Chapter 6, Lipids, Membranes, and the First Cells Flashcards
Plasma membrane (cell membrane)
thin membrane that surrounds every living cell.
Function of cell membrane
selective barrier that keeps damaging substances out and allows needed substances in.
Lipid
Any organic substances that do not dissolve in water but dissolve well in nonpolar organic solvents. Includes: fatty acids, fats, oils, waxes, steroids and phospholipids
hydrocarbons
An organic nonpolar molecule that contains only hydrogen and carbon atoms
isoprene
five-carbon compound that entirely consists of carbon atoms bonded to hydrogen atoms.
Fatty acid
Consists of a hydrocarbon chain bonded at one end to a carboxyl group. Used as building blocks for other lipids. Used by many organisms to store chemical energy, a major component of animal and plant fats and phospholipids
Saturated fatty acids
Hydrocarbon chains that consist of only single bonds between the carbons
Solid at room temperature
Unsaturated fatty acids
If one or more double bonds exist in the hydrocarbon chains
Liquids at room temperature
waxes
A class of lipid with extremely long, saturated hydrocarbon tails
Oils
polyunsaturated fat that is liquid at room temperature.
Three most important type of lipids found in cells
steroids, fats and phospholipids
Steroids
lipid with characteristic four ring hydrocarbon chain structure.
Fats (triacylglycerols or triglyceride)
nonpolar molecules composed of three fatty acid that is linked to glycerol (3 carbon molecule). Energy storage is the primary role of fats
Fats form when dehydration reactions occurs between a hydroxyl group of glycerol and the carboxyl group of a free fatty acid
glycerol
three-carbon molecule that forms the backbone of phospholipids and most fats
Primary role of fats
energy storage in organisms. Stores twice as much chemical energy per gram as carbohydrates due to having higher ratio of bonds with high potential energy to bonds with low potential energy
Free fatty acid
Fatty acids that are not attached to other molecules
Ester linkage
The covalent bond formed between condensation reaction between carboxyl group and hydroxyl group.
Join fatty acids to glycerol to form a fat or phospholipid
Occur when dehydration reactions connect glycerol to three fatty acids
Phospholipids
Contain 2 fatty acid tails linked to a glycerol and it has a phosphate group linked to the glycerol
Cell membranes are made mostly of phospholipids
Phospholipids with fatty acd tails
Found in domains bacteria and Eukarya
Phospholipids with isoprenoid tails
Found in domain archaea
amphipathic
Containing both hydrophilic and hydrophobic regions.
When amphipathic lipids are placed in water they become either micelles or lipid bilayers
Micelles
Tiny spherical aggregates are created when the hydrophilic heads face outwards and interact with water, while the hydrophobic tails interact with each other in the interior
Form from free fatty acid or other amphipathic lipids with single hydrocarbon chains
lipid bilayer
created when lipid molecules align in paired sheets. Hydrophilic heads in each layer face the surrounding solution and the hydrophobic tails face one another inside the bilayer
Phospholipids have bulkier nonpolar regions consisting of two hydrocarbon tails, so they form bilayers
vesicles
small bubble-like structures consisting of lipid bilayers and surrounded by small amount of aqueous solution
liposomes
An artificial vesicle formed by mixing amphipathic lipids such as phospholipids together in an aqueous solution
Permeability
The tendency of a structure, such as a membrane, to allow a given substance to diffuse across it.
Selective permeability
Some substances cross a membrane more easily than other substances do
Factors that profoundly affect permability
lipid bilayers are more permeable when they contain many short, kinked, unsaturated hydrocarbon tails. Its less straight with long, saturated hydrocarbon tails.
Effect of cholesterol molecules on membrane
adding cholesterol molecules to membranes reduces their permeability
level of fludity in a membrane
membrane’s permability depends on its fluidity. When the temp drops, the permeability is low and molecules in the bilayer move more slowly
Diffusion
Spontaneous movement of molecules and ions from high to low concentration is known as diffusion.
concentration gradient
Difference across space in the concentration of a dissolved substance
Passive transport
Movement of molecules from higher concentration to lower concentration and no amount of energy is required
Osmosis
Diffusion of water across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration
Hypertonic
If solution outside the vesicle has a higher concentration of solutes than the interior has. The water moves out of the vesicle and it shrinks
Hypotonic
If solution outside the vesicle has a lower concentration of solutes than the interior has. Water moves into the vesicle via osmosis and it can cause the vesicle to swell or burst
isotonic
If the solute concentrations are equal on both sides of the membrane, there is no movement of water and the vesicle stays the same.
Phospholipid
Type of lipid molecule that is the main component of the cell membrane.
Made up of 2 fatty acids, a phosphate group and glycerol molecule.
Molecule has a hydrophilic head containing a phosphate group and two hydrophobic tails derived from fatty acids
protocells
Simple vesicle-like structures that harbor nucleic acids
Fluid mosaic model
Widely accepted hypothesis that cellular membranes consist of proteins embedded in a fluid phospholipid bilayer.
Scanning electron microscope
A microscope that produces surface images by reflecting electrons off a speciman coated with a layer of metal atoms
integral membrane proteins (transmembrane proteins)
Any membrane protein that spans the entire lipid bilayer
Peripheral membrane proteins
Proteins that bind to membrane lipids or integral membrane proteins without passing through it
ion channels
Type of channel protein that allows certain ions to diffuse across a plasma membrane down an electrochemical gradient
They form pores, or openings in a membrane and the ions diffuse through these pores from high to low concentration regions.
Electrochemical gradient
combined effect of an ion’s concentration gradient and electrical gradient across a membrane that affects the diffusion of ions
Channel proteins
transmembrane protein that forms a pore in a cell membrane which may open or close in response to a signal.
aquaporin
type of channel protein that faciliates the movement of water (osmosis) across a plasma membrane
gated channels
open or close in response to a signal
carrier proteins
transmembrane protein that facilates diffusion of a small moleule across a membrane
facilitated diffusion
Passive movement (diffusion) of a substance across a membrane with the assistance of transmembrane carrier proteins or channel proteins
Difference between channel and carrier proteins
Channels allow movement through a selective pore, much like bridges allow people to cross back and forth over a river. In contrast, carrier proteins selectively pick up a solute on one side of the membrane, then drop it off on the other side.
active transport
movement of ions or molecules from lower to higher concentration with the use of energy. Moves against the concentration gradient
Pump
Any membrane protein that uses energy to change shape and power the active transport of a specific ion or molecule across a membrane in a single direction, against its gradient.
Sodium-potassium pump
A transmembrane protein that uses the energy of ATP to move sodium ions out of the cell and potassium ions into the cell
Most permeable membranes
unsaturated phospholipids
Temp
Cholesterol
Membranes with some degree of permeability
small nonpolar like O2
Small polar/noncharged like H20
Never permeable
ions
Cholesterol
A type of steroid that has a polar hydrophilic hydroxyl group and a nonpolar isoprenoid tail at the bottom
Isoprenoid
structural formula of a chain of linked isoprenes
phospholipid bilayer
Lipid bilayers consisting of phospholipids
Selective permeability of the lipid bilayer
High permeability: Small nonpolar molecules
Medium permeability: small uncharged polar molecules
Low permeability: Large, uncharged polar molecules
No permeability: Small ions
What in the lipid structure effects membrane permeability
Temperature
Cholesterol: More cholesterol to membranes means lower permeability to glycerol
Saturation: An unsaturated membrane is more permeable while a saturated membrane is less permeable
Hydrocarbon tail length: Short hydrocarbon chains go through with higher permeability vs the long hydrocarbon chains
