2.1.5 Biological membranes - Factors affecting membrane structure Flashcards
What factors can affect the movement of molecules across membranes?
Factors that can affect the movement of molecules across membranes are:
- Temperature
- Concentration gradient
- Distance
- Surface area
- Mass of particles
- Solute viscosity
- Solvents
How does temperature affect the movement of molecules across membranes?
Increased temperature means that particles have an increase in kinetic energy therefore increased rate of diffusion.
How does concentration gradient affect the movement of molecules across membranes?
The steeper the concentration gradient, the greater the net movement if particles.
How does distance affect the movement of molecules across membranes?
The shorter the distance particles have to travel the greater the rate of diffusion.
How does surface area to volume ratio gradient affect the movement of molecules across membranes?
Increased area equals greater space for diffusion so more particles can move down the concentration gradient in any given time.
How does the mass of particles affect the movement of molecules across membranes?
Heavier particles move more slowly, therefore they diffuse more slowly.
How does solute viscosity affect the movement of molecules across membranes?
As the viscosity of a solute increases the rate of diffusion decreases. This is because molecules slow down as they have greater difficulty getting through the denser medium.
How do solvents affect the movement of molecules across membranes?
Non-polar or lipid-soluble materials pass through plasma membranes more easily than polar materials, allowing for a faster rate of diffusion.
How does the thickness of the membrane affect the movement of molecules across membranes?
The thinner the exchange surface, the higher the rate of diffusion.
Define Diffusion
Diffusion is the net, or overall movement of particles from a region of higher concentration to a region of lower concentration.
It is a passive process, and continues until there is a concentration equilibrium.
Define Facilitated diffusion
Facilitated diffusion is diffusion across a membrane through protein channels.
Facilitated diffusion is the movement of molecules down a concentration gradient and does not require external energy unlike active transport.
Why are membranes described as partially permeable?
Small polar molecules pass through more easily than larger ones. For example, non-polar molecules such as Oxygen (O2) diffuse through freely down a concentration gradient BUT polar molecules such as water (H2O) can diffuse through membranes but only at a very slow rate.
Why are transport molecules required to move water molecules and other substances across a membrane?
Ions, sugars, amino acids and sometimes water cannot diffuse across the phospholipid bilayer at sufficient rates to meet the cell’s needs and must therefore be transported by a group of integral membrane proteins including channels, transporters, and ATP-powered ion pumps.
What factors affect the rate of facilitated diffusion?
The rate of facilitated diffusion is dependent in the temperature, concentration gradient, membrane surface are and thickness, but is also affected by the number of channel proteins present. The more protein channels, the higher the rates of diffusion overall.
Define Active Transport
Active transport is the movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration.
The process requires energy and carrier proteins.
What is an example of a carrier protein?
Carrier proteins span the membrane and act as ‘pumps’. The sodium-potassium pump is the most important active transport channel, which expends metabolic energy to actively pump sodium ions (Na+) in one direction, out of cells, and potassium ions (k+) in one direction, into cells.
More than one-third of all the energy expended by your body’s cell is spent driving Na+K+ pump channels. This energy is derived from ATP.
The transportation of two different ions in opposite directions happens because energy causes a change in shape of the membrane protein carrier.
Define endocytosis
Is the bulk transport of material into cells.
How does endocytosis occur?
In endocytosis, an invagination of the membrane forms a flask-like depression which envelopes the material; the invagination is then sealed off forming a vesicle containing substances that had been outside the cell.
Define Phagocytosis
The process by which solid substances (e.g. food particles, foreign pathogens) are ingested (usually to be transported to the lysosome for break down) [“cellular-eating”].
Define Pinocytosis
The process by which liquids/solutions (e.g. dissolved substances) are ingested by the cell (allows quick entry for large amounts of substances) [“cellular-drinking”]
Define Invaginates
bends inwards
Describe how phagocytosis occurs.
In phagocytosis, a cell engulfs a particle by wrapping pseudopodia around it and packaging it within a membrane-enclosed sac that is large enough to be classified as a vacuole. The particle is digested after the vacuole fuses with a lysosome containing hydrolytic enzymes.
Describe how Pinocytosis occurs.
In pinocytosis, the cell gulps droplets of extracellular fluid into tiny vesicles.
Why is pinocytosis non-specific in the substances it transports?
Pinocytosis is non-specific in the substances it transports as fluid is taken up by the cell even though the molecules dissolved in the droplets are needed, not the actual fluid. As any and all included solutes are taken into the cell, pinocytosis is described as non-specific.
