BIO 151 Ch. 6 - Lipids, Membranes, and the First Cells

Lipid

any organic substance that is not water soluble, but dissolves in nonpolar solvents

hydrocarbons

containing only hydrogen and carbon atoms

Which 2 nonpolar bonds make up lipids?

C-C and C-H

6 kinds of lipids (specified in the text—in reality there are many kinds)

1. Fatty Acids

2. Fats

3. Oils

4. Waxes

5. Steroids

6. Phospholipids

hydrocarbons

containing only hydrogen and carbon atoms

fatty acid

lipid with a hydrocarbon chain and polar carboxyl group (-COOH)

fatty acid

lipid w/ a hydrocarbon chain and polar carboxyl (-COOH)

kinks

the bent structure in hydrocarbon chains resulting from the presence of one or more double bonds

unsaturated

(of a lipid) containing one or more double bonds

saturated

(of a lipid) having no double bonds

why is the melting point for unsaturated lipids lower?

the absence of double bonds means they have less van der waals interactions, whereas in saturated lipids the double bond “kinks” increase the amount of van der waals interactions which help the lipids stay solids.

hydrogenation

the process of taking unsaturated lipids and saturating them by breaking double bonds and adding hydrogen (think: crisco)

the three lipids most prominently present in cells

1. steroids

2. fats

3. phospholipids

steroid

lipid with a bulky 4 ring structure and a hydroxyl head w/ a carboxyl tail

fats

nonpolar molecules w/ 3 fatty acids linked to a glycerol (C-C and C-H bonds are high PE so they store a lot of energy in organisms)

glycerol

3 carbon molecule forming the “backbone” of lipids

ester bond (ester linkage)

a bond between glycerol and a free fatty acid formed through a dehydration reaction

phospholipid

glycerol + phosphate group and two hydrocarbon chains (isoprenoids OR fatty acids)

amphipathic

contains both hydrophobic and hydrophilic regions

micelles

special aggregates made when a sphere of hydrophilic heads face outside into the water and the hydrophobic tails collect in the middle

lipid bilayer

when lipid molecules align in paired sheets

phospholipid bilayer

when phospholipid molecules align in paired sheets

vesicle

lipid bilayer enclosed around aqueous solution

liposome

artificially made membrane bound vesicles

selective permeability

some substances are able to cross a membrane more easily than others

diffuse through the lipid membrane easily

small nonpolar molecules (O₂, CO₂, N₂)

diffuse through the lipid membrane easily with some deflection

small uncharged polar molecules (H₂O, glycerol)

diffuse through the lipid membrane with deflection

large uncharged polar molecules

cannot diffuse through the lipid membrane without help

small ions

transport proteins

forms a channel in the cell membrane through which molecules can pass

why would an unsaturated fat make a bilayer more permeable

the kinks in the phospholipid tail create gaps in the bilayer

diffusion

spontaneous movement of ions and molecules

concentrated gradient

difference across space in a dissolved substance

passive transport

diffusion of a substance across a membrane

facilitated diffusion

diffusion across a membrane with transport proteins

osmosis

diffusion of water across a lipid bilayer from a low concentration to a high concentration

hypotonic

solution inside the cell is more concentrated than the outside (becomes swollen)

hypertonic

the solution inside the cell is less concentrated than the outside (becomes shrunken).

isotonic

concentrations of solutions inside and outside of the cell are equal, so water exchanges freely with no directional transport

What bilayers can ions and ribonucleotides diffuse across?

fatty acid bilayers (NOT phospholipid)

fluid-mosaic model

the idea that amphipathic proteins could integrate themselves throughout the phospholipid entire bilayer

sandwich model

the idea that proteins only sat on the surface of the lipid bilayer

freeze-fracture electron microscopy

freezing and “fracturing” a sample to see its parts before placing it under a scanning electron microscope

integral membrane proteins (transmembrane proteins)

proteins that span the entire lipid bilayer

detergents

amphipathic molecules that form micelles and whose hydrophobic tails attach to the tails of proteins and lipids to form an isolatable _____-protein complex

ion channels

channels for ions to pass through so they can participate in passive transport (diffusion) through the cell

electrochemical gradient

the combined effect of an ion’s concentration gradient and electrical charge across a membrane that affects the diffusion of ions

gated channels

a transmembrane protein that forms a pore in a cell membrane, which may open or close in response to a signal

aquaporin

channel protein for water

how do channel proteins know what to filter?

side chains on the exposed interior of the protein

facilitated diffusion

passive diffusion across a membrane w/ assistance of transmembrane carrier/channel proteins

carrier (transporter) proteins

a transmembrane protein that facilitates diffusion of a small molecule across a membrane by a process involving a reversible change in shape of the protein.

GLUT-1

a glucose transporter protein

active transport

transport against a gradient that requires energy and assistance of a transport protein

pump

any membrane gradient that requires energy to transport a protein

sodium-potassium pump

actively transports Na+ out of the cell at K+ into the cell against their electrochemical gradients. Takes up 30% of the ATP used in the body.

secondary active transport (cotransport)

transport of an ion or molecule in a defined direction (typ. against its gradient), made possible by the transport of another ion or molecule being moved along its gradient

peripheral protein

a protein sitting on the outside of the bilayer (on the PERIPHERY)

6 things affecting diffusion rate:

1. distance

2. temperature

3. solvent characteristics

4. characteristics of traveling substance

5. concentration of substance

6. characteristics of the barrier