those could detect more than one, and then, and when they come
in different combinations they might trigger the
brain in different ways. And then, many, I mean I could even add that, this could lead to many
combinations being detected which would be different, different smells in the brain, different smells as perceived by brain, perceived by brain. Now, there is some possibility
that each of these genes, maybe they could be coded into proteins in different ways, but they
do tell us each encoding a unique odorant-receptor, so I like, I like going with this one, you don't necessarily have
a one-to-one relationship, each receptor could
recognize multiple molecules, or one molecule could be
bound by multiple receptors, and then the different combinations of all of the above
means that you could have much more than one thousand molecules being detected, and
especially different molecules in different combinations,
you could have thousands upon thousands of smells quote, unquote, being detected.