Скачать или смотреть Endomembrane system_Endoplasmic reticulum,Golgi bodies,Vacuoles,Lysosomes

Endomembrane System
This document outlines the structure and function, and describes components of the endomembrane system (Endoplasmic Reticulum, Golgi apparatus, Lysosomes, Vacuoles) and their coordinated roles in cellular processes.

8.5.3. Endomembrane System
• A system of membrane organelles whose functions are coordinated.
• Crucial for synthesizing, modifying, packaging, and transporting lipids and proteins.
• Includes:
• Endoplasmic Reticulum (ER)
• Golgi complex
• Lysosomes
• Vacuoles
• Organelles NOT part of Endomembrane System: Mitochondria, Chloroplasts, Peroxisomes (due to uncoordinated functions).
8.5.3.1. Endoplasmic Reticulum (ER)
• Discovery: Porter and Thompson (1945); named by Porter (1953).
• A 3-dimensional, complicated, and interconnected system of membrane-lined channels in the cytoplasm.
• Types:
• Smooth Endoplasmic Reticulum (SER):
• Smooth membrane, made of vesicles and tubules.
• Engaged in synthesizing and storing glycogen, lipids, and sterols (e.g., steroidal hormones).
• Rough Endoplasmic Reticulum (RER):
• Ribosomes attached to its outer surface.
• Engaged in synthesizing membrane proteins, proteins for secretion, and storage.
• Functions:
• Cytoskeleton/Ultrastructural Framework: Provides mechanical support.
• Intracellular Transport: Quick transport system.
• Protein Synthesis (RER): Actively involved in synthesizing membrane and other proteins; proteins enter RER channels.
• Precursor Provision: Provides precursors for secretory substances to the Golgi apparatus.
• Membrane Provision: Provides membranes to the nuclear envelope during nuclear differentiation after cell division.
• Lipid Synthesis (SER): Major site for lipid synthesis, including steroidal hormones.
8.5.3.2. Golgi Apparatus (Golgi Complex)
• Discovery: Camillo Golgi (1898) observed a densely stained reticular structure near the nucleus.
• Structure:
• Consists of flat, disc-shaped sacs called cisternae (0.5-1.0 µm diameter) stacked parallel.
• Made up of cisternae, tubules, vesicles, and vacuoles.
• Cisternae are concentrically arranged with a distinct convex cis (forming) face and a concave trans (maturing) face.
• Cis and trans faces are different but interconnected.
• Functions: Performs transformation, synthetic, and secretory roles.
• Secretion: Glandular cells depend on Golgi for secreting substances.
• Secretory material from ER reaches the forming face via vesicles.
• Processed material moves to secretion vesicles, which then fuse with the plasma membrane to release products (reverse pinocytosis).
• Membrane Transformation: Converts one type of membrane into another.
• Glycoprotein Processing: Glycoproteins synthesized in RER lumen pass into Golgi cisternae, then to cell walls and other places via vesicles.
• Hormone Production: Mediates hormone production in endocrine glands.
• New Cell Wall Formation: Secretes pectic compounds (middle lamella) and various polysaccharides for the cell wall.
8.5.3.3. Lysosomes
• "Lysis" (digestive/loose) + "Soma" (body).
• Small vesicles bounded by a single membrane.
• Contain hydrolytic enzymes (lipases, proteases, carbohydrases) in minute crystalline or semi-crystalline granules (5-8 nm).
• Spheroidal to irregular in shape.
• Formed by the joint activity of ER and Golgi bodies.
• Functions:
• Intracellular Digestion: Digest food obtained by phagocytosis.
• Extracellular Digestion: Release hydrolytic enzymes into the external environment via exocytosis.
• Cell Division: Play a role by overcoming agents that repress the mitotic cycle.
Vacuoles
• Membrane-bound space in the cytoplasm.
• Contains water, sap, excretory products, and other materials not useful for the cell.
• Tonoplast: The membrane surrounding the vacuole.
• In Plants: Vacuoles can occupy up to 90% of cell volume.
• In Amoeba: Water vacuoles and contractile vacuoles (important for osmoregulation by pumping excess water out of the cell) are present.
• In Protists: Food vacuoles are present.

Cell Membrane#NCERT#10+1#NEET#Cell-the unit of life
   • Cell Membrane#NCERT#10+1#NEET#Cell-the uni...