Transport across cell membranes Flashcards
(17 cards)
What is the structure of a membrane ?
A hydrophilic phospholipid head who’s is attracted to water and arrange themselves in a bilayer facing outwards
Hydrophobic phospholipid tails repelled by water face inwards along a hydrophobic interior
What are the other components of a membrane ?
Extrinsic protein- on the surface or only in half the membrane which may have charged hydrophilic areas which are attracted to the heads
Protein carrier- transport carrier protein for active transport and facilitated diffusion
Channel protein- intrinsic proteins that have hydrophilic linings that allow passage of polar substances that cannot pass through the phospholipid hydrophobic layer
Glycroprotein- carbohydrate chain attached to protein/lipid on the extra cellular side to form the glycocalyx which helps cells recognise each other
Cholesterol- restricts the movement of other molecules so reduces fluidity
What I h function of the cell membrane ?
Bilayer prevents water soluble substances to pass into or out the cell so it is selectively permeable
Other molecules which are water soluble must use channel protein or carrier protein by facilitated diffusion or active transport
Fluidity of th bilayer allows it to form vesicles which can fuse with other membranes
Surface proteins/extrinsic proteins-glycoproteins/glycolipids ate important for cell recognition and so act as antigens or receptors
What is simple diffusion ?
The movement of molecules or ions from a region of higher concentration to one of lower concentration (passive process) and no atp needed
Fo simple diffusion to occur across the phospholipid bilayer of membrane particles must be small and uncharged
What does the rate of diffusion depend on ?
Concentration gradient
Distance of travel- the shorter distance the faster the rate
Temperature- an increase in temperature increases the molecular kinetic energy so increases the rate
Size of molecule-smaller molecules diffuse more quickly as can pass between phospholipids easier and more kinetic energy if molecule is too big it cannot cross through
Surface area- more surface area, the faster the rate
What is facilitated diffusion?
It is the diffusion of particles across a membrane using protein carriers or channels without needing any ATP energy. It is also a passive process. The channel proteins and carrier proteins are specific to one molecule.
How do carrier proteins work ?
Large molecules attached to carrier proteins the proteins change shape and the molecule is released onto the opposite side of the membrane when used in facilitated diffusion i.e. carrying molecules down a concentration gradient ATP is not required.
How do channel proteins work ?
Channel proteins are aligned with polar groups to make them hydrophilic so that water soluble charged ions can pass through each channel protein is specific to one type of ion they can open and close so that the protein changes shape.
How does facilitated diffusion work ?
It requires the use of channel and carry a proteins to make this work and the molecules attached to the carrier proteins or the protein so that the protein changes shape and the molecule is released onto the opposite side down the concentration gradient
How does active transport work ?
Active transport is against a concentration gradient using ATP and protein carriers but it does not use channel proteins. Nonpolar molecules example water cannot be actively transported as they move freely through the phospholipids.
Further explanation of active transport
It is a very selective process with specific substances being transported. The molecule being moved binds to complementary receptor exercise on the carrier protein. ATP binds to the protein and splits into ADP and PI, which causes the protein to change shape and opens to the opposite side of the membrane releasing the molecule. The phosphate is then released from the protein and the protein reverse to its original shape ready to repeat the process.
What affects active transport ?
Temperature increases ATP production due to increased enzyme activity in respiration respiratory inhibitors prevents respiration so reduced ATP production. The concentration of oxygen present present means more oxygen so more aerobic respiration so more ATP the number of carrier proteins means more active transport will occur.
What is co transport ?
Call transport is the coupon movement of substances across a cell membrane by a carrier protein. This means that two types of molecules are moved across a membrane at the same time. The movement of one is dependent on the movement of the other.
How does co transport work?
It is used in the absorption of amino acids and glucose from the helium into the bloodstream at the first part sodium ions pumped out of the epithelial cell by sodium potassium pumps into the capillary by active transport using ATP. This then creates a lower sodium ion concentration inside the epithelial cell. Sodium ions into the cell from the intestinal lumen down a concentrate gradient through a cold transport protein that only allows the entry with glucose. Glucose is now a high concentration in the cell and so exits to the capillary by facilitated diffusion down a concentration gradient.
What is osmosis?
The movement of water from a solution of high water potential to a solution of lower water potential across a partially permeable membrane
How does osmosis work?
Water moves through special channel proteins called aqua Porins or as it’s still small it can actually move directly across the phospholipids. The greater the number of free water molecules the greater the water potential and pure water has the highest water potential. Every other solution has a negative water potential.
What does isotonic hypertonic hypotonic mean?
Isotonic is a solution of equal water potential hypertonic very concentrated solution with a lower or more negative water potential and hypotonic is a dilute solution with a higher or less negative water potential
