Lysosomes and Their Functions
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Questions and Answers

Which type of enzyme found in lysosomes is responsible for the digestion of RNA?

  • Acid deoxyribonuclease
  • Acid phosphatase
  • Acid ribonuclease (correct)
  • Collagenase

What is the pH level typically found within lysosomes?

  • Alkaline
  • pH 5 (correct)
  • Neutral
  • pH 7

Which enzyme breaks down phosphomonoesters in lysosomes?

  • Cathepsin
  • a-glucosidase
  • Ceramidase
  • Acid phosphatase (correct)

Which of the following enzymes is categorized as a lipid hydrolyzing enzyme in lysosomes?

<p>Phospholipase (D)</p> Signup and view all the answers

Lysosomes are involved in intracellular digestion. Which process do they NOT perform?

<p>Synthesis of DNA (D)</p> Signup and view all the answers

Which type of linkage does collagenase specifically break down?

<p>Collagen fibers (C)</p> Signup and view all the answers

What distinguishes lysosomes from plant cell vacuoles in terms of function?

<p>Lysosomes have a higher enzyme density. (A)</p> Signup and view all the answers

Acid lipase in lysosomes is responsible for the hydrolysis of what substance?

<p>Triacylglycerol (D)</p> Signup and view all the answers

What is the primary function of lysosomes within a cell?

<p>Intracellular digestion and storage (A)</p> Signup and view all the answers

What is the primary function of residual bodies in cells?

<p>To enclose undigested waste products (B)</p> Signup and view all the answers

What is the optimal pH for the hydrolyzing activity of lysosomal enzymes?

<p>Acidic (pH 4.6 to 5) (B)</p> Signup and view all the answers

Where are hydrolases located in bacteria, considering the absence of lysosomes?

<p>In the periplasmic space (A)</p> Signup and view all the answers

What are lipofuscin granules composed of?

<p>Lipid undigested residues (B)</p> Signup and view all the answers

How do lysosomal enzymes protect the cell from being activated in the cytosol?

<p>By maintaining an acidic pH within lysosomes (D)</p> Signup and view all the answers

How are lysosomal enzymes distinguished and concentrated during synthesis?

<p>By their phosphorylated mannose residues (B)</p> Signup and view all the answers

What role does the acrosome of a spermatozoon play?

<p>It digests the zona pellucida during fertilization (A)</p> Signup and view all the answers

What type of reactions do lysosomes facilitate concerning biological macromolecules?

<p>Hydrolysis reactions (A)</p> Signup and view all the answers

What happens to mannose 6-phosphate receptors after lysosomal enzymes are packaged?

<p>They return to the trans Golgi network (B)</p> Signup and view all the answers

What role does the proton pump play in the function of lysosomes?

<p>It transports protons to maintain acidic pH (A)</p> Signup and view all the answers

What is protective about the glycosylation state of the lysosomal membrane?

<p>Protects the membrane from enzymatic digestion (D)</p> Signup and view all the answers

Why are lysosomes absent in plant cells?

<p>Endocytosis and phagocytosis are impossible due to the rigid cell wall (A)</p> Signup and view all the answers

Where do lysosomal enzymes find their substrates for digestion?

<p>In endosomes and phagosomes (B)</p> Signup and view all the answers

What happens to the clathrin coat after clathrin-coated vesicles migrate into the cytosol?

<p>It is released and recycled for future vesicle formation (D)</p> Signup and view all the answers

What is the result of accumulating lipofuscin granules in long-lived cells?

<p>Disturbance of cell metabolism and aging (A)</p> Signup and view all the answers

What is the primary function of permeases in the lysosomal membrane?

<p>To export end products of digestion into the cytosol (A)</p> Signup and view all the answers

What role do proton pumps play in the function of vacuoles?

<p>They decrease the pH within the vacuole lumen. (C), They create a low pH environment in the vacuole. (D)</p> Signup and view all the answers

Which of the following describes the function of vacuoles in plant cells?

<p>They provide mechanical support by generating turgor pressure. (D)</p> Signup and view all the answers

What are the characteristics of primary lysosomes?

<p>They derive from the trans-Golgi network (TGN) (B)</p> Signup and view all the answers

How does the membrane composition of lysosomes differ from that of plasma membranes?

<p>Lysosomes are poorer in cholesterol than plasma membranes (B)</p> Signup and view all the answers

What happens to small vacuoles in dividing plant cells as they mature?

<p>They merge to form a single large vacuole. (B)</p> Signup and view all the answers

What is the primary role of ATPase proton pumps within the lysosomal membrane?

<p>To maintain an acidic pH in the lysosomal lumen (D)</p> Signup and view all the answers

How do vacuoles contribute to intracellular digestion?

<p>Through the presence of hydrolytic enzymes. (A)</p> Signup and view all the answers

What type of proteins are lamp1 and lamp2 classified as?

<p>Non-enzymatic glycoproteins (A)</p> Signup and view all the answers

In what way might vacuoles assist plants in defense mechanisms?

<p>By storing toxic compounds to deter pests. (B)</p> Signup and view all the answers

Why must some undigested wastes be expelled from cells via exocytosis?

<p>To prevent the accumulation of waste within the lysosome (A)</p> Signup and view all the answers

Which statement correctly describes the tonoplast?

<p>It is a single membrane that encloses the vacuole. (B)</p> Signup and view all the answers

What is one way substances are transported into vacuoles aside from active transport?

<p>Intravacuolar pinocytosis. (D)</p> Signup and view all the answers

Lysosomes vary in size, ranging approximately from:

<p>50 nm to 1 µm in diameter (D)</p> Signup and view all the answers

Which of the following statements about lysosomal composition is incorrect?

<p>Lysosomal integral proteins are uniform in function (D)</p> Signup and view all the answers

What percentage of a mature plant cell's volume can the vacuole occupy?

<p>90% (B)</p> Signup and view all the answers

What characterizes primary lysosomes?

<p>They are small vesicles with digestive enzymes that have not participated in hydrolysis. (A)</p> Signup and view all the answers

How are the enzymes of primary lysosomes synthesized?

<p>By ribosomes attached to the rough endoplasmic reticulum. (D)</p> Signup and view all the answers

What happens to primary lysosomes during the process of digestion?

<p>They become secondary lysosomes through fusing with vesicles containing materials. (A)</p> Signup and view all the answers

Which structures directly result from the fusion of primary lysosomes and phagocytosed material?

<p>Heterolysosomes (D)</p> Signup and view all the answers

What role do lysosomes play in the cell defense mechanism?

<p>They digest pathogens such as viruses and bacteria. (B)</p> Signup and view all the answers

What process leads to the formation of autophagolysosomes?

<p>The engulfing of cellular organelles by autophagic vacuoles. (B)</p> Signup and view all the answers

Which signal is used for sorting enzymes in the Golgi apparatus for lysosome formation?

<p>Mannose-6-phosphate (C)</p> Signup and view all the answers

What is the term not commonly used to describe the structures in animal cells that are involved in digestion?

<p>Vacuoles (A)</p> Signup and view all the answers

Flashcards

Lysosomes

Small organelles found in animal cells, enclosed by a single lipid bilayer membrane. They contain a variety of hydrolytic enzymes crucial for cellular digestion and waste processing.

Acid Phosphatase

A marker enzyme often used to identify lysosomes. It breaks down phosphomonoesters (molecules containing phosphate groups attached to a single molecule).

Lysosomal Enzymes

Lysosomes contain various enzymes for breaking down different types of biomolecules. These enzymes are active in acidic environments within the lysosome.

Intracellular Digestion

The enzymes within lysosomes are responsible for degrading various cellular waste products. This process is called intracellular digestion.

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Vacuoles in Plant Cells

Plant cells have vacuoles that share some similarities with lysosomes. These vacuoles can perform functions like storage and enzymatic breakdown.

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Acidic pH of Lysosomes

Lysosomal membranes maintain an acidic pH, providing the optimal environment for the hydrolytic enzymes to function properly.

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Proton Pumps in Lysosomes

Proton pumps in the lysosomal membrane help to maintain the acidic pH within the organelle.

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Role of Lysosomes in Cellular Health

Lysosomes are responsible for breaking down substances like old organelles, pathogens, and cellular debris. They contribute to the overall health and maintenance of the cell.

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Lysosomal Digestion

The process of breaking down ingested materials or worn-out cellular components within lysosomes.

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Gas Vacuoles

Specialized structures in bacteria, different from those found in plants, involved in the regulation of buoyancy.

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Periplasmic Space

The space located between the plasma membrane and the cell wall of bacteria, where some hydrolytic enzymes are found.

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Primary Lysosome

A type of lysosome that is newly formed and originates from the trans-Golgi network (TGN). They contain a full complement of digestive enzymes but have not yet encountered their target material for breakdown.

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ATPase proton pumps

Maintain a specific acidity within the lysosome, crucial for the optimal activity of lysosomal enzymes.

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Lysosome-associated membrane proteins (LAMPs)

Involved in the process of lysosome formation. They contribute to the structural integrity and function of the lysosome.

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Lysosomal Permeases

Proteins that transport molecules selectively across the lysosome membrane.

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Exocytosis

A process where waste materials, often produced during lysosomal digestion, are expelled from the cell.

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Phagocytosis

The process where cellular material is engulfed by the cell membrane and internalized into vesicles called phagosomes, which ultimately fuse with lysosomes for digestion.

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Secondary Lysosomes

Formed when primary lysosomes fuse with vesicles containing material to be broken down. These materials can come from inside or outside the cell.

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Heterolysosome

A type of secondary lysosome formed when a primary lysosome fuses with a phagosome.

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Autophagy

The process where a cell envelops its own worn-out organelles in a membrane, forming an autophagosome.

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Autophagolysosome

A type of secondary lysosome formed when a primary lysosome fuses with an autophagosome.

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Autophagosome

A vesicle formed during autophagy that contains material to be digested by the cell.

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Lysosomes and Defense

Lysosomes can help protect the cell by digesting invading pathogens like bacteria and viruses.

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What are residual bodies?

Residual bodies are small vesicles containing undigested waste materials left over from lysosomal digestion.

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What are lipofuscin granules?

Lipofuscin granules are lysosomes containing undigested substances that accumulate within cells, particularly in long-lived cells like neurons.

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How are lysosomal enzymes synthesized and tagged?

Lysosomal enzymes are synthesized by membrane-bound ribosomes, travel through the endoplasmic reticulum (ER) and Golgi complex, and are tagged with a specific signal: phosphorylated mannose residues.

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What is the role of phosphorylated mannose residues in lysosomal trafficking?

Phosphorylated mannose residues act as a signal for lysosomal enzymes, allowing them to be recognized by specific receptors in the trans-Golgi network (TGN).

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How are lysosomal enzymes packaged and transported?

In the trans-Golgi network (TGN), lysosomal enzymes are packaged into clathrin-coated vesicles, which bud off the TGN membrane and transport the enzymes to their final destination.

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How do mannose 6-phosphate receptors (MPRs) contribute to lysosomal enzyme transport?

Mannose 6-phosphate receptors (MPRs) on the TGN membrane have a clathrin-binding site that recognizes the phosphorylated mannose residues on lysosomal enzymes, facilitating their packaging into clathrin-coated vesicles.

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Why are lysosomes absent in plant cells?

Plant cells lack lysosomes because their rigid cell walls prevent endocytosis and phagocytosis, the processes by which cells internalize materials.

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How do plant cells compensate for the absence of lysosomes?

Plant cells use large central vacuoles for various functions including storage, waste management, and maintaining cell turgor pressure.

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What is the tonoplast?

The single membrane that encloses a plant vacuole.

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What is turgor pressure?

It's the pressure exerted by the vacuole against the cell wall, providing structural support to the plant.

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What is the primary function of plant vacuoles?

Their main function is to store water, but they can also store various other substances like pigments, ions, and waste products.

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How does a large central vacuole form?

When a plant cell matures, numerous small vacuoles fuse to form a single, large central vacuole.

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What is the role of proton pumps in plant vacuoles?

They help regulate the pH of the vacuole. This is vital for the proper functioning of enzymes and other processes within the vacuole.

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How are plant vacuoles similar to lysosomes?

Similar to lysosomes, they contain hydrolytic enzymes that degrade various molecules within the vacuole.

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What is intravacuolar pinocytosis?

This process involves the engulfment of fluids and small particles by the vacuole membrane.

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How are vacuoles involved in autophagy?

It's a process where the vacuole contributes to the breakdown and recycling of old or damaged cellular components.

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Study Notes

Lysosomes

  • Lysosomes are small organelles, spherical or oval in shape, with a single lipid bilayer membrane.
  • They're rich in hydrolytic enzymes.
  • Lysosomes are identified by their acid phosphatase marker.
  • Lysosomal enzymes (e.g., Acid phosphatase, Nucleases, Proteases, Polysaccharidases) break down macromolecules (proteins, lipids, nucleic acids, and carbohydrates).
  • Lysosomes function in intracellular digestion, storage of substances, and cellular defense by breaking down unwanted materials.
  • Lysosomes are present in animal cells; plant cells have vacuoles which share similar functions.
  • Lysosomes maintain an acidic pH (around 4.6-5) inside using proton pumps, crucial for enzyme activity.
  • Lysosomes protect the cell from the leakage of their enzymes into the cytosol by having a glycosylated lumen.

Lysosome Structure and Types

  • Lysosomes come in diverse sizes and morphologies, ranging from 50 nm to 1 µm in diameter.
  • They have a single membrane similar to other cellular membranes but are poorer in cholesterol content.
  • Lysosomes have different types of proteins: ATPase pumps to maintain the acidic pH, permeases for transport of substrates and products, and glycoproteins like acid phosphatase.
  • Primary lysosomes (protolysosomes): Newly formed, contain enzymes and haven't yet taken part in hydrolysis reactions.
  • Secondary lysosomes: Formed by fusion of primary lysosomes with vesicles containing material to be digested. These encompass heterophagosomes/heterolysosomes (outside-derived materials) and autophagolysosomes (intracellular material).
  • Residual bodies: Formed from secondary lysosomes after incomplete digestion of materials; they contain undigested material and are expelled from the cell or accumulate as lipofuscin granules (aging).

Plant Vacuoles

  • Plant vacuoles are analogous to lysosomes, even lacking endocytosis and phagocytosis like animal lysosomes.
  • Mature plant cells contain a single large central vacuole that occupies up to 90% of cell volume.
  • Vacuoles play key roles in providing structural support (turgor pressure), storing materials, and participating in plant defense.
  • The vacuole's membrane (tonoplast) maintains an acidic pH and contains various transport proteins.

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Description

This quiz covers the structure, types, and functions of lysosomes, including their role in intracellular digestion and cellular defense. Learn about enzyme activity and the importance of maintaining an acidic environment within lysosomes. Test your knowledge about these essential organelles.

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