Cell membranes Flashcards
how do phospholipid bilayers form in an aqueous medium?
hydrophobic tails of phospholipids pack together with hydrophilic heads on the outside, forming a bilayer
what are the basic components of phospholipids?
phosphate
glycerol
2 fatty acids
why are phospholipids described as amphiphilic?
they have both hydrophilic and hydrophobic parts
what increases the rigidity of phospholipid membranes?
cholesterol
why is the lipid bilayer asymmetric?
glycolipids are on the extracellular side of the membrane, negative charges are inside the cell
what are phospholipid membranes permeable to?
small neutral molecules (e.g. water and other small uncharged molecules like oxygen and carbon dioxide)
what are phospholipid membranes not permeable to?
- cations
- anions
- small hydrophilic molecules like glucose
- macromolecules like proteins and RNA
what is facilitated diffusion?
movement of hydrophilic molecules down their concentration gradient through protein pores that hide the ionic charges from the hydrophobic core of the lipid bilayer
what are the 3 main functions of membrane proteins?
- transport
- receptors for neurotransmitters, hormones and growth factors
- cell recognition and adhesion
how many ions does the sodium-potassium pump transport?
2 potassium ions into the cell
3 sodium ions out of the cell
what is the sodium-potassium pump driven by?
phosphorylation of an aspartyl residue followed by hydrolysis of the aspartylphosphate
how many subunits does the potassium channel consist of?
4 subunits
in terms of potassium ions, how is equilibrium reached?
when the rate of inward movement of K+ ions down the electrochemical gradient = rate of outward movement down the concentration gradient
what is a membrane potential?
a voltage difference across the membrane, with a negative charge intracellularly - important for signalling in nerves, muscles etc.
what are the 2 consequences of the transport of K+ in and transport of Na+ out of the cell?
- ionic gradients are created
- charge gradient is created: inside of the cell is more negative
which ions have specific pumps that use ATP hydrolysis to provide energy?
- sodium ions
- calcium ions
- hydrogen ions
what does glucose transport into a cell make use of?
the sodium gradient - active transport of Na+ out of the cell allows Na+ to cotransport glucose into the cell as Na+ diffuses back into the cell down a concentration gradient (facilitated diffusion)
describe transport by pinocytosis
engulfment by the membrane of extracellular solute and small molecules
describe transport by phagocytosis
engulfment by the membrane of extracellular objects (bacteria, cell debris, other cells)
describe transport by exocytosis
movement of proteins and other molecules from intracellular vesicles towards the extracellular space by fusion with the cell membrane
how do signals cross membranes?
- using exocytosis (e.g. membranes)
- using lipid-soluble molecules that cross membranes
- using trans-membrane receptors
