1) Please examine the graph within the red box. In the dark the resting membrane potential of a
photoreceptor is -40 mV but upon exposure to light the molecular events show in the figure around the
graph occur. Exposure to light causes the photoreceptor to hyperpolarize, which means the membrane
potential drops to -70 mV. The photoreceptor cell possesses many sodium/potassium ATPase molecules
in its cell membrane [just like every other cell]. Briefly describe in your own words how the cGMP gated
sodium channels show in the figure above are responsible for the change in membrane potential from
the -40 mV under dark conditions to the -70 mV membrane potential when the photoreceptor is kept in
the light. [Please also examine slide 7 in lecture 09C for help with this question] (3 points)
The membrane of the rod’s disc contains rhodopsin, a g-protein coupled receptor that acts as the
primary photoreceptor. When light enters the rod, it will activate retinal. The activation of retinol
isomerizes rhodopsin into its active form which triggers the activation of the Transducin. This rotein will
bind to phosphodiesterase. This will led to the decrease in cGMP in the cell, which is found bound to
sodium channels. cGMP will convert into GMP, so there is no influx of sodiu into the cell.
Hyperpolarization will occure, leading to no action potentials conducted. In the bipolar cells,
neurotransmitters act as inhibitory action potenials, therefore, when there is no action potenials,
depolarization will occur, where at the end of the bipolar cell calcium channes will open and
propagation will occur. The resting potential is at -40, so when light is taken in by the cell, as
aforementioned, there will be hyperpolarization that leads to a decrease in internal cell voltage, to -70.
2) In innate immunity plants [and other organisms] have constitutive innate immune traits and induced
innate immune response. Briefly describe in your own words what the difference is between
constitutive and induced innate responses particularly in light of exposure to a pathogen? [Be sure to
supply an example of each] (2 points)
Innate immunity is the first line of defense against foreign bodies within the body. The constitutive
innate response involves non-specific forms of defense that are already present in the region that the
pathogen is exposed to. This may entail the skin, mucous, saliva, gastric juices, and humoral developed
cells such as natural antibodies, complement proteins, and macrophages. Once this occurs, the induced
innate response will be triggered using PAMPs - pattern-associated molecular pattern- by PRRs – pattern
recognition factors - which will determine foreign bodies from their cell membrane constitution - and
cytokines once foreign bodies have been recognized as foreign or engulfed by other cells that will
present them as foreign. These non-specific defense cells will enter the region – which may include
natural killer cells. Constitutive allows for an immediate response to the presence of foreign bodies, but
there is a greater amplification of cell action in the induced cell response. Induced is only activated in
response to stimuli and signals.
Constitutive innate immunity eliminates PAMPs from the impacted region, downregulating the
induction of induced innate immunity. If PAMPs pass a threshold, the induced innate immunity will be
activated, leading to inflammation and the triggering of adaptive immunity.