Cell Structure and Function Quiz

Cell Structure and Function

• Robert Hooke first observed cells in cork, coining the term.
• Anton van Leeuwenhoek first described living cells, calling them "animacules".
• The cell is the fundamental unit of life.
• Cells exchange materials and energy with their environment.
• ATP is the primary energy form in cells.
• Cells maintained in a suitable lab environment remain viable.
• Multicellular organisms are composed of cells.
• Schleiden and Schwann established that plants and animals are made of cells (1839).
• Virchow's work (1855) stated cells arise from pre-existing cells.
• Weismann added to the cell theory, cells arose from a common ancestor (1880).

Cell Theory

• The cell theory states: all organisms are composed of cells; all cells come from pre-existing cells; the cell is the basic unit of life.

Cell Types

• Prokaryotes:
  • Simplest and oldest cell type, e.g., bacteria.
  • Lack a nucleus and membrane-bound organelles.
  • May have a cell wall, membrane, and flagella.
• Eukaryotes:
  • More complex, with membrane-bound organelles.
  • Characterized by a "true nucleus" containing DNA within a membrane.
  • Protoplasm is the jelly-like substance.
  • Cytoplasm is the protoplasm outside the nucleus.
  • Nucleoplasm is inside the nucleus.
  • Cytosol is the liquid part of cytoplasm, with suspended organelles.
  • Divided into animal and plant cells.

Cell Organelles

• Cell Membrane (All cells):
  • Isolates the cell, regulates entry/exit, maintains form and communication.
  • Primarily composed of phospholipids.
• Cell Wall (Plant cells only):
  • Outermost layer, composed of cellulose and water.
  • Provides structural support.
• Nucleus:
  • Largest organelle, centrally located.
  • Double membrane structure.
  • Controls cell activity, harbors genetic material (DNA).
• Endoplasmic Reticulum (ER):
  • System of membranous sacs.
  • Lipid and protein synthesis.
  • Smooth ER: lipid production, detoxification.
  • Rough ER: protein synthesis (ribosome-studded).
• Ribosomes (All cells):
  • Tiny organelles that build proteins.
  • Composed of RNA and proteins.
  • Free ribosomes (cytoplasm) or bound ribosomes (Rough ER).
• Golgi Apparatus:
  • Stacked membranous sacs.
  • Modifies, sorts, and packages materials, mainly proteins.
• Lysosomes:
  • Digest macromolecules.
• Peroxisomes:
  • Sacs with enzymes.
  • Involved in metabolic reactions.
• Glycosomes:
  • Sacs storing carbohydrates.
• Vacuoles (Mostly in plants, algae, and fungi):
  • Storage of water, nutrients, and waste.
• Mitochondria:
  • Double-membrane organelle.
  • Powerhouse of the cell (cellular respiration, converting glucose to ATP).
  • Contains its own DNA.
• Chloroplasts (Plant cells only):
  • Site of photosynthesis.
  • Double membrane structure.
  • Contains chlorophyll, enzymes for energy conversion.
  • Thylakoid and stroma are internal structures.
  • Contains its own DNA.
• Cytoskeleton:
  • Provides structure and support to the cell.
  • Interactions with motor proteins for movement.
  • Microtubules, microfilaments (actin), intermediate filaments.
• Centrosomes/Centrioles (animal cells):
  • Involved in cell division.
• Cilia and Flagella:
  • Movement of cells or materials.
  • Motile extensions.

Membrane Structure and Function

• Membranes:
  • Single membrane: Endoplasmic Reticulum, Golgi Apparatus, Lysosomes, Peroxisomes, Vacuoles.
  • Double membrane: Nucleus, Mitochondria, Chloroplasts.
  • No membrane: Ribosomes, Cytoskeleton, Cilia, Flagella, Centrioles.
• Membrane structure: Fluid mosaic model.
• Lipid bilayer:
  • Hydrophilic (polar) heads.
  • Hydrophobic (nonpolar) tails.
• Functions:
  • Barrier: Isolates the cell, regulates entry/exit.
  • Selectively permeable: allows certain substances to cross.
• Cell signaling, communication, and recognition: Proteins embedded in the membrane facilitate these functions.

Membrane Components

• Cholesterol:
  • Stabilizes the membrane.
  • Minimizes water permeability.
• Membrane Proteins:
  • Integral: Embedded within the bilayer.
  • Peripheral: Attached to the surface.
  • Functions: transport, enzymatic activity, signaling, intercellular recognition, junctions, adhesion.

Membrane Permeability and Transport

• Selectively permeable: Cell regulates passage of molecules.
• Passive transport (no ATP):
  • Diffusion: Movement from high to low concentration.
  • Osmosis: Water movement across a selectively permeable membrane.
  • Isotonic: equal concentrations inside and outside the cell.
  • Hypertonic: higher concentration outside the cell; cell loses water.
  • Hypotonic: higher concentration inside the cell; cell gains water.
  • Facilitated diffusion: Use of transport proteins for faster movement of molecules.
• Active transport (requires ATP):
  • Movement against concentration gradients.
  • Pumps, using ATP to move molecules.
  • Sodium-potassium pump: example of active transport.
• Exocytosis: Release of substances from the cell.
• Endocytosis: Uptake of substances into the cell. (Phagocytosis, pinocytosis)

Nucleic Acids and Proteins

• Proteins:
  • Made of amino acids.
  • Four levels of structure (primary, secondary, tertiary, quaternary).
  • Functions: enzymes, transport, antibodies, hormones.
• Nucleic Acids:
  • DNA (deoxyribonucleic acid)
    • Stores genetic information.
    • Double-stranded helix.
    • Nucleotide bases: adenine (A), thymine (T), cytosine (C), guanine (G).
  • RNA (ribonucleic acid)
    • Carries out DNA instructions.
    • Single-stranded.
    • Nucleotide bases: A, U, C, G (uracil instead of thymine).
    • Three main types (mRNA, tRNA, rRNA).
• Relationship: DNA dictates protein synthesis, RNA facilitates the process, proteins execute the actions.

Energy in the Cell, Ecosystems, and Enzymes

• Energy in the cell: ATP is the main energy currency.
• Cellular Respiration: Breaks down glucose to release energy as ATP.
• Laws of Thermodynamics:
  • First Law: Energy cannot be created or destroyed, only changed.
  • Second Law: Energy transformations create disorder (entropy).
• Enzymes: Speed up chemical reactions, lowering activation energy.
• Active Site & Substrate Interaction: Specific matching between enzyme and substrate.
• Energy Transfer in Ecosystems: Flow of energy through food chains and webs.
• Photosynthesis: Converts light energy into chemical energy (glucose).