Cell Membranes/Diffusion

Question 1

fluid mosaic model of membrane structure (1972)

Answer 1

proposes that the membrane = phospholipid bi-layer in which proteins are embedded fully/partially

Question 2

2 main components of membrane

Answer 2

1. lipids (mainly amphipathic phospholipids - polar heads & non-polar tails)
2. proteins: integral (embedded in membrane) & peripheral (at surface of membrane)

Question 3

hydrophilic

Answer 3

“water-loving” - polar heads of lipids are hydrophilic

Question 4

hydrophobic

Answer 4

“water-hating” - non-polar tails of lipids are hydrophobic

Question 5

selective permeability of membrane

Answer 5

• certain materials can pass through the membrane in only one direction (i.e. nutrients in, waste out)
• determined by membrane’s unique, asymmetric arrangement of lipids & proteins
• most permeable to small molecules (i.e. water) and lipid-soluble substances

Question 6

3 ways particles can cross a selectively permeable membrane

Answer 6

1. diffusion
2. active transport
3. endo/exocytosis

Question 7

diffusion

Answer 7

aka “passive transport” – occurs naturally

small molecules in area of high concentration move ot an area of lower concentration on the other side of the membrane until the 2 concentrations are equal

Question 8

types of diffusion

Answer 8

1. osmosis

2. facilitated diffusion

Question 9

osmosis

Answer 9

diffusion of water

• when more solute particles outside of cell, cell will shrink as water moves outside to equalize concentration
• when more solute particles inside of cell, cell will swell/burst as water moves inside to equalize concentration

Question 10

facilitated diffusion

Answer 10

diffusion of larger lipid-insoluble (polar) molecules

• an integral carrier protein (specific to each type of molecule) binds to molecule, passes through the membrane, then releases the molecule on the side
• this is how sugars & amino acids diffuse

Question 11

isotonic

Answer 11

equal amt of solute (particles) on either side of membrane

Question 12

hypertonic

Answer 12

more solute particles outside cell than inside

Question 13

hypotonic

Answer 13

more solute particles inside cell than outside

Question 14

active transport

Answer 14

• molecules/ions pumped against the gradient (from areas of low conc. to areas of high conc.)
• requires carrier proteins & ATP

Question 15

sodium-potassium pump

Answer 15

• example of active transport of sodium and potassium ions (which are polar)
• crucial for cell life
• ATP is used to keep moving Na+ ions out of the cell after they diffuse inward & keep K+ ions moving into the cell after they diffuse outward.

Question 16

endocytosis

Answer 16

biomacromolecule outside of the cell is enclosed by an invagination of the cell membrane, creating a vesicle which brings the biomacromolecule into the cell

Question 17

exocytosis

Answer 17

biomacromolecule inside of the cell is enclosed inside the membrane of a vesicle (which breaks off the golgi complex). that vesicle then fuses w/the cell membrane & ejects the biomacromolecule out of the cell.

Question 18

types of endocytosis

Answer 18

1. phagocytosis
2. pinocytosis
3. receptor-mediated endocytosis

Question 19

phagocytosis

Answer 19

endocytosis of large objects (i.e. other cels)

• once a cell is enclosed in a vesicle, it fuses w/lysosomes and is digested
• white blood cells use phagocytosis to destroy harmful bacteria

Question 20

pinocytosis

Answer 20

endocytosis of tiny fluid droplets

- same as phagocytosis but cell membrane “pinches” inward to inward to digest molecule (no vesicle needed)

Question 21

receptor-mediated endocytosis

Answer 21

method of transferring information btwn cells

• receptor proteins (integral) in cell membrane bind with a ligand sent by another cell
• when ligand binds w/receptor protein, it changes the shape of the protein and other nearby proteins
• that change in shape often activates specific enzymes
• enzymes can then catalyze the release of energy from ATP or other high energy molecules
• this powers metabolic/structural changes in the cell based on the information transferred

Question 22

ligand

Answer 22

signaling molecule sent by another cell, usually in the form of a hormone

Question 23

plasma membrane

Answer 23

surrounds all cells and contains specialized “pumps” and “gates” that regulate the passage of materials in and out of the cell.

Question 24

cholesterol

Answer 24

Steroid lipid present in some membranes to stabilize against heat and cold. largely hydrophobic (repels water). cholesterol molecules act as spacers between the tails to reduce solidification during low temperatures, stabilizes the head during elevated temperatures by restricting motion and preventing movement as energy is added to the system.