B2.1 - membranes and membrane transport

Question 1

extracellular

Answer 1

outside of the cell

Question 2

intracellular

Answer 2

inside the cell

Question 3

passive transport

Answer 3

movement of molecules using kinetic energy of the molecule itself, against the concentration gradient

Question 4

phagocyte

Answer 4

white blood cell that engulfs pathogens by endocytosis and destroys them using enzymes and other chemicals

Question 5

phagocytosis

Answer 5

ingestion of solid substances via endocytosis

Question 6

pinocytosis

Answer 6

ingestion of liquids or solutions via endocytosis

Question 7

transmembrane

Answer 7

cell component that extends from one side of a membrane to the other, across the hydrophobic core

Question 8

vesicle

Answer 8

small spheres of membrane that move material within the cell

Question 9

what is the basis of cell membranes?

Answer 9

phospholipids and other amphipathic lipids naturally form sheet-like bilayers in water

Question 10

how does the lipid bilayer act as a barrier?

Answer 10

hydrophobic carbon chains (core membrane) have low permeability to large and hydrophilic molecules (ions and polar) so acts as a barrier between aqueous solutions

Question 11

what happens when the phospholipid molecules are tightly packed?

Answer 11

• large molecules cannot pass through
• small, polar or charged molecules don’t readily pass through hydrophobic core

Question 12

diffusion

Answer 12

passive movement of molecules down a concentration gradient from and area of high to low concentration

Question 13

why does diffusion occur and what substances does it involve?

Answer 13

small, non-polar or uncharged molecules can move between phospholipids
- oxygen, carbon dioxide, steroid hormones

Question 14

how are membrane proteins diverse?

Answer 14

• structure - large combinations of amino acid sequences
• location
• function

Question 15

integral proteins

Answer 15

embedded in one or both of lipid layers in the membrane

Question 16

transmembrane proteins

Answer 16

proteins that extend from the fluid on one side of the membrane to the other side

Question 17

peripheral proteins

Answer 17

proteins attached to one or other surface of the bilayer

Question 18

osmosis

Answer 18

random, passive movement from an area of low solute concentration to high solute concentration across a partially permeable membrane until equilibrium is reached

Question 19

hypotonic

Answer 19

low solute concentration solution

Question 20

hypertonic

Answer 20

high solute concentration solution

Question 21

isotonic

Answer 21

equilibrium solution
- no net movement

Question 22

aquaporins

Answer 22

allow water molecules to move through a pore in their structure, facilitating water molecule movement across a membrane

Question 23

facilitated diffusion

Answer 23

passive transport where diffusion occurs through a channel protein

Question 24

channel proteins

Answer 24

have pores which specific molecules can pass through dependent on size and charge

Question 25

what are 2 examples of channel proteins?

Answer 25

ligand-gated channels - open when a specific signalling molecule binds to the channel protein
voltage-gated channel - open and closed as the charge difference across a membrane changes

Question 26

what is the maximum rate of facilitated diffusion?

Answer 26

depends on the number of channel proteins
- at first, as concentration of ions increase, rate of facilitate diffusion increases
- however this plateaus when channels become saturated with ions

Question 27

pump proteins

Answer 27

• use energy from ATP to transfer specific particles across membranes
• can move particles against a concentration gradient meaning equilibrium isn’t reached
• specific to one type of molecule

Question 28

what are benefits of active transport?

Answer 28

• allows uptake of molecules even when extracellular concentrations are very low
• allows most substances to be absorbed, building up or maintaining specific concentration

Question 29

what is the selectivity of simple diffusion?

Answer 29

• not selective
• depends on size and hydrophobic/hydrophilic properties
• small and non-polar molecules can pass

Question 30

what is the selectivity of facilitated diffusion?

Answer 30

• selective through the use of integral proteins embedded in the membrane
• depends on size, shape and charge
• ions diffuse when channel proteins or protein pumps are open
• large and polar molecules can pass

Question 31

glycoproteins

Answer 31

carbohydrate structures linked to proteins

Question 32

glycolipids

Answer 32

carbohydrate structures linked to lipids

Question 33

where is the carbohydrate located?

Answer 33

extracellular sides of the membrane

Question 34

what is the role of glycoproteins and glycolipids?

Answer 34

• cell adhesion
• cell recognition - due to diverse carbohydrate chains that determine tissue type for transplants

Question 35

what are the 3 main components of the fluid mosaic model?

Answer 35

fluid phospholipids - allow movement of proteins within the membrane
hydrophilic regions - occur where they are exposed to the cytoplasm, phospholipid heads to extracellular fluid
hydrophobic regions - where they are exposed to the membrane bilayer core or phospholipid tails

Question 36

what are examples of the hydrophilic regions?

Answer 36

peripheral membranes, channel protein pores, carbohydrate part of glycoproteins

Question 37

what are examples of the hyrophobic regions?

Answer 37

cholesterol, integral proteins, transmembrane proteins