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
