Cell Membrane Structure and Function Quiz

Study Notes

Functions: Regulates what enters and exits the cell, maintains homeostasis, essential for all cells
Structure: Known as the fluid mosaic model, composed of phospholipids, proteins, and cholesterol

Two layers of phospholipids: Hydrophilic (polar) heads face outwards towards the watery environment, while hydrophobic (nonpolar) tails point inwards, creating a barrier
Fluid nature: Molecules in the cell membrane are not fixed, they can move freely, allowing for flexibility

Integral proteins: Permanently embedded in the membrane, some span the entire membrane (transmembrane proteins)
Peripheral proteins: Adhere temporarily to one side of the membrane
Types of proteins and their functions:
- Transport proteins/ion channels: facilitate movement of molecules across the membrane
- Anchor proteins: attach to other structures, providing stability
- Receptor proteins: bind to signaling molecules, triggering cellular responses
- Enzymes: catalyze reactions
- Glycoproteins: have sugar "nametags" for cell identification, examples include blood types

Stability and movement: Cholesterol keeps the cell membrane from becoming too solid or too fluid, ensuring efficient functioning

Allows: Small, nonpolar molecules like oxygen, carbon dioxide, and water (but slowly due to its polarity)
Doesn't allow: Large molecules, charged molecules (ions), and polar molecules (e.g., glucose)
Important molecules that can't pass directly: Amino acids, carbohydrates, ions

Passive transport: No energy required
- Diffusion: Movement from high concentration to low concentration
- Facilitated diffusion: Uses transport proteins for molecule movement, still passive
- Osmosis: Diffusion of water across a selectively permeable membrane
Active transport: Requires energy (ATP)
- Moves molecules from low concentration to high concentration
- Uses carrier proteins

Hypertonic solution: Higher solute concentration than the cell, water moves out of the cell
Isotonic solution: Equal solute concentration as the cell, no net movement of water
Hypotonic solution: Lower solute concentration than the cell, water moves into the cell

Animal cells:
- Hypertonic: Shrinking, shriveling
- Isotonic: Normal
- Hypotonic: Swelling, lysis (bursting)
Plant cells:
- Hypertonic: Plasmolysis (cell membrane pulls away from cell wall)
- Isotonic: Flaccid (limp)
- Hypotonic: Turgid (normal, firm)

Continues movement of water across the membrane, but no net change in overall concentration

Requires energy (ATP): To move molecules against their concentration gradient
Carrier proteins: Aid in the specific transport of certain molecules

Exocytosis: Release of molecules outside the cell through fusion of a vesicle with the plasma membrane
Endocytosis: Taking in molecules inside the cell by forming a pouch that pinches off as a vesicle
- Phagocytosis: "Cell eating", engulfing large particles
- Pinocytosis: "Cell drinking", taking in fluids and dissolved materials