BIOL 2160 Exam 2 Crousillac

In the semi-permeable plasma membrane, how do nonpolar molecules get across it?

Passive transport (they freely diffuse)

In the semi-permeable plasma membrane, how do polar molecules get across it?

Active transport (they need carrier proteins)

In the semi-permeable plasma membrane, the heads of the phospholipid bilayer are ___, and the tails are ___.

hydrophilic (polar); hydrophobic (nonpolar)

The membrane potential describes the charge where?

Inside the cell, as compared to the outside

What is the membrane potential always approaching?

The equilibrium potential (a number) of the MOST permeable ion

What does "membrane potential is negative" mean?

The intracellular fluid is slightly more negative, and the extracellular fluid is slightly more positive

What is the equilibrium potential?

the membrane potential in which the electrical driving force is equal and opposite to the chemical driving force, making the electrochemical driving force zero

The equilibrium potential can also called described as the number it takes to ___

change the electrochemical gradient

NA+'s equilibrium potential is

+55 mV

K+'s equilibrium potential is

-94 mV

Passive transport (does or does not?) require energy, moves from an area of ___ concentration to an area of ____ concentration, and is energetically ___.

Does not; high to low; downhill

Active transport (does or does not) require energy, moves from an area of ___ concentration to an area of ___ concentration, and is energetically.

Does; low to high; uphill

Driving force is the difference in ___

energy across a membrane (does it push from higher to lower or lower to higher?)

The direction of net flux is passive transport is

DOWN its electrochemical gradient

In passive transport, what is the carriers' preference, and which way is the carrier most likely to transport molecules in the absence of an electrochemical gradient?

No preference, so equally likely to transport molecules in either direction in the absence of an electrochemical gradient.

More solute=

more energy

Carrier proteins in passive transport have what kind of affinity for molecules?

Equal affinities for molecules on either side of the membrane

Transport proteins in active transport have what kind of affinity for molecules?

Have greater affinity for one molecule when the binding site is open to its side than for the other molecule when the binding site is closed to its side

Difference in diffusion through ion channels and facilitated diffusion is?

An empty channel's binding sites are accessible from both sides of the membrane at the same time. A carrier's site is only accessible from one site at one time.

What are the 3 mechanisms are passive transport?

Simple diffusion, facilitated diffusion, and diffusion through ion channels.

Simple diffusion's special entry way?

Disclaimer:

Don't judge me for saying "special entryway"...that is Crousillac's exact quoted terminology.

Does not require a special entryway

Why does simple diffusion occur?

Because of random thermal motion

How do molecules move across the membrane in simple diffusion? What is the net movement?

Freely; down the electrochemical gradient

What is the rate of simple diffusion determined by?

Driving force, membrane surface area, and membrane permeability

What affect will a warmer temperature have on the molecules' rate of diffusion?

The hotter it is, the more energy there is, therefore the more movement there is, so faster rate of diffusion.

What is the special entryway in facilitated diffusion?

Molecules bind to specific carrier proteins in the membrane

What is the net movement of molecules in facilitated diffusion?

Down the electrochemical gradient

What do the molecules do to the carrier proteins when they bind to them during facilitated diffusion?

Change the shape of the carrier protein when it binds to it

What is the (:special entryway:) in diffusion through ion channels

Molecules flow through pores in specific protein channels in the membrane

Another way to think of chemical gradient is

Concentration gradient

Why do ions naturally try to flow from high to low concentrations?

Because of their chemical (concentration) gradient

Why do Na+ and K+ ions not cross the membrane easily, therefore requiring an ion channel to pass through?

Because they have a charge

ps it's positive

ps good luck on the test

What happens as a result of K+ and Na+ ions not being able to use simple diffusion?

The ion concentrations never even out

What is the net flow of molecules in diffusion through ion channels?

Down the electrochemical gradient

What do ions utilize in diffusion through ion channels?

Large, charged pores which open and close like doors

lolz poet and didn't know it

How do ions move through pore in diffusion through ion channels?

By jumping from one site to the next

What determines how permeable a membrane is?

Lipid solubility

Size/shape of molecule

Temperate

Membrane thickness

Direction of net flux (molecular movement) in active transport?

UP the electrochemical gradient

(low concentration to high concentration)

Why does active transport require energy?

To overcome diffusion

What does active transport use to transport molecules?

Transport proteins called "pumps"

What does active transport use to move an ion against its concentration

ATP (this is the energy)

Describe the pumps used in active transport.

They are protein specific and have a fixed number of binding sites.

What is the main difference in active and passive transport (besides the electrochemical gradient)?

Active transport possesses the ability to harness energy (in the form of ATP) and can drive molecules in a preferred direction across a membrane

What are the two mechanisms of active transport?

Primary and secondary

How does primary transport use ATP?

DIRECTLY to provide energy to move molecules against (up) their electrochemical gradient

What 2 things do the pumps used in primary active transport function as?

Transport proteins and enzymes

What are the enzymes used in primary active transport called?

ATPase

What do the enzymes used in primary active transport do?

Catalyze ATP hydrolysis to harness ATP energy.

What is the most common primary active transport pump? What are two other names for it?

Sodium-Potassium Pump

Na+/K+ Pump

Na+/K+ ATPase

How many binding sites does the Sodium Potassium pump have, and how does it use ATP?

3 Na+ pumps and 2 K+ pumps. It uses ATP directly to pump Na+ out of the cell and K+ into the cell AGAINST their electrochemical gradients

When is the sodium potassium pump active?

24/7: it is happening CONSTANTLY

True/false: all cells have a membrane potential

True

True/false: all cells have a sodium potassium pump

False

What is the first step of the sodium potassium pump?

3 Na+ ions inside the cell bind to the transport protein (pump)

What is the second step of the SPP?

What are the products?

What is the affect on affinity?

The binding triggers the phosphorylation of the pump using ATP.

ADP and 1 phosphate group

Na+ affinity decreases, K+ affinity increases

What is the 3rd step in the SPP?

The phosphorylation causes the protein to change shape and open up to the outside of the cell, releasing the 3 Na+ ions into the extracellular fluid

What is the 4th step in the SPP?

2 K+ ions outside the cell bind to the now available transport protein, causing the phosphate group to be released into the intracellular fluid.

What is the 5th step of the SPP?

What is the affect on affinity?

The loss of the phosphate group allows the protein to go back to its original state (open to the inside)

K+ affinities decrease; Na+ affinities increase

What happens in the 6th and final (thank God) step of the SPP?

The 2 K+ ions are released into the cell and the 3 Na+ sites are available again.

In the sodium potassium pump, when there is a phosphate group attached tot the protein, which was is the opening facing?

Towards the inside

How many directions are Na+ and K+ ions transferred in?

They are each transferred in one direction only!! (Na+ out and K+ in)

Why is the sodium potassium pump considered active transport?

The ions are moving up their electrochemical gradient.

What are the products of each cycle through the Na+/K+ pump?

1 ATP hydrolyzed for energy

2 K+ ions into the cell

3 Na+ ions out of the cell

How does secondary active transport work?

It takes advantage of a gradient that has already provided energy.

How does secondary active transport use pre-provided energy?

Through coupling. One molecule moves passively down its electrochemical gradient and releases energy in the form of ATP. This energy is used in secondary active transport to drive the movement of another molecule up its electrochemical gradient.

What are the two types of secondary active transport?

Cotransport and countertransport

Which way are molecules moving in cotransport? In countertransport? Who gives a shit?

Co-in the same direction

Counter-in opposite directions

No one. Not one single person ever in the history of the universe actually cares about this.

Describe Crousillac's "toddler/revolving door" analogy as it refers to cotransport.

Cotransport is like being outside the lobby of a building with a toddler. The toddler is not strong enough to open the revolving door, but you are so you provide the energy. You push the door open, and the toddler takes advantage of your energy and goes through the door behind you.

Describe Crosillac's "toddler/revolving door" analogy as it refers to countertransport

Countertransport is like you being outside of a building and the toddler being in the lobby of the building. He does not have the energy to push open the door, but you do so you push it open and go in, while he takes advantage of your energy to open the door and goes out.

What happens during cotransport?

The inward flow of Na+ ion is coupled with the inward flow of a molecule. Na+ moves passively down its gradient, releasing energy in the form of ATP. The energy is harnessed to drive the molecule against its gradient. Na+ increases the protein's affinity for the molecule when the protein's binding site is facing OUT.

What happens during countertransport?

The inward flow of Na+ is coupled with the outward flow of a molecule. Na+ flows passively down its gradient, releasing energy in the form of ATP. The energy is harnessed to drive the molecule up its gradient. Na+ increases the protein's affinity for the molecule when the protein's binding site is facing IN.

As a review, what are the special entryways of passive transport?

Simple diffusion:

Facilitated diffusion:

Diffusion through ion channels:

SD: none

FD: carrier proteins

DTIC: protein channels (with pores)

As a review, what are the mechanisms of active transport?

Primary:

Secondary:

P: Sodium-Potassium Pump

S: Co- and Countertransport

How does secondary active transport use ATP?

Indirectly.

How much Sodium (Na+) is there outside the cell as there is inside the cell?

What are the exact measurements in mM?

10x as much outside the cell as inside the cell.

145 mM outside

15 mM inside

How much Potassium (K+) is there inside the cell as there is outside the cell?

What are the exact measurements in mM?

30x as much inside the cell as outside the cell.

140 mM inside

4 mM outside

What is the voltage (equilibrium potential) of Na+?

+55 mV

What is the voltage (equilibrium potential) of K+?

-94 mV

In a cell at rest, the membrane potential is ___, Na+ is going ___, and K+ is going ___.

negative

in

out

What are two reasons to explain why the intracellular fluid is slightly more negative than the extracellular fluid?

1. It has an excessive of anions

2. It is constantly giving up 3 positive (Na+) ions, and only getting 2 positive (K+) ions back.

What are two reasons to explain why the extracellular fluid is slightly more positive than the intracellular fluid?

1. It has an excess of cations

2. It is constantly giving up only positive (K+) ions, and gaining 3 positive (Na+) ions.

What determines the chemical driving force?

Trick question it does not change. Ever. It is always the same.

What is the chemical driving force of K+? Of Na+?

K+: always pushing OUT

Na+: always pushing IN

On a test question, how would you find what the chemical driving force is for K+ and Na+?

It does not change, so just memorize that K+ is OUT and Na+ is IN.

What determines the electrical driving force?

It is dependent on the membrane potential.

For the electrical driving force, when the membrane potential is positive, what happens?

Everything out!

Cheesy way to remember: Think "I positively want everything out!!"

For the electrical driving force, when the membrane potential is negative, what happens?

Everything in!

Cheesy way to remember: Think "Be nice and hold your negative words in."

On a test question, how would you find the electrical driving force for Na+ and K+?

Look at the membrane potential!!!!! If it is positive, everything goes out. If it is negative, everything goes in. If it is 0, but a big X.

The electrochemical driving force is related to the charge where?

Inside the cell (definition of membrane potential-don't forget!)

What does the electrochemical driving force take into account?

The chemical driving force AND the electrical driving force.

On a test, how would you find the electrochemical driving force?

Look at the chemical driving force and electrical driving force.

On a test, if you are trying to find the electrochemical driving force and both the chemical driving force and electrical driving force are in, what would you determine the electrochemical driving force to be?

In

On a test, if you are trying to find the electrochemical driving force and both the chemical driving force and electrical driving force are out, what would you determine the electrochemical driving force to be?

Out

On a test, if you are trying to find the electrochemical driving force and one of the driving forces is in and the other is out, how would you determine the electrochemical driving force?

Look at the membrane potential number!!!!

On a test, if you are trying to find the electrochemical driving force and one of the driving forces is in and the other is out, if you see that the membrane potential is a number that is more negative than -94, what would you determine the electrochemical driving force for K+ to be?

In

On a test, if you are trying to find the electrochemical driving force and one of the driving forces is in and the other is out, if you see that the membrane potential is a number that is more positive than +55, what would you determine the electrochemical driving force for Na+ to be?

Out

What is the membrane potential of a cell at rest?

-70 mV

If the membrane potential is equal to the ion's equilibrium potential, what would you say about the ion?

"There is no net movement"

According to Crousillac, what is the most most most important thing to remember (and apply) about osmosis?

It is the DIFFUSION OF WATER

In terms of passive and active transport, how would you describe osmosis?

It is the passive transport of water molecules and the active transport of solute molecules.

In other words, water is going from areas of high concentration to low concentration, but the solute (K+, Na+, glucose, whatever it may be) is going from an area of low concentration to high concentration.