Chapter 4: Cell Membranes & Transport Flashcards
Describe the fluid mosaic model of membrane structure. (And Why is it called Fluid Mosaic?)
the membrane behaves like a fluid where molecules can move freely, giving it flexibility. It’s called a “mosaic” because it’s composed of various types of molecules arranged together, much like tiles in a mosaic.
The fluid mosaic model depicts the membrane as a phospholipid bilayer with hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repelling) tails facing inward.
This structure allows flexibility and stability, with proteins embedded in and on the bilayer contributing to its dynamic nature.
How do hydrophobic and hydrophilic interactions form the phospholipid bilayer?
Hydrophilic heads interact with water on either side of the membrane, while hydrophobic tails avoid water, facing inward. This self-assembly creates a stable bilayer that forms the foundation of cell membranes.
What is the arrangement of cholesterol, glycolipids, and glycoproteins in cell membranes?
Cholesterol molecules are embedded within the bilayer, maintaining fluidity and stability. Glycolipids and glycoproteins are found on the outer layer of the membrane, playing roles in cell recognition and signaling.
What roles do phospholipids, cholesterol, glycolipids, proteins, and glycoproteins play in the membrane?
Phospholipids: form the basic bilayer, controlling permeability.
Cholesterol: stabilizes membrane fluidity, especially at varying temperatures.
Glycolipids and glycoproteins: involved in cell recognition and signaling.
Proteins: facilitate transport (carrier and channel proteins) and act as cell surface receptors in cell signaling.
Outline the process of cell signaling.
Secretion: Cells release specific ligands (signal molecules).
Transport: Ligands travel to target cells.
Binding: Ligands bind to specific receptors on target cells, triggering a response.
Describe simple diffusion and facilitated diffusion.
Simple Diffusion: Movement of molecules from high to low concentration across the phospholipid bilayer without energy or assistance.
Facilitated Diffusion: Passive movement of molecules via carrier or channel proteins from high to low concentration.
Describe osmosis and active transport.
Osmosis: Diffusion of water molecules across a selectively permeable membrane from high to low water potential.
Active Transport: Movement of molecules against their concentration gradient using energy (ATP) via carrier proteins.
Explain endocytosis and exocytosis.
Endocytosis: Cell membrane engulfs materials to form vesicles, bringing substances into the cell.
Exocytosis: Vesicles fuse with the cell membrane, releasing contents outside the cell.
How does surface area to volume ratio (SA:V) affect diffusion?
As cell size increases, the SA:V
ratio decreases, slowing diffusion rates.
Smaller cells with larger SA ratios enable more efficient exchange of substances.
Hypertonic Solution
Has a higher solute concentration than the cell.
Animal Cells: Water leaves the cell, causing it to shrink (crenation).
Plant Cells: Water also exits, causing the cell membrane to pull away from the cell wall (plasmolysis).
Hypotonic Solution
Has a lower solute concentration than the cell.
Animal Cells: Water enters, making the cell swell and potentially burst (lysis).
Plant Cells: Water enters, causing the cell to become turgid (swollen and firm) due to the cell wall’s support.
Isotonic Solution
Solute concentration is the same as inside the cell.
Animal Cells: No net movement of water; cells remain stable.
Plant Cells: Cells are flaccid (slightly limp), as there’s no pressure exerted by water movement.
Explain the movement of water between cells and solutions in terms of water potential.
Water moves from regions of higher to lower water potential. In plant cells, this movement can cause cells to become turgid or plasmolyzed, while in animal cells, it can lead to lysis or crenation.
