Cell Membranes Flashcards
What does it mean by partially permeable
Allows some molecules to enter/exit but not all
Why is the phospholipid bilayer fluid mosaic
Phospholipids constantly moving
Cholesterol, transport and receptor proteins scattered through phospholipids
Some proteins can move sideways
Proteins to polysaccharides = glycoproteins
Lipids attached to lipid = glycolipids
Why does the bilayer not allow polar substances through
Polar molecules are water soluble
And the fatty acid tails are hydrophobic so repel water
What is the function of cholesterol in the cell membrane
Helps maintain shape of cells of animal cells without - especially red blood cells not supported by other cells
How does cholesterol work
Fits between phospholipids by binding to the fatty acid tails
Making phospholipids pack more closely together
Restricting the movement = more rigid
What is the permeability like at 0 and why
Highly permeable
Phospholipids don’t have much energy = packed closely together = rigid
Channel proteins and carrier proteins deform = allow anything through
Ice crystals pierce membrane leaving holes when it thaws
What is the permeability at 0-45 and why
Partially permeable
Phospholipids aren’t packed as close together
And have more energy so move more
What is the permeability like at 45+ and why
Highly permeable
Bilayer breaks down
Water inside cell expands putting p on memebran s
Channel and carrier proteins deform
Is facilitated diffusion passive
Yes
Why do large molecules need transport proteins
Too large
What type of protein do large molecules use
Carrier proteins
What type of protein do polar molecules use
Channel proteins
How do carrier proteins work
- Large molecule attatches
- Protein changes shape releasing the molecule on the other side
Down conc grad
How do channel proteins work
Pores for charged particles of move through down conc grad
What are 3 factors affecting simple diffusion
Conc grad
Thickness of exchange surface
Surface area
How does conc grad affect simple diffusion
High cg = higher rate
As diffusion happens the cg decreases until uqm reached (both sides the same concentration) so diffusion slows over time
How does thickness affect simple diffusion
Thin = rate increases
Shorter diffusion pathway
How does sa affect simple diffusion
Increase sa = rate
More particles can be exchanged in the same amount of time
How does microvilli increase rate of diffusion in small intestine
Microvilli = projections of plasma membrane folding up on itself
Increases sa
What are 2 things that facilitated diffusion depend on
Conc grad
No of transport proteins
How does no of transport proteins affect rate of facilitated diffusion
If all proteins are being used then no more can get through even in conc grad increases
How has the kidney adapted for more facilitée diffusion
Lots of aquaporins (water channel proteins) to speed of water réabsorption
If a solution has a high water potential what does that mean
High water conc
Low solute conc
What 3 things does osomosis rats dépend on
Water potential gradient
Thickness of exchange surface
Surface area
