CP - Structure and Function of the Cell Membrane Flashcards
What are the main constituents of the cell membrane?
Phospholipids and proteins
The term to describe the membrane structure
Fluid Mosaic Model
What is the membrane structure?
A thin, flexible and sturdy barrier that surrounds the cytoplasm of a cell
What is the membrane held by?
Hydrogen bonds
What is the lipid bilayer of the cell membrane?
2 back-to-back (parallel) layers of 3 types of lipid molecules
In water, what do most phospholipids tend to form?
A lipid bilayer structure with the polar head groups at the surface in contact with water and the fatty acid chains in the core screened from water contact
What are scattered among a double row of phospholipid molecules?
Cholesterol and glycolipids
Each phospholipid molecule is _____
amphipathic
What are the features of phospholipids?
Hydrophobic core (non-polar tails) and charged hydrophilic surface (polar heads)
hydrophobic non-polar tails and hydrophilic polar heads
What is an important feature of the hydrophobic core?
It provides a highly impermeable barrier to the passage of charged ions
Membranes are ____ ____ and ____ that can move around within the ____ of the ____ ____
fluid structures, lipids
plane, membrane leaflet
What do lipids rarely do? What happens to the lipid composition of the leaflets because of this?
Lipids rarely flip flop between membrane leaflets so the lipid composition of the leaflets can be asymmetric
What is the fluidity of the membrane determined by (3 factors)?
- Lipid tail length (longer the tail, less fluid the membrane)
- No. of double bonds (more increases fluidity)
- Amount of cholesterol (more decreases fluidity)
What are integral membrane proteins?
They extend into or completely across the cell membrane (transmembrane protein)
What is a feature of integral membrane proteins?
They are amphipathic, hydrophobic regions span the hydrophobic core of the lipid bilayer, which usually consists of non-polar (hydrophobic) amino acids coiled into helices and hydrophilic ends of the proteins interact with the aqueous solution
What are peripheral proteins? what are they easily removed by
They are attached to either the inner or outer surface of the cell membrane and are easily removed from it by changes in ionic strength (increasing ionic strength breaks ionic bond)
Membrane proteins can act as:
Receptors; Cell Identity Markers; Linkers; Enzymes; Ion Channels; Transporter Proteins
What is the selective permeability of the cell membrane? and what is it governed by?
The ability of a particular molecule to cross a cell membrane and is governed by the laws of diffusion
What is the permeability of a molecule dependent on?
Its size, charge and lipid solubility
What is the lipid bilayer permeable to?
- Non-polar, uncharged molecules, e.g. O2, N2, benzene
- Lipid soluble molecules, e.g. steroids, fatty acids, some vitamins
- Small, uncharged polar molecules, e.g. water, urea, glycerol, CO2
What is the lipid bilayer impermeable to?
- Large uncharged polar molecules, e.g. glucose, amino acids
- Ions, e.g. Na+, K+, Cl-, Ca2+, H+
What do membrane proteins do?
They mediate the transport of substances across the membrane that can’t permeate the hydrophobic core of the lipid bilayer
What is diffusion?
The random mixing of particles in a solution as a result of the particle’s kinetic energy, where more molecules move away from a high conc. area to a low conc. area
What factors affect the rate of diffusion?
- Conc. (greater the difference in conc. between the 2 sides of the membrane, faster the rate of diffusion)
- Temp. (higher the temp., faster the rate of diffusion)
- Size (larger the size of diffusing substance, slower the rate of diffusion)
- Surface area (increase in surface area, increases rate of diffusion)
- Diffusion distance (increase in diffusion distance slows rate of diffusion)
- Membrane thickness (thicker the membrane, slower the diffusion)
What is the limit on the size of cells for the rate of diffusion?
20μm - don’t need to know this bc we don’t need to know any numbers hehe (from perla)
What is the conc. gradient?
The selective permeability of the membrane enables a difference in conc. across the membrane to be established
What will diffuse down their conc. gradients?
Non-charged molecules
What is the electrical gradient?
Cells can maintain a difference in charged ions between the inside and outside of membrane, establishing an electrical gradient or membrane potential
What will be influenced by membrane potential in addition to their conc. gradient?
Ions
What will be influenced by the electrochemical gradient (which effects both conc. and electrical gradient)?
Net movement of ions
Membranes ___ ____ and can ____ and ____ ____
mimic capacitors, separate, store charge
How much ~% of resting energy do cells use to maintain conc. and electrical gradients?
~30% (dont needa know this one either xoxoxox)
What does the resting energy that cells use to maintain conc. and electrical gradients represent?
Stored energy
What is osmosis?
The net diffusion of water across a semi-permeable membrane (which is more permeable to water than to solutes) from a high water conc. area to a low water conc. area
What happens when solutions of different solute conc. are separated by a semi-permeable membrane?
There is tendency for water to move from the solution for lesser solute conc. to the solution of greater solute conc.
What happens when an osmotic gradient exists?
Water will want to move to eliminate it
What can osmotic water movement be prevented by?
An opposing force
What is defined as the osmotic pressure of the solution?
The hydrostatic pressure applied to oppose osmosis (prevent the inward flow of water across a semi-permeable membrane)
What property is osmotic pressure and why?
Colligative property, because it only depends on the numbers and not the types of particles in solution
What is the equation of membrane permeability to water (Pw)?
Pw = Pd (through lipid bilayer) + Pf (through water channel), where Pf > Pd
What are the properties of permeability through lipid bilayer (Pd)?
- Small (not a lot of water flow through the bilayer but there is a large amount of water)
- Mercury insensitive (tends to not be blocked by mercury)
- Temp. dependent (higher the temp., the more permeability through the lipid bilayer, can change lipid fluidity)
What are the properties of permeability through water channel (Pf)?
- Large
- Mercury sensitive (mercury can block the channel)
- Temp. independent
What is Pf mediated by? (+ what are these?)
Aquaporins which are channels that allow only water to flow through them without any ions (9 isoforms)
Why do cells have different Pw?
They express different aquaporin isoforms, and you can change Pw of a membrane by changing what aquaporin channels are put into that membrane
How would you calculate the osmolarity of 0.5 NaCl + H2O?
0.5M Na+ + 0.5M Cl - = 1 Osmol
If the solution has the same osmolarity, it is ____
isosmotic
If the solution has a lower osmolarity, it is _____
hyposmotic
If the solution has a higher osmolarity, it is _____
hyperosmotic
If osmosis occurs, what happens?
A change in cell volume
What is tonicity?
The effect a solution has on cell volume
What is tonicity dependent on?
The membrane permeability of the solute so the osmolarity of the solution doesn’t always indicate the effect it will have on cell volume
What occurs in an isotonic solution?
No change in cell volume
What occurs in a hypotonic solution?
Cell swelling and eventually, cell lysis (haemolysis)
What occurs in a hypertonic solution?
Cell shrinkage (crenation)
