Topic 4 - Lipids, Membranes, and Membrane Transport Flashcards
(62 cards)
Lipid
Macromolecule that is nonpolar and insoluble in water (hydrophobic); hydrocarbons that include mostly nonpolar carbon-carbon or carbon-hydrogen bonds
List four functions of lipids
- Energy storage
- Insulation from environment in plants and animals
- Building blocks of many hormones
- Form plasma membrane
What are some examples of lipids?
Fats and oils (aka triglycerides), phospholipids, steroids, waxes, etc.
What are the main components of a fat molecule?
Glycerol and three fatty acids
Saturated fatty acid
Single bonds between neighboring carbons in the hydrocarbon chain - i.e. saturated with hydrogen; compact, solid at room temperature, and inflexible in cold temperature
Ex. butter
Unsaturated fatty acid
Hydrocarbon chain contains a double bond (C=C); fluid, liquid at room temperature, flexible in cold temperature
Ex. vegetable oil
Monounsaturated
One double bond (C=C)
Polyunsaturated
Multiple double bonds
What causes an unsaturated fatty acid to be liquid at room temperature?
Double bonds cause a bend/”kink” that prevents fatty acids from packing tightly, keeping them liquid at room temperature.
Why are fats (triglycerides) important?
Fats are an excellent source of stored energy, may be used for insulation and cushioning
Phospholipids
Plasma membrane constituents that comprise cell’s outermost layer; glycerol backbone linked to a modified phosphate group (polar, hydrophilic head) and 2 fatty acid tails (nonpolar, hydrophobic)
- Tails may be saturated or unsaturated
- Spontaneously form micelles or bilayers in water
Steroids
Chemical messengers; precursors to water-insoluble vitamins (A, K, D, and E) and hormones (testosterone and estradiol)
- Composed of 4 carbon rings
Cholesterol
Sterol found in the plasma membrane of animal cells; located within phospholipid bilayer
Fluid mosaic model
Plasma membrane is a mosaic of components - including phospholipids, cholesterol, proteins and carbohydrates - that gives the membrane a fluid character (i.e. lipids are fluid, mosaic is made of proteins)
Phospholipid bilayer
Barrier that separates the inside of the cell from the outside environment; comprised of phospholipids
Functional membranes must be…
Fluid
What affects the fluidity of the bilayer?
Temperature, size of protein, protein attachment to cytoskeleton, saturation of hydrocarbon tails, and cholesterol
What is the function of cholesterol in the membrane?
Prevents lower temperatures from inhibiting fluidity and higher temperatures from increasing fluidity too much
What are the functions of integral proteins (transmembrane proteins)?
- Transporting/channeling molecules across membrane
- Cell-surface receptors - cell recognition, signal transduction
- Cell-to-cell adhesion; carbohydrate chains attached to some proteins act as labels that identify cell type
- Enzymatic activity
- Attachments to cytoskeleton
What are the functions of peripheral proteins?
- Enzymatic activity
- Attachments to cytoskeleton
- Cell recognitions sites - cell-specific proteins
Integral proteins are found…
Embedded in lipid bilayer
Peripheral proteins are found…
On the periphery of lipid bilayer, attached to either integral proteins or phospholipids
Cell surface markers
Classify cells according to their markers
What are the functions of carbohydrates in the cell membrane?
- Cell recognition (“self” vs. “non-self”)
- Glycoproteins and glycolipids - AKA glycocalyx
- Hydrophilic - attracts H2O to cell’s surface
- Cell-to-cell adhesion
