The role of ABA signaling during water stress in the guard cells in presence and absence of ABA;

a) Anion effl¬ux leads to depolarization of the plasma membrane, which drives K+ effl¬ux. The eff¬lux of ions (A– and K+) reduces the turgor pressure of guard cells, resulting in stomatal closure.

b) Both OST1 and CPKs phosphorylate and thereby activate plasma membrane anion channels, leading to ef¬flux of anions (A–). But  this process can be inhibited directly by PP2Cs 

c) Inhibition of PP2C activity releases the positive regulator kinase OST1 from inhibition, resulting in both phosphorylation and activation of NADPH oxidases (RBOHs)

d) RBOHs catalyze the formation of apoplastic reactive oxygen species (ROS),  which triggers opening of plasma membrane Ca2+-permeable ion channels 

e) The resulting elevation of cytosolic Ca2+ leads to activation of calcium-dependent protein kinases (CPKs), which can also activates the RBOH proteins further promoting Ca2+ infl¬ux into the cytosol.

Which statements belongs to the presence and absence of ABA during signalling;

I. In presence of  ABA

II. In absence of ABA

Which of the following combination from the given above statements is correct?

#Question id: 631

#Unit 1. Molecules and their Interaction Relevant to Biology

Two curves showing the rate versus substrate concentration are shown below for an enzyme-catalyzed reaction. One curve is for the reaction in the presence of substance X. The other curve is for data in the absence of substance X. Examine the curves and tell which statement below is false.

#Question id: 633

#Unit 1. Molecules and their Interaction Relevant to Biology

An amino acid transporter protein is responsible for the transport of a specific amino acid across a membrane. The KI values of several competitive inhibitors of the amino acid transporter are shown above. Based on these data, which of the following is most likely the amino acid transported by this protein?

#Question id: 634

#Unit 1. Molecules and their Interaction Relevant to Biology

An enzyme has a Vmax of 50 micromol product formed (minute x mg protein)-1 and a Km of 10 microM for the substrate. When a reaction mixture contains the enzyme and 5 microM substrate, which of the following percentages of the maximum velocity will be closest to the initial reaction rate?

#Question id: 635

#Unit 1. Molecules and their Interaction Relevant to Biology

The enymatic rate constant (kcat/Km) of orotidine 5ʹ-phosphate decarboxylase is 6 x 10⁷ M^-1s^-1 and the nonenzymatic rate constant (kn) is 3 x 10^-16 s^-1.  What is the value of the enzymeʹs catalytic proficiency?

#Question id: 636

#Unit 1. Molecules and their Interaction Relevant to Biology

DNA polymerase contains a lysine residue that is important for binding to DNA. Mutations were found that converted this lysine to either glutamate, glycine, valine, or arginine. Which mutations would be predicted to be the most and least harmful to the ability of the enzyme to bind DNA?

#Question id: 637

#Unit 1. Molecules and their Interaction Relevant to Biology

Effect of temperature on enzymatic catalysis is analysed by the rate v of a chemical reaction varies with temperature according to the Arrhenius Equation which explains the sensitivity of enzyme reactions to temperature. A plot to determination of the activation energy Ea involves