T4:Transport across cell membranes Flashcards
How are phospholipids an important component for cell membranes?
-hydrophilic heads
on the outside attracted by water
-hydrophobic tails in the centre which are repelled by water
(two taills)
What are the functions of the phospholipids in the membrane ?
-allow lipid soluble substances to enter/leave the cell
-prevent water soluble substances entering
-making the membrane flexible after self sealing
What are the functions of cholesterol in the membrane?
-add strength
-hydrophobic so they prevent water loss
-reduce lateral movement of molecules including phospholipids
-make membrane less fluid at high temperature
What are the functions of glycolipids in the membranes?
-acts as recognition sites
-help maintain the stability of the membrane
-help cells attach to one another and form tissues
Function of glycoproteins in bilayer?
-recognition sites
-helps cells attach to form tissues
-allows cells to recognise eachother
How are protein embedded in a bilayer?
-channel proteins span the layer ,water filled tubes to allow water soluble ions through
-carrier proteins (active transport) bind to ion ,change shape and carry across bilayer
Functions of protein in a bilayer?
-structural support
-allows water soluble ions through
-carrier proteins allow for active transport
-receptors
What is the fluid mosaic model?
fluid- phospholipids can move relative to eachother to provide flexibilty
mosaic-proteins embedded vary in shape and size like a mosaic
What is diffusion
-movement of particles from a place where there is a high concentration to a place where there is low concentration (DOWN conc. gradient)
How do carrier proteins carry out facilitated diffusion?
-large molecule thats specific to protein then binds
-changes shape so its released to inside the membrane
How do proteins channels carry out facilitated diffusion?
-water filled hydrophilic channel cross membrane to allow charged particles through
-only opens at presence of specific water soluble ion
-bind to protein so it changes shape to close on one end and open at other
What is osmosis?
diffusion of water molecules across a partially permeable membrane, from an area of high water potential to an area of low water potential
What is water poteintal?
Water potential is the potential (likelihood) of water molecules to diffuse out of or into a solution.
E.g. Pure water has a water potential of zero. water potential of any solution is always negative (more negative the water potential, the stronger the concentration of solutes)
What does it mean if something is isotonic?
- two solutions have the same water potential
-cant loose or gain water
What does it mean if something is hypotonic ?
-cell is placed in a solution with higher water potential
-swell as water enters via osmosis
What does it mean if something is hypertonic ?
-cell is placed in a solution with lower water potential
-shrink as water exits via osmosis
What factors could affect the rate of osmosis?
-Water potential gradient
-Thickness of the exchange surface-
-Surface area of exchange surface
How to Investigating water potential (RP3)?
-make serial dilutions of know conc of sucrose solution
-weigh mas of potato hips that are equal in length and diameter
-place in sucrose solution for 20 minutes
-remove pat dry and reweigh
-calculate percentage change and plot calibration curve
What is active transport?
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier molecules
-process is very selective, with only specific substances being transported.
How is ATP used in active transport?
-ATP hydrolysed to ADP releases energy so that solutes can be transported
-directly move molecules and ions across plasma membranes (usually against the concentration gradient)
What can increase the rate of movement across membranes?
-villi 1mm
-microvilli 0.6um
-protein channels and carrier proteins
How does co-transport and the work in absorption of glucose?
-sodium ions actively transported out epithelial cells by sodium potassium pump-high conc in lumen
-sodium ions diffuse down conc gradient into cells carrying glucose via sodium–glucose cotransporter proteins
-glucose conc in cell increases
-glucose diffuses out cell into blood down conc gradient through protein channel via facilitated diffusion
What is the permeability of the cell membrane?
-not soluble in lipid cant pass phospholipid bilayer
-too large cant move into channel proteins
-same charge as charge on protein channels cant pass as it repels
-polar molecules have trouble passing the hydrophobic tails
