Common structural elements in proteins such as α-helices or β-sheets are characterized by uniformly repeating, energetically favorable main chain conformations which additionally exhibit a completely saturated hydrogen-bonding network of the main chain NH and CO groups. Although polyproline or polyglycine type II helices (PPII or PGII ) are frequently found in proteins, they are not considered as equivalent secondary structure elements. Which of the following statements are correct about PP and PGs.

A. PGII -like helices form hexagonal bundles which appear to fulfill the criterion of a (largely) saturated hydrogen-bonding network of the main-chain groups

B. main chain NH and CO groups of the central PGII -helix are saturated by either intra- or intermolecular hydrogen-bonds, resulting in a self-contained hydrogen-bonding network

C. The formation of the right-handed PPI helix is possible only with proline residues because of the required cis conformation. 

D. PPII helices seem to be stabilized by main chain-water hydrogen bonds (in the absence of main chain- main chain H-bonds), and tend to have a regular pattern of hydrogen bonds with water. After this, it is not surprising, that PPII helices are found mostly on the protein surface.

#Question id: 10489

#Unit 6. System Physiology – Plant

Malate anions, by contrast, are synthesized in the guard cell cytosol, in a metabolic pathway that uses carbon skeletons generated by

#Question id: 10488

#Unit 6. System Physiology – Plant

Blue light activates a proton pump at the guard cell plasma membrane. The relationship between proton pumping at the guard cell plasma membrane and stomatal opening is evident from the observations that;

 a.) Orthovandate inhibits the fusicoccin-stimulated opening

 b.) fusicoccin stimulates both proton extrusion from guard cell protoplasts and stomatal opening

 c.) CCCP inhibits the fusicoccin-stimulated opening

 d.) CCCP, a proton ionophore that makes the plasma membrane highly permeable to protons resulting stomatal opening

 Which one of the following observation from the above statements should  be correct?

#Question id: 10487

#Unit 6. System Physiology – Plant

During the patch clamp experiments measure outward electric current in picoamps, pA at the plasma membrane of a guard cell protoplast stimulated by two points A and B showing in the graph.

What is A and B

#Question id: 10486

#Unit 6. System Physiology – Plant

A patch clamp study shows a guard cell protoplast treated in the dark with the fungal toxin fusicoccin which is a well-characterized,

#Question id: 10485

#Unit 6. System Physiology – Plant

What is the role of blue light in terms of stomatal study?

a.) Blue light activates a proton-pumping ATPase in the guard cell plasma membrane and leading to stomatal opening

b.) blue-light stimulation lowers the pH of the apoplastic space surrounding the guard cells, and generates the driving force needed for ion uptake and stomatal opening

c.) The sensitivity of guard cells to blue light increases as a function of their zeaxanthin concentration

d.) npq1 mutant opens at higher fluence rates of blue light, whereas the phot1/phot2 mutant fails to show any blue light–stimulated opening

Which one of the following combination is correct?

#Question id: 10483

#Unit 6. System Physiology – Plant

Given below some facts regarding the stomal responses in light condition. Which one of the following would be INCORRECT?