UWL BIO 315 Exam 2

You are growing some animal cells in culture. Like most animal cells, they prefer to grow in relatively high salt media (e.g., 100 mM NaCl).

Unfortunately, you made a dilution mistake last time you made the media, and the media is 100x lower in NaCl than it's supposed to be.

Fortunately, you catch your math mistake before you add it to the cells. This media was ______________, and the result would likely have been _____________. (pick the answer that has the answer to both blanks)

Hypotonic/Hypo-osmotic, the cells would have popped

You are studying a particular kind of Ca2+ transport protein in a purified system (the protein is the only transporter in the membrane).

You find that if you add ATP to the interior of the membrane system, there is a no change in the Ca2+ concentration out side the cell. However, if you add an excess of Na+ ions to the exterior buffer, now there is a net efflux of Ca2+ into the outside.

Based on this result, what kind of transporter do you think you are studying?

Coupled Na+/Ca2+ Antiporter

Cells lining the intestinal epithelia import glucose from the food in the gut and then export the glucose into the blood by passive transport.

In order for the intestinal epithelia cells to take up glucose, the cells must express an active glucose transporter.

true

Based on some careful measurements, you find that a transporter you are studying hydrolyzes one mol of ATP per mol of H+ transported in and mol of K+ transported out.

Which of the following terms best describes your transporter?

antiporter

Based on some careful measurements, you find that a transporter you are studying transports 1 mol of K+ out per mol of Cl- transported out.

Which of the following terms best describes your transporter?

symporter

You are studying a particular kind of Ca2+ transport protein in a purified system (the protein is the only transporter in the membrane).

You find that if you add ATP to the interior of the membrane system, there is a no change in the Ca2+ concentration out side the cell. However, if you add an excess of Na+ ions to the exterior buffer, now there is a net efflux of Ca2+ into the outside.

Based on this result, what kind of transporter do you think you are studying?

Coupled Na+/Ca2+ Antiporter

Which of the following kinds of transporters is likely to have the highest Vmax?

A K+ leak channel

Using a technique called "Patch Clamping", you can isolate a patch of membrane and then control the membrane potential across the patch of membrane (i.e., change the potential difference across the membrane).

You take a small patch of membrane, and change the membrane potential from the resting -70 mV to a lower potential difference of -15 mV and suddenly you detect a sudden influx of Na+ ions across the patched membrane.

Which of the following kinds of transporter is likely to be causing that influx of Na+?

a voltage-gated Na+ channel

Based on some careful measurements, you find that a transporter you are studying hydrolyzes one mol of ATP per mol of Ca2+ transported across the membrane.

Which of the following terms best describes your transporter?

uniporter

Which of the following kinds of transporters is likely to have the lowest Km?

P-ATPase type primary active transporter

You are studying a particular kind of Ca2+ transport protein in a purified system (the protein is the only transporter in the membrane).

In your initial experiments, you find that adding an excess of Ca2+ and Na+ to the exterior of the membrane leads to import of Ca2+ into the "cell". Adding ATP to either the "inside" or exterior has no effect on the rate of Ca2+ import.

Surprisingly, if you leave out the excess Na+ and only add the excess Ca2+, this still leads to import of Ca2+ into the "cell" at the same rate as when you included the excess Na+.

What kind of transporter do you think you are studying?

ion channel

because the membrane is not permanent to many things required by the cell, the cell encodes ______ to allow those impermeant chemicals to cross the membrane

membrane transporter proteins

chemicals moving ____ a gradient do not require an input of energy to move through a transporter protein

down

chemicals moving _____ their gradient require an input of energy. this energy can come from ATP, or other sources

against

if a chemical gradient is made from ions, then that also represents an __________

electrical gradient

electrochemical gradients across an impermeant membrane result in a charge separation across that membrane: a _______

membrane potential

all ____ will have membrane potential

biological membranes

________ can affect the behavior of ions as they move across the membrane, even through open channels

membrane potentials

molecules that cross poorly or cannot cross on their own require help from ________ proteins

transporter proteins (transporters are enzymes)

3 kinds of energy:

ATP: major energy source for almost all cellular reactions, driving anabolism and metabolism either directly or through coupled reactions

NADH: form of red-ox energy storage that is used by cells to drive many anabolic and metabolic reactions

Gradient Energy: cell uses a concentration gradient across cellular membranes to both store energy as well and drive many cellular activities

diffusion of chemicals down a concentration gradient represents an ____ which is a driven release of energy

entropy

if delta S goes up, we subtract from it which makes delta G more

negative, which is good

a chemical gradient held across an impermeable membrane represents a form of ________

stored energy

moving down a concentration gradient releases ______

free energy

moving against a concentration gradient requires an input of _____

free energy

cells can ____ from chemicals moving down their gradient

extract energy

cells must ___ to move a chemical against their gradient

add energy

You usually want a ____ Km and a ____ V max

low, high

at the very least, transporters can make diffusion of molecules down their gradient more likely to _____

occur (such as passive transport because it does not require negative delta G)

active transporters can actually move molecules ______ their gradient (they have some source of negative delta G)

against

transporters provide a path for hydrophilic substrates across the _______ membrane

hydrophobic

channels (transporter)

-provide a complete hydrophilic path across membrane for substrates

-all channels are passive transporters

-some can undergo a conformational change to be closed or open

carriers (transporter)

-shift from being open on one side, to being occluded, to being open on the other side-thus never having a full hydrophilic path across membrane.

-carriers maintain membrane integrity during transport as they carry their substrate across the membrane during a conformational change

-some carriers can be passive transporters

-all active transporters are carriers

-never an open channel

transporters in cell membranes can either be passive or active

passive (no source of negative delta G such as a K+ channel)

active (have a source of negative delta G)

Passive Transport

-transporters that allow chemicals to fall down their gradient and do not need energy

-no power, only a path

Active Transport

-transporters that move chemicals against their gradient and must add energy

-they can couple a form of energy. source of negative delta G from somewhere

The source of energy used to drive transport determines whether an active transporter is primary or _______

coupled

primary active transporters

-use direct energy inputs in the form of ATP, NADH, light etc. to drive transport of a substrate against its gradient.

-typically ATPases

-direct usually ATP

Coupled active transporters

-transport of one substrate (that requires energy) is coupled to transport of another substrate (that releases energy)

-these are called secondary active transporters

-couple movement of one chemical high-low and one low-high

transporters are also characterized based on what direction they transport their substrates:

uniporter: one type of chemical is moved in one direction (can be passive or active)

symporter: two types of chemicals are moved in a single cycle. chemicals move in the same direction across membrane. (often active, but can also be passive)

antiporter: two types of chemicals are moved in a single cycle. the chemicals move in the opposite direction across the membrane. (often active, but can also be passive)

There are ___ main types of membrane transporters that are important to remember; each have different features that work best in different conditions.

6 main types:

Passive: Pore, ion channel, facilitated diffusion carriers

active: primary transporter, coupled transporter, and electrogenic transporter.

primary active transporters can use negative delta G of ATP Hydrolysis to overcome the positive delta G of moving a chemical _______

against its gradient

coupled active transporters can use the negative delta G of moving one chemical down its gradient to overcome the positive delta G of moving a second ________

against its gradient

most ion channels and facilitated diffusion transporters are only passive because they have no other source of negative delta G to overcome the positive delta G of moving a chemical against its gradient

.

passive transporters require conformational changes to drive changes that allow the transporter to move its substate. since passive transporters always move their substrate _____ its concentration gradient, there is enough energy in the gradient to pay for the conformational changes

down

pores are always _____ and provide a path for hydrophilic substrates to cross the hydrophobic membrane, but only down their concentration gradient (PASSIVE) they are like doorways in city walls that are always open

open

facilitated diffusion transporters provide a ____ for substrates to cross the membrane, but only can move them down the concentration gradient (PASSIVE) like a revolving door

path

ion channels are more than just high capacity holes in a membrane:

like a dam

1. ion channels are gated-switched between open/closed by different stimuli.

-voltage gated open/close from changes membrane potential

-ligand gated open/close from the presence absence of ligands

-mechanically gated open/close when physically pushed or pulled

2. ion channels only transport substrates in one direction

3. ion channels are specific for the kind of ion they transport

Primary Active transporters (pay attention to how ATP is used) ACTIVE

-P type ATPases: use phosphorylation (by ATP) to drive conformational changes

-ABC transporters: use ATP-binding to drive conformational changes, while hydrolysis of the bound ATP restores the initial conformation

-F/V type ATPases: use hydrolysis to spin a shaft in their rotary engine

Couples active transporters (pay attention to substrate specifically and how the transporter uses the energy in one gradient to drive transport of a second substrate chemical against its gradient) ACTIVE

-coupled active transporters: use the gradient of one chemical to drive the conformational changes necessary to drive transport of a second substrate chemical. they are specific to particular substrates and till are subject to energetics of transport.

-The Na driven glucose symporter uses the sodium gradient to drive import of glucose. the energy in letting Na move down its gradient has to be larger than the energy required to move the glucose against its gradient