Structure and Function of the Cell Membrane Flashcards
What are the two main consitutients of the cell membrane
Phospholipids and proteins
What is the structure of the membrane
A think, 8nm flexible and sturdy barrier that surrounds the cytoplasm of a cell.
Describe the fluid mosaic modle of the membrane
- “sea of lipids in which proteins float like icebergs”
- membrane is 50% lipid and 50% protein
- lipid is barrier to entry and exit of polar substances
- proteins are “gatekeepers”
What type of bonds hold the membrane together
Hydrogen bonds
What is the lipid bilayer of the cell membrane
Two back-to-back layers of 3 types of lipid molecules
What are scattered among a double row of phospholipid molecules
Cholestrol and glycolipids
What are phospholipids
A lipid consisting of a phosphate molecule
What is the phospholipid bilayer
In water, most phospholipds form a lipid bilayer structure with polar head groups at the surface in contact with water and the fatty acid chains in the core screened from water contact.
What percentage of lipids are phospholipids
75%
What is an important feature of the hydrophobic core
Provides a highly impermeable barrier to the passage of charged ions.
What does the cell membrane control
The passages of substances in and out of the cells
By having the cell membrane control the passages of substances in and out of the cell, what does this allow
- maintain concentration gradients
- spatial organsiaton of chemical and physical processes within the cell
- controlled uptake of nutrietns and discharge of waste products and secretion of molecules
- developement of membrane potential
What does it mean by membrane fluidity
Membranes are fluid structures and lipids can move around within the plane of the membrane leaflet
How is the lipid composition of the leaflets assymetric
Lipids rarely flip-flop between membrane leaflets
What is membrane fluidity determined by
- lipid tail length: longer the tail, the less fluid the membrane
- Number of double bones: more increases fluidity
- amount of cholestrol: more decreases fluidity
What are the two basic classes of membrane proteins
Integral and peripheral
What are integral membrane proteins
They extend into or completly across teh cell membrane (transmembrane protein)
Are integral membrane proteins amphiphatic or not
They are amphiphatic - they have hydrophobic regions that span the hydrophobic core of the lipid bilayer. These regions usually consist of non polar amino acids coiled into helices. The hydrophilic ends of the proteins interact with the aqueous solution.
What do the hydrophobic regions on integram membranes consist of
These regions consists of non-polar amino acids coiled into helices. The hydrophobic ends of the proteins interact with the aqueous solution
What are peripheral membrane proteins
They are attatched to either the inner of outer surface of the cell membrane and can be easily removed from it as well.
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What can membrane proteins act as
- receptors
- cell identity markers
- linkers
- enzymes
- channels
- transporters
What are two common transport functions of membrane proteins
Ion channel and carrier.
What is an ion channel (integral)
Forms a pore through which a specific ion can flow to get across membrane. Most plasma membranes include specific channels for several common ions.
What is a carrier/transporter (integral)
Transports a specific substances across membrane by undergoing a change in shape. Also known as a transporter
What is an example of the use of a carrier (integral)
Amino acids needed to synthesise new proteins, enter body cells via carriers.
What is permeability
Ability of a particular molecule to cross a cell membrane
What does the permeability of a molecule depend on
The molecule’s size, charge and lipid solubility.
The lipid bilayer is permeable to what
- Non-polar uncharge molecules (O2, N2, benzne)
- lipid soluble molecules (steroids, fatty acids, vitamins
- small uncharged polar molcules: water, urea, glycerol, CO2
What is the lipid bilayer impermeable to
- large uncharged poalar molecules: glucose, amino acids
- ions: Na+, K+, Cl-, Ca2+, H+
Membrane proteins mediate the transport of substances across the membrane that can not permeate what
the hydrophobic core of the lipid bilayer
Diffusion
The random mixing of particles in a solution as a result of the particle’s kinetic energy. More molecules move away from an area of high concentraion to an area of low concentration.
For diffusion, is the rate of diffusion faster or slower when there is a higher temperature.
Faster
For diffusion, is the rate of diffusion faster or slower when there is a larger size of the diffusion substance
Slower
For diffusion, is the rate of diffusion faster or slower when there is an increase in surface area
Faster
For diffusion, is the rate of diffusion faster or slower when increasing the diffusion distance
Slower
What is diffusion
Random mixing of particles in a solution as a result of a particle’s kinetic energy.
To increase diffusion, a cell can increase the ___
Membrane area available for exchange (diffusion) of a substance.
How does membrane thickness affect diffusion
The thicker the membrane, the slower the rate of diffusion
What are the two gradients across the cell membrane
Concentration and electrical gradient
Concentration gradient
When non-charged molecules diffuse down their concentration gradients
Electrical gradient
Ions will be influenced by membrane potential in addition to their concentration gradient.
Movement of ions are influenced by what
Electrochemical gradient
The selective permeability of the membrane enables a difference in what
Concentration or concentration gradient
How is an electrochemical gradient established
Cells can maintain a difference in charged ions between the inside and outside of membrane, establishing an electrochemical gradient.
Cells use what to maintain concentration and electrochemical gradients
~30% of resting energy
What is osmosis
Net movement of water through a selectively permeable membrane from an area of high concentration to an area of lower water concentration.
Osmosis occurs if what
Membrane is permable to water but not to certain solutes.
Osmotic water can be prevented by what
An opposing force
Pf is mediated by what
Aquaporins (isoforms)
Properties of Pd
- small
- mercury insensitive
- temp dependent (liquid fluidity)
Properties of Pf
- large
- mercury sensitive
- temp independent
What is osmotic pressure
Pressure applied to a solution to prvent the inward flow of water across a semi-permeable membrane.
if the solution has the same osmolarity, it is what?
Isosmotic
If the solution has lower osmolarity, it is what?
Hyposmotic
If the solution has a higher osmolarity, it is what
Hyperosmotic
What is tonicity
The effect a solution has on cell volume.
What is tonicity dependent on
The membrane permeability of the solute. Hence the osmolarity of a solution does not alwas indicate the effect it will have on cell volume.
What is an isotonic solution
No change in cell volume
What is hypotonic solution
Cause cell swelling and eventually cell lysis
What is hypertonic solution
Causes cell shrinkage
