chapter seven Flashcards
function of plasma membrane
- protects cell from external environment
- mediates cellular transport
- transmits cellular signals
selective permeability
controlled flow of substances in/out of the cell
- some cross more easily than others
staple ingredients of membranes
lipids and proteins
phospholipid bilayers
hydrophilic head, hydrophobic tails
- 2 phospholipids held together by hydrophobic interactions
amphipathic molecules
both polar and nonpolar
fluid mosaic model
membrane is a mosaic of protein molecules bobbing in a fluid layer of phospholipids
evidence for fluid nature of membrane
- cell fusion (hybrid cell)
- movement of proteins
cell fusion (hybrid cell)
mouse and human cells fused, proteins on membranes mixed laterally
movement of proteins
- shifts laterally (sideways)
- slower than lipid movement because larger
- many proteins immobile by attachment to cytoskeleton and ECM
flip flops
lipid can switch from 1 phospholipid layer to another
- need flippers/floppers
- phospholipids can’t do on own
unsaturated hydrocarbons
double bonds (kinked tails) prevent packing and enhance fluidity
saturated hydrocarbons
hydrocarbon tails pack together and decrease fluidity
cholesterol
effects membrane fluidity
- fluidity buffer - resists change
- high temp - membrane less fluid by restraining phospholipid movement
- lowers temp required for membrane to solidify
2 types of membrane proteins
integral and peripheral
integral proteins
penetrate hydrophobic interior of lipid bilayer
- includes transmembrane proteins (span membrane)
- hydrophobic regions consist of 1+ stretches of nonpolar amino acids coiled in a helices
peripheral proteins
not embedded in lipid bilayer, loosely bound to surface
ECM
non-cellular componente of tissues and organs
- contains macromolecules
functions of membrane proteins
- transport
- enzymatic activity
- signal transduction
- cell-cell recognition
- intracellular joining
- attachment to cytoskeleton/ECM
what does cell-cell recognition require?
one protein to be a glycoprotein
importance of cell recognition
sorting of cells/tissues in embryo, rejection of foreign cells
molecule structure of cell recognition
cells bind to molecules (often containing carbohydrates) on ec surface
glycolipids
carbohydrates bonded covalently to lipids
glycoproteins
carbohydrates covalently bonded to proteins
what substances pass by “free” diffusion (passive)
- gases
- small greasy molecules (steroids, non polar substances, hormones)
passive transport
diffusion that requires no energy and travels down the concentration gradient
- gradient represents potential energy
diffusion
movement of particles of any substance so they spread out into available space
net movement
more movement in one direction, down concentration gradient for passive diffusion
osmosis
diffusion of free water across selectively permeable membrane (artificial/cellular)
salt sucks
solute (salt) will “suck” water towards it
3 types of tonicity
hypertonic, hypotonic, isotonic
hypertonic
concentration outside of cell greater so water leaves cell
- cell shrivels and becomes crenated
hypotonic
concentration inside of cell is greater, so water enters cell
- cell swells and bursts
isotonic
no net movement of water across membrane, same rate both directions
osmoregulation
control of solute concentrations and water balance
types of osmoregulation states
turgid, flaccid, plasmolyzed
turgid
- very firm, healthy state for plants
- cell swells w/ water by cell wall exerts pressure back (turgor pressure)
flaccid
- when plant cells are isotonic
- no water enters (limp)
plasmolysis
if cell is in hypertonic environment, water lost to environment causes PM to pull away from cell wall
plasmolyzed
shrunken plant cell membrane, inward/away from cell wall
facilitated diffusion
polar molecules and ions diffuse with the help of transport proteins
what are transport proteins specific for?
the substances they move
2 types of proteins in facilitated diffusion
- channel proteins
- carrier proteins
channel proteins
have hydrophilic channel that certain molecules/ions use as tunnel through membrane
- ion channels
- some function as gated channels in response to stimuli
- aquoporins
aquaporins
function to pass water molecules through membrane in certain cells
carrier proteins
hold on to passengers and change shape in way that shuttles them across membrane
active transport
pumping a solute across a membrane against the concentration gradient, uses energy from ATP hydrolysis
- carrier proteins
why is active transport necessary?
enables cell to maintain internal concentration of small solutes that differ from environment concentrations
how does ATP activate active transport?
transfers terminal phosphate group to transport protein
ex. of active transport
sodium-potassium pum, ion pump w. hydrogen ion concentration, cotransport
sodium-potassium pump
exchanges Na+ for K+ across PM of animal cells
membrane potential
voltage across membrane
- inside of cell compared to outside
ion pump that uses hydrogen ion concentration
electrogenic pump that transports protons (H+) out of cell and transfers + charge from cytoplasm to ec solution
electrogenic pump
transport protein that generates voltage across membrane
cotransport (H+ and sugar)
- transport protein couples downhill diffusion to uphill
- transport of 2nd substance against own concentration gradient
- (plant cell) gradient of H+ generated by ATP-powered protein pumps drive active transport of amino acids and sugars into cell
2 types of bulk transport
exocytosis and endocytosis
exocytosis
cell secretes certain molecules by fusion of vesicles with PM
3 types of endocytosis
- phagocytosis
- pinocytosis
- receptor-mediated endocytosis
endocytosis
cell takes in molecules by forming vesicles w/ PM
phagocytosis
engulfs/eats particle by extending pseudopodia around its and packaging it in food vacuole
pinocytosis
gulps/drinks droplets of ec fluid, vesicles (tiny) formed by infolding of PM
receptor-mediated endocytosis
special type of pinocytosis that enables cell to acquire bulk quantities of specific substances even if substances are concentrated in ec fluid
oligosaccharide
short chain
difference between cytoplasm and cytosol
- cytoplasm - includes organelles except nucleus
- cytosol - just the liquid
is bulk transport active or passive?
active
what is a Na/K pump also called?
Na/K ATPase
