CH.6: Lipids, Membranes, and the First Cells

Plasma membrane

Separates life from nonlife, selective barrier.

Selective barrier

Allows entry of needed materials, excludes harmful ones.

Chemical reactions

Facilitated by sequestering appropriate chemicals.

Lipids

Carbon compounds insoluble in water due to nonpolarity.

Hydrocarbons

Nonpolar molecules containing only carbon and hydrogen.

Hydrophobic

Repellent to water; does not mix with it.

Isoprenoid

Hydrocarbon chain, functions in pigments and hormones.

Fatty acid

Hydrocarbon chain bonded to a carboxyl group.

Saturated fatty acid

Only single bonds between carbons, maximum hydrogens.

Unsaturated fatty acid

Contains one or more double bonds, creates kinks.

Polyunsaturated fatty acid

Multiple double bonds in hydrocarbon chain.

Saturation

Affects physical state; influences healthiness of lipids.

Solid lipids

Highly saturated, stiff at room temperature.

Liquid lipids

Highly unsaturated, remain liquid at room temperature.

Triglycerides

Type of lipid made from glycerol and fatty acids.

Steroids

Lipids with a four-ring carbon structure.

Fats

Energy storage lipids, composed of triglycerides.

Hydrocarbon tails

Long chains in lipids affecting their state.

Chemical structure of lipids

Varies widely, allowing diverse functions.

Carboxyl group

Functional group in fatty acids, polar.

Kink in chain

Caused by double bonds in unsaturated fatty acids.

Phospholipids

Glycerol linked to phosphate and two hydrocarbon chains.

Steroids

Lipids with a bulky four-ring structure.

Testosterone

Hormone steroid important for male development.

Estrogen

Hormone steroid important for female development.

Cholesterol

Component of plasma membranes, a type of steroid.

Fats

Composed of three fatty acids linked to glycerol.

Triacylglycerols

Another name for fats or triglycerides.

Ester Linkage

Bond formed between glycerol and fatty acids.

Hydrophobic Region

Non-polar tail of phospholipids, repels water.

Hydrophilic Region

Polar head of phospholipids, interacts with water.

Phospholipid Bilayers

Lipid bilayers formed by phospholipids in water.

Micelles

Spherical aggregates formed by free fatty acids.

Lipid Bilayers

Paired sheets of lipid molecules in membranes.

Selective Permeability

Ability of membranes to control substance passage.

Small Nonpolar Molecules

Cross bilayers quickly due to size and polarity.

Large Polar Molecules

Cross bilayers slowly, if at all.

Dehydration Reaction

Process linking glycerol and fatty acids to form fats.

Amphipathic Lipids

Molecules with both hydrophilic and hydrophobic regions.

Artificial Membranes

Lab-created lipid structures for experimental purposes.

Liposomes

Artificial vesicles formed from phospholipids.

Planar Bilayers

Lipid bilayers across openings in glass/plastic.

Energy Storage

Primary role of fats due to high-energy bonds.

Entropy in Lipid Organization

Spontaneous processes decrease entropy at lipid level.

Phospholipids

Molecules forming cell membranes, varying in properties.

Hydrocarbon Tails

Fatty acid chains affecting membrane fluidity and permeability.

Saturation

Presence of double bonds in hydrocarbon tails.

Unsaturated Tails

Contain double bonds, causing kinks in structure.

Saturated Tails

No double bonds, leading to tighter packing.

Cholesterol

Steroid that increases membrane density and reduces permeability.

Membrane Permeability

Ability of substances to cross the membrane.

Hydrophobic Interactions

Forces holding tails together in membranes.

Temperature Effect

Lower temperatures decrease membrane fluidity and permeability.

Diffusion

Movement from high to low concentration regions.

Concentration Gradient

Difference in solute concentrations across a space.

Equilibrium

State where molecules are evenly distributed, no net movement.

Passive Transport

Substances cross membranes without energy input.

Osmosis

Diffusion of water across selectively permeable membranes.

Hypertonic Solution

Higher solute concentration outside the cell.

Hypotonic Solution

Lower solute concentration outside the cell.

Isotonic Solution

Equal solute concentrations inside and outside the cell.

Cell Swelling

Occurs in hypotonic solutions due to water influx.

Cell Shrinking

Occurs in hypertonic solutions due to water efflux.

Entropy

Measure of disorder, increased by diffusion.

Fluidity

Ability of phospholipids to move within the bilayer.

Packing Density

Tightness of phospholipid tails affecting permeability.

Selective Permeability

Membrane's ability to allow certain substances to pass.

Osmosis

Movement of water across a semipermeable membrane.

Protocells

Simple vesicle-like structures containing nucleic acids.

Lipid Bilayers

Double layer of lipids forming cell membranes.

Ribonucleotides

Building blocks of RNA, negatively charged.

Phospholipids

Basic structural components of cell membranes.

Fluid-Mosaic Model

Membrane structure with dynamic proteins and lipids.

Integral Membrane Proteins

Proteins that span the entire membrane.

Peripheral Membrane Proteins

Proteins that bind to membrane surfaces.

Ion Channels

Membrane proteins that allow ion passage.

Electrochemical Gradients

Concentration and charge differences across membranes.

Channel Proteins

Selective proteins facilitating ion or molecule diffusion.

Aquaporins

Channel proteins specifically for water transport.

Gated Channels

Channels that open or close in response to signals.

Facilitated Diffusion

Passive transport assisted by membrane proteins.

Carrier Proteins

Proteins that transport substances across membranes.

GLUT-1

Carrier protein that transports glucose into cells.

Active Transport

Movement of substances against their concentration gradient.

Sodium-Potassium Pump

Active transport mechanism for Na+ and K+ ions.

Na+/K+-ATPase

Pump using ATP to transport sodium and potassium.

Secondary Active Transport

Transport driven by electrochemical gradients.

Selective Permeability

Membrane's ability to control substance passage.

Passive Transport

Movement of substances without energy input.

Concentration Gradient

Difference in substance concentration across a membrane.

Transmembrane Proteins

Proteins that extend across the lipid bilayer.

Hydrophilic Residues

Amino acids that attract water inside channel pores.

Dynamic Mosaic

Fluid arrangement of proteins and lipids in membranes.

Membrane Structure

Arrangement of lipids and proteins in biological membranes.

Transport Mechanisms

Processes for moving substances across cell membranes.