B2.1 Membranes and membrane transport

Question 1

Function of membrane (2)

Answer 1

separate cytoplasm from external environment

separate interior of organelles from each other + from cytosol

Question 2

Structure of phospholipids (3)

Answer 2

same as triglyceride but phosphate joins to 3rd OH instead of fatty acid

2 non-polar fatty acid chains

amphipathic molecules - hydrophilic phosphate head, hydrophobic fatty acids

Question 3

Define amphipathic molecules

Answer 3

molecules with both hydrophobic and hydrophillic properties

Question 4

Reasons for formation of phospholipid bilayer or micelle (2)

Answer 4

hydrophobic tails point inward + away from water/aqueous environment

hydrophilic heads point outward + towards aqueous environment

Question 5

Purpose of cell membrane (2)

Answer 5

separate internal components/organelles of cell from outside environment

regulate movement of substances

Question 6

Lipid bilayers as barriers (3)

Answer 6

lipid-soluble non-polar molecules are permeable

ions are impermeable

large uncharged polar molecules (glucose) are mostly impermeable

Question 7

Why are ions impermeable to a lipid bilayer (2)

Answer 7

ions have + and - charges so will interact will polar water

hydrophobic tails of bilayer repel hydrophilic ions

Question 8

Why are large uncharged polar molecules mostly impermeable to a lipid bilayer (2)

Answer 8

mostly hydrophillic due to being polar

hydrophobic tails of bilayer repel hydrophillic molecules

Question 9

Why are lipid-soluble non-polar molecules permeable to a lipid bilayer

Answer 9

no polarity = not repelled by hydrophobic tails

Question 10

Factors which affect permeability of biological membranes (2)

Answer 10

size of molecule - smaller molecules more likely to pass

hydrophobic nature - hydrophobic molecules more likely to pass through instead of polar molecules

Question 11

Define simple diffusion

Answer 11

movement of molecules from a region of high concentration to a region of low concentration down a concentration gradient

Question 12

Movement of oxygen in body as an example of simple diffusion (3)

Answer 12

red blood cells transport oxygen from lungs to body’s cells

oxygen diffuses from alveoli to RBCs in capillaries surrounding alveoli

oxygen diffuses from high concentration in RBC to low concentration in cells

Question 13

Movement of carbon dioxide in body as an example of simple diffusion (3)

Answer 13

CO2 diffuses from cells (high CO2 concentration) to blood (lower CO2 concentration)

CO2 reaches lungs

CO2 diffuses from blood (high CO2 concentration) to alveoli (low CO2 concentration)

Question 14

2 types of membrane proteins (2)

Answer 14

integral proteins

peripheral proteins

Question 15

Features of integral proteins (3)

Answer 15

embedded in lipid bilayer

channel proteins - hydrophilic interior + hydrophobic exterior allows charged particles to pass through by diffusion

carrier proteins - involved in active + passive transport by changing shape

Question 16

Features of peripheral proteins (3)

Answer 16

hydrophilic

found on surface of membrane

interact with hydrophilic regions of integral proteins + phospholipid heads

Question 17

Functions of membrane proteins (4)

Answer 17

Transport

Recognition

Receptors

Enzymes

Question 18

Transport as a function of membrane proteins (2)

Answer 18

facilitate movement of molecules inside + outside cell

channel + carrier proteins

Question 19

Recognition as a function of membrane proteins (2)

Answer 19

help in cell-cell recognition

distinguishes immune system from self and non-self cells

Question 20

Receptors as a function of membrane proteins (2)

Answer 20

bind to signaling molecules like hormones + neurotransmitters

binding triggers a chain of intracellular reactions

Question 21

Enzymes as a function of membrane proteins

Answer 21

membrane proteins can catalyse reactions

Question 22

Structure of aquaporins (2)

Answer 22

4 subunit channels

inner channels are hydrophillic

Question 23

Function of aquaporins (2)

Answer 23

allows passage of water through cell membrane

bidirectional - water can flow in from either direction (depending on CG)

Question 24

Define facilitated diffusion

Answer 24

movement of particles from HC to LC facilitated/assisted by transport proteins

Question 25

Selectivity of ion protein channels (2)

Answer 25

pore size specific to certain ions hydrophillic interior of channel proteins are specific to particular ions

Question 26

Opening/closing of ion protein channels (3)

Answer 26

voltage-gated - respond to changes in voltage ligand-gated - respond to binding of substance respond to pressure

Question 27

Structure of pump proteins (4)

Answer 27

ATP binds to carrier protein protein undergoes a conformational change + transfers molecules to the other side of the membrane once transported, phosphate groups leaves protein restored to original shape

Question 28

Function of active transport for protein pumps (3)

Answer 28

take up essential nutrients remove waste material from cell maintain correct ion concentrations inside cells

Question 29

Define selective permeabiltiy

Answer 29

property of cell membranes that allow certain molecules to enter a cell

Question 30

Structure of glycolipids (4)

Answer 30

covalent bonding of carbohydrates to lipids ampiphatic located on external surface of membrane carbohydrate extends outside of membrane

Question 31

Structure of glycoproteins (2)

Answer 31

covalent bonding of carbohydrate chains to protein molecules carbohydrate group sticks out into the extracellular environment

Question 32

Functions of glycoproteins +glycolipids

Answer 32

cell recognition

Question 33

Cell recognition of glycoproteins + glycolipids (2)

Answer 33

act as "markers" on cell surface help cell to cell communication

Question 34

Cell adhesion of glycoproteins + glycolipids

Answer 34

help cells to bind to other cells

Question 35

Cell signalling of glycoproteins + glycolipids

Answer 35

act as receptors for enzymes + molecules in cell signalling

Question 36

Structure of saturated fats in membranes (3)

Answer 36

no kinks in chains chains fit together better higher melting points

Question 37

Function of saturated fats in membranes

Answer 37

make membrane denser + more rigid

Question 38

Structure of unsaturated fats in membranes

Answer 38

have kinks in their fatty acid chains lower melting points

Question 39

Function of unsaturated fats in membranes (2)

Answer 39

prevent lipids from packign together maintains fluidity in the membrane

Question 40

Example of adaptation in membrane composition to environment (2)

Answer 40

Cold-blooded organisms increase proportion of unsaturated fatty acids in membranes regulating the fluiditity of membranes

Question 41

Structure of cholesterol (2)

Answer 41

4 steroid rings + hydrocarbon chain - hydrophobic polar hydroxyl group - hydrophillic

Question 42

Location of cholesterol (2)

Answer 42

hydrophobic region attaches/interacts with hydrophobic phospholipid tail hydrophillic region attaches/interacts with hydrophillic phospholipid head

Question 43

Function of cholesterol in lipid bilayer (3)

Answer 43

low temperatures - cholesterol prevents fatty acid chains of the phospholipids from fitting closely together prevents membranes from freezing high temperatures - cholesterol reduces fluidity

Question 44

Define endocytosis (3)

Answer 44

moves particles into cell cell membrane engulfs particles membrane pinches off to form vesicle with particles

Question 45

Examples of endocytosis (2)

Answer 45

phagocytosis - white blood cells engulfing pathogens pinocytosis - cells takes in extracellular fluid

Question 46

Define exocytosis (3)

Answer 46

moves particles out of cell vesicles move to membrane + fuse to it particles inside released

Question 47

Examples of exocytosis (2)

Answer 47

proteins in golgi apparatus released in vesicles waste products secreted by cell

Question 48

Function of CAM cells (cell-adhesion molecules)

Answer 48

allow cells to bind together to form tissues

Question 49

How CAM cells prevent cancer (2)

Answer 49

adhesion - cells stay stuck together + behave normally signals to cells to stop dividing