Cellular processes Flashcards
What is the general structure of the membrane?
A thin, 8nm (8 x10-9 metre) flexible and sturdy barrier that surrounds the cytoplasm of a cell
What is the fluid mosaic model?
The Fluid mosaic model describes membrane structure “sea of lipids in which proteins float like icebergs”
Membrane is __% lipid and __% protein
50%, 50%
What is the membrane held by?
hydrogen bonds
what is a lipid?
lipid is barrier to entry or exit of polar substances
proteins are _______ who __________
gatekeepers, regulate traffic
what does the lipid bilayer of the cell membrane look like? (2)
- Two back-to-back layers of 3 types of lipid molecules
- Cholesterol and glycolipids scattered among a double row
of phospholipid molecules
phospholids comprise of what? (3)
- 75% of lipids
- Phospholipid bilayer = 2 parallel layers of
molecules - Each molecule is amphipathic (has both a polar & nonpolar region)
what are membranes in terms of membrane fluidity? (2)
• Membranes are fluid structures and lipids can move around within the plane of the membrane
leaflet
• Lipids rarely flip flop between membrane leaflets therefore the lipid composition of the leaflets can
be asymmetric.
What is fluidity determined by? (3)
- Lipid tail length - the longer the tail, the less fluid the membrane
- Number of double bonds (more double bonds increases fluidity)
- Amount of cholesterol (more decreases fluidity)
What are integral proteins?
extend into or completely across cell
membrane (transmembrane protein)
What are peripheral proteins?
attached to either inner or outer surface
of cell membrane and are easily removed from it
are intergral proteins amphiphilic or amphpathic?
Amphipathic
How do you describe integral proteins? (4)
• Integral proteins are amphipathic
• They have hydrophobic regions that span
the hydrophobic core of the lipid bilayer
• These regions usually consists of non polar
amino acids coiled into helices
• Hydrophilic ends of the
proteins interact with the
aqueous solution
What can membrane proteins act as? (6)
- Receptor Proteins
- Cell Identity Markers
- Linkers
- Enzymes
- Ion Channels
- Transporter Proteins
What does the molecular organisation of the membrane result in?
The molecular organisation of the membrane results in
selective permeability – the membrane allows some
substances to cross but excludes others
what is the lipid bilayer permeable and impermeable to? (5)
– Permeable to nonpolar, uncharged molecules - O2, N2 benzene
– Permeable to lipid soluble molecules – steroids, fatty acids, some
vitamins
– Permeable to small uncharged polar molecules: water, urea,
glycerol, CO2
– Impermeable to large uncharged polar molecules – glucose, amino
acids
– Impermeable to ions Na+, K+, Cl-
, Ca2+, H+
what do membrane proteins mediate?
Membrane proteins mediate the transport of substances across the
membrane that can not permeate the hydrophobic core of the lipid bilayer
more molecules move away from an area of high concentration to an area of low concentration. What affects the rate of diffusion? (5)
• the greater the difference in concentration between the 2 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 diffusing substance, the slower the
rate of diffusion
• an increase in surface area, increases the rate of diffusion
• increasing diffusion distance, slows rate of diffusion
what does the rate of diffusion set a limit to?
The rate of diffusion sets a limit on the size
of cells of about 20 µm
How does a cell increase diffusion?
To increase diffusion a cell can increase the
membrane area available for exchange
(diffusion) of a substance
What is the diffusion consequences of membrane thickness?
Membrane thickness – the thicker the
membrane the slower the rate of diffusion
diffusion is very fast over _____________
small distances
what is concentration gradient?
non charged molecules will diffuse down their
concentration gradients