chapter 2 pt 1 Flashcards
all living cells exist in an
aqueous medium
the cell membrane separates
contents of cell from extracellular fluid surrounding cell
the cell membrane is selectrively
permeable and controls traffic in and out of cell
the cell membrane is made of
phospholipids, proteins, and other macromolecules
cells will die if
the membrane does not function properly
phospholipids have
fatty acid tails and a phosphate group head
phospholipids: fatty acid tails are
hydrophobic: non polar, dont dissolve
phospholipids: phosphate group head is
hydrophilic: polar, dissolves
phospholipid bilayer: phospholipids align according to
water solubility
fluid mosaic model:
phospholipids = scaffold
proteins (+ other macromolec.s) embedded = mosaic
in a fluid mosaic model, the molecules in membrane can
move about freely - fluid
cell membrane + phos. bilayer must be
fluid + flexible (viscosity like veg. oil)
if the phosph. bilayer is too fluid, it
permits too much substance entry
if the phosph. bilayer isnt fluid enough, it
prevents too much substance entry
factors affecting phosph. bilayer fluidity
temperature
percentage of double bonds in fatty acids
length of fatty acids
cholesterol
fluidity of phosph. bilayer: temperature
increase temp, increase fluidity
decrease temp, decrease fluidity (gel state)
fluidity of phosph. bilayer: % unsaturated fatty acids in phospholipids
double bonds form kinks in tails => less tightly packed => membrane LESS viscous
fluidity of phosph. bilayer: fatty acid tail length
longer = more intermolecular attractions
held together more tightly, REDUCES fluidity
most common length of fatty acid = 16-18 carbons
fluidity of phosph. bilayer: cholesterol in membrane
cholesterol = mortar, fills in small gaps in phosp. structure, IMPROVES IMPERMEABILITY to small, water-soluble molecules like glucose
acts as membrane ANTIFREEZE AGENT: decreases fluidity at high temp + vice versa
proteins determine membrane’s
specific functions
two types of membrane proteins:
peripheral + integral
membrane proteins: PERIPHERAL
loosely/temporarily bound to surface of membrane/integral proteins
membrane proteins: INTEGRAL
- penetrate lipid bilayer, usually across whole membrane
- stabilize membrane, link with cell cytoskeleton
- transport proteins
membrane proteins determine membrane function by performing:
- transport
- reaction catalysis
- cell recognition
- signal reception + transduction
membrane protein functions: transport
substances across cell membrane
membrane protein functions: reaction catalysis
carry out chem reactions
membrane protein functions: cell recognition
carb. chains protruding from glycoproteins enable cells to recognize each other + identify harmful intruders (disease bacteria)
membrane protein functions: signal reception and transduction
receptor proteins bind to signal molec.s (e.g. hormones) and change shape + initiates cellular response to signal
the proteins’ domains
anchor molecules
proteins anchoring molecule: within membrane
nonpolar amino acids: hydrophobic, anchor protein into membrane
proteins anchoring molecule: outer surfaces of membrane
polar amino acids: hydrophilic, extend into extracellular fluid and into cytosol
membrane carbohydrates: play a key role in
cell-cell recognition
membrane carb.s: ability of a cell to distinguish
one cell from another (antigens: toxins, bacteria, foreign material that initiates immune response => antibodies production)
membrane carb.s: important in organ and
tissue development
membrane carb.s: basis for rejection of
foreign cells by immune system
