Transport Across Membranes Flashcards
Plasma membrane, Diffusion, Ficks law, Osmosis, Hypotonic/Hypertonic/Isotonic, Active transport, Endocytosis, Exocytosis
What forms the basis of a cell membrane?
Phospholipid bilayer
What is the fluid mosaic model?
The phospholipids are constantly moving relative to each other (fluid structure)
Proteins are distributed along the membrane giving it selective permeability (mosaic)
What can pass through the bilayer?
Small non-polar molecules like O2, large polar molecules need proteins to pass through
Lipid soluble molecules can pass through by simple diffusion
What does cholesterol do to the structure and function of the membrane?
Strength and stability which prevents leakage and prevents lateral movement
Facilitates diffusion along the membrane
Channel protein
Facilitates diffusion and actively transports ions
Carrier protein
Bind to hormones and allow a cell to respond. Only certain cells have certain receptors
Specific receptors (protein molecule)
Enzyme-substrate complexes are formed on the membrane by…
Enzymes
Present on the outer surface of the membrane and are important in cell recognition, sometimes acting as antigens detecting foreign invaders
Glycoproteins
Allows water to pass through the membrane by osmosis
Aquaporin
It is a passive process that measures the net movement of molecules from a higher concentration to a lower concentration across a partially permeable membrane
Diffusion
Four factors that effect the rate of diffusion:
. Temperature - Increasing the kinetic energy increases the movement of molecules
. SA - More “space” so molecules to pass through so faster
. Concentration gradient - Concentration difference increases the rate of diffusion
. Diffusion difference - Thinner surface means the molecules will pass through faster
Proteins help molecules pass through the bilayer
Facilitated diffusion
What happens if the temperature is increased too much?
Proteins in the membrane could denature making the membrane ‘leaky’
Fick’s law
Rate of diffusion is proportional to:
(surface area x concentration gradient)/Diffusion distance
Net movement of water molecules from a higher water potential to a lower water potential through a partially permeable membrane
Osmosis
Water molecules collide with the membrane which exerts a pressure measured in kPa
Water potential
What is the highest water potential?
0kPa - pure water, adding a solute make the solution negative
Why does adding a solute make the solution have a negative water potential
Water is a di-pole and is attracted to the charges on the ions, therefore the number of free moving molecules decreases
Hypotonic -
Water moves in which results in swelling & lysis in animal cells and turgor of plant cells
Hypertonic -
Water moves out which results in shrivelling in animal cells and plant cell membrane pulling away from the cell wall/plasmolysed in plant cells
Isotonic -
No net movement
Transporting molecules against their concentration gradient using carrier proteins specific with a complimentary binding site and uses ATP
Active transport
Transport using vesicles from inside the cell to outside. Also used to move enzymes and glycoproteins from the golgi to the cell surface membrane (REQUIRES ATP)
Exocytosis
Transport using vesicles from outside the cell to inside. The cell surface membrane is “pulled” inwards to form a vesicle and any material next to it are enclosed (REQUIRES ATP)
Endocytosis
