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Questions and Answers
What type of organelle are mitochondria classified as?
What type of organelle are mitochondria classified as?
Which component of the mitochondria is responsible for ATP production?
Which component of the mitochondria is responsible for ATP production?
What is the shape of mitochondria as seen under supravital staining?
What is the shape of mitochondria as seen under supravital staining?
Which statement about the inner membrane of mitochondria is correct?
Which statement about the inner membrane of mitochondria is correct?
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How do mitochondria replicate themselves?
How do mitochondria replicate themselves?
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What is the primary function of ribosomes?
What is the primary function of ribosomes?
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What is found in the matrix space of mitochondria?
What is found in the matrix space of mitochondria?
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Which organelle is NOT classified as membranous?
Which organelle is NOT classified as membranous?
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What type of proteins extend across the lipid bilayer and allow passage of water-soluble molecules?
What type of proteins extend across the lipid bilayer and allow passage of water-soluble molecules?
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What is the primary function of the cell coat (Glycocalyx)?
What is the primary function of the cell coat (Glycocalyx)?
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Which of the following processes is categorized as active transport?
Which of the following processes is categorized as active transport?
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What function does the cell membrane NOT perform?
What function does the cell membrane NOT perform?
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Which type of endocytosis involves the non-specific uptake of dissolved substances?
Which type of endocytosis involves the non-specific uptake of dissolved substances?
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In terms of lipid transport, which of the following substances can easily diffuse through the lipid bilayer?
In terms of lipid transport, which of the following substances can easily diffuse through the lipid bilayer?
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What is the role of peripheral (extrinsic) proteins in the cell membrane?
What is the role of peripheral (extrinsic) proteins in the cell membrane?
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What structure does the cell membrane exhibit due to the presence of hydrophilic heads?
What structure does the cell membrane exhibit due to the presence of hydrophilic heads?
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What is the primary function of free ribosomes within the cell?
What is the primary function of free ribosomes within the cell?
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Which type of ribosomes are responsible for the formation of polysomes?
Which type of ribosomes are responsible for the formation of polysomes?
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What does the presence of ribosomes contribute to the cytoplasm?
What does the presence of ribosomes contribute to the cytoplasm?
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What is a primary function of the smooth endoplasmic reticulum (SER)?
What is a primary function of the smooth endoplasmic reticulum (SER)?
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Which of the following substances is NOT synthesized by the smooth endoplasmic reticulum?
Which of the following substances is NOT synthesized by the smooth endoplasmic reticulum?
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How are attached ribosomes different from free ribosomes in terms of their location?
How are attached ribosomes different from free ribosomes in terms of their location?
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What type of cells prominently features the smooth endoplasmic reticulum?
What type of cells prominently features the smooth endoplasmic reticulum?
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Which characteristic distinguishes rough endoplasmic reticulum from smooth endoplasmic reticulum?
Which characteristic distinguishes rough endoplasmic reticulum from smooth endoplasmic reticulum?
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What is the primary role of secretory vesicles in the cell?
What is the primary role of secretory vesicles in the cell?
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Which of these is NOT a function of the Golgi apparatus?
Which of these is NOT a function of the Golgi apparatus?
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What characterizes primary lysosomes?
What characterizes primary lysosomes?
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Lysosomal enzymes are optimally active at which pH?
Lysosomal enzymes are optimally active at which pH?
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Secondary lysosomes are formed through a specific process. Which of the following describes this process?
Secondary lysosomes are formed through a specific process. Which of the following describes this process?
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Residual bodies are formed in lysosomes as a result of what?
Residual bodies are formed in lysosomes as a result of what?
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What process do lysosomes primarily engage in to defend against pathogens?
What process do lysosomes primarily engage in to defend against pathogens?
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What is the main structural feature of lysosomes as seen through an electron microscope?
What is the main structural feature of lysosomes as seen through an electron microscope?
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What is the primary role of the phospholipid bilayer in the cell membrane?
What is the primary role of the phospholipid bilayer in the cell membrane?
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How does the trilaminar appearance of the cell membrane manifest under an electron microscope at high magnification?
How does the trilaminar appearance of the cell membrane manifest under an electron microscope at high magnification?
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Which component of the cell membrane is responsible for filling the gaps between fatty acid tails?
Which component of the cell membrane is responsible for filling the gaps between fatty acid tails?
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What distinguishes integral proteins from peripheral proteins in the plasma membrane?
What distinguishes integral proteins from peripheral proteins in the plasma membrane?
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What does the term 'plasma membrane' refer to?
What does the term 'plasma membrane' refer to?
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Which component of the cell membrane is primarily hydrophilic?
Which component of the cell membrane is primarily hydrophilic?
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What is a key characteristic of peripheral (extrinsic) proteins?
What is a key characteristic of peripheral (extrinsic) proteins?
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Which is NOT true about the structure of the cell membrane?
Which is NOT true about the structure of the cell membrane?
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Study Notes
Cytology
- The study of cells, tissues, organs, and organ systems.
Cell
- The structural and functional unit of an organism.
- Composed of:
- Protoplasm
- Cell membrane
- Cytoplasm
- Nucleus
Cytoplasm
- Contains:
- Cytoplasmic organelles
- Inclusions
- Cytoskeleton
- Cytosol (matrix)
Cell Membrane (Plasmalemma)
- Surrounds all cells.
- Also known as plasma membrane.
- Some organelles are also surrounded by similar membranes.
- Both are called unit membranes.
- Not visible under a light microscope (L.M) due to its thinness (7.5-10 nm).
- Visible under an electron microscope (E.M):
- Low magnification: Appears as a single electron-dense line.
- High magnification: Appears as two electron-dense lines separated by an electron-lucent line, creating a trilaminar appearance known as the unit membrane.
- Comprised of:
- Phospholipids
- Cholesterol
- Proteins
Phospholipids
- Form the backbone of the plasma membrane.
- Create a bilayer with hydrophilic phosphate heads directed outwards and hydrophobic fatty acid tails directed inwards.
Cholesterol
- Present in the lipid bilayer.
- Exists in a 1:1 ratio with phospholipids.
- Fills gaps between fatty acid tails.
Proteins
- Located within the lipid bilayer.
- Two types:
- Integral (intrinsic):
- Embedded in the lipid bilayer.
- Can move within the bilayer.
- Transmembrane proteins extend across the bilayer, protruding from both sides and forming channels for water-soluble molecules.
- Peripheral (extrinsic):
- Associated with the cytoplasmic or extracellular surface of the cell membrane.
- Integral (intrinsic):
Cell Coat (Glycocalyx)
- Site: External surface of the cell membrane.
- Structure: Fine filamentous material of varying thickness, as seen under E.M.
- Chemically: Oligosaccharides conjugated with membrane proteins (glycoproteins) and lipids (glycolipids).
- Function:
- Cell recognition
- Protection
- Intercellular adhesions
Functions of the Cell Membrane
- Maintains structural integrity of the cell.
- Controls movement of substances into and out of the cell (selective permeability).
- Recognizes antigens, including foreign cells and altered cells.
- Transports essential substances such as hormones through specific receptors.
- Establishes transport systems for specific molecules:
- Passive transport: Movement across the membrane without energy expenditure.
- Active transport: Requires energy expenditure to move substances against their concentration gradient.
Sodium and Potassium Transport
- Certain ions, like sodium and potassium, are actively transported through transmembrane channels.
- Some ions pass passively.
- Lipid-soluble substances like steroid hormones diffuse rapidly through the lipid bilayer.
Mass Transfer
- Involves vesicles or vacuoles that are formed from or fuse with the cell membrane:
-
Endocytosis: Taking substances into the cell.
- Fluid-phase pinocytosis (cell drinking): Non-specific uptake of substances dissolved in fluid.
- Phagocytosis (cell eating): Engulfing large particles like bacteria, cell fragments, and cells.
-
Exocytosis: Releasing cell products into the extracellular compartment.
- Vesicles containing products fuse with the cell membrane, releasing their contents to the exterior.
-
Endocytosis: Taking substances into the cell.
Cytoplasmic Organelles
-
Membranous organelles: Surrounded by a membrane similar to the cell membrane.
- Mitochondria
- Rough endoplasmic reticulum (RER)
- Smooth endoplasmic reticulum (SER)
- Golgi apparatus
- Lysosomes
-
Non-membranous organelles: Not surrounded by a unit membrane.
- Free ribosomes
- Microtubules
- Centrioles
- Cilia
- Flagella
- Filaments
Mitochondria
- Site: Present in all cells except mature red blood cells.
- Size, number, and shape vary depending on the cell type.
- Number increases in cells with high metabolic activity, such as liver cells.
- L.M: Stainable with supravital stains like Janus green, appearing as green rod, ovoid, or thread-like bodies.
- E.M:
- Rounded or oval structure enclosed by two trilaminar unit membranes.
- Outer membrane is smooth.
- Inner membrane is folded into shelf-like structures called cristae.
- Intermembrane space: Narrow space between outer and inner membranes.
- Matrix space: Large space enclosed by the inner membrane.
- Elementary particles: Closely packed club-shaped particles attached to the inner surface of the inner membrane.
- Self-replicating by fission.
- Function:
- Energy house of the cell, producing ATP.
- Calcium regulation in the cytoplasm.
- Can synthesize proteins due to the presence of DNA, RNA, and ribosomes.
Ribosomes
- Non-membranous organelles present in all cells except mature red blood cells.
- Manufactured in the nucleolus and released into the cytoplasm.
- Two types:
- Free ribosomes: Scattered in the cytoplasm, synthesize proteins for internal use.
- Attached ribosomes: Attached to membranes forming the RER, responsible for synthesis and segregation of proteins for secretion.
- Composed of proteins and rRNA.
- Stainable with hematoxylin, toluidine blue, and methylene blue (basic dyes).
- Each ribosome consists of two subunits: small and large.
- L.M: Responsible for cytoplasmic basophilia due to their rRNA content.
- Free ribosomes: Diffuse basophilia.
- Attached ribosomes: Localized basophilia.
- Polyribosomes (polysomes): Several ribosomes attached to a thread of mRNA, forming groups or rosettes, either free or attached to the RER.
Smooth Endoplasmic Reticulum (SER)
- L.M: Not visible, but gives acidophilic staining to cytoplasm when present in large amounts.
- E.M: Branching network of tubules in the cytoplasm, not studded with ribosomes.
- Function:
- Synthesizes steroid hormones in steroid-secreting cells (e.g., adrenal cortex).
- Synthesizes phospholipids for all cell membranes.
- Prominent in steroid-secreting cells of the adrenal cortex.
- Detoxifies drugs in liver cells.
- Participates in glycogen, cholesterol, and lipid synthesis.
- Regulates calcium levels in striated and cardiac muscle.
Golgi Apparatus
- Site: Found near the nucleus.
- Structure: Stacked flattened membrane-bound sacs called cisternae.
- Function:
- Modification of secretory proteins.
- Concentration and packaging of secretory products into vesicles.
- Modification, segregation, and packaging of lysosomal enzymes.
- Synthesis of membrane proteins and membrane recycling.
Lysosomes
- Membranous cell organelles containing hydrolytic enzymes.
- Origin: Synthesized in rER and transported to the Golgi complex.
- Contents: Hydrolases like acid phosphatase, proteases, nucleases, and lipases.
- Optimal activity at pH 5.
- Site: Found in all cells except mature erythrocytes, but are numerous in phagocytic cells.
- Structure:
- L.M: Visible by specific histochemical reactions for acid phosphatases.
- E.M: Rounded small membranous vesicles.
- Types:
- Primary lysosomes: Newly formed, homogenous, not involved in digestion.
- Secondary lysosomes: Formed after fusion of primary lysosomes with other substances, heterogeneous in appearance.
- Residual body: Indigestible material remaining in secondary lysosomes, released by exocytosis.
- Function:
- Intracellular digestion of materials from inside and outside the cell.
- Heterophagy: Break-down of materials from outside the cell, such as bacteria for cellular defense.
- Autophagy: Break-down of worn-out cell components, providing a source of nutrients and energy.
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Description
Test your knowledge on cytology and cell structure. This quiz covers the study of cells, their components, and essential functions. Explore topics such as the cell membrane, cytoplasm, and organelles.
