Active Transport: Protein-Mediated Movement Up the Gradient

Question 1

How does active transport differ from facilitated diffusion?

Answer 1

active transport makes it possible to move solutes up a concentration gradient, or against an electrochemical gradient (away from equilibrium)

Question 2

active transport always requires?

Answer 2

an input of energy

Question 3

active transport couples…

Answer 3

endergonic transport to an exergonic process, usuallu ATP hydrolysis

Question 4

Active transport performs three important cellular functions..

Answer 4

1. uptake of essential nutrients
2. removal of waste
3. maintenance of non equilibrium concentrations of certain ions

Question 5

active transport allows..

Answer 5

the creation and maintenance of an internal cellular environment that differs greatly from the surrounding environment

Question 6

in active transport, diffusion is non directional with respect to the membrane…

Answer 6

diffusion is directed by concentrations of the transported substances. ie active transport have an intrinsic directionality

Question 7

examples of active transport?

Answer 7

1. Na+/K+ pump in animal cells
2. The Na+/glucose symporter
3. Light driven proton transport

Question 8

How can active transport mechanisms be divided? What are the different mechanisms?

Answer 8

Can be divided based on the sources of energy and whether or not two solutes are transported at the same time. Either direct or indirect

Question 9

What is indirect active transport?

Answer 9

the accumulation of solute molecules or ions on one side of the membrane is coupled directly to an exergonic chemical reaction, most commonly the hydrolysis of ATP

Question 10

indirect active transport:

transport proteins driven directly by ATP hydrolysis are called..

Answer 10

transport ATPases, or ATPase pumps

Question 11

direct active transport depends on…what are the differences and what are the similarities?

Answer 11

Four types of transport ATPases, which differ in size, structure, mechanism, locomotion, and roles, all use the energy of ATP hydrolysis to transport solutes against a concentration gradient or electrochemical potential

Question 12

What are the four types of transport ATPases used in direct active tranport?

Answer 12

1. P-type ATPase (P for phosphorylation)
2. V-type ATPase ( V for vacuole)
3. F-type ATPase ( F for factor)
4. ABC-type/ATP Binding Cassette transporters

Question 13

How do P-type ATPases work in direct active transport?

Answer 13

P-type ATPases are reversibly phosphorylated by ATP as part of the transport mechanism, with a specific aspartic acid residue becoming phosphorylated in each case

Question 14

structure of P-Type ATPases involved in direct active trasport?

Answer 14

they have 8-10 transmembrane segments in a single polypeptide, which crosses the membrane multiple times

Question 15

Where are the P-Type ATPases located that are involved in direct active transport?

Answer 15

most P-type pumps are located in the plasma membrane where they are responsible for maintaining an ion gradient across the membrane (example Na+/k+ pump)

Question 16

What do the V-type ATPases do in direct active transport?

Answer 16

pump protons in to such organelles as vacuoles, vesicles, lysosomes, endosomes, and the golgi complex

Question 17

Structure of V-type ATPases used in direct active transport?

Answer 17

• have two multisubunit components
  1. an integral component embedded within the membrane
  2. a peripheral component that juts out from the membrane surface - contains ATP binding site

Question 18

Where are the F-Type ATPases used in direct active transport located?

Answer 18

Found in bacteria, mitochondria, choloroplasts

Question 19

What are F-type ATPases involved in and what is the structure?

Answer 19

involved in proton transport and have two multisubunit components

1. integral membrane component, called Fo, which is a transmembrane pore for proteins
2. peripheral membrane component, called F1, which includes the ATP binding site

Question 20

How do F-Type ATPases work in direct active transport?

Answer 20

They can use the energy of ATP hydrolysis to pump protons against their electrochemical gradient

Question 21

How can F-type ATPases facilitate the reverse process of what they do in direct active transport?

Answer 21

ATP is synthesized, driven by the exergonic flow of proteins down their gradients: ATP synthases
ATP can be used as an energy source to generate ion gradients: can be used as an energy source to synthesize ATP

Question 22

What does the “cassette” part in ABC (ATP binding cassette) transporters mean? (direct active transport)

Answer 22

the cassette describes the catalytic domain of the protein that binds ATP as an integral part of the transport process

Question 23

What is the ABC transporter involved in?

Answer 23

• Importers involved in the uptake of nutrients

- exporters pump antibiotics or drugs out of the cell; drug resistance

Question 24

ABC transporters have how many domains? (direct active transport) where are they?

Answer 24

-four domains: on separate polypeptides in most cases
two are highly hydrophobic and are embedded in the membrane
other two are peripheral and are associated with the cytoplasmic side of the membrane

Question 25

relationship between ABC transporters and human tumors? (MDR)

Answer 25

some human tumors are resistant to drugs that normally inhibit growth of tumors: the resistant cells have high concentration of ABC transporters called MDR - multi drug resistant transporter proteins

Question 26

What is indirect active transport?

Answer 26

when favorable movement of one solute down its gradient drives the unfavorable movement of the other up its gradient

• inward transport of molecules up their concentration gradient is often coupled to, and driven by, the simultaneous inward movement of Na+ ions or protons down their electrochemical gradients
• not powered by ATP hydrolysis
• can be symport or antiport

Question 27

Symport mechanisms of indirect active transport:
most cells continuously pump either Na+ ions or protons out of the cell (Na+/K+ pump in animals) what happens b/c of this ?

Answer 27

• resulting high extracellular concentrations of Na+ can be harnessed as a power source instead of ATP
• indirectly related to ATP b/c the pump that maintains the Na+ ion gradient is driven by ATP

Question 28

Proton gradients drive indirect active transport in many organisms: most organisms rely on what? what do fugal and plants use?

Answer 28

proton gradients rather than the Na+ gradients (animal specific)
- fungal and plants use protons symport for the uptake that creates and maintains the proton electrochemica potential