Biol 266 : Unit 5

Reminder : make flashcard for PPT # 15-16

Cell membranes are permeable to___________________.

large uncharged polar molecules and charged molecules

Transfer of these water-soluble molecules depends on ________________

membrane transport proteins.

Extracellular Concentration of Na+?

150mM

Intracellular Concentration of Na+?

10mM

Extracellular Concentration of K+?

5mM

Intracellular Concentration of K+?

140mM

Extracellular Concentration of Ca ²⁺?

10 ^ -3 mM

Intracellular Concentration of Ca ²⁺?

10 ^ -7 mM

At the plasma membrane, excesses of positive and negative charges accumulate giving rise to the _______________ with the inside of the cell membrane being _________ and the outside being _________.

membrane potential ; negative ; positive

Two types of transport:

Passive and Active

Passive Transport:

Does not require external energy, only a concentration gradient. The molecule travels down its concentration gradient.

What does it mean when molecules travels down its concentration gradient?

From high concentration to low.

What does it mean when molecules travels against its concentration gradient?

From low concentration to high.

Active transport:

Molecules are transported against their concentration gradient, requires energy.

Passive Transport Diffusion :

Gases, hydrophobic molecules and small polar uncharged molecules are able to dissolve in the lipid bilayer, diffuse across it, and then dissolve in the aqueous solution on the other side of the membrane

For non-electrolytes, the rate of passive transport (diffusion) is dependent upon its _____________.

Partition coefficient and size

Partition coefficient :

A measure of its ability to partition between aqueous and hydrophobic environments.

Two molecules of equal partition coefficient – the _____ one diffuses faster than the _____.

smaller ; larger

Direction of transport is only determined by the ___________.

concentration gradient

Facilitated diffusion requires __________.

membrane proteins and a concentration gradient, but no energy

During facilitated diffusion, the passage of _____ and ______ molecules is mediated by ______ that enable the transported molecules to cross the membrane without directly interacting with its ___________ interior.

polar ; charged ; proteins ; hydrophobic

Active transport requires a ___________________ that is coupled to an energy-consuming reaction (__________).

membrane transport protein ; hydrolysis of ATP

Examples of Active transport: 

The proton pump of the lysosome / The sodium/potassium pump of the plasma membrane.

The proton pump of the lysosome generates the ______________.

low lumenal pH

The sodium/potassium pump of the plasma membrane that generates the differences in internal and external ________________.

Na+ and K+ concentrations.

Classes of transport proteins:

ATP-powered pumps / Chanel proteins (ion) / Carrier proteins (transporter)

ATP-powered pumps:

1-1000 molecules/sec, couples hydrolysis of ATP to the transport of a molecule against its concentration gradient.

Channel proteins (ions):

10^7-10^8 molecules/sec, transport ions down their concentrations gradient through a hydrophilic pore in the membrane protein.

Carrier proteins (transporters):

10^2-10^4 molecules/sec, Bind water-soluble molecules on one side of the membrane and deliver them to the other side. Involves a conformational change in the protein.

Uniports:

Work in passive diffusion and are selective for one type of molecule. They move molecules down their concentration gradients.

Differences between uniport and simple diffusion:

Rate of substance movement is higher for uniporters / Partition co-efficient is irrelevant for uniporters (no contact with the hydrophobic lipid environment) / Uniport transport is limited by the number of uniporters in the membrane / Transport with a uniporter is specific

_____ is the main uniporter for glucose in ______ (blood cells).

GLUT1 ; erythrocytes

Specificity (km):

A measure of the affinity of an enzyme for its substrate. The lower it is, the tighter the binding between the two.

Km is the ______ _______. At or above the km favours the ______ . Below the km favors the _______.

binding constant ; binding ; release

Outward-open, favours glucose ________.

binding

Inward open favours glucose _______.

release

A __________ and an __________ use an existing electrochemical gradient rather than direct ATP hydrolysis to move one of the molecules _________ its concentration gradient and a second molecule _________ its gradient. Referred to as ___________ _________ transport.

symporter ; antiporter ; against ; down ; secondary active

If the glucose is missed in the cell of the gut. It will get secreted in the ________.

kidney

Some cells have aquaporins - channels that facilitate the flow of water molecules through the plasma membrane. For these cells, what do you think regulates the rate and direction of water diffusion across the membrane?

Solute concentrations on either side of the membrane.

What effect would you predict lengthening the fatty acids of the lipids in a bilayer would have on the sodium-glucose carrier transport rate?

It would slow down.

Classes of pumps :

P-class / V-class / F-class / ABC superfamily

If solute concentration equal or exceed km favours ________ ; if below km favours ___________.

binding ; release

What causes the E1 to change into E2 ?

Phosphorylation

What causes the E2 to change back into E1 ?

Dephosphorylation

____________ by ATP causes a conformational change that exposes the Ca2+ to the exterior face and __________ the Ca2+ affinity, releasing the ions into the cell exterior. __________________ regenerates the E1 conformation

Phosphorylation ; lowering ; Dephosphorylation

K+/H+-ATPase:

Found in parietal cells of the stomach, produces acidic environment.

Na+/K+-ATPase: ________ by the poison ouabain. By altering the __________ , it indirectly affects the Na+/Ca2+ exchanger that pumps Ca2+ out of the cells, leading to _________ intracellular Ca2+.

inhibited ; Na+ gradient ; elevated

CFTR (cystic fibrosis transmembrane conductance regulator): Member of the ____ _______. Is _________ but rather a _________ of Cl-, coupled to both ATP hydrolysis and ATP binding.

ABC superfamily ; not a pump ; transporter

Two properties distinguish ion channels from a simple hole in the membrane:

Selectivity and gating

Selectivity:

Some ions pass through, others do not. This depends on the diameter and shape of the ion, and on the charges that line the channel.

Gating:

Channels are not continuously open. Rather, they open in response to a stimulus for a short period of time.

Three types of gating:

Voltage-gated / Ligand-gated / Mechanically-gated

Voltage-gated:

Respond to changes in electric potential across the membrane.

Ligand-gated:

Respond to the binding of a ligand.

Mechanically-gated:

Respond to mechanical force.

Neurons (nerve cells), like all cells, have a membrane potential due to ______ concentration at the membrane. The potential is _______ for neurons.

Na+ ; ~-60 mV

When a signal comes in (from another neuron), voltage-gated Na+ channels _____ , __________the membrane. If sufficiently depolarizing, _____ channels open, causing more ________.

open ; depolarizing ; more ; depolarization

At ________ the electrochemical driving force for sodium is ___ . The channels then assume an ___________ state where they cannot be stimulated for a period of time. This ensures the signal moves _______ from the initial site.

+40 mV ; 0 ; inactivated ; away

At the nerve terminals, _____________ are activated. The influx of calcium leads to ______ of vesicles containing __________. The neurotransmitter that fails to bind to the receptor on the _________ membrane is either degraded or taken up again by the __________ membrane.

Ca2+ channels ; release ; neurotransmitter ; postsynaptic ; presynaptic

Postsynaptic receptors can be either _______ (receptor is the ion channel) or ____________ (receptor is not an ion channel but signals to the ion channel)

ionotropic ; metabotropic