Topic 2 - B : Cell membranes
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What are cell membranes composed of
Protein carbohydrate lipid
What are glycoproteins
proteins with carbohydrate attached
What are glycolipids
lipid with carbohydrate attached
How are phospholipids arranged in membrane
Head is hydrophilic tail is hydrophobic Bilayer : head faces out, tail faces in as tails face in, the centre is hydrophobic, therefore the membrane doesn’t allow water-soluble substances through it small non polar substances can diffuse through the membrane
What is the function of cholesterol in membrane
type of lipid that’s present in all cell membranes, they go between phospholipids bind to hydrophobic tails of phospholipids this restricts movement of the phospholipids making the membrane less fluid and more rigid Main function is to provide membrane with structure
Define diffusion
net movement of particles from area of higher concentration to lower concentration.
diffusion details
passive process down concentration gradient
Define facilitated diffusion
net movement of particles from an area of higher concentration to lower concentration using carrier or channel proteins factors affecting it: concentration gradient number of channel or carrier proteins
Carrier proteins
move large molecules across membrane, down concentration gradient large molecule attaches to carrier protein in membrane protein changes shape releases molecule on opposite side of membrane
Channel proteins
diffuse charged particles
Define osmosis
movement of water particles through a partially permeable membrane from area of higher concentration to lower concentration Factors affecting it: water potential gradient thickness of exchange surface surface area
define isotonic
two solutions have the same water potential
define active transport
movement of molecules from lower to higher concentration using carrier and co transporter proteins
difference between carrier proteins in active transport and facilitated diffusion
active transport moves solutes from low to high, whereas facilitated diffusion move from higher to lower active transport requires energy and FD doesnt
Describe co transporters
bind two molecules at a time. Concentration gradient of one of the molecules is used to move the other molecule against its conc gradient
Describe co transport and the absorption of glucose
Sodium ions actively transported out of the epithelial cells in ileum by the sodium pump. This creates conc. gradient. Sodium ions diffuse from the lumen of ileum into epithelial cell. This is done via sodium glucose co transporters Glucose is carried into cell Glucose then diffuses out of cell into blood down its conc. gradient through protein channel by FD