Lipids, Membranes, and the First Cells

Flashcards covering the structure and function of lipids, cell membranes, membrane permeability, and various passive and active transport mechanisms.

Lipid functions

Structural material, energy storage, photosynthetic pigments, and signaling (hormones).

Isoprenoids

Branched hydrocarbon chains formed by linking isoprenes.

Fatty acids

Unbranched hydrocarbon chains joined to a carboxyl group.

Saturated fatty acid

A fatty acid with no double bonds in its hydrocarbon chain.

Unsaturated fatty acid

A fatty acid with one or more cis double bonds in its hydrocarbon chain, which cause kinks.

Fats (Triglycerides)

Lipids formed via dehydration reactions, consisting of a glycerol molecule and three fatty acids.

Phospholipids

Membrane lipids that include a hydrophilic head (charged or polar) and hydrophobic nonpolar tails.

Glycolipids

Membrane lipids in which a carbohydrate is attached to a diglyceride.

Lipid micelles

Spherical structures formed by lipids with bulky heads and single hydrocarbon tails in water, where hydrophilic heads interact with water and hydrophobic tails interact with one another.

Lipid bilayers

Two layers of lipids with cylindrical shapes, where hydrophilic heads interact with water and hydrophobic tails interact with one another.

Liposomes

Spherical lipid bilayers that enclose water.

Membrane permeability

The ease with which solutes can cross a membrane.

High membrane permeability

Characteristic of small, nonpolar molecules like O2, CO2, N2.

Moderate membrane permeability

Characteristic of small, uncharged polar molecules like H2O, glycerol.

Low membrane permeability

Characteristic of large, uncharged polar molecules like glucose, sucrose, and small ions like Cl-, K+, Na+.

Cholesterol's effect on membrane permeability

Reduces membrane permeability to solutes like glycerol.

Phospholipid movement

Phospholipids are in constant lateral motion within the bilayer but rarely flip to the other side.

Passive transport

Movement of substances across a membrane down their electrochemical gradient without requiring energy.

Diffusion

Passive movement of small, uncharged molecules across a lipid bilayer from a region of higher concentration to lower concentration.

Osmosis

The net movement of water across a selectively permeable membrane from a region of higher water concentration (lower solute concentration) to a region of lower water concentration (higher solute concentration).

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A solution with a higher solute concentration outside the cell than inside, causing net water flow out and cell shrinkage.

Hypotonic solution

A solution with a lower solute concentration outside the cell than inside, causing net water flow in and cell swelling or bursting.

Isotonic solution

A solution with an equal solute concentration inside and outside the cell, resulting in no net water movement.

Crenation

The shrinking of an animal cell, typically a red blood cell, due to water loss in a hypertonic solution.

Hemolysis

The bursting of a red blood cell due to excessive water intake in a hypotonic solution.

Plasmolysis

The process in plant cells where the protoplast shrinks and pulls away from the cell wall due to water loss in a hypertonic environment.

Amphipathic proteins

Proteins with both hydrophilic (polar and charged) and hydrophobic (nonpolar) regions, allowing them to integrate into lipid bilayers.

Fluid-mosaic model

The current model of cell membranes, describing them as a fluid bilayer of phospholipids with proteins embedded in or associated with it.

Integral membrane protein

A protein embedded within the phospholipid bilayer of a cell membrane.

Peripheral membrane protein

A protein associated with the surface of the phospholipid bilayer, not embedded within it.

Transporter proteins

Plasma membrane proteins that move substances across the membrane.

Receptor proteins

Plasma membrane proteins that bind to signaling molecules and trigger a cellular response.

Enzymes (membrane-bound)

Plasma membrane proteins that catalyze reactions at the membrane.

Anchoring proteins

Plasma membrane proteins that attach the membrane to the cytoskeleton or other cells/ECM.

Recognition proteins

Plasma membrane proteins, often glycoproteins, that act as identification tags for cells.

Glycoprotein

A protein with an oligosaccharide attached, involved in cell recognition.

Facilitated diffusion

Passive movement of molecules across the cell membrane with the help of membrane proteins (channels or carriers) down their electrochemical gradient.

Channel protein

A membrane protein that forms a pore through the membrane, allowing specific ions or small molecules to pass down their electrochemical gradient.

CFTR (Cystic Fibrosis Conductance Transmembrane Regulator)

A chloride channel protein that facilitates the diffusion of chloride ions across the membrane; a mutant form causes cystic fibrosis.

Aquaporin

A channel protein that specifically allows water molecules to pass through the membrane, but blocks other molecules and most ions.

Ion channel

A type of channel protein that facilitates the passage of specific ions across the membrane, often regulated by voltage or ligands.

Carrier protein

A membrane protein that binds to specific molecules and changes shape to transport them across the membrane down their electrochemical gradient (e.g., GLUT-1 for glucose).

Active transport

Movement of molecules across a membrane against their electrochemical gradient, requiring energy (usually ATP) and protein pumps.

Sodium-Potassium Pump (Na+/K+-ATPase)

An active transport pump that uses ATP to move 3 Na+ ions out of the cell and 2 K+ ions into the cell.

Endocytosis

The process by which a cell takes in substances by engulfing them in a vesicle formed from the plasma membrane.

Phagocytosis

'Cell eating,' a type of endocytosis where the cell engulfs large particles or other cells.

Pinocytosis

'Cell drinking,' a type of endocytosis where the cell takes in extracellular fluid and dissolved solutes.

Exocytosis

The process by which a cell expels substances by fusing a vesicle containing the substances with the plasma membrane.