Cell basics and membrane structure

Exam 1

Eukaryotic cell

Contains membrane

Prokaryotic cell

Does NOT contain membrane

Organelle

A membrane

Typical mammalian cell size

10 to 100 micrometers (µm) across

1 µm equals how many meters

10^-6 meters

1 nm equals how many meters

10^-9 meters

4 classes of macromolecules ("building blocks" of cells)

Proteins, carbohydrates, nucleic acids, lipids

Proteins are made of

Amino acids

Carbohydrates are made of

Monosaccharides ("sugars")

Nucleic acids are made of

Nucleotides

Lipids are made of

Fatty acids and other components

Plasma membrane main functions

Barrier between cytoplasm and outside; virtually impermeable to charged/polar molecules; allows selective transport; provides surface area for protein

Glycerophospholipid structure

A polar/hydrophilic head group (choline, phosphate, glycerol) attached to two nonpolar/hydrophobic fatty acid tails

Hydrophilic

"Water-loving", polar, interacts favorably with water (phospholipid head)

Hydrophobic

"Water fearing”, nonpolar, avoids water, (phospholipid tails)

Is water charged?

No

Is water polar?

Yes

Lipid micelle

A single layer of lipids arranged with hydrophobic tails pointing inward and hydrophilic heads facing outward toward water

Lipid bilayer

Two layers of lipids with hydrophobic tails facing each other (inward) and hydrophilic heads facing water on both outer surfaces

Liposome

A spherical vesicle enclosed by a lipid bilayer, with an aqueous (watery) interior

Fluid mosaic model

Model describing the membrane as a fluid lipid bilayer containing a "mosaic" of embedded and associated proteins

Integral membrane protein

A protein embedded within (spanning) the lipid bilayer

Peripheral membrane protein

A protein loosely associated with the membrane surface, not embedded in the bilayer

Lipid-anchored protein

A protein attached to the membrane via a covalently linked lipid molecule

Membrane asymmetry

Lipid bilayers are distributed asymmetrically, the two leaflets/sides of the membrane are not identical in composition

Why does membrane lipid composition matter?

It determines membrane curvature, fluidity, bilayer thickness, and the degree of osmosis

Molecules that are membrane-PERMEABLE (no protein needed)

Gases (CO2, N2, O2) and ethanol are fully permeable; water and urea are only slightly permeable

Molecules that are membrane IMPERMEABLE (need a protein to cross)

Large uncharged polar molecules (glucose, fructose), ions (K+, Mg2+, Ca2+, Cl-) and charged polar molecules (amino acids, ATP, proteins, nucleic acids)

Course goal #1

Build a cell with a functional (plasma) membrane

Course goal #2

Make the cell able to survive

Course goal #3

Make the cell able to "talk"