Biological Membranes, Signal Transduction, Hormones ...

Among the phospholipids of plasma membrane, phosphatidylcholine, sphingomyelin, phospatidylserine and phosphoethanolamine are distributed asymmetrically along the plasma membrane. Phosphatidylcholine and sphingomyeline are found in the outer leaflet of plasma membrane whereas phosphatidylserine and phosphoethanolamine are found in inner leaflet. Cholesterol is distributed in both leaflets.

Epinephrine and norepinephrine are secreted by adrenal medulla in response to stress of any kind and during emergency situations. Hence, they are also called emergency hormones of flight or fight.

In 1935, Davson-Danielli proposed plasma membrane is the three-layered symmetric structure. After that in 1959 and 1972, Robertson and Singer-Nicolson proposed the distinct structural model in details respectively, where Singer-Nicolson Model of plasma membrane was widely accepted.
In 1925, Gorter-Grendel proposed the lipid bilayer membrane of the plasma membrane.

Steroid hormones such as cortisol, testosterone, estradiol and progesterone mostly regulate gene expression and chromosome function by the interaction of hormone receptor complex with the genome. So, these can easily pass through the cell membrane of the target cell and bind to a receptor inside it.

All of them are correct except option C as G-protein coupled receptor is activated by the external signal in the form of ligand or signal mediator.

Histidine is the only amino acid that does not act as neurotransmitter.

Except IAA or Indole acetic acid, all hormones help in breaking the dormancy of seed.

The effects of IP₃ and DAG are similar to activate the second messenger as Ca⁺⁺ via activating protein kinase C (PKC) in phosphoinositide cascade.

Integrins are heteromeric protein which bind to tripeptide sequence Arg-Gly-Asp and expressed in a cell-specific manner.

Cadherin, selectin, integrin and Igs are considered as cell adhesion molecules. Cadherins have stable cell junction to form desmosome whereas integrin forms hemidesmosome and it binds to an extracellular matrix protein ligand. Ig binds to integrin as ligand but the cell junction is unstable.

G-protein is the trimeric protein made up of alpha, beta and gamma subunits when alpha subunit binds to GDP and interacts with adenylate cyclase.

Classical cadherine is one of the examples of juxtacrine signalling. This type of signalling requires physical contacts of adjacent cells through interaction with receptor protein.

Steroid hormones interact with nuclear receptor of target cells and do not increase the activity of target enzyme.

Rapid movement of potassium ion out of the guard cell causes stomata closure.

The resting membrane potential is maintained by differences in both ion concentrations and electron gradient, which is established by the proper distribution of sodium and potassium through sodium-potassium ion channel.

cAMP is the hydrophilic molecule which cannot transverse the plasma membrane easily. To overcome the permeability, more hydrophobic derivatives are used resulting that there was no tissue specificity and all cells increased cAMP level. As a result, non-specific and massive responses are formed.

Penguin is an arctic animal. So, it possesses more unsaturated fatty acid and cholesterol. Due to heavy low temperature, the membrane fluidity is increased for preventing the freezing of plasma membrane. So after examining the protein under the microscope, photobleaching of cell membrane has started, but due to high membrane fluidity, the photobleaching will be recovered gently.

As cAMP level decreased, there was no specific signalling to active PKA and PKC. As PKA and PKC are important key enzymes to regulate various metabolic pathways which are inter-related to each other leading to respiratory, urinary and neural disorders.

The membrane fluidity of Indian bird is lower than penguin. So, the fluorescence recovery after photobleaching will be increased very soon.

Auxine helps to promote the meristemic tissue, i.e. root. Cytokinine prevents senescence or aging. Ethylene stimulates lateral growth of plant tissue. ABA or abscisic acid is used for changing sex of unisexual plant; it has an economical value.