To further investigate the cellular response in photoreceptor cells, we will now look at the actual effect of cGMP within the phototransduction pathway. Again, we will compare what happens in the dark and in the presence of light to understand how an electric signal is generated in either condition. Comparing both conditions (in the dark or under the light), researchers have measured the molar concentration of cytosolic cGMP and recorded the membrane potential of rod cells by placing micro-electrodes on either side of their plasma membrane (see figure below). A negative membrane potential means that there are more negatively charged ions inside the cell compared to outside the cell, or equivalently, that there are less positively charged ions inside the cell compared to outside the cell. A positive membrane potential means that there are more negatively charged ions outside the cell compared to inside the cell, or equivalently, that there are less positively charged ions outside the cell compared to inside the cell. The readings are presented below: In the dark Inside of the cell [CGMP] = 14 mM -10mV Outside of the cell In the presence of light Inside of the cell [CGMP] = 4 μM -70mV Outside of the cell 11. Based on the cytosolic concentration of cGMP and the membrane potential readings in both conditions, what can you conclude about the role of cGMP during phototransduction? A. CGMP helps maintain a constant membrane potential B. Light increases the concentration of cytosolic cyclic-GMP (CGMP) C. Light decreases the concentration of cytosolic GMP D. CGMP increases the membrane potential (= depolarization from -70mV up to -10mV) E. CGMP decreases the membrane potential (= hyperpolarization from -10mV down to -70mV).

describe how signal amplification is accomplished in target cell

Suppose that initially there are 100 Nat and 25 K+ ions inside the cell, near the sodium-potassium pump. After how many cycles is the number of Na ions the same as the number of Kions inside the cell? With the initial values for each type of ion provided above, how many ions of each type are in the cell? What is the total number of ions at this time? Show your work and explain.

Researchers who study those rods cells have performed a series of experiments to better understand this phototransduction pathway and the role of this PDE protein in patients that suffer from night blindness. In one experiment, researchers have measured the cytosolic concentration of cGMP (cyclic- GMP) under different light intensities (exposure = 10 min) in both the presence and the absence of the PDE6i inhibitor. The results are as follow: the cytosolic concentration of cGMP (cyclic-GMP) decreases as light intensity increases, but only in the absence of the PDE6i inhibitor (see figure below). Without PDE6i cGMP concentration (A.U) 25 20 15- 0- 0 0.1 0.2 0.3 Light intensity (A.U) 25 0.4 20 15 - 10 5 0 GMP concentration (A.U) cGMP concentration (A.U) 25 20 15- o 0- 0 0.1 With PDE6i 0.2 0.3 Light intensity (A.U) 0.4 25 20 0 GMP concentration (A.U) 10. What is the likely function of the cytosolic cGMP in this phototransduction pathway? A. It is a competitive inhibitor of PDE B. It is a…

fill in the blanks In signal transduction, termination of the active Gas is by (                  ) and termination of the cAMP signal is by (                  ).

Condition: In photosynthesis there are various kinase enzymes that convert ATP --> ADP + Pi. A mutation causes these kinase enzymes to stop working. What impact will this have to photosynthesis? Explain why. (Specific values are not required, just an indication of overall effect and reasons why.)

Given the effect of myosin heavy chain phosphorylation on myosin II assembly/disassembly, why might it make sense to find this kinase near the contractile ring as the process of cell division is concluding?

What is the actual “signal” that is being transduced inany signal transduction pathway, such as those shownin Figures 11.6 and 11.10? In what way is this information being passed from the exterior to the interior ofthe cell?

Explain Cessation of Activity in Signal Transduction Pathways?

In 40 words or fewer, explain what an enzyme cascade is in the context of signal transduction pathways, and why these might be beneficial to the organism.