Chapter 4 - Transport across cell membranes Flashcards
what is the structure of a phospholipid? (2)
hydrophillic head - phosphate
hydrophobic tail - fatty acids
function of phospholipid bilayer? (3)
- allow lipid soluble substances through
- prevent water soluble substances
- make membrane flexible and self sealing
what is the purpose of extrinsic proteins? (2)
- mechanical support
- with glycolipids act as cell receptors
purpose of intrinsic proteins? (4)
- channels, water soluble molecules
- cell surface receptors for identification/hormones
- structural support
- help cells adhere together
features of cholesterol? (2)
- very hydrophobic
- pull together tails of phospholipids of bilayer
functions of cholesterol? (3)
- reduce fluidity of phospholipids and other molecules
- make membrane more rigid at high temperatures
- prevent water leakage/dissolved ions
functions of glycolipids? (3)
- recognition sites
- stability of membrane
- formation of tissues - attach together
functions of glycoproteins? (3)
- cell recognition sites
- form tissues
- allows cells to recognise one another
why are most molecules not able to diffuse across the phospholipid bilayer? (4)
- not lipid soluble
- too large
- charged
- same charges as protein channels
why is it important for the cell surface membrane to remain fluid?
flexibilty, able to change shape
definition of diffusion?
net movement of molecules from a region of high conc. to region of low conc.
define facilitated diffusion
diffusion involving proteins to allow large/charged molecules across plasma membranes
definition of osmosis?
passage of water from area of high water potential to are of low water potential through a selectively permeable membrane
what is the water potential of pure water?
0kPa
what is active transport?
movement of molecules/ions from region of low - high conc. using ATP and carrier proteins
process of active transport? (4)
- molecule binds to carrier
- ATP binds on outside of cell to carrier protein then splits
- causes carrier to change shape and molecule released in cell
- phosphate + ADP released and carrier reverts to original shape
how is the rate of movement across membranes in the ileum maximised? (2)
- microvilli
- high quantities of carrier/channel proteins
how is a favourable conc. gradient maintained in the ileum? (3)
- constant digestion or carbs
- continuous blood flow, extensive capillary network
- facilitated diffusion
outline co-transport in the ileum (4)
- sodium ions actively transported out of epethelial cells into blood
- higher conc. in lumen
- sodium ions diffuse down gradient through co-transport channels carrying with it amino acids or glucose
- glucose/amino acids pass into blood by facilitated diffusion
