fluid mosaic model
the idea that a biological membrane consists of a fluid phospholipid bilayer in which proteins are embedded and float freely
glycolipid vs glycoprotein
glycolipid - any membrane lipid that is bound to a carb and acts as a messenger or receiver
glycoprotein - membrane component that contains a sugar or carb, bound to amino acid
membrane asymmetry
the proteins and other components of one half of the lipid bilayer differs from the other half
phospholipids in bilayer
structure depends on density, saturation and temperature
sterols in bilayer
regulate biological processes and sustains domain structure of cell membrane where they’re considered membrane reinforces, stabilizes fluidity
membrane proteins
(transport, enzymatic active, triggering signals, attachment and recognition)
5 jobs
structure determines function and makes it unique
transport occurs through a hydrophilic protein channel with shape shifting proteins
some are associated with respiration and photosynthesis
they have triggering signals that bind to specific chemicals and changes membranes
they have attachment and recognition where they attach to inner and outer parts of the membrane and acts as a site for cytoskeleton elements and cell to cell recognition
integral membrane proteins
protein embedded into the lipid bilayer
at least one region that interacts with the hydrophobic core
most are transmembrane proteins that span across the entire membrane bilayer with regions exposed to the aqueous environment on the inside and outside of the cell
peripheral membrane proteins
proteins on the surface of the membrane
held by non covalent bonds
doesn’t interact with the hydrophobic core
most are on the cytosol side with some on the cytoskeleton
exchanging of substances in cells
complex process since they must be able to take in nutrients, expel waste and communicate with the environment and surrounding cells
the plasma membrane is highly selective, it must be able to take in large food molecules while keeping tiny valuable molecules from leaving
passive vs active transport
passive transport is the movement of a substance across a membrane without expending energy, whereas active transport moves substances across the membrane against their concentration gradient using pumps which requires energy
three types of passive transport
simple diffusion
facilitated diffusion
osmosis
two types of active transport
primary active transport
secondary active transport
simple diffusion
the ability of small and nonpolar substances to move across a membrane unassisted due to concentration differences
soluble lipid molecules
facilitated diffusion
facilitated transport of ions and polar molecules through a membrane via protein complexes
carried out by channel and carrier proteins
channel and carrier proteins
facilitated transport
channel - form hydrophilic pathways for water and certain ions
other channel proteins facilitate ion transport
carrier - bind to specific solute, such as glucose, to transport across lipid bilayer
selective
these two proteins facilitate the transport of ions via diffusion
osmosis
passive diffusion of water across a membrane
lower concentration to greater solute concentration
hypotonic - lower solute conc than another solution
hypertonic - has a higher solute conc
isotonic- same solute conc
primary active transport
a pump moves positively charged ions against the concentration gradient through a membrane using ATP
ATP breaks down to form ADP and a phosphate group
phosphate group attaches to the pump (creates high energy state) and changes the binding site to fit the ion and creates a passage to the higher conc area
creates electrochemical gradient
electrochemical gradient
form of stored potential energy caused by a difference in conc gradients of ions
involved in the movement of ions associated with nerve impulse transmission
secondary active transport
uses the concentration gradient of an ion, established by a primary pump, as its energy source
facilitated by symport and antiport
symport vs antiport
facilitates secondary active transport
symport - solute that moves through the membrane channel in the same direction as the driving ion
antiport - the driving ion moves through the membrane channel in one direction, providing energy for active transport of another molecule in opposite direction
mostly Na ions are exchanged by antiport
endocytosis and exocytosis
only small molecules like amino acids or monosaccharides can be transported by active or passive transport so eukaryotic cells use endocytosis and exocytosis to export and import larger molecules
endocytosis
imports proteins, larger molecules or even cells from the exterior of the cell into the cytosol
uses energy to fold cell membrane around extracellular fluid to create a vessicle containing proteins and other substances
three types are pinocytosis, receptor-mediated and phagocytosis
pinocytosis
type of endocytosis to import larger molecules
extracellular water is taken in a long with the molecules in the solution
receptor-mediated
type of endocytosis to import larger molecules
molecules are bound to other cell surface by receptor proteins
receptor proteins collect into a pit, coated in a network of proteins called clathrin
coated pit breaks free of membrane to form vessicle, loses clathrin and may fuse with lysosome
enzymes in lysosome break down the molecules to use throughout the cell
