Extracellular matrix comprises of various proteins and polysaccharides that assemble into an organized meshwork. This associates with the cells that produce them. Given below are a few statements regarding different components of the matrix. A. Collagen is the major protein of the extracellular matrix and is a long, and triple-stranded helical structure. B. Hyaluronan which is produced in large quantities during wound healing is a type of glycosaminoglycan (GAG) that contains sulfated sugar and is covalently linked to the core protein. C. Syndecans are plasma membrane proteoglycans that interact with the actin cytoskeleton and signaling molecules of the cell cortex. D. Decorin is a small proteoglycan secreted by fibroblasts and contains 1-10 GAG chains. Which one of the following options represents INCORRECT statement/s?
B only
Extracellular Matrix Components
The extracellular matrix (ECM) is a complex network of secreted molecules that provides structural support, regulates cell behavior, and plays crucial roles in tissue development and homeostasis. It comprises various proteins like collagen and elastin, and polysaccharides, primarily glycosaminoglycans (GAGs) and proteoglycans.
The question asks us to identify the incorrect statement among the given descriptions of different ECM components.
Analyzing Statements on ECM Components
- Statement A: Collagen is the major protein of the extracellular matrix and is a long, and triple-stranded helical structure.
This statement is correct. Collagen is the most abundant protein in the ECM of animals. Collagen molecules are typically composed of three polypeptide chains that wrap around each other to form a characteristic triple helix.
- Statement B: Hyaluronan which is produced in large quantities during wound healing is a type of glycosaminoglycan (GAG) that contains sulfated sugar and is covalently linked to the core protein.
This statement is incorrect. Hyaluronan (also known as hyaluronic acid) is indeed a type of glycosaminoglycan and is produced in large quantities during processes like wound healing, where it helps in hydration and cell migration. However, Hyaluronan is unique among the major GAGs because it is unsulfated. Furthermore, it does not exist as a proteoglycan; it is not covalently linked to a core protein, but rather exists as a free, very large polysaccharide chain.
- Statement C: Syndecans are plasma membrane proteoglycans that interact with the actin cytoskeleton and signaling molecules of the cell cortex.
This statement is correct. Syndecans are a family of transmembrane proteoglycans found on the surface of cells. Their extracellular domain binds to various ECM components and growth factors, while their intracellular domain interacts with components of the actin cytoskeleton and signaling molecules within the cell cortex, thus acting as links between the ECM and intracellular pathways.
- Statement D: Decorin is a small proteoglycan secreted by fibroblasts and contains 1-10 GAG chains.
This statement is generally considered correct in the context of identifying the most incorrect statement. Decorin is classified as a small leucine-rich proteoglycan (SLRP). It is secreted by fibroblasts and other cells and typically contains one GAG chain (either chondroitin sulfate or dermatan sulfate). While the range "1-10" might be broader than the most common structure (one chain), the core description of Decorin as a small proteoglycan from fibroblasts is accurate.
Identifying the Incorrect Statement
Based on the detailed analysis, Statement B contains factual inaccuracies regarding the chemical nature and structural association of Hyaluronan. Hyaluronan is unsulfated and is not covalently linked to a core protein, unlike most other GAGs that form proteoglycans.
Conclusion
Therefore, the incorrect statement is Statement B.
The option that correctly identifies the incorrect statement(s) is the one listing only B.
Important Questions from Cellular communication
In a neuron, proteins and membranes are primarily synthesized in the cell body. These materials must be transported down the axon to the synaptic region using microtubules in an anterograde fashion. Such axonal transport is directed by
Acetylcholine is a potent neurotransmitter, which is released from the neurons. After release they diffuse across the synaptic cleft and combine with nicotinic acetylcholine receptor molecules in the membrane of the postsynaptic cell. The interaction of acetylcholine with the nicotinic acetylcholine receptor produces large transient increase in the permeability of the membrane to specialized ions resulting in signal transduction for nerve impulse. Acetylcholine receptor is a
Column X represents the type of junctions and column Y represents the proteins associated with the junctions.
Column X
Column Y
A.
Anchoring junction
i.
Claudins
B.
Occluding junction
ii.
Delta-Notch
C.
Channel-forming junction
iii.
Desmoglein
D.
Signal-relaying junction
iv.
Connexin
Which one of the following options is a correct match between terms of Columns X and Y?
Bacteria employ various mechanisms to invade or enter host cells, which are either phagocytic or non-phagocytic in nature. Given below are some of the mechanisms which are generally used for carrying out this process.
A. Some bacteria express a protein called invasin that is recognized by host-cell β1 integrins.
B. Actin polymerization along with assembly of clathrin coat results in the internalization of bacteria by zipper mechanism.
C. Some bacteria, including Salmonella enterica, use trigger mechanism to inject a set of effector molecules in the cytosol through type III secretion system.
D. Some bacteria attach to host cell surface receptors inducing local elevation of Ca2+ in cell cytosol, leading to the fusion of lysosomes with bacteria containing plasma membrane vesicles.
Which one of the following represents the combination of correct mechanisms for invading non-phagocytic cells?
In C. elegans, PAR proteins segregate at the cell cortex in the zygote to establish cell polarity. This is dependent on the regulation of the cortical actin cytoskeleton by RhoA. An investigator sought to directly inhibit actin polymerization to analyze the impact of this inhibition on PAR protein localization. Which one of the following chemicals would be the most suitable?
