Questions 118-121 refer to the following cellular processes.Show answers
(A) Phagocytosis
(B) Exocytosis
(C) Endocytosis
(D) Transcytosis
(E) Apoptosis
118. Movement of plasma membrane receptors from the basolateral surface to the apical surface of polarized epithelial cells
119. Up-regulation of glucose transporters at the plasma membrane
120. Selective retrieval of cell-surface proteins for recycling or degradation
121. Neurotransmitter release
Questions 124-126 refer to the following protein-modifying reagents.
(A) Chymotrypsin
(B) Cyanogen bromide
(C) Iodoacetamide
(D) Phenylglyoxal
(E) Pyridoxal 5′-phosphate
124. Forms a Schiff-base linkage with the epsilon-amino group of lysine residues
125. Specifically cleaves polypeptides on the carboxyl side of methionine residues
126. Generally used as a sulfhydryl-modifying reagent
Questions 127-129 refer to the following cell structures.
(A) Thylakoid membrane
(B) Nuclear lamina
(C) Eubacterial cell wall
(D) Plant cell wall
(E) Endoplasmic reticulum
127. Its assembly is inhibited by penicillin.
128. It is formed from polymeric fibrils composed of cellulose cross-linked by pectin and hemicellulose.
129. It is the site of dolichol phosphate function.
It is important here to notice that one answer can be right for several questions.
Now lets try to describe each process announced. So phagocytosis is process of "eating" external organells by the cell. It is quite close to endocytosis, when – in contrast – molecules are being absorbed. Exocytosis is opposite process – secretion of molecules into external space. It can be hormones, antibodies and so on. Transcytosis is interesting process of transporting molecules from apical (absorbing) space of polarized cells to basolateral space, which happens, for example, when antibodies are transported through baby rat's gut. Main idea is that molecules are absorbed into internal vesicles (as during endocytosis) and then after several steps containers' content is exposed as during exocytosis. No target molecules are left in cell's plasma. Interesting is that cell can regulate exposure of some proteins in the cell membrane using transcytosis. During latent phase (e.g. while there is no great need in glucose) transporters are stored incorporated in vesicles inside the cell. But in case of emergency (or if cell is stimulated, by insulin in our case) that vesicles fuse into plasma membrane and transporters expose into extracellular space and begin to work. Last one is apoptosis which is self-destroying of the cell. That happens if crucial malfunction appear or cell's mission was fulfilled. So the answer are like that. I suppose, answer D is suitable for both two first questions.
118 D. 119 D. 120 C. 121 B.
Chymotripsin is protein, enzyme actually, of so-called class of proteases. It cleaves specific polypeptide regions near serine, so it is called serine protease.
Cyanogen bromide is simple small molecule CNBr and, as written in wikipedia, is used to immobilize proteins by gluing them to agarose gel during chromatography. But more important is that CNBr cleaves polypeptide chains at C-terminus of methionine.
Iodoacetamide is substance that can bind covalently with cysteine to prevent formation of disulfide bonds. So it can be called sulfhydryl modifying reagent.
Phenylglyoxal modifies arginine.
Pyridoxal 5′-phosphate (or PLP) is active form of vitamin B6. As written in wikipedia (again, yeah) it forms Schiff-base linkage the ε-amino group of a specific lysine group of the aminotransferase enzyme.
124 E. 125 B. 126 C.
This questions uncovers very specific properties of very important and well-known objects. So I will not discuss all of them, but just give right answers and some interesting details if I find any.
All options are common in one: they are membranes or structures, that acts like membranes – support shape (cell walls and nuclear lamina) and protect internal content. But they have different structure, functions and behavior.
127 C. Notice that eubacteria is synonym for bacteria.
128 D. 129 E. Dolichol phosphate acts in formation of membrane-associated glycoproteins, so I suppose its site is on the ER membrane.
Now lets try to describe each process announced. So phagocytosis is process of "eating" external organells by the cell. It is quite close to endocytosis, when – in contrast – molecules are being absorbed. Exocytosis is opposite process – secretion of molecules into external space. It can be hormones, antibodies and so on. Transcytosis is interesting process of transporting molecules from apical (absorbing) space of polarized cells to basolateral space, which happens, for example, when antibodies are transported through baby rat's gut. Main idea is that molecules are absorbed into internal vesicles (as during endocytosis) and then after several steps containers' content is exposed as during exocytosis. No target molecules are left in cell's plasma. Interesting is that cell can regulate exposure of some proteins in the cell membrane using transcytosis. During latent phase (e.g. while there is no great need in glucose) transporters are stored incorporated in vesicles inside the cell. But in case of emergency (or if cell is stimulated, by insulin in our case) that vesicles fuse into plasma membrane and transporters expose into extracellular space and begin to work. Last one is apoptosis which is self-destroying of the cell. That happens if crucial malfunction appear or cell's mission was fulfilled. So the answer are like that. I suppose, answer D is suitable for both two first questions.
118 D. 119 D. 120 C. 121 B.
Chymotripsin is protein, enzyme actually, of so-called class of proteases. It cleaves specific polypeptide regions near serine, so it is called serine protease.
Cyanogen bromide is simple small molecule CNBr and, as written in wikipedia, is used to immobilize proteins by gluing them to agarose gel during chromatography. But more important is that CNBr cleaves polypeptide chains at C-terminus of methionine.
Iodoacetamide is substance that can bind covalently with cysteine to prevent formation of disulfide bonds. So it can be called sulfhydryl modifying reagent.
Phenylglyoxal modifies arginine.
Pyridoxal 5′-phosphate (or PLP) is active form of vitamin B6. As written in wikipedia (again, yeah) it forms Schiff-base linkage the ε-amino group of a specific lysine group of the aminotransferase enzyme.
124 E. 125 B. 126 C.
This questions uncovers very specific properties of very important and well-known objects. So I will not discuss all of them, but just give right answers and some interesting details if I find any.
All options are common in one: they are membranes or structures, that acts like membranes – support shape (cell walls and nuclear lamina) and protect internal content. But they have different structure, functions and behavior.
127 C. Notice that eubacteria is synonym for bacteria.
128 D. 129 E. Dolichol phosphate acts in formation of membrane-associated glycoproteins, so I suppose its site is on the ER membrane.
