Biology Quiz: Cell Biology and Stem Cells

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: Small (1-10 μm), lack a nucleus, DNA in a nucleoid region (single circular chromosome).
• Prokaryotic Cells: Contain plasmids (small circular DNA, often for antibiotic resistance).
• Prokaryotic Cells: Use 70S ribosomes for protein synthesis.
• Prokaryotic Cells: Have a cell wall made of peptidoglycan, flagella for movement, and pili for attachment or conjugation.
• Eukaryotic Cells: Larger (10-100 μm), possess a membrane-bound nucleus with linear chromosomes.
• Eukaryotic Cells: Employ 80S ribosomes in the cytoplasm, and 70S ribosomes in mitochondria and chloroplasts.
• Eukaryotic Cells: Have compartmentalized organelles bound by membranes.

Organelles and Their Functions

• Nucleus: Houses the cell's DNA, controls cell activities via transcription, has a double membrane with pores, and contains a nucleolus for rRNA synthesis.
• Mitochondria: Site of ATP synthesis through aerobic respiration; the inner membrane forms cristae, and the matrix contains enzymes for the Krebs cycle.
• Ribosomes: Synthesize proteins; free in the cytoplasm (internal use) or bound to the rough endoplasmic reticulum (secretion).
• Rough Endoplasmic Reticulum (RER): Processes and folds proteins synthesized by bound ribosomes.
• Smooth Endoplasmic Reticulum (SER): Synthesizes lipids, steroids, and detoxifies harmful substances.
• Golgi Apparatus: Modifies, packages, and sorts proteins and lipids into vesicles, and forms lysosomes.
• Lysosomes: Contain hydrolytic enzymes for digestion (autophagy, autolysis).
• Chloroplasts (plant cells): Site of photosynthesis in thylakoid membranes and stroma.
• Vacuole (plant cells): Stores cell sap (ions, sugars), maintains turgor pressure for support.
• Cytoskeleton: Provides structure and support; includes microtubules (shape, transport), microfilaments (movement, cytokinesis), and intermediate filaments (strength).

Microscopy

• Light Microscope: Magnification up to x1500, resolution ~200 nm, observes live specimens.
• Electron Microscope (TEM): High resolution, observes internal details.
• Electron Microscope (SEM): 3D images of surfaces.

Cell Theory and Organisms

• Cell Theory: All living organisms are made of cells, cells arise from pre-existing cells, and the cell is the basic unit of structure and function.
• Unicellular Organisms: Single-celled organisms like bacteria and protozoa.
• Multicellular Organisms: Made of many specialized cells, like plants (cell wall) and animals.

Measuring Size and Magnification

• Magnification Formula: Magnification = Image size / Actual size.
• Units: Ensure consistent units (mm to μm: 1 mm = 1000 μm, 1 μm = 1000 nm).
• Eyepiece Graticule: Calibrate against a stage micrometer to measure specimen size.

Plant and Animal Cells

• Plant Cells: Visible features include cell wall, plasma membrane, nucleus, cytoplasm, chloroplasts, and a large central vacuole.
• Animal Cells: Visible features include plasma membrane, nucleus, and cytoplasm (organelles not readily apparent without staining).
• Comparison: Plant cells have a cell wall and chloroplasts, while animal cells typically lack both; plant cells have a large vacuole, while animal cells have smaller, temporary vacuoles.

Electron Microscopy

• Advantages: Higher resolution (~0.1 nm), greater magnification (up to x500,000).
• Disadvantages: Specimens must be dead (vacuum environment), preparation and staining is time-consuming (heavy metals).

Bacteria

• Structure: Cell wall of peptidoglycan, plasma membrane, cytoplasm with 70S ribosomes and enzymes, nucleoid with circular DNA, plasmids as additional DNA, flagella for movement, and pili for attachment and conjugation.
• Reproduction: Binary fission (asexual reproduction).

Comparing Prokaryotic and Eukaryotic Cells (Summary)

• Size: Prokaryotic (1-10 μm), Eukaryotic (10-100 μm).
• Nucleus: Prokaryotic (absent), Eukaryotic (present).
• DNA: Prokaryotic (circular, not associated with histones), Eukaryotic (linear, associated with histones).
• Organelles: Prokaryotic (non-membrane bound), Eukaryotic (membrane-bound).
• Ribosomes: Prokaryotic (70S), Eukaryotic (80S).
• Cell Wall: Prokaryotic (peptidoglycan), Eukaryotic (cellulose, not in animals).

Viruses

• Description: Non-cellular, 20-300 nm size, protein coat (capsid) surrounding nucleic acid (DNA or RNA), some have a lipid envelope.
• Types: DNA viruses (adenoviruses), RNA viruses (influenza, HIV).
• Reproduction: Obligate intracellular parasites (replicate within a host). Lifecycle: Attachment → Entry → Replication → Assembly → Release.

Biological Molecules and Biochemistry

• Biochemistry: Studies chemical processes in living organisms.
• Biomolecules: Carbohydrates, lipids, proteins, nucleic acids, and water; important for structure, energy storage, and function.
• Elements: Mostly carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), and sulfur (S).

Carbohydrates

• Structure: Contain C, H, O in a 1:2:1 ratio (e.g., glucose: (CH2O)6).
• Monosaccharides: Single sugar units (glucose, fructose, galactose).
• Disaccharides: Two monosaccharides linked by glycosidic bonds (e.g., maltose, sucrose, lactose).
• Polysaccharides: Long chains of monosaccharides (starch, glycogen, cellulose).
  • Starch (plant energy storage): Amylose (unbranched), amylopectin (branched).
  • Glycogen (animal energy storage): highly branched.
  • Cellulose (plant cell wall): β-glucose chains with hydrogen bonds.

Lipids

• Structure: Contain C, H, and O, lower O proportion than carbohydrates.
• Triglycerides: Glycerol + 3 fatty acids (ester bonds).
  • Saturated fatty acids (solid at room temp).
  • Unsaturated fatty acids (liquid at room temp).
• Phospholipids: Glycerol + 2 fatty acids + phosphate group; hydrophilic head, hydrophobic tails - key membrane component.
• Steroids: Four fused carbon rings (e.g., cholesterol, hormones).

Proteins

• Structure: Contain C, H, O, N, and sometimes S.
• Monomer: Amino acids (central carbon, amino group, carboxyl group, R group).
• Peptide bonds: Link amino acids through condensation reactions.
• Protein Structure Levels: Primary (sequence), Secondary (α-helix, β-sheet), Tertiary (3D folding), Quaternary (multiple polypeptide chains combined).
• Functions: Enzymes, structural components (collagen, keratin), transport (hemoglobin), immune response (antibodies).

Water

• Structure: Polar molecule (O-H bonds).
• Properties: Solvent (dissolves polar substances), high specific heat (regulates temperature), high latent heat of vaporization (cooling), cohesion/adhesion (capillary action), ice density (less dense than liquid water).

Enzymes

• Definition: Biological catalysts that speed up reactions without being consumed.
• Structure: Globular proteins with an active site (substrate binding).
  • Lock-and-key model
  • Induced-fit model
• Action: Lower activation energy to speed up reactions. Highly specific to substrates. Reusability.
• Investigation Techniques: Measure gas production (oxygen), color change (starch), mass loss.

Factors Affecting Enzyme Action

• Temperature: Optimal temperature for maximum activity; denaturation at high temperatures.
• pH: Optimal pH range; disruption at non-optimal pH.
• Substrate concentration: Increased rate up to saturation point where all enzyme sites are occupied.
• Enzyme concentration: Directly proportional to reaction rate (substrate not limiting).
• Cofactors: Non-protein molecules (coenzymes, metal ions) aiding enzyme activity.

Enzyme Inhibitors

• Competitive inhibitors: Compete with substrate for active site; overcomeable by increasing substrate concentration.
• Non-competitive inhibitors: Bind to allosteric site, altering enzyme shape; not overcomeable by increasing substrate.
• Irreversible inhibitors: Form covalent bonds with the enzyme, permanently inactivating it.

Immobilized Enzymes

• Definition: Enzymes attached to a surface for reuse, stability and product separation.
• Methods: Adsorption, entrapment, covalent bonding.
• Applications: Industrial processes and biosensors.

Membranes

• Definition: Selectively permeable barriers regulating substance movement.
• Structure (Fluid Mosaic Model): Phospholipid bilayer (hydrophilic heads, hydrophobic tails); embedded proteins (integral, peripheral), cholesterol (stability), glycolipids/glycoproteins (recognition).
• Components' Roles: Phospholipids (barrier), proteins (transport, signaling), cholesterol (fluidity), glycoproteins/glycolipids (recognition).

Cell Signaling

• Process: Reception (ligand binding), transduction (intracellular events), response (cellular activity).
• Signaling Types: Autocrine, paracrine, endocrine.
• Receptor Types: Ion channel, G-protein coupled, enzyme-linked.

Movement Across Membranes

• Passive Transport (no energy): Diffusion (high to low concentration), facilitated diffusion (channel/carrier protein assistance), osmosis (water movement).
• Active Transport (requires energy): Moves substances against their concentration gradient (carrier proteins involved).
• Bulk Transport: Endocytosis (phagocytosis, pinocytosis), exocytosis (release of substances).

Growth, Reproduction, and Chromosomes

• Growth: Increase in cell number through mitosis (cell division).
• Reproduction: Single-celled organisms reproduce via mitosis; multicellular organisms via cell division for repair, growth, development.
• Chromosomes: DNA tightly coiled around histones (chromatin); sister chromatids joined at centromeres; telomeres (protective caps). Diploid (2n), haploid (n).

The Cell Cycle and Mitosis

• Cell Cycle: The series of events from one cell division to the next. Interphase (G1, S, G2) and M phase (mitosis and cytokinesis).
• Mitosis Stages: Prophase (condensation, spindle formation), metaphase (alignment), anaphase (separation), telophase (decondensation, nuclear envelope reformation).
• Cytokinesis: Cytoplasm division. In animals - cleavage furrow, in plants - cell plate.

Telomeres and Stem Cells

• Telomeres: Protective DNA sequences at chromosome ends, shortened with each division. Telomerase maintains them.
• Stem cells: Undifferentiated cells with self-renewal and differentiation capacity (embryonic, adult).

Cancer

• Definition: Uncontrolled cell division leading to tumors.
• Causes: Mutations in genes regulating cell division, carcinogens, genetic predisposition.
• Tumor Types: Benign (non-invasive), malignant (invasive, metastasizing).
• Treatments: Surgery, chemotherapy, radiation, immunotherapy.

Test your knowledge on key concepts in cell biology, including stem cells, cancer, and the roles of organelles. This quiz covers essential topics such as the differences between embryonic and adult stem cells, characteristics of tumors, and the cell theory. Perfect for biology students wanting to reinforce their understanding of cellular functions.