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BIO 317 > 4 - Sensory Systems and G-Proteins; Second Messengers and Effectors > Flashcards

4 - Sensory Systems and G-Proteins; Second Messengers and Effectors Flashcards

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1
Q

How many major families of G proteins are there?

A

4

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2
Q

What G-proteins are found in class I?

A

Gs and Golf

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3
Q

What do the G-proteins in class I do?

A

Activate AC

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4
Q

What G-proteins are found in class II?

A

Gi, Go, and Gt (transducin)

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5
Q

What do the G-proteins in class II do?

A

Inhibit AC, activate potassium channels, function in photoreceptors, etc.

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6
Q

What G-proteins are found in class III?

A

Gq

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7
Q

What do the G-proteins in class III do?

A

Activate phospholipase C-beta

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8
Q

What G-proteins are found in class IV?

A

G12/13

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9
Q

What do the G-proteins in class IV do?

A

Regulate actin cytoskeleton

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10
Q

In which class of G-proteins can the beta/gamma subunit also play a role?

A

Class II

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11
Q

True or false: our range is vision (in terms of light intensity) is fairly broad

A

True: we can detect light in many orders of magnitude

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12
Q

What happens in scotopic conditions?

A

No color vision, poor acuity

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13
Q

What does scotopic mean?

A

Vision in very low light settings

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14
Q

What cells are active in scotopic conditions?

A

Rods

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15
Q

What does mesopic mean?

A

Vision in fairly low light settings

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16
Q

What happens in mesopic conditions?

A

Start to use cones

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17
Q

What cells are active in mesopic conditions?

A

Rods and cones

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18
Q

What does photopic mean?

A

Vision in broad daylight

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19
Q

What happens in photopic conditions?

A

Good color vision, best acuity

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20
Q

What cells are active in photopic conditions?

A

Cones

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21
Q

How does perception and interpretation relate to vision?

A

The background and your expectations influences what we see

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22
Q

What is the path of light in the eye?

A

Goes through pupil and lens to shine on retina

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23
Q

What are the layers of the retina (in the same order that light would see them)?

A

Ganglion cells, bipolar cells, photoreceptor cells, endothelial cells

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24
Q

What cells connect to the nerve fiber in vision?

A

Ganglion cells

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25
Q

Which cells are excited by light?

A

Photoreceptors (rods and cones)

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26
Q

How does membrane potential change the cell?

A

Opens ion channels to further change membrane potential

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27
Q

What happens to the membrane potential when ion channels are closed?

A

Resting potential of the neuron

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28
Q

What happens to the membrane potential when ion channels are open?

A

Ions rush into or out of the cell, changing the membrane potential

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29
Q

What happens to the membrane potential when ion channels are inactived?

A

There is no change, since the channel does not open, even in response to a new signal

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30
Q

What is a depolarization?

A

Membrane potential becomes more positive (positive ions flow in, or negative ions flow out)

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31
Q

What is a hyperpolarization?

A

Membrane potential becomes more negative (negative ions flow in, or positive ions flow out)

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32
Q

If the membrane potential becomes more positive, what is this called?

A

Depolarization

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33
Q

If the membrane potential becomes more negative, what is this called?

A

Hyperpolarization

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34
Q

How does an action potential work in a typical neuron?

A
  1. Depolarization leads to influx of sodium
  2. This leads to a hyperpolarization with an outflux of potassium
  3. Sodium-potassium pump works to restore membrane potential
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35
Q

What happens when a photoreceptor gets stimulated by light?

A

It hyperpolarizes (becomes more negative)

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36
Q

What happens to a photoreceptor if there is no stimulus?

A

It depolarizes (becomes more positive)

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37
Q

How does a photoreceptor stay depolarized with no stimulus?

A

Leaky Na+ channels (influx of positive charge)

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38
Q

How does a photoreceptor hyperpolarize with a stimulus?

A

Na+ channels close (stops influx of positive charge)

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39
Q

What molecule is responsible for phototransduction (detects light)?

A

Retinal

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40
Q

What is the form of retinal in the dark?

A

11-cis-retinal

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41
Q

What is the form of retinal in the light?

A

all-trans-retinal

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42
Q

How does retinal transduce the light signal?

A

The change in conformation (cis -> trans) causes a change in the receptor, thus starting the signal cascade

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43
Q

What is rhodopsin?

A

An opsin molecule with an embedded retinal molecule

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44
Q

What is opsin?

A

A GPCR that interacts with retinal to form rhodopsin

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45
Q

What type of signaling is used in vision?

A

Indirect signaling through the second messenger cGMP

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46
Q

What is similar to rhodopsin (in terms of structure)?

A

Adrenaline receptor

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47
Q

Who discovered the G-protein associated with vision?

A

Lubert Stryer

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48
Q

What did Lubert Stryer do?

A

Discover transducin

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49
Q

What is another name for Gt?

A

Transducin

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50
Q

What does transducin do?

A

G-protein for the vision system

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51
Q

What are the levels of cGMP in the dark?

A

High levels

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52
Q

What are the levels of cGMP in the light?

A

Low levels

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53
Q

What does transducin do?

A

Activated cGMP phosphodiesterase (PDE)

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54
Q

What does guanylate cyclase (GC) do?

A

Converts GTP into cGMP

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55
Q

What does cGMP PDE do?

A

Converts cGMP into GMP

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56
Q

Why are there high levels of cGMP in the dark?

A

GC makes cGMP, and PDE is not active to break it down

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57
Q

Why are there low levels of cGMP in the light?

A

PDE is activated by transducin in light, which breaks down cGMP into GMP

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58
Q

What subunit of transducin activates PDE6?

A

aGt

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59
Q

What PDE is found in the vision system?

A

PDE6

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60
Q

What are the subunits of PDE6?

A

2 regulatory subunits (gamma) and 2 catalytic subunits (alpha and beta)

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61
Q

How does Gt interact with the subunits of PDE6?

A

2 molecules of aGt bind to the 2 regulatory gamma subunits, thus activating the alpha/beta subunits of PDE6

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62
Q

How does cGMP interact with ion channels?

A

cGMP binds to ion channels to open them

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63
Q

Why are ion channels opened in the dark?

A

High levels of cGMP bind to the ion channels to open them

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64
Q

Why are ion channels closed in the light?

A

Low levels of cGMP prevents many from binding to the ion channels, thus keeping them closed

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65
Q

How is PDE inactivated after starting a signal?

A

RGS5 and Gbeta5 bind to aGt to increase GTPase activity, thus inactivating it and PDE

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66
Q

What needs to be done (in terms of signaling) to detect rapid movement?

A

Rhodopsin signaling must be rapidly shut down

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67
Q

How long does the shut down of the vision system take?

A

~50 ms

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68
Q

How does calcium function in the vision system?

A

Calcium sensing proteins detect a fall in intracellular concentration, and then stimulate GC to make more cGMP

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69
Q

How is rhodopsin downregulated?

A

Phosphorylation of rhodopsin by a rhodopsin kinase

70
Q

How is rhodopsin signaling completely blocked?

A

Arrestin binds to a tri-phosphorylated rhodospin, stopping signaling

71
Q

If there are less than three phosophates on rhodopsin, how is the activity changed?

A

There is less, but some, activity compared to no phosphorylation

72
Q

What does the photoreceptor cell do when it is depolarized?

A

Constantly releases neurotransmitter

73
Q

What does the photoreceptor cell do when it is hyperpolarized?

A

Stops releasing neurotransmitter

74
Q

What does the photoreceptor cell do when it is in darkness?

A

Constantly releases neurotransmitter (depolarized)

75
Q

What does the photoreceptor cell do when it is in light?

A

Stops releasing neurotransmitter (hyperpolarized)

76
Q

What neurotransmitter is released by photoreceptors?

A

Glutamate

77
Q

What does glutamate do to bipolar cells?

A

Inhibits them

78
Q

When the photoreceptor is in darkness, what happens to the bipolar cells?

A

Inhibited (glutatmate released by photoreceptor)

79
Q

When the photoreceptor is in light, what happens to the bipolar cells?

A

Activated (glutatmate is not released by photoreceptor)

80
Q

Why use a slow indirect receptor for vision, which needs to be immediate?

A

Sensitivity and amplification

81
Q

How is sensitivity achieved in vision?

A

Driven by the number of ion channels (more ion channels means more light is needed to hyperpolarize cell)

82
Q

How is amplification achieved in vision?

A

Each component activates several downstream components

83
Q

Besides sensitivity and amplification, how can the slow speed of the response be compensated in vision?

A

Sandwiched discs have a small volume with lots of proteins, so there is reduced distance between signaling components

84
Q

True or false: rods can respond to one photon of light

A

True: the amplification in the system allows for a sensitive response

85
Q

How do the components amplify in response to one photon?

A

One photon -> 500 Gt activated -> 500 PDE activated -> 10^5 cGMP hydrolyzed -> 250 Na channels close -> 10^6 Na ions over 1 second don’t enter cell -> alter membrane potential by 1 mV -> signal to brain

86
Q

How does a bipolar cell interact with a ganglion cell?

A

It is an excitatory synpase (stimulates ganglion cells when it is stimulated, or not inhibited)

87
Q

When is the bipolar cell hyperpolarized?

A

When the photoreceptor is depolarized, and releases inhibitory neurotransmitter

88
Q

When is the bipolar cell depolarized?

A

When the photoreceptor is hyperpolarized, and stops releasing inhibitory neurotransmitter

89
Q

When is the ganglion cell activated?

A

When the bipolar cell is activated (in light) and releases neurotransmitter

90
Q

When is the ganglion cell inhibited?

A

When the bipolar cell is inhibited (in darkness) and doesn’t release neurotransmitter

91
Q

What type of synapse is between a photoreceptor and a bipolar cell?

A

Inhibitory synapse

92
Q

What type of synpase is between a bipolar cell and a ganglion cell?

A

Excitatory synpase

93
Q

What is visual adaptation?

A

The change in sensitivity of our eyes to high and low light levels

94
Q

True or false: rod signaling is reduced after prolonged exposure to bright light?

A

True: this is part of visual adaptation

95
Q

How are the proteins in a rod cell distributed in darkness?

A

Transducin is transported to outer rod segments (where signal transduction happens), while arrestin is transported elsewhere (does not interact)

96
Q

Why is transducin found in the outer rod segments in darkness?

A

Transducin activates the signal, which is needed in low light conditions

97
Q

Why is arrestin found elsewhere in rod cells in darkness?

A

Arrestin stops the signal, which is not needed in low light conditions

98
Q

How are the proteins in a rod cell distributed in bright light?

A

Arrestin is transported to outer rod segments (where signal transduction happens), while transducin is transported elsewhere (does not interact)

99
Q

Why is transducin found elsewhere in rod cells in bright light?

A

Transducin activates the signal, which is not needed in bright light conditions

100
Q

Why is arrestin found in the outer rod segments in bright light?

A

Arrestin stop the signal, which is needed in bright light conditions

101
Q

Why does the distrubution of rod proteins change in different light levels?

A

This allows for high sensitization in low light levels, and low sensitization at high light levels

102
Q

What is the contrast range of rod cells (due to visual adaptation)?

A

100,000 fold range

103
Q

What are the two types of photoreceptors?

A

Rods and cones

104
Q

When are rods active?

A

In low light conditions

105
Q

When are cones active?

A

In bright light conditions

106
Q

Which photoreceptors are responsible for color?

A

Cones

107
Q

What does Sidenafil (Viagra) do?

A

Inhibits PDE

108
Q

What is the normal signaling pathway for smooth muscle cells (without Viagra)?

A

Neuronal inputs lead to NO, which activates GC to produce cGMP from GTP. cGMP then activates PKG, which leads to vasodilation (increased blood flow)

109
Q

What is the effect of Viagra?

A

Increased blood flow (vasodilation)

110
Q

Why does Viagra lead to vasodilation (increased blood flow)?

A

Viagra inhibits PDE, thus keeping cGMP levels high. This stimulates PKG, thus leading to vasodilation

111
Q

How does Viagra interact with vision?

A

Viagra also inhibits PDE6 (in the eyes), causing some side effects such as blue aberrations

112
Q

Why can Viagra cause blue aberrations (and not green or red aberrations)?

A

Viagra impacts PDE6 in S-cones (blue sensitivity) more than M/L cones

113
Q

Where does olfaction take place?

A

In the olfaction bulb

114
Q

What cells are in the olfaction bulb that receive the signals from receptors?

A

Glomeruli

115
Q

How do signals reach the glomeruli?

A

Oderant bind to odor receptors, which travels through olfactory receptor cells, epithelium, and bone to reach glomeruli

116
Q

What does the glomeruli do after reciving a signal?

A

Passes the signal to mitral cells to be sent to the brain

117
Q

What are glomeruli?

A

Groups of neurons

118
Q

How are glomeruli grouped?

A

The same type of receptor (spread throughout the epithelium) converge at one glomeruli

119
Q

True or false: One mitral cells codes for one odorant molecule

A

True: the receptors that recognize a specific odorant all converge on one mitral cell

120
Q

What is the second messenger in olfaction?

A

cAMP

121
Q

What G-protein is associated with olfaction?

A

Golf

122
Q

How does Golf work?

A

Activates AC, which produced cAMP. cAMP then opens ion channels to cause an action potential

123
Q

What ion channels are present in olfaction?

A

Sodium, chloride, and calcium

124
Q

How do the ion channels change when there is an olfaction signal?

A

Calcium channels open, bringing in calcium and sodium. Calcium binds to chloride channels, moving chloride out. They also bind (with CAM) to calcium/sodium exchangers to move calcium out and more sodium in

125
Q

What allows for specific odorant detection (in terms of the receptor)?

A

Variability of amino acid sequence

126
Q

How does the brain interpret a smell?

A

Different combinations of signals from glomeruli are processed as a smell

127
Q

Why is a dog’s smell better than a humans?

A

More receptors, bigger brain region for processing smells, can smell in 3D (each nostril processes separately)

128
Q

How do genes evolve with different functions?

A

Copies of duplicated genes diverge

129
Q

What is an example of genes with different functions due to duplication?

A

Lysozyme (enzyme to protect against bacterial infection) and alpha-lactalbumin (helps in milk production)

130
Q

How can gene evolution occur?

A

Exon shuffling, and exon duplication (occurs during recombination)

131
Q

What is a trichromatic view?

A

Can see reds, blues, and greens

132
Q

What is a dichromatic view?

A

Can see blues and greens

133
Q

What is a monochromatic view?

A

Can only see shades (no blues, greens, or reds)

134
Q

What light has the longest wavelength?

A

Red

135
Q

What light has the shortest wavelength?

A

Blue

136
Q

In old world primates, how are color pigments organized in the genes?

A

Blue gene is on an autosome, and both red and green genes are on X chromosome

137
Q

In old world primates, what kind of vision can males see?

A

Trichromatic (X chromosome has two genes, autosome has 1)

138
Q

In old world primates, what kind of vision can females see?

A

Trichromatic (X chromosome has two genes, autosome has 1)

139
Q

What vision genes are found on the Y chromosome?

A

None

140
Q

In new world primates, how are color pigments organized in the genes?

A

Blue gene is on an autosome, and X chromosome has either one red, one green, or one yellow gene

141
Q

In new world primates, what kind of vision can males see?

A

Dichromatic (autosome has 1, X chromsome has 1 of 3 possible options)

142
Q

In new world primates, what kind of vision can females see?

A

Either dichromatic or trichromatic, depending on the X chromosomes

143
Q

If a new world primate female is dichromatic, what can you say about the X chromosomes?

A

They both have the same color gene (both red, green, or yellow)

144
Q

If a new world primate female is trichromatic, what can you say about the X chromosomes?

A

They have two different color genes (from red, green, and yellow)

145
Q

How did color vision evolve?

A

Mutations allows for the different color pigments seen in new world primates. A duplication error then causes the two genes to be on one X chromosome, as seen in old world primates

146
Q

How can the plasticity of the brain be seen in color vision?

A

A mouse with a new gene can see more and different colors, and can recognize it (can use the new gene)

147
Q

What is the evolutionary advantage of color vision and being trichromatic?

A

Better contrast with surroundings (see when food is ripe, etc.)

148
Q

How can women have tetrachromaticity?

A

Mutation in one of the X gene shifts the spectrum slightly

149
Q

If activation of 10% rhodopsin gives a maximal response, how does activation of 90% rhodposin affect the speed of response?

A

The speed increases

150
Q

Why does having 90% rhodopsin increase the speed compared to 10% rhodopsin?

A

More rhodopsin activation leads to more PDE activity, thus reducing cGMP more, and thus closing the ion channels faster

151
Q

How is the concentration and speed of responses different for rhodopsin?

A

The concentration to get a max response can be low, and be steady at higher numbers of receptors. The speed will increase with more receptors, since more channels close simultaneously

152
Q

What is another example of cis/trans signaling?

A

Proline can be cis or trans, and can be switched by isomerases

153
Q

Why does the visual system depolarize at a different membrane potential than other neurons?

A

So there can be less noise, and thus more sensitivity (based on dynamics of the cell)

154
Q

What phenomena makes vision sensitive to even a single photon?

A

It’s easier to interrupt a constantly inhibited cell compared to generating a strong enough signal to create response

155
Q

Do multiple cones and rods share the same pathway?

A

Both; there are both converging and diverging pathways

156
Q

What differentiates the three cones cells?

A

The structure of the opsin, which heavily predominates in a certain cone cell

157
Q

How is smell and taste processed together?

A

Through upper brain circuitry

158
Q

How come you can’t see color in low light conditions?

A

Cones are not activated under low light

159
Q

True or false: glutamate is only inhibitory

A

False: glutamate is primarily excitatory, but can also be inhibitory

160
Q

Why does imparing the speed of a response get interpreted as blue?

A

Blue light is filtered as it reaches the retina, while other light isn’t

161
Q

Why do we have greater acuity in the center of our vision?

A

Cones are found in the center of the eye

162
Q

Why does our periphery vision not have color?

A

Rods are found in the periphery of the eye

163
Q

Where is the most sensitive opsin found?

A

In the rod cells

164
Q

True or false: light is not detected by the photoreceptors when we are asleep

A

False: light is still detected, but we are not consciously aware of it

165
Q

True or false: the G-proteins for vision and olfaction are the same, the receptors are different

A

False: the G-proteins are different between vision (transducin) and olfaction (Golf)

166
Q

What do mitral cells do?

A

Take the signal from glomeruli and send it to the brain

167
Q

What compensates for the vision system having a high metabolic cost?

A

Very sensitive system of light detection

168
Q

What mechanisms does visual adaptation use?

A

Relocation of arrestin / transducin to different segments of rods

169
Q

What does visual adaptation refer to (in terms of the conditions)?

A

From bright light to darkness (not from darkness to bright light)

170
Q

What is the change in photoreceptors in visual adaptation?

A

From cones to rods (only from bright light to darkness)

BIO 317 (27 decks)

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