Membranes and Transport Flashcards
(12 cards)
Fluid Mosaic Model
The cell membrane is composed of a phopholipid bilayer with embedded proteins
The fludity of the memrbane is influenced by
unsaturated fatty acids - increase fluidity
ssaturated fatty acids - decrease fluidity
cholesterol - stabilizes membrane fludity; acts as a buffer
Membrane proteins and functions
integral proteins: spans the memrbane involved in tranasprt and signaling
periphreal proteins: attached to the surface, invovled in cell recognition and signaling
transport across membranes
Simple Diffusion: Small, nonpolar molecules (O₂, CO₂) move freely.
Facilitated Diffusion: Polar molecules (glucose, ions) require transport proteins (channel or carrier).
Osmosis: Water moves across membranes via aquaporins.
Tonicity and water balance
Hypotonic solution: More water outside → Water enters the cell (can burst in animal cells, turgid in plant cells).
Hypertonic solution: More water inside → Water exits the cell (cell shrivels, plasmolysis in plants).
Isotonic solution: Equal water movement in and out (normal conditions for animal cells).
passive and active transport
Passive Transport: No energy required (diffusion, osmosis, facilitated diffusion).
Active Transport: Moves substances against their concentration gradient (low → high) using ATP.
Na⁺/K⁺ Pump: Moves Na⁺ out and K⁺ in, essential for nerve signaling.
Proton Pump: Creates a proton gradient used for ATP synthesis.
Bulk transport
Endocytosis:
Phagocytosis: “Cell eating” (engulfs large particles).
Pinocytosis: “Cell drinking” (engulfs extracellular fluid).
Receptor-mediated endocytosis: Specific molecules bind to receptors before being engulfed.
Exocytosis: Large molecules are secreted out of the cell (e.g., hormone release).
Explain the fluid mosaic model and describe the role of cholesterol in membrane fluidity.
The fluid mosaic model describes the cell membrane as a flexible bilayer of phospholipids with embedded proteins. Cholesterol stabilizes fluidity by preventing tight packing in cold temperatures and reducing excessive movement in high temperatures.
Describe how osmosis affects an animal cell placed in a hypotonic solution and a plant cell placed in a hypertonic solution.
In a hypotonic solution, an animal cell will swell and may burst (lysis). A plant cell in a hypertonic solution will undergo plasmolysis as water leaves the cell, causing it to shrink inside its cell wall.
Explain how the sodium-potassium (Na⁺/K⁺) pump works, including its role in maintaining membrane potential.
The Na⁺/K⁺ pump moves 3 Na⁺ out and 2 K⁺ into the cell using ATP. This creates an electrochemical gradient necessary for nerve impulses and muscle contractions.
Draw the molecule that makes up the majority of the cell membrane, indicating and
naming the hydrophobic and hydrophilic components.
okay so it looks like sperms going one way and going the other. the whole structure is the phospolipid bilayer. the tail-ish part is the hydrophobic tail and the head is the hydrophilic head. The top is extracellular and the bottom is intracellular.
Describe factors that affect a molecule’s ability to enter the cell and how these are
dealt with, including determining how a molecule is likely to enter the cell.
A molecule’s ability to enter the cell depends on its size, polarity, and charge. Small, nonpolar molecules diffuse freely across the phospholipid bilayer, while large, polar, or charged molecules require facilitated diffusion, active transport, or ion channels. If a molecule is very large, the cell may use endocytosis to engulf it, ensuring proper regulation of substances and maintaining homeostasis.
Recognize and describe the different types of transport across a membrane
(diffusion, facilitated diffusion, osmosis, active transport, large cargo transport).
Provide example(s) of each type of transport.
Diffusion is the passive movement of small, nonpolar molecules (e.g., oxygen and carbon dioxide) across the membrane from high to low concentration. Facilitated diffusion uses transport proteins to help larger or polar molecules, like glucose, cross the membrane without energy input. Osmosis is the diffusion of water through a selectively permeable membrane, often regulated by aquaporins, as seen in kidney cells maintaining water balance. Active transport requires ATP to move substances against their concentration gradient, such as the sodium-potassium pump in nerve cells, while large cargo transport involves endocytosis (e.g., white blood cells engulfing bacteria) and exocytosis (e.g., neurons releasing neurotransmitters).
