Topic 1.4: Membrane Transport

Question 1

What are the two qualities of cellular membranes?

Answer 1

semi-permeable and selective

Question 2

Define semi-permeable in terms of the membrane

Answer 2

only certain materials may freely cross – large and charged substances are typically blocked

Question 3

Define selective in terms of the membrane

Answer 3

membrane proteins may regulate the passage of material that cannot freely cross

Question 4

Define passive transport

Answer 4

involves the movement of material along a concentration gradient (high concentration ⇒ low concentration)

Question 5

What involves the movement of material along a concentration gradient (high concentration ⇒ low concentration)?

Answer 5

passive transport

Question 6

What are the 3 main types of passive transport?

Answer 6

simple diffusion, osmosis, and facilitated diffusion

Question 7

Define simple diffusion

Answer 7

movement of small or lipophilic molecules (e.g. O2, CO2, etc.)

Question 8

Define osmosis

Answer 8

the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration (until equilibrium is reached)

Question 9

Define facilitated diffusion

Answer 9

the passive movement of molecules across the cell membrane via the aid of a membrane protein

Question 10

Define active transport

Answer 10

involves the movement of materials against a concentration gradient (low concentration ⇒ high concentration)

Question 11

What involves the movement of materials against a concentration gradient (low concentration ⇒ high concentration)?

Answer 11

active transport

Question 12

Define primary (direct) active transport

Answer 12

Involves the direct use of metabolic energy (e.g. ATP hydrolysis) to mediate transport

Question 13

Define secondary (indirect) active transport

Answer 13

Involves coupling the molecule with another moving along an electrochemical gradient

Question 14

Define diffusion

Answer 14

the net movement of molecules from a region of high concentration to a region of low concentration

Question 15

What are the 3 factors that affect the rate of diffusion?

Answer 15

temperature, molecular size, and steepness of gradient

Question 16

Define osmolarity

Answer 16

a measure of solute concentration, as defined by the number of osmoles of a solute per litre of solution (osmol/L)

Question 17

Define hypertonic

Answer 17

Solutions with a relatively higher osmolarity are categorised as hypertonic (high solute concentration ⇒ gains water)

Question 18

Define hypotonic

Answer 18

Solutions with a relatively lower osmolarity are categorised as hypotonic (low solute concentration ⇒ loses water)

Question 19

Define isotonic

Answer 19

Solutions that have the same osmolarity are categorised as isotonic (same solute concentration ⇒ no net water flow)

Question 20

Define the sodium-potassium pump

Answer 20

An integral protein that exchanges 3 sodium ions (moves out of cell) with two potassium ions (moves into cell)

Question 21

What is the first step of the sodium-potassium pump?

Answer 21

Three sodium ions bind to intracellular sites on the sodium-potassium pump

Question 22

After the Three sodium ions bind to intracellular sites on the sodium-potassium pump What is the next step of the sodium-potassium pump?

Answer 22

A phosphate group is transferred to the pump via the hydrolysis of ATP

Question 23

After A phosphate group is transferred to the pump via the hydrolysis of ATP What is the next step of the sodium-potassium pump?

Answer 23

The pump undergoes a conformational change, translocating sodium across the membrane

Question 24

After The pump undergoes a conformational change, translocating sodium across the membrane What is the next step of the sodium-potassium pump?

Answer 24

The conformational change exposes two potassium binding sites on the extracellular surface of the pump

Question 25

After The conformational change exposes two potassium binding sites on the extracellular surface of the pump What is the next step of the sodium-potassium pump?

Answer 25

The phosphate group is released which causes the pump to return to its original conformation

Question 26

After The phosphate group is released which causes the pump to return to its original conformation What is the next step of the sodium-potassium pump?

Answer 26

This translocates the potassium across the membrane, completing the ion exchange

Question 27

What is the first step of vesicular transport?

Answer 27

Materials are transported from the ER when the membrane bulges and then buds to create a vesicle surrounding the material

Question 28

After Materials are transported from the ER when the membrane bulges and then buds to create a vesicle surrounding the material What is the next step to vesicular transport?

Answer 28

The vesicle is then transported to the Golgi apparatus and fuses to the internal (cis) face of the complex

Question 29

After The vesicle is then transported to the Golgi apparatus and fuses to the internal (cis) face of the complex What is the next step to vesicular transport?

Answer 29

Materials move via vesicles from the internal cis face of the Golgi to the externally oriented trans face

Question 30

After Materials move via vesicles from the internal cis face of the Golgi to the externally oriented trans face What is the next step to vesicular transport?

Answer 30

While within the Golgi apparatus, materials may be structurally modified (e.g. truncated, glycosylated, etc.)

Question 31

After While within the Golgi apparatus, materials may be structurally modified (e.g. truncated, glycosylated, etc.) What is the next step to vesicular transport?

Answer 31

Material sorted within the Golgi apparatus will either be secreted externally or may be transported to the lysosome

Question 32

After Material sorted within the Golgi apparatus will either be secreted externally or may be transported to the lysosome What is the next step to vesicular transport?

Answer 32

Vesicles containing materials destined for extracellular use will be transported to the plasma membrane

Question 33

After Vesicles containing materials destined for extracellular use will be transported to the plasma membrane What is the next step to vesicular transport?

Answer 33

The vesicle will fuse with the cell membrane and its materials will be expelled into the extracellular fluid

Question 34

Define endocytosis

Answer 34

The process by which large substances (or bulk amounts of smaller substances) enter the cell without crossing the membrane

Question 35

What is The process by which large substances (or bulk amounts of smaller substances) enter the cell without crossing the membrane?

Answer 35

endocytosis

Question 36

What is the first step of endocytosis?

Answer 36

An invagination of the membrane forms a flask-like depression which envelopes the extracellular material

Question 37

After An invagination of the membrane forms a flask-like depression which envelopes the extracellular material, what is the next step of endocytosis?

Answer 37

The invagination is then sealed off to form an intracellular vesicle containing the material

Question 38

What are the two main types of endocytosis?

Answer 38

phagocytosis and pinocytosis

Question 39

Define phagocytosis

Answer 39

The process by which solid substances are ingested (usually to be transported to the lysosome)

Question 40

Define pinocytosis

Answer 40

The process by which liquids / dissolved substances are ingested (allows faster entry than via protein channels)

Question 41

Define exocytosis

Answer 41

The process by which large substances (or bulk amounts of small substances) exit the cell without crossing the membrane

Question 42

What happens during exocytosis?

Answer 42

Vesicles (typically derived from the Golgi) fuse with the plasma membrane, expelling their contents into the extracellular environment

Question 43

Define kidney dialysis

Answer 43

involves the external filtering of blood in order to remove metabolic wastes in patients with kidney failure