The yeast Gal4 transcription activator comprises two domains: a DNA binding domain and an activation domain. The DNA-binding domain allows Gal4 to bind to appropriate DNA sequences located near genes that are required for metabolism of the sugar galactose. The activation domain binds to components of the transcriptional machinery (including RNA polymerase), attracting them to the promoter, so the regulated genes can be turned on. In the absence of Gal4, the galactose genes cannot be turned on. When Gal4 is expressed normally, the genes can be maximally activated. When Gal4 is massively overexpressed, however, the galactose genes are turned off. Choose correct explanation for this regulation?

A. In order for Gal4 to work properly, the DNA-bound Gal4 recruits many proteins, including RNA polymerase, to the promoter.

B. When there is too much Gal4 in the cell, the free and DNA-bound Gal4 will compete for the limited quantities of these other components.

C. In the presence of excess Gal4, those components are tied up in unproductive complexes with free Gal4, thereby preventing their recruitment to the promoter.

D. cells that massively overexpress Gal4 grow poorly because of the reduced availability of critical components of the transcription machinery.

E. Over concentration of Gal4 prevent suppressors to bind with DNA

#Question id: 12192

#Unit 6. System Physiology – Plant

#Question id: 12191

#Unit 6. System Physiology – Plant

#Question id: 11902

#Unit 6. System Physiology – Plant

A chemiosmotic model  has been proposed  to explain Polar transport , following steps are involve in the transport of auxin polarly;

a) IAA enters the cell either passively in the undissociated form (IAAH) or by secondary active cotransport in the anionic form (IAA–)

b) The cell wall is maintained at an acidic pH by the activity of the plasma membrane H+- ATPase

c) In the cytosol, which has acidic pH, the IAAH form predominates

d) The anions exit the cell via auxin anion efflux carriers that are concentrated at the basal ends of each cell in the longitudinal pathway

Which of the following is the correct statements about the polarly transporting of auxin?

#Question id: 11850

#Unit 6. System Physiology – Plant

The first step in polar transport is auxin influx. According to the model, auxin can enter plant cells from any direction by either of two mechanisms:

a) Passive diffusion of the protonated (IAAH) form across the phospholipid bilayer

b) Secondary active transport of the dissociated (IAA–) form via a 2H+–IAA– symporter

c) Active diffusion of the protonated (IAAH) form across the phospholipid bilayer

Find out the correct statements of about diffusion of IAA.

#Question id: 11849

#Unit 6. System Physiology – Plant

According to chemiosmotic model for polar auxin transport, auxin _____A_______is driven by the______B________ across the plasma membrane, while auxin ___C_____is driven by the_________D_________

#Question id: 11848

#Unit 6. System Physiology – Plant

Polar transport is specific for active auxins, such as