Study eCentre

Anterograde transport refers to the forward movement of proteins and lipids from the endoplasmic reticulum (ER) towards their final destinations, such as the Golgi apparatus, plasma membrane, or extracellular space. This process is a highly regulated and directional pathway, which ensures that proteins follow a proper route, allowing cells to maintain organisation, compartmentalisation and functional efficiency. The transport is carried out using vesicles, and involves several organelles and protein complexes working in coordination. This process can be described in five major steps, beginning in the rough ER and progressing toward the cell membrane or beyond: Step 1: Protein Synthesis and Folding in the Rough ER Anterograde transport begins with the synthesis of proteins on membrane-bound ribosomes of the rough ER. As the proteins are translated, they are inserted into the ER lumen or membrane. Within the ER, they undergo initial folding, assembly, and modifications, including N-linke...

The targeting of soluble lysosomal proteins, such as hydrolytic enzymes, to endosomes and lysosomes is a well-organised and highly regulated process. This mechanism ensures that such enzymes reach the lysosomes accurately, where they are needed for intracellular digestion, and are not secreted outside the cell. This entire process takes place through a series of interconnected steps, involving specific molecular signals, vesicle formation and organelle targeting, which begins in the rough endoplasmic reticulum (RER) and ends in the lysosome. Step 1: Synthesis in the Rough Endoplasmic Reticulum (RER) Soluble lysosomal enzymes are synthesised by ribosomes attached to the rough ER. As the mRNA is translated, the growing polypeptide is inserted into the ER lumen. Inside the ER, these proteins are properly folded and undergo N-linked glycosylation, which prepares them for further modifications in the Golgi. Step 2: Transfer to the Golgi Apparatus From the ER, the glycosylated proteins are t...

SAQ Fill in the blanks:  a) The basic unit of microtubules is …………… . Answer: α β tubulin heterodimers b) α tubulin occurs at ............. end, and β tubulin is at .............. of microtubules. Answer: plus, minus c) GTP-GTP tubulin cap stabilises and promotes the .................. . Answer: polymerisation of microtubules d) The plus end-directed motor protein of microtubules is …………. . Answer: kinesin e) The hydrolysis of GTP from β-tubulin causes …………. of microtubules. Answer: Depolymerisation f) The cellular function of γ-tubulins is. ………..... . Answer: nucleate the growth of MTs  g) Colchicine binds to ………… . Answer: free tubulin SAQ 2 a) Classify the microtubules involved in mitosis. Microtubules play a central role during mitosis by forming the mitotic spindle, which ensures the correct segregation of chromosomes into daughter cells. These microtubules are dynamically reorganized during cell division and can be classified into three main types, based on their...

In eukaryotic cells, protein trafficking is a highly regulated and stepwise process that ensures proteins reach their correct destination either within the cell or outside of it. Two major organelles that perform central roles in this process are the  Endoplasmic Reticulum (ER) and the Golgi Complex.  Together, these organelles carry out multiple interconnected functions such as protein synthesis, folding, quality control, modification, sorting, and vesicle-mediated transport. Their roles are highly coordinated and form the backbone of the endomembrane trafficking system. Role of the Endoplasmic Reticulum (ER) The ER is the first organelle involved in the protein trafficking pathway. It exists in two forms, rough ER (RER) and smooth ER (SER). Among these, the rough ER is primarily involved in protein trafficking. It is called "rough" because it is studded with ribosomes, which are the sites of protein synthesis. The RER plays several important roles in protein trafficking: Sy...

The endomembrane system is a group of interconnected membrane-bound organelles found in eukaryotic cells. This system is responsible for the synthesis, modification, transport, and sorting of proteins and lipids within the cell. All organelles in this system are either physically connected or communicate with each other through vesicle-mediated transport. This system helps in maintaining the organisation, compartmentalisation and communication between different parts of the cell. The word "endomembrane" means "within the membrane" and this system is very important for keeping the cell functioning smoothly. Main Components of the Endomembrane System There are six major components that make up the endomembrane system. These are: 1. Nuclear Envelope The nuclear envelope is a double membrane that surrounds the nucleus. It contains nuclear pores that allow the controlled exchange of materials (like mRNA and proteins) between the nucleus and the cytoplasm. Its outer membr...

The trafficking of soluble lysosomal enzymes from the trans-Golgi network (TGN) and sometimes the cell surface to the lysosomes is a highly regulated, multistep process. This mechanism ensures that lysosomal hydrolases are specifically recognized, sorted and delivered to their correct destination without getting misdirected or secreted. This sorting is based mainly on mannose-6-phosphate (M6P) tags present on the enzymes, which act as a signal for targeting. There are five major steps in this trafficking pathway: 1. Tagging with Mannose-6-Phosphate in the Golgi Apparatus Soluble lysosomal enzymes are first synthesized in the rough endoplasmic reticulum (RER) and transported to the cis-Golgi. Inside the Golgi, they are modified by a two-step enzymatic reaction: An enzyme called  N-acetylglucosamine-1-phosphotransferase  attaches a phosphorylated N-acetylglucosamine (GlcNAc-P) group to the mannose residue of the N-linked oligosaccharides on the enzyme. Another enzyme removes the...

SAQ 1 a) Microfilaments, composed of the protein ……………………play a key role in cell movement and contraction. b) The cytoskeleton is essential for the proper segregation of chromosomes during …………………… c) The cytoskeleton is crucial for the maintenance of ……………………the balance of solutes inside and outside the cell. Answer: homeostasis. d) The dynamic nature of actin filaments involves constant ……………………and depolymerization. e) Actin-binding proteins like ……………………regulate the branching of actin filaments. f) In treadmilling, the addition of……………………to the barbed end occurs while monomers are simultaneously removed from the pointed end. Answers:  (a) actin, (b) mitosis, (c) homeostasis, (d) polymerisation, (e) Arp2/3 complex, (f) G-actin SAQ 2  a) What is the cortical cytoskeleton? The cortical cytoskeleton is a specialized and dynamic part of the cell's cytoskeleton located just beneath the plasma membrane. It is primarily composed of actin filaments (microfilaments) along with assoc...