Transport across the membrane Flashcards
How do lipid soluble molecules move?
They enter through bilayer by dissolving in the phospholipid
What are examples of lipid soluble molecules?
Alcohols, steroids and hormones
How do small molecules move across a membrane?
They move through gaps between the phospholipids
What are examples of small molecules?
Oxygen, carbon dioxide and some water molecules
What molecules can be transported without proteins (simple diffusion)?
Lipid soluble molecules and small molecules
How doo small charged particles move across a membrane?
They can move through ion channels
What is an example of a small charged particle?
Ions
How do larger molecules move across membrane?
They move through protein transporters
How does water move across a membrane?
Through aquaporins
What are aquaporins?
Protein channels with a hydrophilic centre?
What can protein channels be?
They may be gated
What moves through protein channels or by protein carriers (facilitated diffusion)?
Small, charged particles, larger molecules and water
What are examples of larger molecules?
Glucose and lipid insoluble molecules
What is diffusion?
The net movement of molecules or ions from a region of their high concentration to a region of their lower concentration until the concentrations are equal
What happens when dynamic equilibrium is reached?
The particles are still moving but are in a constant state of random motion due to kinetic energy
What direction can particles move in in diffusion?
Any direction
What is the movement of diffusion?
There is an overall net movement
What kind of process is diffusion?
A passive process as no ATP is used
What are factors effecting diffusion?
Surface area of the membrane, difference in concentration on either side of the membrane, the thickness of the membrane, size and type of molecule and temperature
How is surface area of a membrane increased?
By membrane folds and microvilli
How is surface area of a membrane increased in the digestive system?
Villi with microvilli within the intestine increase the SA of intestine to increase the rate of diffusion
How is surface area of the membrane increased in the gas exchange system?
There are many alveoli with many divisions of tissue to increase surface area of the lungs
How do substance move when there is a difference in concentration?
They move down a concentration gradient until the 2 concentrations are equal
What does a larger difference in concentration mean?
Diffusion will be faster
How is difference in concentration used in the gas exchange system?
Blood maintains a high concentration gradient through ventilation
How does thickness of a membrane vary?
It is usually the same as it is made of phospholipids
How is thickness of the membrane affected in the gas exchange system?
In alveoli, the capillaries are close to the epithelial cells lining in the lung, so the distance is short and they also have thin 2 cell layer
How do gases move?
They are small and can slip between phospholipid molecules easily
Why cannot water not pass easily?
It is polar
What si the effect of temprature on diffusion?
Higher temperature increases kinetic energy
What is Ficks law?
Rate of diffusion ∝ (surface area x difference in concentration) / thickness of exchange surface
What is facilitated diffusion?
Diffusion requiring a specific transmembrane protein
How do carrier proteins work?
They bind to substance, change its shape and move it across
How does active transport work>
A specific substrate binds to a carrier on one side and there is a conformational change of carrier, then the substrate is released on the other side
What kind of process is active transport?
It is an active process with ATP required
What direction does active transport go in?
Against a concentration gradient
What is needed for active transport?
Transport proteins which are specific due to their binding site which has a complementary fit with a particular molecule
What is cytosis?
It is a bulk transport of large materials through vesicles
What is phagocytosis?
Transport of large particles/cells/parts of cells through the membrane
What is pinocytosis?
The movement of fluids across the membrane (solutions/suspension of particles)
What is an example of a substance that moves by pinocytosis?
Lipids in the small intestine
What is an example of phagocytosis?
White blood cells engulfing bacteria
