AP Biology Unit 2 Notes: Cell Structure and Function

Living things:

• The cell is the basic unit of life

  • As the surface area-to-volume ratio decreases, cells become less efficient

• Light microscopes are used to study stained or living cells

• Electron microscopes are used to study detailed structures that aren’t easily seen with light microscopy

Prokaryotic cell:

• Much smaller and simpler than the eukaryotic cell; the inside is filled with cytosol and cytoplasm

  • NO membrane-bound organelles like in eukaryotes, only a plasma membrane

    • Includes bacteria and archaea

• Genetic material is found in one continuous, circular DNA molecule in the nucleoid

• Most have a peptidoglycan cell wall surrounding the lipid plasma membrane

• Contains small ribosomes

Eukaryotic cell:

• Much more complex than prokaryotes; including fungi, protists, plants, and animals

• Plasma membrane is the outer envelope, made of phospholipids and proteins arranged in the fluid-mosaic model

  • Semipermeable and regulates substances going in and out

  • Integral proteins are firmly bound to the membrane and are amphipathic (both hydrophobic and hydrophilic)

    • Transmembrane proteins are integral proteins extending through the membrane

  • Adhesion proteins form junctions between adjacent cells

  • Receptor proteins (like hormones) serve as docking sites for arrivals at the cell

  • Transport proteins form pumps that use ATP to transport solutes across the membrane

  • Channel proteins form channels that selectively allow the passage of certain ions/molecules

  • Cell-surface markers (glycoproteins, lipids, glycolipids) are exposed on the extracellular surface and help with cell recognition and adhesion

  • Carbohydrate side chains are also on the outer surface

• Nucleus is largest organelle; directs what goes on, has DNA in chromosomes

  • In nucleolus, rRNA is made and ribosomes are assembled

• Ribosomes are sites of protein synthesis; are round with a large subunit and a small subunit

  • Made of ribosomal RNA (rRNA) and proteins; can be free floating or attached to the endoplasmic reticulum

• Endoplasmic reticulum: continuous channel extending into many regions of the cytoplasm; provides mechanical support and transportation

  • Rough ER compartmentalized cell and has ribosomes

  • Smooth ER makes lipids, hormones, and steroids; helps break down toxic chemicals

• Golgi complex: modifies, processes, and sorts proteins after they’ve been synthesized by ribosomes on the rough ER

  • Packaging and distribution center for material to be sent out of the cell; packages products in vesicles, which bring them through the plasma membrane

• Mitochondria: converts energy from organic molecules to useful energy for the cell - ATP

  • Has inner membrane with folds (cristae), which separates the matrix from the inter-membrane space

  • Outer membrane separates inter-membrane space from the cytoplasm of the cell

• Lysosomes have sacs which carry digestive enzymes used to break down old, worn-out organelles, debris ,or large ingested particles

  • Made when vesicles containing specific enzymes from the trans-Golgi sue with vesicles during endocytosis

  • Essential during apoptosis

• Vacuoles

  • Fluid-filled sacs that store water, food, waste, salt, or pigment

• Peroxisomes:

  • Detoxify substances and produce H2O2 as a product; has enzymes that then break down the peroxide into water and oxygen

• Cytoskeleton

  • Network of protein fibers, including microtubules and microfilaments that determine the shape of the cell

    • Microtubules are made of tubulin and participate in cell division and movement

    • Microfilaments are important for movement; thin and rodlike, made of actin, which are joined together and broken apart as needed

• Cilia and flagella

  • Locomotive properties; make beating motions to help cell move

Plant cells vs. animal cells

• Plant cells have a cellulose cell wall (rigid layer), chloroplasts containing chlorophyll, a large vacuole (central vacuole)

• Plant cells don’t have centrioles

Transport:

• Transport - ability of molecules to move across the cell membrane

  • Depends on semi permeability of the plasma membrane, and the size and charge of particles going through

  • Small, hydrophobic (nonpolar) molecules pass easily

  • Aquaporins are water-specific channels

• When there is a high concentration of something, it mill move into an area with lower concentration down a concentration gradient; this is diffusion

  • Hydrophobic molecules do simple diffusion because they just drift through the membrane

  • When diffusion uses channel-type proteins, it is facilitated diffusion

  • Diffusion is always passive transport because it requires no outside energy

• Active transport uses ATP (or other energy), while passive doesn’t

  • Active moves things from low concentration —> high

  • Passive is high to low concentration

  • Active examples: phagocytosis, pinocytosis, Na-K+ pump

• Passive transport includes diffusion, facilitated diffusion, and osmosis

Water stuff!

• Osmosis is diffusion of water across the membrane

  • Larger quantities go through aquaporins

  • Water moves into areas with a higher solute concentration b/c diffusion!

• Osmolarity is the total solute concentration in a solution

• Tonicity is the relevant concentrations of solute inside and out of a cell

  • Hypertonic is more solute inside than in the external environment

  • Isotonic is equal concentrations of solute and solvent inside and out

  • Hypotonic means less solute and more solvent inside than in the environment

  • Water goes from hypotonic to hypertonic; solutes go from hypertonic environment to hypotonic

  • In an isotonic environment, there is dynamic equilibrium

• Water in plant cells:

  • Water going out of cells in hypertonic environment - plasmolysis

  • isotonic: equal solute and water means cells are flaccid

  • Environmental hypotonicity means water goes in and cells are turgid

  • Cell walls expand to maintain turgor pressure; turgidity is the optimum state

• Water in animal cells:

  • Hypertonic: shriveled

  • Isotonic: normal

  • Hypotonic: lysed or burst

• Water potential measures the tendency of H2O to move via osmosis

  • Calculated from the pressure potential and the solute potential

  • Water potential = pressure potential + solute potential