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What is the primary function of lysosomes in a cell?
Which type of lysosome is formed from the fusion of primary lysosomes with phagosomes?
What is contained within lysosomes that allows them to function effectively?
Which of the following is NOT a role of lysosomes?
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In what process do residual bodies play a significant role?
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What condition results from genetic defects in lysosomal hydrolases?
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What structural feature of lysosomes helps maintain their acidic environment?
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Which of the following statements about lysosomes is true?
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What is the primary function of the Rough Endoplasmic Reticulum (RER)?
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Which disease is directly associated with a deficiency in hexosaminidase-A?
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Which function is NOT associated with the Smooth Endoplasmic Reticulum (SER)?
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What characteristic distinguishes the Rough Endoplasmic Reticulum from the Smooth Endoplasmic Reticulum?
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What is a consequence of the immaturity of the Smooth Endoplasmic Reticulum in newborns?
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Which of the following correctly defines a proteasome?
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Which type of cells is primarily responsible for synthesizing steroid hormones?
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What accumulates in lysosomes, leading to severe neuronal degeneration in a specific condition?
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What is the primary function of ubiquitin in cellular processes?
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Which of the following compounds are primarily produced through the beta oxidation process in peroxisomes?
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What key activity do peroxisomes perform to manage excess hydrogen peroxide?
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What is the consequence of defective peroxisomal proteins in the case of X-chromosome-linked adrenoleukodystrophy?
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Which type of ribosomes are primarily associated with the endoplasmic reticulum?
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Why are peroxisomes significant in kidney and liver cells?
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What distinguishes peroxisomes from lysosomes in terms of structure?
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What type of organelle is primarily responsible for synthesizing proteins in the cytoplasm?
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What is the primary function of ribosomes in nerve cells?
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Which of the following statements about the cytoskeleton is true?
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Which type of filament is classified as a microfilament?
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In which of the following cells would you find vimentin filaments?
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What structure is primarily associated with the process of mitosis?
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Which type of filament is NOT included in intermediate filaments?
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What is the significance of centrioles in eukaryotic cells?
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Which of the following best describes the structure of microtubules?
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What is the primary structure found in cilia that aids in their movement?
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Which organelle would be abundant in steroid biosynthesis cells observed under electron microscopy?
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What is the function of radial projections extending from the microtubule doublets in cilia?
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Which of the following is a symptom of immotile cilia syndrome?
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What structure in the basal body of cilia is identical to centrioles?
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What is one main characteristic that differentiates flagella from cilia?
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Which component of cilia contributes to their ability to move particles in one direction?
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How is the protein structure of cilia associated with immotile spermatozoa in Kartagener syndrome?
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Study Notes
Lysosomes
- Membranous, rounded vesicles that act as the cell's digestive system.
- Found in abundance in phagocytic cells like macrophages, neutrophils, and osteoclasts.
- Visible under a light microscope (LM) using special histochemical methods that detect their enzymes.
- Contain hydrolytic enzymes that are active under acidic pH conditions.
- The lysosomal membrane maintains an acidic environment for enzyme function and prevents the enzymes from destroying the cell.
Types of Lysosomes
Primary Lysosomes
- Newly formed from the Golgi apparatus.
- Small, homogeneous vesicles.
Secondary Lysosomes
- Large, heterogeneous vesicles that result from the fusion of primary lysosomes with phagosomes.
Functions of Lysosomes
- Digest foreign bodies like bacteria, providing cellular defense against invaders.
- Digest old organelles, replacing cellular components to maintain cell health.
- Digest entire cells after death (rupture of membrane), leading to postmortem autolysis.
- Help sperm to penetrate the ovum during fertilization.
- In the thyroid gland, break down inactive hormones into their active form.
- Residual bodies play a role in the aging process.
Lysosomal Storage Disorders
- Genetic defects in the production of specific lysosomal acid hydrolases can lead to the accumulation of specific molecules that cannot be degraded.
- Most defects are inherited as single gene autosomal recessive traits.
Examples of Lysosomal Storage Disorders
- Lysosomal glycogen storage disease (acid maltase deficiency): Accumulation of glycogen due to lack of breakdown.
- Tay–Sachs disease: Deficiency of the enzyme hexosaminidase-A, leading to accumulation of sphingolipids.
- Accumulation of lipids in lysosomes causes severe neuronal degeneration.
Endoplasmic Reticulum (ER)
Types of Endoplasmic Reticulum
- Rough Endoplasmic Reticulum (RER):
- Smooth Endoplasmic Reticulum (SER):
Rough Endoplasmic Reticulum (RER)
- Membranous organelle.
- LM: Localized cytoplasmic basophilia in certain cells.
- EM: Network of membranous vesicles and flat tubules (cisternae) covered with ribosomes.
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Function: Synthesizes proteins in attached ribosomes; separates proteins from cytosol within its cisternae. This includes:
- Formation of secretory proteins exported outside the cell.
- Formation of lysosomal enzymes.
- Formation of plasma membrane proteins.
Smooth Endoplasmic Reticulum (SER)
- Membranous organelle.
- LM: Not visible.
- EM: Network of branching, anastomosing tubules without ribosomes.
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Function: Functions vary depending on the cell. Some key functions include:
- In steroid-secreting cells: Synthesis of steroid hormones (e.g., cells of the adrenal cortex).
- In liver cells:
- Detoxification of certain drugs.
- Contains enzymes involved in utilizing glucose from glycogen.
- Immaturity of SER in liver cells causes physiological jaundice in newborns
- Synthesis of phospholipids for all cell membranes.
- Columnar absorptive cells of the small intestine: Lipid synthesis.
- Skeletal and cardiac muscle: Regulates calcium levels essential for muscle contraction.
- Parietal cells of the stomach: Responsible for concentrating Cl- ions to form HCl.
Proteasomes
- Non-membranous organelles composed of four stacked rings, each with seven proteins including proteases.
- Have a regulatory particle at each end that contains ATPase and recognizes proteins attached to ubiquitin.
- Function: Responsible for removing and restricting the activity of nonfunctional proteins.
- Ubiquitin: A cytoplasmic protein that attaches to nonfunctional proteins.
- Alzheimer's disease and Huntington's disease are neurologic disorders caused by accumulation of proteins inside the cells due to failure of degradation by proteasomes.
Peroxisomes (Microbodies)
- Membranous organelles that contain oxidative enzymes.
- Similar to lysosomes but larger.
- LM: Not demonstrated.
- EM: Finely granular homogeneous contents, less dense than lysosomes.
Functions of Peroxisomes
- Beta oxidation of long-chain fatty acids yielding H2O2.
- Detoxify noxious agents and kill microorganisms.
- Reduce excess H2O2 using catalase enzymes to produce O2 and H2O.
- Lipid metabolism.
- Abundant in liver and kidney cells.
Peroxisomal Disorders
- Defects in peroxisomal proteins can cause many disorders due to the organelle's role in metabolic pathways.
- X-chromosome-linked adrenoleukodystrophy: A common peroxisomal disorder caused by a defective membrane protein involved in transporting very long-chain fatty acids into the peroxisome for beta oxidation.
- Accumulation of these fatty acids in body fluids destroys myelin sheaths in nerve tissue, leading to severe neurological symptoms.
Ribosomes
- Small, rounded or oval cytoplasmic organelles.
- Free Ribosomes: Freely distributed in the cytoplasm and mitochondrial matrix.
- Attached Ribosomes: Attached to the membranes of endoplasmic reticulum (ER) and the outer nuclear membrane.
- Polysomes: Ribosomes held together by messenger RNA (mRNA).
Ribosomes Structure & Origin
- LM: Minute basophilic granules.
- Free Ribosomes: Diffuse cytoplasmic basophilia.
- Attached Ribosomes: Localized cytoplasmic basophilia, known as Nissl granules in nerve cells.
- EM: Composed of two subunits, a large and a small one.
- Origin: Formed in the nucleolus from RNA and protein (ribonucleoprotein).
Functions of Ribosomes
- Free Ribosomes: Synthesize proteins for cell growth and regeneration.
- Attached Ribosomes: Synthesize proteins for secretory activity and the formation of secretory granules.
Cytoskeleton
- Made of proteins.
- Acts as a structural framework for the cell.
- Maintains cell shape, stabilizes cell attachments, and plays a role in cell motility.
- Includes microtubules and microfilaments.
Microtubules
- Found in all cells individually or in groups.
- LM: Difficult to see, appear as filaments.
- EM: Long, slender tubules.
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Function:
- Form the cell's skeleton (cytoskeleton).
- Move cytoplasm.
- Involved in amoeboid movement of leukocytes.
- Move microvilli.
- Separate cytoplasm during cell division.
- Transport substances within the cytoplasm.
- Form spindle fibers during cell division.
Microfilaments
- Found in most cells individually or in groups.
- LM: Difficult to see.
- EM: Threads-like structures.
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Types of Intermediate Filaments:
- Keratin (tonofilaments): Found in epithelial cells.
- Vimentin Filaments: Found in fibroblasts and mesenchymal cells.
- Desmin Filaments: Found in all forms of muscles.
- Neurofilaments: Found in nerve cells.
- Glial Filaments: Found in neuroglial cells of the central nervous system (CNS).
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Function:
- Muscle contraction.
- Preserve cell shape.
- Motility of cilia and flagella.
- Separation of cytoplasm during cell division.
Centrioles
- Non-membranous organelles found in cells capable of mitosis, near the nucleus.
- Located between the nucleus and the free surface of the cell or between the nucleus and the Golgi complex.
- Mature muscle and nerve cells lack centrioles.
- LM: Two centrioles appear as small bodies surrounded by pale cytoplasm (centrosome matrix) forming the centrosome.
- EM: Two cylinders perpendicular to each other, Each wall is made of nine peripheral bundles of microtubules (triplets). Each bundle consists of three fused microtubules (27 microtubules).
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Function:
- Initiate cell division and spindle formation.
- Serve as the organizing center for microtubule polymerization (MTOC).
- Formation of cilia and flagella.
Cilia and Flagella
- Contain cytoplasm and microtubules enclosed by a cell membrane.
Cilia
- Motile, hair-like projections arising from the free surfaces of certain epithelial cells (lining epithelium of the upper respiratory tract).
- LM: Single or in large numbers.
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EM: Covered by a plasmalemma. Composed of an axoneme (shaft), basal body, and rootlet.
- Axoneme: Contains 20 microtubules: nine peripheral pairs of fused microtubules (doublets) and a central pair of individual microtubules (9+2).
- Basal Body: Structures with the same structure as a centriole, with a wall consisting of nine triplet microtubules (9+0).
- Rootlet: Microtubules that anchor the basal body to the cytoplasm.
- Function: Beat in one direction to move particles or fluids.
Flagella
- Single, long processes (100-200 μm) found in the tail of spermatozoa.
- Structure: Similar to cilia but longer and larger.
- Function: Propulsion for movement.
Ciliopathies
- Mutations in proteins of cilia and flagella lead to disorders.
- Kartagener or Immotile Cilia Syndrome: Characterized by immotile spermatozoa, male infertility, and chronic respiratory infections due to the lack of cilia's cleansing action in the respiratory tract.
Case Scenario Summary
- Examination of an adrenal cortex sample reveals cells with an abundance of cholesterol and other steroid hormone biosynthesis precursors, giving them a "spongy" appearance.
- The abundance of smooth endoplasmic reticulum (SER) would explain this observation, as SER is responsible for steroid hormone synthesis in cells like those in the adrenal cortex.
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Description
Explore the fascinating world of lysosomes, the cell's digestive system. This quiz covers their structure, types, and essential functions in cellular defense and maintenance. Test your knowledge of lysosomal activity and its significance in cell health.
