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)
