AP Biology Unit 2 Review: Cell Structure and Function

Biological Tools:

Light microscope → study cells (light shined through a sample) magnify 1000x, resolution. Pro: Live cell/specimens

Electron microscopes → scanning (surface, electrons bounce off) vs. tunneling (internal mechanisms), 10^6x. Con: Dead organisms/specimens

Cell fractionation → blender centrifuge spins & separates the particle → layers of the cell

Useful Formulas:

  • Sphere

    • Area = 4(pi)r²

    • Volume = 4/3(pi)r³

  • Solutions

    • Water potential = solute potential

    • Solute potential = -iCRT

      • -i → ions that break up (ex: 1.0 M for sucrose)

      • C → molar concentration, (ex: 1 mol/L)

      • R → pressure constant, 0.0831 (L*bars/mol*K) or 0.00831 (L*MPa/mol*K)

      • T → temperature (Kelvin, K), 273 + Co

Cell Structure:

  • Phospholipids → hydrophilic (head), hydrophobic (tail) - amphipathic

    • “Kinks” → unsaturated fatty acids (less stability, more fluid)

    • Rigid → saturated fatty acids (more stable, more compact)

  • Water - water → extracellular & intercellular (aqueous)

  • Phospholipid bilayer + proteins

  • Proteins: Integral (inside), transmembrane (across), peripheral (outside, but connected)

  • Cholesterol

    • Low temperatures → prevents membrane from hardening

    • High temperature → keeps membrane solid

Plasma Membrane (“Fluid Mosaic Model”):

  • Small, hydrophobic molecules pass easily

  • Transport proteins → channel, carrier

    • Channel: aquaporins - let water molecules through, lipoproteins with a pore (sometimes gated) allowing specific ions

      • > rate of transportation

    • Carrier: integral glycoproteins that bind with a specific solute (physical change to move to molecule)

  • Diffusion

    • High concentration to low concentration (high hill → rolling down to a lower hill, no ATP

  • Osmosis - passive transfusion of water

    • Water flows from high to low in its own water concentration without ATP

  • Facilitated diffusion

    • Passive transport (high to low)

    • Help with protein

    • No ATP

  • Active transport (low hill → high hill, carrying rock)

    • Protein + ATP

      • Membrane pumps → transmembrane carrier proteins, solute specific, R-group (folding)

        • ATP hydrolyzes → phosphate group is removed & attached to the pump

        • Phosphorylation → conformational change (protein’s shape) - adjusting the microenvironment within the protein channel & shuttling solutes across membrane

        • Ex: sodium potassium pump and proton pump → accumulate ions on one side of a membrane (then use during cotransport or ATP synthase)

      • Endocytosis → Bringing substances into the cell in larger quantities

        • Ex: Phagocytosis (cell eating), Pinocytosis (cell drinking), Receptor mediated (specific ligands bind to cell surface receptors - vesicle formation)

      • Exocytosis → Fusion of a vesicle with the plasma membrane for molecules to exit the cell (shipped out by Golgi or waste)

  • Concentration gradient / electrochemical gradient

    • Ions - repulsed

      Williams, Dan / Unit 2 The Cell Membrane

  • Selective permeability - homeostasis (constant internal conditions)

    • Small & nonpolar molecules - pass easily through the phospholipid bilayer

    • Large & charged molecules (ex: glucode, sodium) - pass through embedded proteins

    • Cell walls (permeability barriers) - structural support (different polysaccharides)

Cells:

  • Hypertonic → more solutes outside, less solutes inside (water rushes out)

    • Lower water concentration & potential

  • Hypotonic → more water outside, less water outside (water rushes in, stability in plants)

    • Higher water concentration & potential

  • Isotonic → equal concentrations (stability in animals)

    • Moving at equal rates in both directions

    • Cytolysis → osmoregulation

  • Osmosis → movement of water, passive transfusion of water

    • Water flows from high to low in its own water concentration without ATP

  • Greatest efficiency: Greatest Volume:surface area ratio

    • A lot of membrane folding (ex: branching)

      • Metabolism - proteins, carbs, gases, wastes, ions, & ligands

Animal vs. Plant Cells:

  • Animal

    • Nucleus → brain, center, genetic codes (function)

      • Nuclear pore - outside and inside communication

      • Nucleolus - clump of DNA (creates ribosome) - not an organelle

      • Nucleoplasm - inside nucleus

      • Nuclear envelope - double membrane, protection

    • Rough Endoplasmic reticulum (ER) → creates membrane, metabolism - detoxify toxins (protein production & initial folding) + compartmentalizes the cell & intracellular transport

      • Interconnected folded membranous sacs - continuous w/ nuclear envelope

    • Smooth ER → like rough (detoxification for lipid synthesis)

    • Cilium → oars of a boat - push liquid around

    • Ribosome → creates proteins, made of rRNA & protein (translation - central dogma) - rough ER

    • Lysosome → break things down (stomach, digests)

      • Hydrolytic enzymes - cell recycling & apoptosis (scheduled cell death)

    • Vacuole →

    • Centriole → cell division

    • Centrosome → two centrioles

    • Peroxisome → detoxifies alcohol

    • Golgi apparatus (body/complex) → packages protein & lipids from rough ER (processed, sorting, transported, shipping)

      • Series of flattened stacks

      • Receiving side - cis face

      • Opposite side - trans face (secretory vesicles bud off)

    • Secretory vesicles → Truck for the packages

    • Mitochondria → powerhouse of the cell (generates ATP)

      • Two membranes (bilayer) - matrix, christic, endosymbiotic theory → archeria - bacteria (ingulfs, food)

  • Plant Cells

    • Mitochondria → smooth outer layer, inner layer (cristae) & fluid matrix

      • Cellular respiration - ATP

      • Greater folding of inner membrane → greater surface area + more ATP

      • Krebs cycle - oxidizes sugar (matric) while the electron transport chain & ATP synthesis (cristae)

    • Cell walls → structural support

    • Central vacuole → holds extra water & dissolved solutes

      • Turgor pressure - more water

      • + Paramecia - pumps water

    • Chloroplast - endosymbiont (bigger organism takes in a smaller organism - independent prokaryotes)

      • Thylakoids granum & stroma (sacks)

        • Inner thylakoid membranes stacked into grana surrounded by liquid stroma

      • Compartmentalization - divides light & dark reactions

        • Light - thylakoid membrane + pigment chlorophyll & electron transport chain → Calvin cycle forms sugars (stroma)

      • Perform photosynthesis - harnesses sunlight + store it in sugars

    • Evidence of endosymbiosis - chloroplast & mitochondria

      • Double membrane

      • DNA

      • Ribosomes

      • Replicated independently

      • Size of existing prokaryotic cells

    • No centrioles & lysosomes (campbell)

Eukaryotes vs. Prokaryotes:

  • Eu- Membrane-bound organelles and nucleus, DNA linearly in multiple chromosomes

    • Protists, fungi, plants, & animals

  • Pro- No membrane-bound organelles or nucleus, DNA in a circular loop

    • Bacteria & archaea

  • Both have

    • Ribosomes

    • DNA

    • Cytoplasm

    • Plasma membrane