Cell Biology Quiz - Organelles and Functions

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Questions and Answers

Which of the following accurately describes organelles?

Inert and non-essential components

Living, permanent structures with vital functions (correct)

Temporary structures within the cell

Metabolic waste produced by the cell

What distinguishes inclusions from organelles?

Inclusions are non-living and often temporary. (correct)

Inclusions consist of membranous structures.

Inclusions are essential for cellular function.

Inclusions are permanent, while organelles are not.

What is the primary role of the cytosol?

To provide a protective membrane around the organelles.

To serve as a rigid structure for the cell.

To facilitate chemical reactions and support organelles. (correct)

To store genetic information of the cell.

Which of the following is NOT a characteristic of the plasma membrane?

It is easily visible under H&E staining. Signup and view all the answers

Which component contributes to the structure of the plasma membrane?

Phospholipid bilayer and cholesterol Signup and view all the answers

What is a primary function of peroxisomes in the liver?

Detoxify ethanol Signup and view all the answers

Which of the following is produced from the breakdown of long chain fatty acids in peroxisomes?

Acetyl-CoA Signup and view all the answers

What do free ribosomes primarily synthesize?

Proteins for use within the cell Signup and view all the answers

What is the role of ubiquitin in relation to proteasomes?

To tag proteins for destruction Signup and view all the answers

Which of the following correctly describes a defect in proteasomes?

Accumulation of unwanted proteins Signup and view all the answers

What process describes the active movement of substances into a cell by forming vesicles?

Endocytosis Signup and view all the answers

Which type of endocytosis involves the uptake of specific ligands through receptors on the cell membrane?

Receptor mediated endocytosis Signup and view all the answers

What is the main role of clathrin in receptor mediated endocytosis?

To form the coated vesicle Signup and view all the answers

What cellular process is characterized as the movement of substances from inside to outside the cell by forming vesicles?

Exocytosis Signup and view all the answers

What condition is most likely to arise from a deficiency of growth hormone (GH)?

Dwarfism Signup and view all the answers

What structural feature of mitochondria increases the surface area for ATP formation?

Cristae Signup and view all the answers

Which of the following statements is true regarding mitochondria?

They contain their own DNA and can self-replicate. Signup and view all the answers

Which component of the mitochondrial inner membrane is crucial for ATP formation during oxidative phosphorylation?

ATP synthase Signup and view all the answers

What is the primary characteristic of the heads of phospholipid molecules?

Charged and hydrophilic Signup and view all the answers

Which type of membrane protein is specifically associated with channels and carriers?

Transmembrane proteins Signup and view all the answers

What function do glycoproteins and glycolipids serve at the cell membrane?

Cell to cell adhesion and receptor sites Signup and view all the answers

What best describes peripheral proteins?

They are loosely attached to both surfaces of the cell membrane. Signup and view all the answers

How do saturated fatty acid tails affect membrane properties?

They restrict movement and increase membrane stability. Signup and view all the answers

Which of the following is NOT a function of integral proteins?

Providing structural support to the cytoskeleton Signup and view all the answers

What property allows phospholipid molecules to form the bilayer structure in cell membranes?

They possess both hydrophilic and hydrophobic regions. Signup and view all the answers

Which component of the membrane is responsible for stability and modulating fluidity?

Fatty acid tails Signup and view all the answers

What is the primary component that forms microtubules?

Alpha and beta tubulin subunits Signup and view all the answers

During cell division, what structure is formed by microtubules?

Mitotic spindle Signup and view all the answers

What is a key role of microtubules in cellular function?

Facilitate intracellular transport Signup and view all the answers

What structure is referred to as the microtubule-organizing center (MTOC)?

Centrosome Signup and view all the answers

What is the diameter of a microtubule?

24 nm Signup and view all the answers

Which structure is not constructed from microtubules?

Filopodia Signup and view all the answers

How are the triplets of microtubules in a centriole arranged?

9 triplets in a circular pattern Signup and view all the answers

What is the main function of contractile rings during cell division?

Divide the cytoplasm between daughter cells Signup and view all the answers

What is the primary function of the flagellum in humans?

To assist in the movement of sperm Signup and view all the answers

What structural similarity does the shaft of the flagellum share with the axoneme of a cilium?

Both consist of 9 peripheral doublets and 2 central singlets Signup and view all the answers

What type of granules are visible in the liver cells when stained with PAS?

Magenta red granules Signup and view all the answers

Which of the following statements about chromatin is correct?

Chromatin is composed of DNA, histones, and non-histone proteins Signup and view all the answers

Which organelle is described as the largest membranous organelle inside the cell?

Nucleus Signup and view all the answers

What color do lipofuscin granules appear as when viewed under a microscope?

Brown Signup and view all the answers

Which type of pigments are classified as exogenous?

Tattoo marks Signup and view all the answers

What process occurs at the site of the nucleus?

Transcription of RNA Signup and view all the answers

Study Notes

Cell Biology Study Notes

Revision 1, BMS111 covering Histology and Cell Biology, from Fall 2024-2025 at Galala University.

Cytoplasm

Organelles: Living, permanent, essential, active components with vital functions.
Inclusions: Non-living, temporary, not essential (except in some cases), inert, metabolic products.
Cytosol: Semifluid cytoplasmic matrix.

Cell Organelles

Membranous: Covered by membrane. Includes cell (plasma) membrane, mitochondria, rough endoplasmic reticulum (rER), smooth endoplasmic reticulum (SER), Golgi apparatus, lysosomes, and peroxisomes.
Non-membranous: Uncovered by membrane. Includes ribosomes and proteosomes, and cytoskeleton.

Cell Membrane

Definition: The limiting membrane of the cell; also called plasma membrane or plasmalemma.
L.M.: Difficult to see with H&E stains; very thin (8-10nm). Special stains like Ag and PAS are used.
E.M.: Trilaminar appearance: 2 electron-dense layers separated by an electron-lucent zone. A cell coat (glycocalyx) on the outer surface only.

Molecular Structure of Cell Membrane

Lipid Component:
- Phospholipid bilayer
- Cholesterol
Protein Component: (50%)
- Peripheral proteins
- Integral proteins
Carbohydrate Component: Oligosaccharide chains linked to membrane proteins (glycoproteins) and phospholipids (glycolipids). Located only on the outer surface.

Phospholipid Bilayer

Heads: Hydrophilic (attracted to water), charged, polar, and directed towards aqueous solutions.
Tails: Hydrophobic (repelled by water), non-charged, non-polar, and directed inwards away from aqueous solutions.

Cholesterol

Function:
- Maintains membrane stability by restricting phospholipid movement.
- Modulates membrane fluidity.

Membrane Proteins

Peripheral (extrinsic): Small molecules, loosely attached to both surfaces of the cell membrane, outside the lipid bilayer.
Integral (intrinsic): Larger molecules, firmly attached to the cell membrane and embedded within the lipid bilayer

Membrane Proteins (Integral)

Some are partially embedded within the lipid bilayer.
Others extend across the entire membrane (transmembrane proteins).
Functions: Channels, carriers, and receptors.

Carbohydrate Component (Glycocalyx)

Oligosaccharide chains linked to membrane proteins (glycoproteins) and phospholipids (glycolipids).
Located on the outer surface of the plasma membrane only.
Function in cell adhesion, cell identification, and as receptors for ligands.

Transport across cell membrane

Endocytosis: (Active movement of substances INTO the cell)
- Phagocytosis
- Pinocytosis
- Receptor-mediated endocytosis
Exocytosis: (Active movement of substances OUT of the cell)

Receptor-Mediated Endocytosis

Receptors (integral proteins) accumulate at the cell membrane to bind specific ligands.
They associate with clathrin to form coated pits.
Coated pits invaginate and pinch off, forming coated vesicles that contain ligands and their receptors.
Clathrin is dissociated and recycled.
Examples of uptake of hormones and uptake of LDL.

Medical Application: Dwarfism

Caused by GH deficiency or non-functioning GH receptors at cell membrane of target cells.

Mitochondria

Definition: Membranous organelles responsible for cell respiration and energy production (powerhouses of the cell) .
Site: all cells except RBCs.
Number: More in active cells like liver cells (1000/cell).
Histological structure:
- L.M: Cytoplasmic acidophilia (if abundant), large number of basic membrane proteins.
- E.M: Oval or rounded vesicles; surrounded by two membranes (outer and inner). The inner membrane is folded into cristae which increases the surface area for ATP synthase (enzyme for oxidative phosphorylation).

Mitochondria (Continued)

Matrix: Contains oxidative enzymes (citric acid cycle), mitochondrial DNA, RNA and few ribosomes. Dense granules rich in calcium (catalysts).
Functions: Produce ATP; self-replicating organelles by simple fission.

Endoplasmic Reticulum (ER)

Rough Endoplasmic Reticulum (rER): has attached ribosomes; Site of protein synthesis; initial glycosylation of proteins, transport proteins to Golgi complex.
Smooth Endoplasmic Reticulum (sER): Does not have attached ribosomes; Site of lipid and glycogen synthesis, calcium release in muscle, detoxification of drugs, neonatal jaundice.

Golgi Complex

E.M: Flattened, parallel curved saccules; interconnected and arranged one above the other, forming a stack.
Surface: Has cis (immature) and trans (mature) faces.
Functions:
- Chemical modification of proteins and lipids (for lysosomes, secretion, and plasma membrane), by adding carbohydrates.
- Packaging and sorting of products like hormones into secretory vesicles (exocytosis) and formation of lysosomes.

Lysosomes

L.M: Containing hydrolytic enzymes (acid phosphatase).
E.M:
- Primary Lysosomes: Newly released from Golgi apparatus; enzymes are inactive; homogenous.
- Secondary Lysosomes: Formed by fusion of primary lysosomes with vacuoles; enzymes are active; heterogeneous.

Secondary Lysosomes: Types

Heterolysosomes: Primary Lysosome + phagosome
Multivesicular Bodies: Primary Lysosome + pinocytic vesicle
Autolysosomes: Primary lysosome + old organelle.
Residual Bodies: Vesicles containing undigested materials; eliminated via exocytosis.

Peroxisomes

Content: Membranous organelles containing oxidative enzymes (catalase and oxidase), produce and degrade hydrogen peroxide (H₂O₂).
Importance:
- Synthesis and degradation of hydrogen peroxide to kill microorganisms.
- Liver detoxification of ethanol (alcohol).
- β-oxidation of long-chain fatty acids.

Ribosomes

Types: Free ribosomes and attached ribosomes.
Structure: Composed of ribonucleic acid (rRNA) and protein; formed of large and small subunits.
Free ribosomes: synthesize proteins used inside the cell (e.g., mitochondria, nucleus)
Attached ribosomes: synthesize proteins packaged, modified and transported to Golgi complex, then to the destination (e.g., secretory proteins, cell membrane proteins), lysosomes.

Proteasomes

Definition: Barrel-shaped organelle responsible for the active degradation of cytoplasmic proteins tagged with ubiquitin.
Functions:
- Removes excess enzymes and unnecessary proteins.
- Removes proteins incorrectly folded.
- Destroys viral proteins.

Cytoskeleton

Microtubules:
- Diameter: 24 nm.
- Structure: Long hollow cylinders with walls of 13 parallel protofilaments formed by polymerization of α & β tubulin subunits.
- Stability: Dynamic, each filament has 2 ends (+ and -).
- Functions: Cell shape and support; intracellular transport of organelles, vesicles, and macromolecules; formation of mitotic spindle, centrioles, cilia, and flagella.
Microfilaments: (Actin filaments)
- Diameter: 5-7 nm.
- Structure: Double helix of two filaments formed by polymerization of G-actin monomers.
- Stability: Dynamic.
- Functions: Cell support, cell shape changes (endocytosis, exocytosis, amoeboid movements), contractile ring during cell division, muscle contraction, and microvilli cores.
Intermediate Filaments: (various types)
- Diameter: 8-12 nm.
- More structural support in cell, mainly forming a network around the nucleus

Centrioles

Structure: Two cylindrical structures perpendicular to each other, surrounded by a matrix of tubulin(MTOC). The wall of each cylinder consists of 9 bundles (triplets) of microtubules (3 x 9 = 27 microtubules).
Functions: Form mitotic spindle during cell division. Regulate growth of new microtubules in non-dividing cells. Share in the formation of cilia and flagella.

Cilia and Flagella

Cilia: Finger-like cytoplasmic projections covered by cell membrane, consisting of 9 peripheral doublets + 2 central singlets formed by polymerization of microtubules.
Flagella: Similar structure to cilia but longer, used for cell movement. In humans: tail of sperm for movement,.

Cell Inclusions

A - Stored Food:
- Carbohydrates: Glycogen granules in liver and muscle cells
- Fats: Large globules in fat cells or small droplets in liver cells.
B - Pigments:
- Endogenous: Hemoglobin (RBCs), Melanin (skin and hair), Lipofuscin (residual bodies)
- Exogenous: Carbon and dust particles, Carotene (carrots), tattoo dyes

Nucleus

Definition: Largest membranous organelle inside the cell. Contains the cell's DNA in the form of chromosomes, site of transcription of 3 primary types of RNA.
Components (by EM): Nuclear envelope, Chromatin, Nucleolus, Nuclear Sap.

Chromatin

Definition: Genetic material consisting of DNA double helix + histones + non-histone proteins
Forms:
- Euchromatin: Extended (uncoiled) chromatin; transcriptionally active; electron lucent, predominates in active cells, visible in LM
- Heterochromatin: Condensed (coiled) chromatin; transcriptionally inactive; electron dense, predominates in inactive cells like lymphocytes, visible in LM

Cell Cycle

Interphase: The time between two successive cell divisions (90% of the cycle). Divided into 3 phases: Gap 1 (G1), Synthesis (S), Gap 2 (G2) phases.
Mitosis: Cell division (M phase), has 4 main steps: Prophase, Metaphase, Anaphase, Telophase

Apoptosis

Definition: Active programmed cell death
Features: Chromatin condensation, nucleus breakdown, blebbing of plasma membrane, fragmented into apoptotic bodies which phagocytosed by macrophages

Stem Cells

Definition: Undifferentiated cells capable of self-renewal and differentiation (production of different specialized cells).
E.M. Features: The nucleus primarily contains euchromatin(active genes); The cytoplasm contains numerous polyribosomes and mitochondria
Types: Embryonic stem cells and adult stem cells (bone marrow, adipose tissue, placenta, GIT, liver, skin, and blood vessels).

Cell Renewal

Static: Cells that no longer divide (central nervous system, cardiac muscle).
Stable: Cells that divide episodically and slowly to maintain normal tissue structure (Liver, smooth muscle, endothelial).
Rapidly renewing: Cells that divide continuously (blood cells, epidermal cells, cells of the digestive tract).

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Test your knowledge on cell biology concepts related to organelles, inclusions, and the plasma membrane. This quiz covers their structures, functions, and roles in cellular processes. Perfect for students studying cytology or cellular physiology.