5.1 (2.1.5) Structure and roles of the plasma membrane

describe phospholipids as a component of the plasma membrane

forms a bilayer, composed of a phosphate head and 2 hydrocarbon fatty-acid tails

describe glycoproteins as a component of the plasma membrane

intrinsic proteins with attached carbohydrate chain. involved in cell adhesion and cell signalling

glycolipids in plasma membrane

lipids with attached carbohydrate chains. acts as antigens allowing the immune system to recognise the cell as self

cholesterol in plasma membrane

maintains fluidity and increases stability

channel proteins in plasma membrane

facilitates the diffusion of ions or polar molecules across the membrane providing a pathway via a hydrophilic channel

carrier proteins in the plasma membrane

facilitates both passive transport and active transport across the membrane by changing the shape

define simple diffusion

the passive movement of particles from a region of high concentration to a region of low concentration until equilibrium is reached

define facilitated diffusion

the passive movement of polar molecules/ions from a region of high concentration to a region of low concentration through channel or carrier proteins until equilibrium is reached

explain fluid-mosaic model

fluid because the plasma membrane is not a fixed shape as phospholipids and proteins move around. mosaic because the surface has the appearance of a mosaic through all the separate components

define intrinsic proteins

proteins which pass through the bilayer as channels for transport of substances in and out of the cell

define extrinsic proteins

proteins on the outer layer of the bilayer. involved in cell signalling, serve as receptors for hormones, containing binding sites, provide structural support

define hydrophobic

repelled by water

define hydrophillic

attracted to water

define differentitation

the selective expression of genes in a cell’s genome to develop having a specific function

define partially permeable membrane

a membrane that allows some substances through but not others

define receptor sites

extrinsic proteins that bind to chemical signals which trigger a response by the cell

define cell signalling

when chemicals bind to the receptor to elicit a response from the cell which causes a cascade of events inside the cell

define target cell

specific cells which hormones act on

factors affecting rate of facilitated diffusion

temperature, concentration gradient, membrane surface area and thickness, number of channel proteins present

describe how molecules move across a membrane by active transport using carrier proteins

1) the molecule binds to the receptors in the channel of the carrier protein on the outside of the cell 2) ATP binds to the carrier protein on the outside of the cell and is hydrolysed 3) binding of the phosphate molecule to the carrier protein causes the protein to change shape which opens up the inside of the cell 4) the molecule is released to the inside of the cell 5) the phosphate molecule is released from the carrier protein and recombines with ADP to form ATP 6) the carrier protein returns to its original shape

define exocytosis

the bulk transport of substances out of the cell

define endocytosis

the bulk transport of substances into the cell

examples of exocytosis

secretion of substances using vesicles

examples of endocytosis

phagocytosis and pinocytosis

how does an increase in temperature affect the plasma membrane

phospholipids will have more kinetic energy and move more becoming more fluid. this means it loses its structure. as the temp increases more the cell will break down completely as a loss of structure increases the permeability of the membrane making it easier for particles to cross through it. channel and carrier proteins will be denatured

how do organic solvents affect the plasma membrane

will dissolve membranes, disrupting cells.