Exam 13: Intracellular Membrane Traffic

How can the formation of tubular structures, as opposed to spherical vesicles, in the early endosomes facilitate recycling of membrane proteins such as cell-surface receptors?

Indicate whether each of the following processes is topologically similar (Y) or not similar (N) to formation of intralumenal vesicles in multivesicular bodies. Your answer would be a four-letter string composed of letters Y and N only, e.g. YYYY. ( ) Fission of peroxisomes ( ) Formation of clathrin-coated vesicles ( ) Budding of HIV from infected cells ( ) Cytokinesis

What is the cellular function of plant vacuoles?

Consider a perfectly assembled clathrin cage that is composed of 12 pentagons and 20 hexagons and therefore resembles a soccer ball. How many clathrin heavy chains are there in this cage? Write down the number as your answer, e.g. 24.

Indicate which one of the indicated types of coat proteins (A, B, and C) in the schematic diagram below corresponds to COPI, COPII, and clathrin, respectively. Your answer would be a three-letter string composed of letters A to C only, e.g. CBA.

A protein that is normally not expressed in epithelial cells has been induced in these cells and has been engineered such that a GPI anchor is attached to it as it is processed in the ER. Would you expect to find this protein in the apical (A) or basolateral (B) domain of the plasma membrane in these cells? Write down A or B as your answer.

Sort the following events to reflect the order in which they occur during the formation of vesicles from the ER destined for the Golgi apparatus. Your answer would be a four-letter string composed of letters A to D only, e.g. DACB. (A) Sar1 GTP hydrolysis (B) Sar1 GTP binding (C) Sar1-Sec23 binding (D) Sar1 membrane association

Phosphoinositides mark different cellular membranes and play key roles in protein trafficking inside the cell. Among them, PI(4,5)P₂ is involved in receptor-mediated endocytosis as well as phagocytosis at the plasma membrane. This phosphoinositide …

Which of the following pathways does NOT directly deliver materials to lysosomes?

Indicate true (T) and false (F) statements below regarding receptor-mediated endocytosis of LDL particles. Your answer would be a four-letter string composed of letters T and F only, e.g. TTTF. ( ) LDL receptors are normally degraded in the lysosome along with their LDL ligands. ( ) LDL receptors that do not bind to extracellular LDL cannot be internalized in clathrin-coated vesicles. ( ) A mutation that impairs the attachment of an LDL receptor to a clathrin-coated pit would cause depletion of blood LDL levels. ( ) LDL receptors at the plasma membrane are usually concentrated in clathrin-coated pits.

Indicate true (T) and false (F) statements below regarding glycosylation of proteins in the endoplasmic reticulum and the Golgi apparatus. Your answer would be a four-letter string composed of letters T and F only, e.g. TTTF ( ) Glycosylation can promote protein folding. ( ) The glycosylation state of a protein can determine its fate along the secretory pathway. ( ) Glycosylation makes a protein more accessible to proteases and other proteins. ( ) Glycosylated proteins are generally more flexible.

How does the affinity of M6P receptor proteins for the mannose 6-phosphate marker change between the TGN and early endosome? Which coat protein is mainly responsible for their transport from the TGN to the endosome?

How many protons [or, more accurately, hydronium ions (H₃O⁺)] are there in a spherical lysosome that is about 0.6 µm in diameter and maintains an interior pH of about 5.0? Recall that the volume of a sphere of radius r is calculated as V = 4/3 × π × r³, and that pH = -log [H⁺]. Avogadro's constant is approximately 6 × 10²³ molecules/mole.

Lysosomes are the principal site of cellular digestion. They …

Which of the following is NOT correct regarding M6P receptors and KDEL receptors?

You know that a particular sequence at the C-terminus of the lectin ERGIC53 enhances its exit from the endoplasmic reticulum (ER). You create two mutant versions of the protein, one without the suspected sequence (1) and one in which the sequence is replaced with an ER retention signal (2). You transfect a fibroblast cell line with a plasmid that encodes either wild-type ERGIC53 (0) or one of the engineered versions of it (1 or 2). After inducing the expression of the proteins, you lyse the cells and either treat the lysate with endoglycosidase H (Endo H) or leave the lysate untreated, as indicated below. You then separate the proteins by SDS-PAGE and perform a Western blot to detect the bands corresponding to ERGIC53. Your results are represented in the following drawing. Which lanes (A to C) do you expect to correspond to each of the proteins 0, 1, and 2, respectively? Your answer would be a three-letter string composed of letters A to C only, e.g. CAB.

If this protein is unable to hydrolyze its bound GTP, invaginated clathrin-coated pits accumulate but fail to pinch off from the plasma membrane. In neurons, long vesicle necks collared by the protein are observed and presynaptic endocytosis is blocked. This protein …

Sort the following events to reflect the order in which they occur during vesicle docking onto a target membrane, starting with an inactive Rab in the cytosol. Your answer would be a four-letter string composed of letters A to D only, e.g. DACB. (A) Rab is bound to its effector (tethering protein) on the target membrane. (B) Rab is bound to its Rab-GDI. (C) Rab is bound to the membrane in its GTP-bound form. (D) Rab dissociates from the membrane.

Indicate whether each of the following descriptions better applies to COPI- (1), COPII- (2), or clathrin- (3) coated vesicles. Your answer would be a four-digit number composed of digits 1 to 3 only, e.g. 1322. ( ) They mediate transport from the ER to the cis Golgi network. ( ) Their coat protein forms a three-legged structure called a triskelion. ( ) They are pinched off from their donor compartment by a dynamin collar. ( ) They are involved in retrograde transport in the Golgi apparatus.

Indicate whether each of the following descriptions better applies to the cisternal maturation model (C) or the vesicle transport model (V) for the organization of the Golgi apparatus. Your answer would be a four-letter string composed of letters C and V only, e.g. CVCV. ( ) Golgi cisternae are static organelles. ( ) Golgi cisternae exchange material exclusively by retrograde vesicular transport. ( ) A cis Golgi cisterna becomes a medial cisterna which becomes a trans cisterna. ( ) Any protein that passes through the Golgi apparatus should be incorporated into transport vesicles several times.