L21 Flashcards
The cell membrane controls the passages of substances into and out of cells. This allows:
- Concentration gradients to be maintained;
- The spatial organisation of chemical and physical processes within the cell;
3.The controlled up-take of nutrients and discharge of waste prod ucts and the secretion of
molecules;
- The development of a membrane potential.
Membrane fluidity is determined by
- Number of double bonds: more increases fluidity
- Amount of cholesterol: more decreases fluidity
- Lipid tail length: longer, less fluid
What are the main membrane proteins?
1, Integral
- Peripheral
Membrane proteins can act as
A membrane protein is like somone just there: they
C (see) and R ef L E C T
- Receptors;
- Cell Identity Markers;
3, Linkers; - Enzymes;
- Channels;
- Transporters.
What is the membrane selective to? aka selective permeability
- Permeable to nonpolar, uncharged molecules: O, N2
- Permeable to lipid soluble molecules: steroids, fatty acids, some vitamins;
- Permeable to small polar uncharged molecules: water, urea, glycerol, CO2
- Impermeable to large uncharged polar molecules: glucose, amino acids;
- Impermeable to ions : Na+, K+, Cl-
, Ca2+, H+.
What are the principals of Diffusion? aka the laws of diffusion
- More molecules move away from an area of high concentration to an area of low concentration.
- The greater the difference in concentration between the two sides of the membrane, the faster the rate of diffusion.
- The higher the temperature, the faster the rate of diffusion.
- The larger the size of the diff using substance, the slower the rate of diffusion.
- An increase in surface area increases the rate
of diffusion. - Increasing diffusion distance slows the rate of diffusion; so diffusion is only very fast
over small distances.
Define diffusion
Diffusion is the random mixing of particles in a solution as a result of the particle’s kinetic energy
Explain Stored energy
Cells can maintain a difference in charged ions between the inside
& outside of membrane establishing an electrical gradient or membrane potential. Membranes
mimic capacitors and can separate and store charge. Cells use about 30% of resting energy to
maintain concentration and electrical gradients. These gradients represent stored energy. Ions
will be influenced by the membrane potential in addition to their concentration gradient. The net
movement of ions across a membrane will be influenced
Define Osmosis
Osmosis is the net diffusion of water across a semi-permeable membrane.
How thick is the membrane structure?
8nm
What is the fluid mosaic model
Fluid mosaic model describes membrane structure
What are the proportions of membrane, lipids, proteins in the membrane? and what holds these together?
membrane is 50 % lipid & 50 % protein
held together by hydrogen bonds
How are peripheral proteins connected to the membrane? and how can you break these off?
ionic chargers and using ionic solution
What are the main constituents of the cell membrane?
phospholipids and proteins
What is in the inside of a integral protein?
Non polar amino acids coiled into helices
What are the physical consequences of diffusion?
The rate of diffusion sets a limit on the size of cells of about 20 µm
To increase diffusion a cell can increase the membrane area available for exchange (diffusion) of a substance
Membrane thickness –the thicker the membrane the slower the rate of diffusion
Diffusion is very fast over small distances
What are the gradients across the cell membrane?
Concentration gradient -non charged molecules will diffuse down their concentration gradients
Electrical gradient -ions will be influenced by membrane potential in addition to their concentration gradient. Movement of ions will be influenced by the electrochemical gradient
What enables a difference in concentration or concentration gradient across the membrane to be established?
Selective permeability of the membrane
How much resting energy do cells use to maintain concentration and electrical gradients?
around 30%
What do gradients repersent?
stored energy
When is the only time Osmosis can occur?
Only occurs if membrane is permeable to water but not to certain solutes
Pw = ???
Pw = Pd (membrane is permeable to water but not to certain solutes) + Pf (aquaporins)
What are the properties of Pd (through the lipid bilayer)?
Small
Mercury insensitive
Temp dependent (lipid fluidity
What are the properties of Facillitated diffusion? (Through water channel)
Large
Mercury sensitive
Temp independent
