Cell Biology Quiz: Organelles and Functions

Cytology Lecture Two

• Cells are the basic structural and functional unit of living organisms.
• They exhibit diverse functional specializations for organism survival, growth, and reproduction.
• Cells are self-replicating, self-regulating, and self-governing biological systems.
• Key cell activities include metabolism (e.g., absorption, synthesis, respiration, excretion), growth and regeneration, irritability (excitability), movement, and reproduction. Aging and death are also part of the cell cycle.
• Cell numbers are estimated to be around 100 trillion (10¹²).
• There are over 250 different named cell types.
• Cell shapes include round, oval, columnar, multipolar, polygonal, cylindrical, fusiform, pyramidal, and pyriform.
• Cell sizes range from 5µm to 120µm in diameter.
• Cells perform various functions depending on their type and location in the body.

Cell Structure (Diagram)

• Microtvillus
• Plasma membrane
• Nuclear envelope
• Golgi apparatus
• Microtubules
• Nucleolus
• Rough endoplasmic reticulum
• Centrosome
• Lysosome
• Mitochondrion

Specialized Cell Functions

• Movement: Muscle cells
• Synthesis and secretion of enzymes: Pancreatic acinar cells
• Synthesis and secretion of mucous substances: Mucous-gland cells
• Synthesis and secretion of steroids: Cells in the adrenal glands, testes, and ovaries
• Ion transport: Cells of the kidney and salivary glands
• Intracellular digestion: Macrophages and other white blood cells
• Transformation of stimuli into nervous impulses: Sensory cells
• Metabolites absorption: Cells in the intestine

Cells — Light Microscope View

• Cell nucleus (chromatin)
• Cell cytoplasm
• Cell boundary
• Cell shape
• Interstitial space
• Red blood cell

Components of Eukaryotic Cells

• Cell membrane
• Cytoplasm
• Karyoplasm (nucleus)
• Centrioles
• Secretory granules
• Microtubules
• Nuclear membrane
• Chromatins
• Golgi Apparatus
• Nucleolus
• Glycogen
• Ribosomes
• Lysosomes
• Mitochondrion
• Rough endoplasmic reticulum
• Microfilaments
• Smooth endoplasmic reticulum

Cell Membrane

• The cell membrane's structure appears as a trilaminar layer, each layer 2.5 nm in diameter.
• This appearance makes it known as the "unit membrane".
• It is composed of lipids (approx. 90% by volume, 50% by weight), proteins (10% by volume, 50% by weight) and carbohydrates.
• Phospholipids contain a hydrophilic polar phosphate-containing head and hydrophobic nonpolar fatty acid tails. This arrangement creates the lipid bilayer.
• Cholesterol regulates membrane fluidity and structural integrity.
• Integral proteins (intrinsic) transverse the membrane, while peripheral proteins (extrinsic) are located on one surface.

Membrane Proteins

• Pumps, channels, receptors, linkers, enzymes and structural proteins are functional categories of membrane proteins.

Carbohydrates

• Occur as oligosaccharides, attached to plasma membrane proteins (glycoproteins) and lipids (glycolipids).
• Project from the outer surface of the outer leaflet of the plasma membrane.
• Contribute to the glycocalyx (cell coat), responsible for cell adhesion, enzyme and antigen binding, and cell-to-cell recognition.

Cytoplasm

• The cytoplasm is the cellular material outside the nucleus but within the plasma membrane.
• It is composed of cytosol (cellular fluid), organelles, cytoskeleton, and inclusions.

Organelles

• Endoplasmic reticulum (RER, SER)
• Golgi complex (body or apparatus)
• Lysosomes
• Peroxisomes (microbodies)
• Mitochondria
• Endosomes and phagosomes
• Proteasomes
• Ribosomes

Ribosomes

• About 20 × 30 nm in size.
• Composed of ribosomal RNA (rRNA) and specific ribosomal proteins.
• Exist in large and small subunits occurring as free ribosomes and polyribosomes (polysomes).

Polyribosomes

• Occur as clusters along a single strand of mRNA.
• Free polyribosomes synthesize structural proteins and enzymes for intracellular use.
• Attached polyribosomes produce proteins to be secreted or destined for the ER, Golgi apparatus, lysosomes, or cell membrane.

Cytoskeleton

• A gel-like network composed of protein filaments.
• Three filament types are microtubules, intermediate filaments and microfilaments

Microtubules

• Tubular, with 24nm outer diameter and 5nm wall thickness.
• Built from tubulin heterodimers (a and b).
• Include 13 protofilaments.
• Contain microtubule-associated proteins (MAPs) which include Kinesin (towards plus end), and Dynein (towards minus end).
• Microtubules are involved in intracellular transport, maintaining cell shape, intracellular compartmentalization and cell migration.

Intermediate Filaments

• Characterized by width between microtubules and microfilaments (10-12nm).
• Stable and contribute to cell mechanical strength.
• Formed from tetramers of rod-like proteins.
• Include various types, most common are Lamins, Keratin/Cytokeratin, Vimentin, Desmin, Neurofilaments and Glial fibrillary acid protein.

Microfilaments (Actin Filaments)

• Measure 5–7 nm in diameter and composed of polymers of globular G-actin monomers, assembling as a double-stranded helix of filamentous F-actin.
• G-actin is continually added to preexisting filaments to regulate growth and branching.
• Involved in intracellular transport, cytokinesis, endocytosis, muscle contraction and cytoplasmic streaming

Centrioles

• Cylindrically shaped structures found in pairs, perpendicular to one another.
• Constructed from nine triplets of microtubules.
• Associated with centrosomes, they control microtubule polymerization, transmit physical organizing forces, control movements of organelles and vesicles, and form basal bodies of cilia and flagella..

Inclusions

• Metabolically inactive materials located in the cytoplasm.
• Types include lipid droplets, glycogen granules, pigments (e.g., hemosiderin, lipofuscin, melanin), and crystals

Nucleus

• Oval, elongated, or flattened.
• Roughly 5-10 µm in diameter.
• Composed of nuclear envelope, chromatin, nucleolus, and nucleoplasm

Nuclear Envelope

• Double membrane separated by the perinuclear cisternal space (~30 - 50 nm).
• Outer membrane is continuous with the endoplasmic reticulum, often displaying ribosomes.
• Inner membrane is associated with structural proteins (lamins).

Chromatin

• Composed of DNA and associated proteins (histones and nonhistones).
• Organized into nucleosomes.
• Exists in two variations during interphase: heterochromatin (dense, transcriptionally inactive) and euchromatin (dispersed, transcriptionally active)

Nucleolus

• Round, nonmembranous bodies.
• Site of rRNA synthesis and ribosome assembly. Contains nucleostemin.

Nucleoplasm

• Nuclear components besides chromatin and nucleolus, including proteins, metabolites and the intranuclear lamina/structures.

Cell Renewal

• Somatic cells are categorized by mitotic activity as renewing (e.g., rapidly renewing cells, slowly renewing cells), stable (e.g., quiescent cells), and static (e.g., permanent cells).

Cell Cycle

• A self-regulated series of events controlling cell growth and division.
• Phases include Interphase (G1, S, G2) and Mitosis (M).

G1 Phase

• Longest phase (variable hours to days).
• Cell growth, nutrient gathering, RNA/protein synthesis and centriole duplication.
• Governed by two checkpoints (DNA damage checkpoint, restriction checkpoint)

S Phase

• DNA replication and histone synthesis occur (7.5 - 10 hours).
• Checkpoint(s): DNA-damage

G2 Phase

• Further cell growth and cytoplasmic organelle reorganization (~3.5 – 4.5 – 1 hrs).
• Checkpoints (DNA damage, unreplicated DNA).

Mitosis

• A phase of nuclear division

Other Information

• Lysosomes - Contain hydrolytic enzymes, breakdown molecules, active at acidic pHs (-0.05 to 0.5 µm)
• Peroxisomes - Oxidative enzymes, including catalase, produce H2O2; related to lipid metabolism and degradation. (0.2 – 0.5 µm)
• Mitochondria - Double membrane structures with an inner membrane forming cristae; cellular respiration occurs here.

Test your knowledge on cell biology in this quiz focused on organelles and their functions. Questions cover rough and smooth endoplasmic reticulum, Golgi complex structure, and other essential cellular components. Perfect for students in biology courses!