Active Transport Flashcards
Describe active transport
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
What kind of molecules does active transport move?
uncharged molecules against the concentration gradient
and
ions against the electrical gradient
What are the two requirements for active transport?
an integral membrane protein
a source of energy
T or F: active transport does not require energy - why/why not?
FALSE
it requires energy because the molecules or ions are moving against a gradient
What are the proteins that participate in active transport called?
pumps
list the 3 types of active transport
primary active transport
secondary active transport
light-driven active transport
What kind of pump is used in primary active transport?
ATP-driven pump
Explain primary active transport
ATP hydrolysis is used to move a molecule against its electrochemical gradient
What kind of pump is used in secondary active transport?
Coupled transporter
Explain secondary active transport
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
Which type of active transport directly uses ATP?
primary
What energy source does secondary transport use?
the stored energy in the gradient from one molecule moving down the gradient
Describe uniporters
Transport proteins that move only one molecule at a time in one direction
T or F: uniporters are involved in facilitated diffusion
true
How many molecules do coupled transporters move?
two molecules
Describe symporters
transport proteins that move two molecules at the same time in the SAME direction
Either both up the gradient or both down the gradient
Describe antiporters
transport proteins that move two molecules at the same time in OPPOSITE directions
What is a co-transported ion? give an example
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
T or F: the greater the electrochemical gradient of the co-transported ion, the more the second molecule is pumped into the cell
true
Why is Na+ usually a cotransporter?
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
Compare & contrast between primary and secondary active transport
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
What kind of transport proteins can be involved in primary transport? secondary?
PRIMARY:
uniporters, symporters, or antiporters
SECONDARY:
symporters or antiporters
Which kind of transport is driven by ATP hydrolysis? which isn’t?
Primary is
secondary isn’t
How many transport proteins/complexes are used in primary transport? secondary?
PRIMARY: just one, even if more than one solute is involved
SECONDARY: always involves a separate transport protein or complex
Explain the separate transporter protein/complex that secondary transport requires
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
Why is a separate transport protein/complex important for secondary transport?
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
Describe the structure of a transport protein?
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
Where are the binding sites located on a transport protein in regards to the membrane?
the transport protein spans the membrane and the binding sites are usually around the middle of the membrane
T or F: transport proteins have binding sites that are exposed to both sides of the membrane at a time
FALSE
only exposed to one side at a time and it depends on the conformation of the protein
What are ATP-driven pumps also called?
ATPases
What are the 3 types of ATPases/ATP-driven pumps?
P-type pumps
ABC transporters
V-type proton pump
Describe the structure of ATP
adenine base bonded to a tri-phosphate ribose sugar
What happens to ATP when water is added?
the bond between two terminal phosphates breaks and releases:
ADP and inorganic phosphate
What kind of pumps are included in the category of P-type pumps? ie., what kind of solutes do they move?
all cation pumps
cations like H+, K+, Na+, Ca2+
What is the main purpose of P-type pumps?
establishing and maintaining ion gradients across cell membranes
How do P-type pumps function?
by phosphorylating themselves
during the pumping cycle, a phosphate is transferred from ATP to the transport protein
Where are P-type pumps located?
usually in eukaryotic plasma membranes
Give examples of solutes P-pumps move
H+
Na+ / K+
Ca2+
Give examples of P-type pumps
Na+ / K+ pump
plant/fungus proton pump
Ca2+ pumps of muscle cells
H+ / K+ pump of mammalian stomach
How do P-type pumps work?
Phosphorylation of a protein changes its conformation
- PHOSPHORYLATION: phosphate added to amino acid hydroxyl groups = conformation change
- DEPHOSPHORYLATION: phosphate is removed = conformation change
What two enzymes are involved in phosphorylation of P-type pumps?
kinase and phosphatase
Which enzyme is used to phosphorylate the P pump?
kinase
Which enzyme is used to dephosphorylate the P pump?
phosphatase
Is [Na+] higher or lower inside the cell? what about [K+]?
[Na+] is 10-30x lower inside cells compared to the outside
[K+] is 10-30x higher inside cells compared to outside
Where is the P-type Na+/K+ ATPase found?
in almost all animal cells
Give examples of the differences in concentrations the P-type Na+/K+ ATPase is responsible for maintaining
Concentrations of
Na+ K+ H+ Ca2+ H+ Mg2+ Cl-
In an average cell, about how much ATP is used for fuelling the Na+/K+ pump?
~33%
Even more in neurons
What is the cytoplasmic concentration of Na+? what is its extracellular concentration?
cytoplasmic: 5-15 mM
EC: 145 mM
What is the cytoplasmic concentration of K+? what is its extracellular concentration?
cytoplasmic: 140 mM
EC: 5 mM
What kind of pump is the Na+/K+ pump? what kind of transporter protein does it use?
P-type ATP driven pump that uses antiporters
Describe how the Na+/K+ pump works?
- it hydrolyzes ATP to ADP to self-phosphorylate with the organic phosphate released
- transports 3 Na+ OUT and 2 K+ IN for every ATP hydrolyzed (every cycle)
Which direction are Na+ ions pumped? K+?
Na+ pumped OUT of cell
K+ pumped INTO of cell
How many Na+ ions are pumped out and how many K+ ions pumped in?
3 Na+
2 K+
for every ATP hydrolyzed
What does the unequal pumping of Na+ and K+ contribute to?
the membrane potential
What kind of pump is the Na+/K+ pump as a result of the unequal charges inside and outside the cell?
electrogenic pump
because it generates an electrical potential across the gradient due to the inside being less positive than the outside
How many conformations does the Na+/K+ ATPase have?
2 conformations:
E1
E2
Describe the E1 conformation of the Na+/K+ ATPase
open to INSIDE of cell
high affinity for Na+ ions
Low affinity for K+ ions
Describe the E2 conformation of the Na+/K+ ATPase
open to OUTSIDE of cell
high affinity for K+ ions
low affinity for Na+ ions
How does the Na+/K+ ATPase switch between its two conformations?
by phosphorylation via kinase by hydrolysis of ATP and dephosphorylation via phosphatase
Describe electrogenic pump and give an example
a pump that helps generate the negative membrane potential of most cells
ex. the Na+/K+ ATPase
Which Na+/K+ ATPase conformation has high affinity for Na+? for K+?
E1 has high affinity for Na+
E2 has high affinity for K+
Which direction is the E1 conformation open to?
inside the cell
Which direction is the E2 conformation open to?
outside the cell
What are the main steps of the Na+/K+ ATPase?
- in E1: open to inside of cell with high affinity for Na+
- Na+ binds
- hydrolysis of ATP releases phosphate to bind to pump= phosphorylation
- conformational change from E1 to E2 = pump now faces outside of cell
- Na+ leaves to outside because affinity changes
- in E2: affinity for K+ is high
- K+ binds
- Dephosphorylation = phosphate leaves causing conformational change back to E1
- In E1: pump is open inside and has low affinity for K+ so K+ leaves into cell
- starts again
What kind of pump is common in epithelial cells of the intestine?
Symporters driven by Na+
with amino acid or sugar usually
What is the second molecule moved by the symporters in epithelial cells of the intestine?
amino acid or sugar
How do the pumps in the epithelial cells of the intestine help us absorb food?
the symporters that move amino acids or sugar from food are driven by the Na+ gradient
Describe transcellular transport
movement of a solute from the lumen across the entire epithelial layer into the blood
What kind of transporters are on the apical side of the epithelial cells of the intestine?
active transporters (usually Na+ symporters like the Na+/glucose symporter)
What is the function of the transporters on the apical side of the epithelial intestine cells?
build the concentration of sugars and amino acids in the cell
What structure on the apical side of intestine epithelial cells helps the transporters?
microvilli create a lot of space for transporters
What kind of transporters are on the basal side of intestinal epithelial cells? give a specific example
uniporters, specifically GLUT2 (glucose transporter)
How do transporters on the basal side of epithelial intestine cells function?
uniporters like GLUT2 allow nutrients to leave the cell PASSIVELY towards the blood
Is the movement of nutrients from the intestine epithelial cell to the blood active or passive?
passive
How many Na+ and glucose molecules does the Na+/glucose symporter bind on WHICH side of the epithelial cell?
2 Na+
1 glucose
on the extracellular side because the Na+/glucose symporter is on the apical side of the epithelial cell
How is the electrochemical gradient of Na+ maintained so that the transcellular transport across epithelial intestine cells never dissipates?
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
