9/7/22 Flashcards
to survive and grow cells must…
1) exchange molecules with environment
2) import nutrients (sugars and aa’s)
3) eliminate metabolic waste products
4) regulate concentration of inorganic ions in cytosol and organelles
molecules that diffuse across lipid bilayer of plasma membrane
CO2 and O2
membrane transport proteins
span lipid bilayer
provide private passageways across the membrane for select substances
what type of molecules can be transported across the cell membrane?
inorganic ions and small, water-soluble molecules
transporters
shift small organic molecules or inorganic ions from one side of the membrane to the other by changing shape
channels
form tiny hydrophilic pores across the membrane through which such substances can pass by diffusion
ion channels
permit passage of inorganic ions
ions are electrically charged, their movement causes electrical force (voltage) across the membrane
human body function
transform nutrients from foods using metabolic processes into biological structures and chemical energy
what type of lipids spontaneously form membrane structures?
amphipathic lipids!
when fatty acid touches water, micelle is formed
micelle structure
carboxyl group faces water, hydrophobic groups face inside and hide from water
phospholipid
ultimate amphipathic lipid
amphipathic
has both hydrophobic (tails) and hydrophilic (heads) properties
phospholipid bilayer
tails inside, heads outside
cell membrane image
cell membrane structure is
- highly dynamic
- FLUID
- phosphatidyl choline bilayer
cell membrane is composed of
carbon/palmitic
nitrogen
oleic
oxygen
water oxygens
phosphorous
cell membrane structure: heterogeneous or homogeneous?
Highly heterogeneous!
contains lipid fluid and lipid raft domains
requirements for unicellular organism to survive and replicate
- import metabolic substrates
- export metabolic waste
- maintain cell volume
each membrane type in a cell possesses a…
unique lipid composition
where in plasma membrane is cholesterol most present?
lipid rafts!
more rigid structures
phosphatidylcholine
most common lipid in organelles
where is cholesterol produced and where is it stored
produced in ER, but there is low concentration of cholesterol in ER bc it sends it mostly to plasma membrane
sphingolipids
tag our cells for identification
EX: blood type
aquaporins
transport water across lipid bilayer
carriers aka
transporters
transporters
- bind substrates with high stereospecificity
- transport rates are well below the limits of free diffusion
- saturable
channels
- stereospecificity < transporters
- transport >>> transporters
- non saturable
uniporters
membrane transport protein that transports single species of substrate across cell membrane
symporters
proteins that simultaneously transport 2 molecules across a membrane in the same direction
antiporters
cotransporter and integral membrane protein that uses secondary active transport of 2 of more DIFFERENT molecules or ions across phospholipid membrane
transporters are everywhere in the cell
cell membrane, lysosome, mitochondria
types of transporters
facilitated
single solute
coupled
counter transport
GLUT
glucose transporter (uniporter or single solute)
SGLT
sodium-linked glucose transporter (symporters, or coupled)
Slc26
chloride/bicarbonate exchanged (antiporter, or counter)
can facilitated transporters generate a conc gradient?
NO!
secondary active transport
occurs when endergonic (uphill) transport of one solute is coupled to the exergonic (downhill) flow of a different solute
primary active transporters aka
pumps
pumps
present in all cells in body
directly couples energy of ATP hydrolysis to transmembrane ion movement
create ion gradients
what are gradients?
a form of chemical energy
energy is stored in transmembrane ion gradients
what is required to create gradients?
energy
if there is a leak of ions across a membrane,
the cell needs to spend energy to restore the gradients
how is energy in ion gradients captured?
transport proteins!
EX: electron transport chain, proton gradient, and ATP production in mitochondria
osmosis
water molecules diffuse directly across lipid bilayer
SLOW PROCESS!
aquaporins
specialized channel proteins in plasma membrane of some cells that greatly facilitate the flow of water
curvy paper towel roll shaped
ion channels purpose
speed passage of ions across membranes by providing an aqueous path across the membrane
ion channels (rhyme)
diffuse at high RATES
have a GATE regulated by a biological signal
when ion channel gate is open
ions move through channel, in direction dictated by ion’s charge and the electrochemical gradient
epithelia function
separates interior of body from external world
epithelia structure
multicellular layers of cells joined together, side to side
layers contain diff cells:
- stratified (as in epidermis, outer skin layer)
- simple epithelium (only one cell thick, lining of gut)
epithelial tissue is
purely cellular and avascular
what does epithelial tissue cover?
all free surfaces: cutaneous, mucous and serous, glands
EX: gut lining, liver, pancreas, gall bladder, lungs, kidneys
functions of epithelia
- protective barrier
- secretion of specialized products (hormones, milk, tears)
- excrete waste
- absorption of nutrient
- exchange O2 and CO2
- detect signals (light, sound, chemicals)
epithelial lining is…
polarized!
displays two faces: apical surface and basal surface
epithelial lining apical surface
free and exposed to the air or watery fluid
epithelial lining basal surface
attached to a sheet of connective tissue called the basal lamina
polarity of epithelial cells depends on…
junctions that the cells form with one another and with the basal lamina
tight junctions are formed by…
interactions btwn strands of transmembrane proteins (occludin and claudins) on adjacent cells
tight junctions functions
- restrict paracellular pathway in the epithelia
- act as a barrier to solute diffusion
- modulation of tight junctions may alter nutrients and drug bioavailability
tight and leaky epithelia BOTH
impermeable to large hydrophilic molecules, including proteins
leaky epithelia is more permeable to…
small molecules and ions
maybe relation to inflammatory diseases of intestine
vectorial transport
transport of an ion or molecule across an epithelium in only one direction (EX: nutrient absorption in the gut)
requires transport proteins to be nonrandomly distributed between apical and basolateral plasma membrane
transcellular transport
substances travel through cell, passing through both apical and basolateral membrane
paracellular transport
substances transfer across an epithelium by passing through the intercellular space between cells
