Lecture 2.1 - Membranes, Channels and Transport Flashcards
- separates the cytoplasm from the external environment
- one of the most important cell organelles
- highly selective permeable barrier that surrounds all living cells
- controls how molecules and compounds move in and out of the cell
- important for proper nutrition, maintenance of irritability of the cells, and homeostasis
cell membrane
cell membranes are __ __ __ barrier
highly selective permeable
cell membranes controls how molecules and compounds move ___ of cell
in and out
importance of cell membrane
- proper nutrition
- maintenance of irritability
- homeostasis
- signal detection
- cell-to-cell communication
for organization and localization of specific functions
compartmentalization
thickness of cell membrane
6-23 nm
what happens when the cell membrane sustains different concentrations of certain ions on their two sides
lead to concentration gradient
participates in the transport of substances
protein structures
- model that describes the organization of cell membranes
- phospholipids drift and move like a fluid
- bilayer is a mosaic mixture of phospholipids, steroids, proteins, and other molecules
fluid mosaic model
membrane composition
- phospholipids
- proteins
- carbohydrates
how are lipids and protein molecules in the cell membrane kept together
non-covalent interactions
impermeable to the passage of most water-soluble molecules
lipid bilayer
fundamental structure of the membrane
lipid molecules
- usually span from one side of the phospholipid bilayer to the other, but can also sit on one of the surfaces
- can slide around the membrane very quickly and collide with each other, but selfom flip from one side to the other
- responsible for most of the membrane’s properties
proteins
Two types of proteins based on where they are found
- integral proteins
- peripheral proteins
- embedded in the lipid bilayer
- provide a mechanism for trans-membrane transport
integral proteins
different trans-membrane transport integral proteins provide a mechanism for
- passive transport pores and channels
- active transport pumps and carriers
- membrane-linked enzymes
- chemical signal receptors and transducers
associated with the surface of the membrane via electrostatic interaction
peripheral proteins
how are the peripheral proteins associated with the surface of the membrane
via electrostatic interaction
what do proteins inside the surface maintain
cell shape or cell motility
catalyze reactions in the cytoplasm
enzymes
what are receptor proteins used for
- cell signaling
- cell recognition
Different major cell functions of the proteins in plasma membrane
- transport
- enzymatic activity
- signal transduction
- intercellular joining
- cell-cell recognition
- attachment to the cytoskeleton and extracellular matrix (ECM)
Special functions of proteins
- adhesion proteins
- recognition proteins
- receptor proteins
- enzymes
- transport proteins (active and passive)
- found on the outer surface and attached to the proteins or sometimes to the phospholipids
- form a cell coat outside the cell membrane
carbohydrates
Different types of carbohydrates on the cell membrane
- glycoproteins
- glycolipids
carbohydrate chains attached to membrane proteins
glycoproteins
carbohydrate chains attached to the lipid element of the cell membrane
glycolipids
- defined as a thick mixture of protein lipids and post-translational sugar structures
- surround all living cells and act as a buffer
Glycocalyx
functiono of glycocalyx
- protection
- cell recognition
facilitate cellular recognition
glycolipid
serve as receptor for chemical signals
glycoproteins
what is the side chain of glycoproteins
oligosaccharide side chain
Primary types of lipids
- phosphoglycerides
- sphingolipids
- sterols
glycerol backbone
phosphoglycerides
backbone made of sphingosine bases
sphingolipids
cholesterol, nonpolar and only slightly soluble in water
sterols
amphipathic lipids
- phosphoglycerides
- sphingolipids
what does the differences in the lengths of the two fatty acid tails and composition influence
fluidity
binds weakly to phospholipids making the membrane less fluid but stronger
cholesterol
how are membrane molecules help in place
relatively weak hydrophobic interactions
Two possible movement of phospholipids
- lateral movement
- flip-flop
frequent movement of phospholipids
lateral movement
rare movement of phospholipids
flip-flop
influenced by temperature and constituents
membrane fluidity
what influences membrane fluidity
temperature and constituents
fluid membrane
unsaturated hydrocarbon tails with kinks
viscous membrane
saturated hydrocarbon tails
- wedged between phospholipid molecules in the plasma membrane of animal cells
- at warm temperature, it restrains the movement of phospholipids and reduces fluidity
- at cool temperatures, it maintains fluidity by preventing tight packing
steroid cholesterol
what does steroid cholesterol do at warm temperatures
restrains movement of phospholipids and reduce fluidity
what does steroid cholesterol do at cool temperatures
maintains fluidity by preventing tight packing
enzymes that break down protein
Proteolytic enzymes (proteases)
- consists of physically breaking apart (fracturing) a frozen biological sample
- used to split the cell membrane apart
freeze-fracture technique
what was seen when a cell membrane was freeze fractured
protein particles interspersed with a smooth matrix, supporting fluid mosaic model
- rate at which a substance can passively penetrate a cell membrane
- influenced by inherent properties of both the membrane and the substance
membrane permeability
Different Transport Systems
- passive process
- active transport (pumping)
- no energy expenditure and move down their normal gradient
- simple diffusion/lipid diffusion
- osmosis
- facilitated diffusion
passive processes
- requires metabolic energy
- moves substances against their gradients
active transport (pumping)
Different types of passive transport
- simple diffusion/lipid diffusion
- osmosis
- facilitated diffusion/passive transport
Three basic routes in transport systems
- dissolving in lipid phase
- diffusion through labile or fixed aqueous channels
- carrier-mediated transport
- dissolves directly in the lipid bilayer
- enters the aqueous phase on the opposite side
dissolving in the lipid phase
- solute molecule remains in the aqueous phase
- diffuses through aqueous channels (water-filled pores in the membrane)
diffusion through labile or fixed aqueous channels
water-filled pores in the membrane
aqueous channels
- solute molecule combines with a carrier molecule dissolved in a membrane
- carrier “mediates” of “facilitates” the movement of the solute molecule across the membrane
carrier-mediated transport
random thermal motion of suspended or dissolved molecules causes their dispersion from regions of higher concentration to regions of lower concentrations
diffusion
each substance diffuse down its __ concentration gradient, independent of the concentration gradies of other substances
own
diffusion of a substance across a biologial membrane
passive transport
Diffusion is __ because in this process the particle uses free energy (potential energy).
exergonic
states that the rate of diffusion across a membrane is directly proportional to the concentration gradient of the substance on the two sides of the membrane and inversely related to the thickness of the membrane
Fick’s Law of Diffusion
According to Fick’s Law, diffusion is proportional to what?
- concentration gradient
- difference in partial pressure
intrinsic factors governing diffusion across membranes
- size rules
- polarity rules
- ionic rules
size rule ex.
water > urea
polarity rule ex.
non polar > polar
ionic rule ex.
O2 > OH-
Five factors where the rate of diffusion depends on
- size
- temperature
- steepness of concentration gradient
- charge
- pressure
Factors that influence mobility of solute molecules
- lipid solubility
- hydrogen bond with water
- molecular weight
- molecular shape
- partition coefficient
mobility with high lipid sobility
high
mobility with high hydrogen bond with water
low
ratio of the distribution of a substance between two different liquid phases
partition coefficient
rate of influx increases in proportion to the concentratin of the solute in the extracellular fluid
non-saturation kinetics