Cell Biology: Intracellular Compartments & Protein Sorting PDF

Starting point for protein synthesis and folding. **Endoplasmic Reticulum (ER)**...

Starting point for protein synthesis and folding. **Endoplasmic Reticulum (ER)** **Rough ER (RER)**: Ribosomes synthesize proteins for secretion or organelle use. Modifies, sorts, and packages proteins for **X-linked Adrenoleukodystrophy**: Mutation in **Golgi Apparatus** various destinations. ABCD1 gene causes fatty acid accumulation, impacting the brain and adrenal glands. **Overview of Intracellular **Lysosomes** Contains enzymes for digestion within acidic **Genetic Disorders Related to Peroxisomes** **Peroxisomal Disorders** Compartments and Protein Sorting** environments. **Zellweger Syndrome**: Caused by a defect in peroxisome biogenesis, leading to severe Conducts oxidative reactions, breaks down developmental issues and often fatal early in **Peroxisomes** fatty acids, detoxifies harmful substances. life. Stores genetic material, coordinates activities **Nucleus** (growth, metabolism, protein synthesis). **Biogenesis**: Forms from existing peroxisomes or ER-derived vesicles. Powerhouse of the cell, generating ATP through **Mitochondria**  **Peroxisome Biogenesis and cellular respiration. **Peroxisomal Targeting Signals (PTS)**: Short Protein Import** amino acid sequences direct proteins to  **Protein Import** peroxisomes, using PTS1 (C-terminal) or PTS2 (N-terminal) signals. Composed of membrane-bound cisternae organized into compartments. **Cis side**: Receiving side, closer to the ER. **Structure**: Membrane-bound, containing **Polarity** enzymes for oxidation reactions. **Trans side**: Sending side, closer to the **Structure of the Golgi Stack** plasma membrane. **Oxidases**: Produce hydrogen peroxide (H₂O₂) during substrate oxidation. **Cis-Golgi Network (CGN)**: Receives vesicles **Key Enzymes and Reactions** **Peroxisomes: Structure and from ER. **Catalase**: Breaks down H₂O₂, prevents Enzymatic Functions** oxidative damage. **Medial Golgi**: Site of protein processing and **Compartments** modifications. **Detoxification**: Converts H₂O₂ into water and **Golgi Apparatus Structure and oxygen. Function** **Trans-Golgi Network (TGN)**: Final stage of **Detoxification and Biosynthetic Functions** protein sorting and packaging. **Biosynthesis**: Produces essential molecules  like cholesterol and bile acids. **Glycosylation**: Addition of carbohydrate chains for protein stability and function. **Protein Processing**: Further glycosylations, **Structure**: Spherical vesicles with acid hydrolases functioning optimally at acidic pH.  **Functions of the Golgi Apparatus** **Modification and Sorting of Proteins** sulphations, and phosphotransferase tagging for lysosome targeting. **Primary Lysosomes**: Contain enzymes but no substrates. **Membrane and Lysosome Formation**: Generates new lysosomes, recycles or creates  membranes as needed. **Secondary Lysosomes**: Formed when primary lysosomes fuse with vesicles containing **Types of Lysosomes** materials to digest. **Lysosomal Proteins**: Mannose-6-phosphate **Residual Bodies**: Contain undigested (M6P) tags in cis-Golgi direct proteins to materials, may be expelled or remain in the cell. lysosomes. **N-Glycosylation** (initiated in ER and **Acidic Environment Maintenance**: H⁺ pumps continued in Golgi) **Membrane and Secreted Proteins**: Further on membranes keep the pH low by actively **Lysosome Structure and Function** modified to complex glycoproteins with sugars pumping protons into the lumen. like N-acetylglucosamine, galactose, and sialic acid. Lysosomal enzymes tagged with M6P in Golgi, **Protein Glycosylation Process in recognized by M6P receptors in TGN, **Transport to Lysosome** **Lysosome Biogenesis and Function** the Golgi** **Lysosomal Proteins**: M6P receptor in TGN transported in vesicles that fuse with binds and packages for lysosome delivery. endosomes to mature into lysosomes. **Regulated Secretion Pathway**: Specific **Phagocytosis**: Engulfs large particles. **TGN Sorting Mechanisms** signals direct proteins to secretory vesicles. **Endocytosis**: Internalizes smaller particles. **Constitutive Secretion Pathway**: Proteins without signals transported to cell surface by  **Autophagy**: Digests cellular components. **Lysosomal Degradation Pathways** default. **Microautophagy**: Engulfs small cytoplasmic  portions directly. **KDEL Sequence** (soluble ER-resident proteins): Keeps proteins in ER. **ER Retention Signals** Orientation established in ER is conserved **KKXX Motif** (ER transmembrane proteins): throughout vesicular transport, including  **Membrane Protein Orientation** **Orientation of Transmembrane Retains membrane proteins in ER. orientation of glycoproteins in Golgi and Proteins** **Retention and Retrieval Signals** beyond. Proteins escaping to Golgi are retrieved **Retrieval Mechanism** through CGN receptors recognizing these  signals and sending them back to ER.