Active Transport

Question 1

Describe active transport

Answer 1

movement of uncharged molecules or ions across the membrane against the concentration gradient or electrochemical gradient which requires an integral membrane protein and a source of energy

Question 2

What kind of molecules does active transport move?

Answer 2

uncharged molecules against the concentration gradient

and

ions against the electrical gradient

Question 3

What are the two requirements for active transport?

Answer 3

an integral membrane protein

a source of energy

Question 4

T or F: active transport does not require energy - why/why not?

Answer 4

FALSE

it requires energy because the molecules or ions are moving against a gradient

Question 5

What are the proteins that participate in active transport called?

Answer 5

pumps

Question 6

list the 3 types of active transport

Answer 6

primary active transport
secondary active transport
light-driven active transport

Question 7

What kind of pump is used in primary active transport?

Answer 7

ATP-driven pump

Question 8

Explain primary active transport

Answer 8

ATP hydrolysis is used to move a molecule against its electrochemical gradient

Question 9

What kind of pump is used in secondary active transport?

Answer 9

Coupled transporter

Question 10

Explain secondary active transport

Answer 10

As one molecule moves down the gradient, energy is released and stored in the gradient and then used to drive the movement of a second molecule against the electrochemical gradient

Question 11

Which type of active transport directly uses ATP?

Answer 11

primary

Question 12

What energy source does secondary transport use?

Answer 12

the stored energy in the gradient from one molecule moving down the gradient

Question 13

Describe uniporters

Answer 13

Transport proteins that move only one molecule at a time in one direction

Question 14

T or F: uniporters are involved in facilitated diffusion

Answer 14

true

Question 15

How many molecules do coupled transporters move?

Answer 15

two molecules

Question 16

Describe symporters

Answer 16

transport proteins that move two molecules at the same time in the SAME direction

Either both up the gradient or both down the gradient

Question 17

Describe antiporters

Answer 17

transport proteins that move two molecules at the same time in OPPOSITE directions

Question 18

What is a co-transported ion? give an example

Answer 18

An ion that when moved, its electrochemical gradient creates a large driving force for the active transport of a second molecule

ex. Na+ is a co-transported ion

Question 19

T or F: the greater the electrochemical gradient of the co-transported ion, the more the second molecule is pumped into the cell

Answer 19

true

Question 20

Why is Na+ usually a cotransporter?

Answer 20

it has a very strong gradient because it is very concentrated outside the cell and not much inside so it makes it a good driver of coupled active transport

Question 21

Compare & contrast between primary and secondary active transport

Answer 21

PRIMARY:

• always requires ATP (Exergonic)
• uniporters, symporters, antiporters
• always has ATPase activity
• uses one transport protein/complex even if more than one solute

SECONDARY:

• moves one solute against gradient (exergonic) and one solid with (endergonic)
• endergonic reaction driven by exergonic reaction (NO ATP)
• symport or antiport
• no ATP hydrolysis
• gradient for exergonic reaction set up by separate transporter protein/complex

Question 22

What kind of transport proteins can be involved in primary transport? secondary?

Answer 22

PRIMARY:
uniporters, symporters, or antiporters

SECONDARY:
symporters or antiporters

Question 23

Which kind of transport is driven by ATP hydrolysis? which isn’t?

Answer 23

Primary is

secondary isn’t

Question 24

How many transport proteins/complexes are used in primary transport? secondary?

Answer 24

PRIMARY: just one, even if more than one solute is involved

SECONDARY: always involves a separate transport protein or complex

Question 25

Explain the separate transporter protein/complex that secondary transport requires

Answer 25

In order for an ion to be transported against its gradient, a second transporter separate from the original transporter needs to be set up to maintain the co-transporter's passive gradient

Question 26

Why is a separate transport protein/complex important for secondary transport?

Answer 26

it maintains the gradient of the molecule that moves passively the passive movement of one of the molecules releases energy which is stored in the gradient and used to power the movement of the second molecule against its gradient

Question 27

Describe the structure of a transport protein?

Answer 27

10+ alpha helices that span the membrane with solute binding sites about midway through the membrane and only exposed to one side of the membrane at a time depending on the protein conformation

Question 28

Where are the binding sites located on a transport protein in regards to the membrane?

Answer 28

the transport protein spans the membrane and the binding sites are usually around the middle of the membrane

Question 29

T or F: transport proteins have binding sites that are exposed to both sides of the membrane at a time

Answer 29

FALSE only exposed to one side at a time and it depends on the conformation of the protein

Question 30

What are ATP-driven pumps also called?

Answer 30

ATPases

Question 31

What are the 3 types of ATPases/ATP-driven pumps?

Answer 31

P-type pumps ABC transporters V-type proton pump

Question 32

Describe the structure of ATP

Answer 32

adenine base bonded to a tri-phosphate ribose sugar

Question 33

What happens to ATP when water is added?

Answer 33

the bond between two terminal phosphates breaks and releases: ADP and inorganic phosphate

Question 34

What kind of pumps are included in the category of P-type pumps? ie., what kind of solutes do they move?

Answer 34

all cation pumps cations like H+, K+, Na+, Ca2+

Question 35

What is the main purpose of P-type pumps?

Answer 35

establishing and maintaining ion gradients across cell membranes

Question 36

How do P-type pumps function?

Answer 36

by phosphorylating themselves during the pumping cycle, a phosphate is transferred from ATP to the transport protein

Question 37

Where are P-type pumps located?

Answer 37

usually in eukaryotic plasma membranes

Question 38

Give examples of solutes P-pumps move

Answer 38

H+ Na+ / K+ Ca2+

Question 39

Give examples of P-type pumps

Answer 39

Na+ / K+ pump plant/fungus proton pump Ca2+ pumps of muscle cells H+ / K+ pump of mammalian stomach

Question 40

How do P-type pumps work?

Answer 40

Phosphorylation of a protein changes its conformation 1. PHOSPHORYLATION: phosphate added to amino acid hydroxyl groups = conformation change 2. DEPHOSPHORYLATION: phosphate is removed = conformation change

Question 41

What two enzymes are involved in phosphorylation of P-type pumps?

Answer 41

kinase and phosphatase

Question 42

Which enzyme is used to phosphorylate the P pump?

Answer 42

kinase

Question 43

Which enzyme is used to dephosphorylate the P pump?

Answer 43

phosphatase

Question 44

Is [Na+] higher or lower inside the cell? what about [K+]?

Answer 44

[Na+] is 10-30x lower inside cells compared to the outside [K+] is 10-30x higher inside cells compared to outside

Question 45

Where is the P-type Na+/K+ ATPase found?

Answer 45

in almost all animal cells

Question 46

Give examples of the differences in concentrations the P-type Na+/K+ ATPase is responsible for maintaining

Answer 46

Concentrations of ``` Na+ K+ H+ Ca2+ H+ Mg2+ Cl- ```

Question 47

In an average cell, about how much ATP is used for fuelling the Na+/K+ pump?

Answer 47

~33% Even more in neurons

Question 48

What is the cytoplasmic concentration of Na+? what is its extracellular concentration?

Answer 48

cytoplasmic: 5-15 mM EC: 145 mM

Question 49

What is the cytoplasmic concentration of K+? what is its extracellular concentration?

Answer 49

cytoplasmic: 140 mM EC: 5 mM

Question 50

What kind of pump is the Na+/K+ pump? what kind of transporter protein does it use?

Answer 50

P-type ATP driven pump that uses antiporters

Question 51

Describe how the Na+/K+ pump works?

Answer 51

1. it hydrolyzes ATP to ADP to self-phosphorylate with the organic phosphate released 2. transports 3 Na+ OUT and 2 K+ IN for every ATP hydrolyzed (every cycle)

Question 52

Which direction are Na+ ions pumped? K+?

Answer 52

Na+ pumped OUT of cell | K+ pumped INTO of cell

Question 53

How many Na+ ions are pumped out and how many K+ ions pumped in?

Answer 53

3 Na+ 2 K+ for every ATP hydrolyzed

Question 54

What does the unequal pumping of Na+ and K+ contribute to?

Answer 54

the membrane potential

Question 55

What kind of pump is the Na+/K+ pump as a result of the unequal charges inside and outside the cell?

Answer 55

electrogenic pump because it generates an electrical potential across the gradient due to the inside being less positive than the outside

Question 56

How many conformations does the Na+/K+ ATPase have?

Answer 56

2 conformations: E1 E2

Question 57

Describe the E1 conformation of the Na+/K+ ATPase

Answer 57

open to INSIDE of cell high affinity for Na+ ions Low affinity for K+ ions

Question 58

Describe the E2 conformation of the Na+/K+ ATPase

Answer 58

open to OUTSIDE of cell high affinity for K+ ions low affinity for Na+ ions

Question 59

How does the Na+/K+ ATPase switch between its two conformations?

Answer 59

by phosphorylation via kinase by hydrolysis of ATP and dephosphorylation via phosphatase

Question 60

Describe electrogenic pump and give an example

Answer 60

a pump that helps generate the negative membrane potential of most cells ex. the Na+/K+ ATPase

Question 61

Which Na+/K+ ATPase conformation has high affinity for Na+? for K+?

Answer 61

E1 has high affinity for Na+ E2 has high affinity for K+

Question 62

Which direction is the E1 conformation open to?

Answer 62

inside the cell

Question 63

Which direction is the E2 conformation open to?

Answer 63

outside the cell

Question 64

What are the main steps of the Na+/K+ ATPase?

Answer 64

1. in E1: open to inside of cell with high affinity for Na+ 2. Na+ binds 3. hydrolysis of ATP releases phosphate to bind to pump= phosphorylation 4. conformational change from E1 to E2 = pump now faces outside of cell 5. Na+ leaves to outside because affinity changes 6. in E2: affinity for K+ is high 7. K+ binds 8. Dephosphorylation = phosphate leaves causing conformational change back to E1 9. In E1: pump is open inside and has low affinity for K+ so K+ leaves into cell 10. starts again

Question 65

What kind of pump is common in epithelial cells of the intestine?

Answer 65

Symporters driven by Na+ | with amino acid or sugar usually

Question 66

What is the second molecule moved by the symporters in epithelial cells of the intestine?

Answer 66

amino acid or sugar

Question 67

How do the pumps in the epithelial cells of the intestine help us absorb food?

Answer 67

the symporters that move amino acids or sugar from food are driven by the Na+ gradient

Question 68

Describe transcellular transport

Answer 68

movement of a solute from the lumen across the entire epithelial layer into the blood

Question 69

What kind of transporters are on the apical side of the epithelial cells of the intestine?

Answer 69

active transporters (usually Na+ symporters like the Na+/glucose symporter)

Question 70

What is the function of the transporters on the apical side of the epithelial intestine cells?

Answer 70

build the concentration of sugars and amino acids in the cell

Question 71

What structure on the apical side of intestine epithelial cells helps the transporters?

Answer 71

microvilli create a lot of space for transporters

Question 72

What kind of transporters are on the basal side of intestinal epithelial cells? give a specific example

Answer 72

uniporters, specifically GLUT2 (glucose transporter)

Question 73

How do transporters on the basal side of epithelial intestine cells function?

Answer 73

uniporters like GLUT2 allow nutrients to leave the cell PASSIVELY towards the blood

Question 74

Is the movement of nutrients from the intestine epithelial cell to the blood active or passive?

Answer 74

passive

Question 75

How many Na+ and glucose molecules does the Na+/glucose symporter bind on WHICH side of the epithelial cell?

Answer 75

2 Na+ 1 glucose on the extracellular side because the Na+/glucose symporter is on the apical side of the epithelial cell

Question 76

How is the electrochemical gradient of Na+ maintained so that the transcellular transport across epithelial intestine cells never dissipates?

Answer 76

the Na+/K+ pump on the basal side of the cell moves the Na+ molecules that were brought in by the Na+/glucose transporter back out of the cell on the basal side