Lipids and Membranes

Flashcards covering key vocabulary related to lipids, membrane structure, and transport mechanisms from Chapter 6 of the lecture notes.

Plasma membrane (cell membrane)

Life's defining barrier that separates life from nonlife, serving as a selective barrier, allowing material exchange, keeping damaging materials out, and facilitating chemical reactions.

Lipids

A diverse class of nonpolar and hydrophobic molecules composed primarily of carbon and hydrogen atoms, with widely varying structures and not considered polymers.

Triglycerides/Fats and oil

Lipids used for long-term energy storage, composed of three fatty acids linked to glycerol.

Phospholipids

Amphipathic lipids that are an essential component in membranes, featuring a polar head and nonpolar tails.

Steroids

Lipids distinguished by a bulky, four-ring structure; examples include hormones and cholesterol, which is a component in membranes.

Glycerol

A sugar alcohol that, along with fatty acids, makes up a triglyceride.

Fatty acids

Hydrocarbon chains bonded to a carboxyl functional group (-COOH), which are components of triglycerides and phospholipids.

Saturated hydrocarbon chains

Fatty acid chains that consist of only single bonds between the carbons, making them solid at room temperature.

Unsaturated hydrocarbon chains

Fatty acid chains that contain one (monounsaturated) or more (polyunsaturated) double bonds between carbons, making them liquid at room temperature.

Waxes

Saturated lipids with extremely long hydrocarbon tails that form particularly stiff solids at room temperature.

Cis-fats

Unsaturated fatty acids where hydrogen atoms at the double bond region are on the same side of the carbon chain, typically found in nature.

Trans-fats

Unsaturated fatty acids where hydrogen atoms at the double bond region are on opposite sides of the carbon chain, primarily produced during food processing through hydrogenation.

Hydrogenation

The addition of hydrogen atoms to unsaturated fatty acids, converting liquid fats into semi-solid or solid forms and often creating trans fatty acids.

Cholesterol

An important steroid component of plasma membranes in many organisms, a precursor to vitamin D and sex hormones, and a fluidity buffer in membranes.

Amphipathic

A characteristic of membrane-forming lipids, meaning they contain both a polar, hydrophilic region (head) and a nonpolar, hydrophobic region (tail).

Selective permeability

The property of phospholipid bilayers that allows small or nonpolar molecules to move across quickly, while charged or large polar substances cross slowly, if at all.

Fluidity buffer

The role of cholesterol in membranes, where it prevents phospholipid tails from packing too tightly at lower temperatures (increases fluidity) and forces them closer together at high temperatures (decreases fluidity).

Passive transport

Movement of substances across a membrane without a direct input of energy, including diffusion, osmosis, and facilitated diffusion.

Diffusion

The random movement of molecules from a region of high concentration to a region of low concentration (down the concentration gradient) until evenly distributed.

Equilibrium

The state when molecules or ions are randomly distributed, with no net movement across a membrane, though individual molecules are still moving.

Osmosis

The diffusion of water across a selectively permeable membrane from regions of low solute concentration to regions of high solute concentration, diluting the higher concentration.

Hypotonic solution

A solution with fewer solutes compared to another solution, causing water to move into a cell by osmosis, making the cell swell.

Hypertonic solution

A solution with more solutes compared to another solution, causing water to move out of a cell by osmosis, making the cell shrink.

Isotonic solution

A solution that has the same amount of solutes as another solution (e.g., inside a cell), resulting in no net water movement and stable cell size.

Osmotically active solutes

Stationary solutes (e.g., ions like sodium) that cannot move freely across a membrane, influencing water movement during osmosis.

Turgor pressure

The fluid pressure that pushes the plasma membrane against the cell wall in plant cells, maintained by a hypotonic extracellular solution.

Fluid Mosaic Model

A model describing membranes as containing phospholipids (providing basic structure) and proteins (with multiple functions).

Peripheral proteins

Proteins that bind to membrane lipids without passing through the membrane, found on either the interior or exterior of the cell.

Integral (transmembrane) proteins

Proteins that span the membrane, involved in the transport of selected ions and molecules across the plasma membrane.

Transport proteins

Transmembrane proteins that move molecules across the membrane, categorized into channels, carrier proteins/transporters, and pumps.

Facilitated diffusion

A type of passive transport where substances move across a membrane down their concentration gradient with the help of protein channels or carrier proteins.

Protein channel

A type of transport protein that forms a protein-lined passageway across the membrane, allowing water molecules or specific ions/molecules to move simultaneously down their concentration or electrochemical gradients at a rapid rate.

Electrochemical gradient

Occurs when ions build up on one side of a plasma membrane, establishing both a concentration gradient and a charge gradient, which represents potential energy for ion movement.

Gated channels

Ion channels that open or close in response to specific signals such as the binding of a particular molecule (ligand-gated), a change in voltage across the membrane (voltage-gated), or mechanical stimuli (stretch-gated).

Aquaporins

Ligand-gated protein channels that permit water to rapidly cross the plasma membrane, found in tissues like kidneys and the brain.

Glymphatic system

A system in the brain that mainly functions during sleep to clear interstitial metabolic waste and distribute nutrients, facilitated by aquaporins.

Carrier proteins (transporters)

Transport proteins that move a variety of ions and molecules across cell membranes down their concentration gradient by binding specific substrate molecules and undergoing a conformational change, but at a slower rate than channels.

Active transport

Movement of substances across a membrane against or up their concentration gradient, directly requiring an input of energy (e.g., ATP) or utilizing an existing gradient.

Primary active transport

A type of active transport where ATP is directly required and used at the pump to move substances against their gradient.

Secondary active transport (co-transport)

A type of active transport where an existing electrochemical gradient (often maintained by primary active transport) powers the movement of one molecule down its gradient while simultaneously moving another molecule up its gradient, without direct ATP hydrolysis at the transporter.

Sodium–potassium pump (Na+/K+-ATPase)

An example of primary active transport that uses ATP to cotransport 3 Na+ ions out of the cell for every 2 K+ ions into the cell, moving both against their concentration gradients.