lecture 10 cell membranes part 2 Flashcards
cell membranes are described as a ____ ______ of lipids and proteins
fluid mosaic
_____ are dispersed among lipids
proteins
how do lipids and proteins move with the plane of the membrane
move back and forth, spin on axis, change positions
they DO NOT move up and down
what is membrane fluidity determined by
the movement of phospholipids
why do phospholipids move
because of van der waals forces that are weak and transient. they are constantly breaking and forming
when does the flip flop between lipids
when new membrane is synthesized in presence of enzyme
how does decrease in temperature impact membrane fluidity
it decreases
how does increase in temperature impact membrane fluidity
increases
what can happen to membrane if it is too fluid
melt - there are too few VDW forces to hold membrane together
what happens when membrane is too cold
it has gelled or become viscous
what do cells need to maintain a specific degree of fluidity
membranes
what factors of membranes are effected by changes in membrane fluidity
membrane permeability and the functioning
what type of organism can be most impacted by temperature
ectoterms
what are ectotherms
organisms whose body temp is regulated bu their environment
how do cells maintain proper membrane fluidity
-adjust degree of phospholipid tail saturatino
-adjust ohospholpid tail length
what does cholesterol help with in membrane
helps to buffer the fluidity of membranes o there is less fluid change due to temperature changes
-decrease fluidity at higher temps
-increase fluidity at lower temps
why is proper membrane fluidity important
-too fluid: membranes become leaky (deadly)
-too stiff: may slow or inhibit motion of integral proteins or may slow r prevent membrane fusion or budding
what are vesicles important for
expression on cell surface
integral proteins need to ______ _______ to do job
change shape
what does bulk transport move
large molecules in and out of a cell and depends on membrane fusion or budding
exocytosis
large molecules are secreted when a vesicle fuses with the plasma membrane
endocytosis
large molecules are taken in when the plasma membrane pinches inward forming a vesicle
active transport
transport of small molecules that requires energy and a transport protein
passive transport
of small molecules, does not require energy, may involve transport proteins
what are two characteristics of molecules that can slip between phospholipids to cross a membrane? What size do they have to be?
-uncharged
-nonpolar
-small
example of molecule that can slip between phospholipids to cross a membrane?
-CO2
-O2
-N2
-steroid molecules
example of molecules that cannot cross between phospholipids to cross a membrane?
-Na
-glucose
-ions
-macromolecules
-amino acids
-nucleotides
amino acids and nucleotides are
large uncharged polar molcules
diffusion
movement of molecule from area of high concentration to area of low concentration
what increases diffusion
temperature and larger concentration rate
when is diffusion at equilibrium
when diffusion in each direction = each other
facilitated diffusion uses _______ protein and ________ protein
carrier and channel
is protein needed for simple diffusion
no protein
