2. Membranes and Transport I Flashcards
Membrane function
____ barrier
Keep external components out of cell interior
Retain cell constituents
____ control
Selectively control entry and exit
permeability
border
Membrane structure
Fluid mosaic bilipid membrane - mix of ____ and ____
Not just proteins bobbing in sea of lipid
Both lipid and protein arrangement highly ____
• Half of surface area - ____, that are highly structured
lipids
protein
structured
proteins
Lipid bilayer is amphipathic Amphipathic: both ____ and ____ portions
With phospholipids, only heads stable next to ____ - bilayer
- Energetics - most ____ arrangement for these phospholipids
- Occurs ____
polar nonpolar water favorable spontaneously
Membrane fluidity varies
- Membrane fluidity influenced by distribution of ____
- ____, length and ____ of fatty acid chains decrease fluidity
- ____: Clusters of cholesterol, proteins sphingolipids
lipids
cholesterol
saturation
rafts
Rafts cluster signaling proteins
- Many signaling processes require multiple players
- Rafts provide island to cluster key ____ together receptors/enzymes, internalization with ____
- Multiple cellular processes require ____
____ is important when it comes to activation via NT Necessary to optimize chances of achieving the signal we need
signalling components
caveolae
proximity
Lipid rafts relevant to dentistry
• Membrane vesicles (MVs) from ____ enter human gingival epithelial cells more when ____ intact
P. gingivalis
lipid rafts
P. gingivalis enters cells via lipid rafts
• Suggest entry via raft allows bacteria to evade ____ more readily
digestion
Membrane lipids summary
- Lipid molecules are ____: they have a hydrophilic polar component and a hydrophobic non- polar tail
- Lipids are ____ distributed on the outer and inner leaflets of the membrane
- Membrane fluidity varies with ____ content and degree of ____ of fatty acid chains; key proteins for many signaling processes are clustered in ____
amphipathic asymmetrically cholesterol saturation rafts
Membrane proteins
- Critical to how we control processes across the membrane
- ____ = gap junction protein
connexin 26
Classes of membrane proteins
Integral proteins - span ____
Peripheral proteins
- restricted to one ____
- ____ within membrane or ____ to membrane lipids
• Optimize ____ that occurs across membrane
bilayer
side
move
anchored
Functions of membrane proteins
- ____ (pumps/carriers/channels)
- Structural - anchors etc maintain membrane integrity
- Receptors/signaling
- Enzymes
- ____ – antibody recognition
Transport
glycoproteins
Transport membrane proteins
• Transporters
◦ Make sure that ____ compounds get
across the membrane
◦ Allows ____
charged/uncharged
selectivity
Types of membrane transport How to get across the membrane?
- ____ across bilayer
- Facilitated diffusion
- ____
- ____ - Active transport
- ____
- ____
• Active
◦ Direct/indirect requirement for ____ against gradient
• ____
◦ Simple
◦ Facilitated
‣ ____ used to aid diffusion (channel mediated
and carriers)
diffusion channel carrier ATP passive proteins
Transport across membranes • Cell membranes are selective, semi- permeable barriers • Molecules move across cell membranes by – Simple diffusion • Follows \_\_\_\_ gradient – Facilitated diffusion • Follows \_\_\_\_ gradient – Active transport • Uses energy to go \_\_\_\_ EC* gradient
EC
EC
against
Diffusion
• Process whereby molecules move and intermingle because of ____ motion
random thermal Brownian
Fick’s First Law of Diffusion
Diffusion across a membrane is proportional to:
- ____ of membrane (involved in diffusion)
- difference in ____ on the two sides
J = -DA(∆c/∆x)
where:
J - net rate of ____ in moles or grams/unit time;
D - diffusion ____ of the solute;
A - ____ of the membrane;
∆c - ____ difference across the membrane;
∆x - membrane ____
D – inversely proportional to ____ of particle and ____ of solvent (big globs move slowly through thick muck)
area solute concentration diffusion coefficient area concentration thickness size viscosity
A note on equations: Equations can only describe ____ processes
A bit of understanding goes further than straight memorization
Qualitative understanding of diffusion and osmosis equations Quantitative understanding of Nernst and GHK equations
simple
What about crossing the membrane? The same laws apply J = -DA(∆c/∆x)
Diffusion of a solute through a cell membrane depends on:
– membrane ____ - ∆x
– ____ difference - ∆c
– ____ of membrane - A
– ____ and ____ of solute (lipid solubility) - 1/D – ____of solvent -1/D
• Big difference is that small uncharged molecules much more ____ in lipid bilayer
• The more charged and larger you are, the more difficult to cross the membrane
◦ Preference for uncharged
• More ____ - more difficult to diffuse
thickness concentration area size charge viscosity
soluble
viscous
Effective range of diffusion
– Diffusion time ____ with the ____ of distance
- Diffusion fine for very ____ distances (cell ~ 10 um dial)
- Need other forces to move further in reasonable time: nervous and circulatory system
increases
square
short
Permeability across membrane
Dependent on • \_\_\_\_ • charge • \_\_\_\_ solubility • membrane thickness
- O2, CO2, N2 - ____ and small, travel across the membrane quickly
- H2O - ____
- Glucose - ____
- Ions - ____ charge, do not cross the hydrophobic barrier too well
size lipid uncharged polarized size positive
How do compounds cross mucosal membrane in oral cavity?
- Diffusion via ____ pathways
- Barriers you will have to use ____
paracellular
transport
Facilitated diffusion:
Transport across membranes with a little help from the ____
• Many large and/or charged molecules cannot diffuse across the bilipid membrane
• Specialized proteins aid in the crossing
• Transport called facilitated diffusion if proteins provide a ____ through membrane to avoid lipid barrier
•____ transport
- ____
- ____
proteins route passive carriers channels
Facilitated diffusion
• Diffusion of a solute mediated by carrier proteins
– via ____ conformational change
• Solutes move down their ____ gradients
– no exogenous ____ required
• Enzyme that transports across membrane
• Unlike simple diffusion, facilitated diffusion can reach a ____, ____ – carrier as enzyme
• Facilitated diffusion exhibits
– ____ specificity
– ____
– ____ inhibition
• Presence of enzyme kinetics:
◦ ____ - how fast
◦ ____
ping-pong electrochemical energy maximum (Vmax) Km chemical sterospecificity competitive
Vmax
Km
Saturation of facilitated diffusion
The carrier protein can only ____ so quickly > formation of a Vmax
flip-flop
Facilitated diffusion by ion channels
Ion channels:
– Ions flow through the pore
– “downhill” so no exogenous ____ required
– ____: many roles in rapid signaling
– Conformational change to gate open triggered by ____, ____, ____,
– ____ varies
– More details tomorrow
energy fast voltage ligands stretch selective
What ion channels are targets in dentistry?
• ____ channels
◦ Lidocaine blocks these
• ____ channels
◦ If patient’s are on blockers, may interfere with ____
sodium
potassium
heart
Active transport
• Active transport expends ____ to move solutes “uphill” against gradients and keep ions from ____
• Requires energy input
– Primary active transport uses ATP (____)
– Secondary active transport couples energy from ____
• Transporter has properties of carrier protein – ____, ____
energy equilibrium ATPases gradients Vmax stereospecificity
Primary active transport Na-K-ATPase
- Transport of ions against ____
- Uses ____ of cell ATP - critical to function
- Found in all ____ cells
- Electrogenic – 3 ____+/2 ____+ drives a net charge across membrane (only ____ mV)
- Main role is to set up ____
gradient 33-70% animal Na K 2-4 gradients
Half of your food goes to power the ____
Na/K ATPase
Model for operation of the Na+-K+ ATPase pump
- Binding of 3 ____ inside
- Hydrolysis of ____ for energy
- Release of ____ outside
- Binding of 2 ____ outside
- ____
- Release of ____ inside
Energy is used to pump Na+ and K+ against
their gradients
- Binding of ATP occurs after binding of three Na+ ions
- Binding of K+ triggers the ____
Na+ ATP Na+ K+ dephosphorylation K+
dephosphorylation
Ouabain blocks the Na-K ATPase
- Ouabain – digitalis ____, selective for ____ pump,
- Ouabain binds ____ side
- Used clinically to slow ____ when troubled e.g atrial ____
- Now use related ____
- Don’t use too much word ouabain from Somali “waabaayo “ translated as “____”
glycosides Na/K extracellular heart fibrillation digoxin arrow poison
Active transport pump H-ATPase
- Complex multisubunit structure
- ____ portion that hydrolyzes ATP into ADP
- ____ portion uses this energy to move H+ across gradient
- Uses energy of ____ to transport protons against their gradient
- Useful in building ____ and ____
- Used in ____
- Changes the proton gradient; pushes H+ against their gradient
V1
V0
ATP
bone
teeth
lysosomes
H-ATPase
- vH-ATPase present in intracellular ____
- H-ATPase is also present on ____ in some cells
- Important in bone ____
- Blocking H-ATPase with ____ inhibits tooth eruption
- Mandibular and maxillary ____ and molars are not present in Atp6i-/- mice.
• Makes areas more acidic - important in bone degradation
• Changes in AA structure can lead to differences in the enzymes function
— Some may have no ____
— Some may result in stark ____
organelles plasma membrane resorption bafilomycin incisors effect differences
Inhibition of H-ATPase proton pump in stomach reduces ____
• ____ can contribute to tooth decay, so blocking HATPase in stomach can help oral health.
acidity
acid reflux
Secondary active transport
Doesn’t require binding of ____
Utilizes gradient of another particle (e.g., ____) to provide energy
Gradient ultimately established by ____
Direction of exchange can be the same (____) or opposite (____)
Binding of Na+ triggers ____ changes in protein
• Na+ is the energy source in nearly all active transport
◦ Cxn within the cell is very ____
• Na+ is going along gradient, but it can bring other molecules along for the ride
• Mechanism:
◦ Upon Na+ binds, ____ change resulting in opening of site
for ____
• ____ eventually brings the Na+ back out (which is why we
use so much energy)
ATP Na+ ATP symport antiport allosteric
low
allosteric
glucose
NaKATPase
Na/amino acid sympor
- Coupling energy of Na+ movement to concentrate ____
- If 2 Na+ translocated each cycle, greater ____, can concentrate AAs at higher concentration
amino acids
driving force
Symport and Antiport
• Use gradient established by pumps • Let ions like Na+ run down \_\_\_\_ • Couple this energy to that needed to move another \_\_\_\_ in – \_\_\_\_: same direction, or – \_\_\_\_: opposite direction • Degree to which ion can
be accumulated across membrane determined by ____ of driving ion and ____.
gradient ion symport antiport gradient charges
Na+/H+ Antiporter
- In most cells to keep proton levels below gradient
- Important in ____ cells in adaption to ____ taste (right), kidney, ____, lungs etc.
- Coupled with the ____…
- Na+ enters, while the H+ ____…
- Located closely to the NaKATPase…
taste bud
sour
gut
NAKATPase
exits
Active or passive transport? It’s all about the gradients
Intestinal epithelium: [glucose] ____ in than out
- Na+ gradient established using ____ active transport – ATP hydrolysis powers ____ pump
- Use energy of Na+ to get ____ into the cell using secondary active transport
- Let glucose flow out down the ____ through carrier using ____ diffusion
higher active NaK glucose gradient facilitated
Most cells and tissues use multiple transporters
- Na/H, Cl/HCO3 - regulating ____
- NaKATPase
- ____
pH
aquaporin
Transporters in ameloblasts
• Why channels
needed to
make enamel?
Slc26al, Slc26a6 or Slc26a7 = Sat1, Pat1, and Sut2 respectively, all exhibit chloride, bicarbonate exchanger activities. Mutations lead to multiple disorders induced by the disruption of ion homeostasis. Enamel maturation involves ____
regulation mediated by multiple ion transport/ exchange activities
across plasma and endosome membranes
Here, the ameloblasts are making enamel
Why are there channels that make enamel?
• as you move out some of these ____, ____, ____ transporters here, you can see changes in the enamel
rods are arranged
• It seems counter intuitive that transporting HCO3 can affect the enamel
• The ____ dependent changes that these biochemical structures go through are critical in
development
• Why channels in lysosomes?
The lysosomes are very ____, so they are important
pH Na HCO3 H pH acidic
Osmosis
• ____ of diffusion
• Forces based on ____ motion that want to make
levels of water the same among compartments
If membrane permeable to water and impermeable to solute, ____ will move to equal concentration.
____ - Pressure needed to stop water movement
inversion
Brownian
water
osmotic pressure
Cell in isotonic solution
Isotonic – no net ____
movement
Cell in HYPERtonic solution
Hypertonic solution outside, water ____ cell to equalize concentrations
Cell ____
leaves
shrinks
Cell in HYPOtonic solution
Hypotonic solution outside, water moves ____ cell to equalize concentrations
Cell ____
into
swells
Effects of osmolarity
Red blood cell exposed to range of osmolarities
Water moves to ____ solute concentrations
HypOtonic solution makes the cell an “O”
equalize
What is the osmotic pressure of
physiologic saline?
• In physiologic saline (____ mM NaCl), red blood cells retain the size/shape they normally have in plasma.
• This NaCl concentration is called ____.
π = RTφic
RT = R is the ideal gas constant, T is the absolute temperature; RT = 22.4 atm φ=phi = osmotic coefficient = 0.93 because Na+ & Cl- don’t completely separate i= number of ions formed by dissociation of solute = 2 because Na + Cl C = molar concentration of solute = 154 mOsm
154
isotonic
Aquaporins
Water crosses membranes through ____, or water channels
- ____ diffusion for water
- ____ is the driving force
aquaporins
facilitated
osmotic pressure
Aquaporins
Different types of aquaporins - vary in their ____, distribution and ____
• Knocking out just the aquaporin transporter isn’t necessarily ____… usually have backups…
regulation
roles
fatal
Water crosses membrane through aquaporins
- Permeability of membrane to water much ____ than predicted by its ____ permeability
- Water passes through membrane through ____
- Amino acids of proteins ____ when facing lipids, ____ in canal – provides ____ stability
higher lipid aquaporins non-polar polar energetic
Water crosses membrane through aquaporins
• Defective distribution of ____ in salivary gland of Sjögren’s syndrome with reduced ____ secretion
Why doesn’t your mouth swell when you drink a glass of water?
• Why don’t your teeth fall out when you eat a salty pretzel?
AQP5
saliva
Transport Summary
• ____ molecules diffuse across membrane – rate based on concentration ____, size etc
• ____ molecules use protein transporters to cross
• In facilitated diffusion, solutes flow ____
• In primary and secondary active transport an ____ input is required
• Osmotic pressure created by limited permeability of ____
• Coincident presence of multiple ____ necessary for cell function
uncharged/small gradient charged/larger downhill energy solutes transporters
