Following statements are regarding to double fertilization in angiosperms.

A. One sperm cell fuses with the egg cell to produce the zygote that will develop into the new embryonic plant.

B. The second sperm cell fuses with the usually binucleate central cell, giving rise to the

endosperm, the tissue that nourishes the developing embryo. This second event is not “true” fertilization in the sense of male and female gametes undergoing fusion.

C. The second sperm cell fuses with the usually binucleate central cell, giving rise to the

endosperm, the tissue that nourishes the developing embryo. This second event is “true” fertilization in the sense of male and female gametes undergoing fusion.

D. During fertilization in angiosperm, when the sperm cells are released, the egg undergoes a flux of Ca2+. Then, chemicals released from the egg appear to make the sperm competent for cell fusion.

Which of the following statements are true?

#Question id: 908

#Unit 1. Structure and Function of Biomolecules

Molecular chaperones are a class of proteins that play a role

#Question id: 909

#Unit 1. Structure and Function of Biomolecules

Most proteins denature at both high and low pH. At high pH, the ionization of internal tyrosines is thought to be the main destabilizing influence, whereas at low pH, the protonation of buried histidines. A titration curve for the unfolding of the enzyme ribonuclease is shown in Figure. Given the relation between the titration curves for protein unfolding and histidine protonation, which of the following conclusion can be drawn correctly?

A. The sharp transition in graph indicates a highly cooperative process; when the protein starts to unfold, it completes the process rapidly

B. The sharp transition in graph indicates a highly noncooperative process

C. Several buried histidines can ionize when the chain starts to unfold, so that when one goes, they all go together due to cooperative behaviour of protein folding

D. Buried histidine (pK of 4 in this example) becomes accessible to solvent, its pK will shift toward its normal value of 6, significantly steepening its titration curve.

#Question id: 910

#Unit 1. Structure and Function of Biomolecules

Experiments on denaturation and renaturation after the reduction and reoxidation of the —S—S— bonds in the enzyme ribonuclease (RNase) have shown that:

#Question id: 911

#Unit 1. Structure and Function of Biomolecules

The correct order for molecular chaperone–mediated protein folding is:

I – exchange of ATP for ADP on chaperone

II – chaperone undergoes conformational change, which affects protein folding

III – chaperone binds to exposed hydrophobic residues on unfolded protein

IV – folded protein is released

#Question id: 912

#Unit 1. Structure and Function of Biomolecules

Which of the following is correct about the native state of a protein

a. is unaffected by changes in temperature and pH.

b. corresponds to the highest Gibbs free energy state.

c. is determined by its primary amino acid sequence.

d. corresponds to the lowest entropic state.

#Question id: 913

#Unit 1. Structure and Function of Biomolecules

The appropriate folding of a newly translated product is essential, and continual misfolding often leads to disease, especially in vertebrates. This misfolding, particularly in the situation of prion diseases, may be due to