Membranes

Question 1

cell membrane: general features

Answer 1

• selectively permeable
• fluid mosaic
• protects the cell
• bind to cytoplasm and extracellular matrix
• controls content of cytoplasm
• sense molecules and other cells in the environment

Question 2

lipids: general features

Answer 2

• diverse class biological molecules
• don’t mix well with water
• non polar
• fats, phospholipids, steroids
• hydrophobic
• consist of hydrocarbons

Question 3

phospholipids: features

Answer 3

• most abundant lipid in plasma membrane
• amphipathic (has both hydrophobic and hydrophilic regions)
• 2 fatty acids (tail) + phosphate group attached to glycerol (head)

Question 4

micelles:

Answer 4

• small objects forming naturally
• hydrophobic tails point inwards
• aid in transport and absorption of complex lipids and fat soluble vitamins (vit A)

Question 5

fluid mosaic model:

Answer 5

• membrane is a fluid structure with mosaic of various proteins embedded in it
• phospholipids in plasma membrane can move around in bilayer
• about as fluid as salad oil

Question 6

significance: cholesterol in warm/cool temps

Answer 6

• controls fluidity of membranes
• 37˚ restrains movement of phospholipids
• cool temp: prevents tight packing

Question 7

Frye and Edidin’s experiment:

Answer 7

• membrane fusion
• human and mouse membrane proteins labelled with fluorescent antibodies
• proteins intermixed

Question 8

carbohydrates found:

Answer 8

• exterior of membrane

Question 9

significance: ER and Golgi apparatus in building membrane

Answer 9

• determines asymmetrical distribution of proteins, lipids, associated carbohydrates in plasma membrane

Question 10

molecules which pass through membrane easily:

Answer 10

• gases (CO2, N2, O2)
• water
• small, uncharged nonpolar molecules (urea, ethanol)

Question 11

molecules which pass through membrane difficultly:

Answer 11

• charged polar molecules (amino acids, ATP)
• ions (K+, Mg2+, Ca2+, HCO3-, H2PO4)
• large uncharged nonpolar molecules (glucose)

Question 12

list membrane proteins:

Answer 12

• peripheral
• integral
• transmembrane

Question 13

peripheral protein:

Answer 13

• bound to surface f membrane

Question 14

integral protein: what type

Answer 14

• penetrate hydrophobic core

- amphipathic

Question 15

transmembrane protein:

Answer 15

• integral proteins which span membrane

Question 16

membrane proteins: types

Answer 16

• transport
• structural
• enzymes
• cell-to-cell interaction proteins
• cell communication

Question 17

hydrophobic domains in transmembrane proteins region of integral protein:

Answer 17

• stabilise it within lipid bilayer

Question 18

list six major functions of membrane proteins:

Answer 18

• transport
• enzyme activity
• signal transduction
• cell-cell recognition
• intercellular joining
• attachement to cytoskeleton and extracellular matrix (ECM)

Question 19

osmosis:

Answer 19

• diffusion of water across selectively permeable membrane

- moving from low solute conc. to higher

Question 20

hypotonic:

Answer 20

• lower solute conc. than intracellular fluid

- lysed (burst)

Question 21

isotonic:

Answer 21

• same solute conc. as intracellular fluid

Question 22

hypertonic:

Answer 22

• higher solute conc. compare to intracellular fluid (shrivelled)

Question 23

diffusion:

Answer 23

• small substances spread out evenly into available space

Question 24

facilitated diffusion:

Answer 24

• transport proteins speed up passive movement of molecule across plasma membrane
• channel proteins (ion channels) open/close responding to stimulus (gated channels)

Question 25

transport protein: and eg.

Answer 25

• allow passage of hydrophilic substances across membrane
• channel proteins: tunnel
• carrier proteins: bind to molecules and change shape to shuttle them across membrane
• specific to substance it moves

Question 26

list types of transport proteins:

Answer 26

• uniport

- co-transport (symport, antiport)

Question 27

uniport:

Answer 27

• single substance moved in single direction

Question 28

co-transport:

Answer 28

symport: 2 different substanced moved together same direction
antiport: 2 substances in both directions

Question 29

significance: aquaporins

Answer 29

• normally lipid bilayer blocks/ slows flow of polar molecules (water)
• aquaporins membrane channels allow water to cross cell membrane

Question 30

gated channels: trigger eg.

Answer 30

• some need to be triggered
• absence of acetylcholine, ion channel is closed
• if acetylcholine binds to receptor, channel opens

Question 31

active transport: eg

Answer 31

• requires energy ATP

- sodium potassium pump

Question 32

membrane potential:

Answer 32

• voltage difference across a membrane

Question 33

how is voltage created: and electrochemical gradient

Answer 33

• differences in distribution of positive/negative ions

two combined forces drive diffusion of ions across a membrane:

• chemical force (ionic conc. gradient)
• electrical force (effect of membrane potential on ionic movement)

Question 34

how ion pumps maintain membrane potential:

Answer 34

• electrogenic pump (transport protein) generates voltage across membrane
• animal: sodium potassium pump
• plants/bacteria/fungi: proton pump

Question 35

sodium potassium pump:

Answer 35

• active transport
• 3 sodium leave cell, 2 potassium enter
• 3 NA bind to pump (cytoplasmic side)
• ATP hydrolysis phosphorylates pump -> releases NA
• 2 K bind on extracellular side
• phosphate group released -> allow K in