Given below are a few steps in clathrin‐coated vesicle formation in the secretory pathway. (A) Receptor‐ligand recognition and binding (B) Recruitment of adapter protein and clathrin (C) Vesicle formation (D) Uncoating of clathrin coats Choose the option that correctly identifies the sequence of events in making a clathrin‐coated vesicle.
A, B, C, D
Clathrin-coated vesicles play a crucial role in transporting proteins and lipids within cells, particularly in processes like endocytosis and transport from the trans-Golgi network. The formation of these vesicles involves a series of coordinated steps at the membrane.
Clathrin-Coated Vesicle Formation Sequence
The process of forming a clathrin-coated vesicle from a donor membrane involves the following steps in a specific order:
- (A) Receptor-ligand recognition and binding: The process begins when specific cargo molecules (ligands) bind to their corresponding receptors embedded in the donor membrane (e.g., plasma membrane, trans-Golgi network). This binding is the initial signal that marks the area for vesicle formation.
- (B) Recruitment of adapter protein and clathrin: Once the receptor-ligand complex is formed, it attracts and recruits adapter proteins (like AP complexes) to the membrane site. These adapter proteins serve as a link between the receptors and the clathrin coat proteins. Clathrin proteins, which are triskelions, then assemble onto the adapter proteins, forming a lattice-like structure on the cytosolic side of the membrane.
- (C) Vesicle formation: The assembly of the clathrin lattice induces curvature in the membrane, causing it to bud outwards or inwards. As more clathrin triskelions are added and polymerize, the membrane invaginates further. Accessory proteins, such as dynamin, are then recruited to the neck of the budding vesicle to facilitate the final pinching off (scission) of the membrane, resulting in a free clathrin-coated vesicle.
- (D) Uncoating of clathrin coats: Shortly after the vesicle buds off from the donor membrane, the clathrin coat, and often the adapter proteins, are rapidly disassembled and removed. This uncoating step is essential because the clathrin coat needs to be removed for the vesicle membrane to be able to fuse with its target membrane.
Therefore, the correct sequence of events in the making of a clathrin-coated vesicle, from the initial signal to becoming a fusion-competent vesicle, is the sequential progression through receptor binding, adapter and clathrin recruitment, vesicle budding, and finally, uncoating.
The order of events is:
(A) Receptor-ligand recognition and binding → (B) Recruitment of adapter protein and clathrin → (C) Vesicle formation → (D) Uncoating of clathrin coats
This sequence corresponds directly to the options provided.
Important Questions from Cell Division and Cell Cycle
During cell cycle, entry in the S-phase is tightly regulated. This is possible because:
A. APC/C promotes ubiquitination of S-phase cyclins and mitotic cyclins, marking them for proteolyses at the mitotic exit.
B. Cyclin B1 helps in the activation of S-phase CDKs only in late G1.
C. As mitotic CDK activity declines in late mitosis, cdc14 phosphatase activates APC/C by dephosphorylating Cdh1, thus promoting formation of APC/CCdh1
D. Securin keeps S-phase cyclins in inactive state till late G1.
Which one of the options represents all correct statements?
Following statements were made about cell cycle regulation:
A. De novo synthesis and destruction of Cyclin B are essential for cell cycle progression in yeast.
B. De novo synthesis and destruction of Cyclin B and the related Cyclin dependent Kinase (CDK) are essential for cell cycle progression.
C. CDK activity is regulated by both activating and inhibitory phosphorylation.
D. Retinoblastoma (Rb) functions as an inhibitor of G2 to M transition.
E. Inactivation of Sic 1 is essential for transition into S phase.
Which one of the following represents the combination of the correct statements?
The table below lists cell cycle regulatory proteins and their known functions
Which one of the following options represents the correct match between cell cycle regulatory proteins with their known functions?Cell Cycle regu latory proteins Function A Cdk-activating kinase (CAK) (i) Suppresses G1/S-Cdk and S-Cdk activation in G1; helps cells withdraw from cell cycle when they terminally differentiate; phosphorylation by Cdk2 triggers its ubiquitylation by SCF. B Wee1 kinase (ii) Suppresses G1/S-Cdk and S-Cdk activities following DNA damage C p27 (mammals) (iii) Phosphorylates inhibitory sites in Cdks: primarily involved in suppressing Cdk1 activity before mitosis D p21 (mammals) (iv) Phosphorylates an activating site in Cdks Following statements were made about the characteristics of cyclin proteins:
A. Synthesis of M-cyclin is dependent on the cyclin mRNA that is newly transcribed after every cycle.
B. Destruction of M-cyclin toward the end of mitosis is driven by ubiquitin independent proteolytic system.
C. G1 cyclins can be activated by mitogenic factors.
D. Retinoblastoma (Rb) is a key target of the activated cyclin D - Cdk 4/6 complex.
E. While cyclin A1 expression is ubiquitous, cyclin A2 expression is restricted to the germ cell lineages.
Which one of the following options contains a combination of all correct statements?
To test the impact of cAMP on protein kinase A conformation in cells, an investigator made FRET biosensor by fusing two fluorescent proteins at the N-and C-terminus of protein kinase A. In the absence of cAMP in the cellular milieu, no FRET signal was detected. However, upon cAMP addition, a strong emission at 530 nm was observed. What could be the best configuration of fluorophores that were used by the investigator?
