cell membranes and transport

State what is meant by the term fluid mosaic.

• phospholipids can move around laterally;

• proteins randomly scattered on surface;

Explain why the cell membrane may be described as fluid

lipids / proteins can move laterally / change place;

State two functions of the proteins in the plasma membrane.

transport / receptors / cell recognition / attachments sites / enzymes;;

Explain how carbon dioxide cross the plasma membrane

• diffusion;

• down concentration gradient;

• as dissolved CO2;

Explain how glucose cross the plasma membrane

• active transport;

• glucose binds to carrier protein;

• protein changes shape to carry glucose across;

• cotransport with Na+;

Explain how concentration of ions are kept high outside the cell and low within.

• active transport with ATP;

• pump moves ion out;

• cannot re-enter because phospholipid membrane is impermeable to ions;

Suggest and explain the features of an OmpF porin as a membrane transport protein

• channel protein; formed from polypeptides / quaternary structure;

• hydrophilic R-groups face inwards / line channel;

• allows facilitated diffusion;

• increases permeability for osmosis / movement of water;

• no specific binding sites / not selective / allows more than one type of substance;

• globular;

Explain the movement of a protein and reducing sugar across Visking tubing membrane.

• reducing sugar diffused into tubing, down concentration gradient;

• reducing sugar small enough to move through;

• protein too large to move into tubing;

Suggest and explain how mucin strands are transported out of the goblet cells

• exocytosis;

• bulk transport;

• vesicles form from Golgi body;

• vesicles moved my microtubules / cytoskeleton;

• vesicles fuse with cell surface membrane;

• active process / requires ATP;

• mucin hydrophilic, cannot pass through hydrophobic core;

Outline one way in which testosterone molecules could enter their target cells.

• passive diffusion; down concentration gradient; through hydrophobic core;

• endocytosis; desc vesicle formation; ATP required;

Suggest and explain why cytokine molecules are not able to cross the cell surface membrane to enter their target cells

• hydrophilic; cannot cross hydrophobic core;

• too large;

• no specific transport proteins;

Explain why the production of breast milk can be described as an example of a cell signaling process.

• hPRL is signalling molecule;

• acts on target cells;

• PRLP is cell surface membrane receptor;

• hPRL binds to PRLR; complementary / specific;

• leads to specific response in mammary gland cell / secondary messengers, enzymes activated;

Explain how chemicals which stimulate tissue repair in liver cells is an example of cell signaling.

• chemicals released are signaling molecules;

• liver cells are target cells;

• signaling molecule bind to receptors; complementary / specific;

• response is cell division;