BIOL 2160 Chapter 4

Does the cell membrane structure act more like a solid or liquid? What is it referred to as?

liquid

fluid mosaic model

The ____ ____ is semi-permeable.

plasma membrane

___ or ___ molecules can freely diffuse across the plasma membrane.

Small

nonpolar

____ and ____ molecules need ____ ____ to carry them across the plasma membrane.

Large

polar

carrier proteins

____ ____ across the plasma membrane does NOT require energy.

Passive transport

____ ____ across the plasma membrane requires energy.

Active transport

During passive transport, molecules move across the membrane from ___ energy to ___ energy.

high

low

The energy of a solution depends on the ____. The more ___, the more __.

solute concentration.

solute

energy

In passive transport, solutes move from areas of ___ concentration to ___ concentration.

high

low

The amount of __ in a solution depends on the amount of solute in a solution.

energy

For a typical cell, there is always about ___ times more ___ on the outside of the cell than the inside of the cell.

10

sodium (Na+)

For a typical cell, there is always about ___ times more ___ on the inside of the cell than the outside of the cell.

30

potassium (K+)

Can charged molecules participate in simple diffusion? Can the ion concentrations of charged molecules even out?

No, they require aid of other proteins.

No.

___ is the difference in energy across a membrane.

Driving force

What are the three types of driving force?

chemical

electrical

electrochemical

___ pushes from higher to lower energy.

Driving force 2

The ___ is a reflection of membrane potential.

electrical gradient

___ is the ratio of the inside of the cell to the ratio of the outside of the cell.

Membrane potential

At rest, is the inside of a cell positive or negative? What exact number?

negative

-70mV

The amount of electrical driving force depends on the ____.

membrane potential

Most, if not all healthy cells, have a ___ membrane potential.

negative

Do intracellular fluids or extracellular fluids contain more anions?

intracellular fluids

__ fluids contain more anions than __ fluids. As a result, cells tend to have a __ membrane potential.

intracellular

extracellular

negative

When cells have a negative membrane potential, the electrical driving force of cations is ___.

inward

When cells have a negative membrane potential, the ___ draws cations inward.

electrical driving force

___ is determined by the electrical driving force and and the chemical driving force.

Electrochemical driving force

The ___ of an ion is the membrane potential at which the electrical driving force on the ion is both equal and opposite to the chemical driving force.

equilibrium potential

The equilibrium potential of an ion is the membrane potential at which the electrical driving force on the ion is ____ to the chemical driving force.

both equal and opposite

The electrochemical driving force on an ion is set by the difference between the ion's ____ and ___.

equilibrium potential

membrane potential

The ____ on an ion is set by the difference between the ion's equilibrium potential and membrane potential.

electrochemical driving force

What equation determines equilibrium potential?

Nernst equation

For sodium to go inside a cell, the cell must have a very ___ charge.

positive

What is the absolute key concept I need to understand?

the membrane potential, at ANY time, is always approaching the equilibrium potential of the MOST permeable ion

The ___ potential, at ANY time, is always approaching the __ potential of the MOST ___.

membrane potential

equilibrium potential

permeable ion

The __ gradient tends to push K+ outside the cell, while the __ gradient tends to push K+ inside of the cell. Why?

chemical gradient

electrical gradient

there is more K+ in the cell than outside the cell when the cell is at rest

At rest, the __ gradient for K+ is stronger than the __ gradient. However, this changes when the cell reaches K+'s equilibrium potential, ____.

chemical

electrical

-94mV

What is the equilibrium potential for K+? Which gradient is stronger when this occurs?

-94mV

electrical gradient

What will K+ do at -94mV?

This is potassium's equilibrium potential, so there is no net current of potassium at -94mV. At -95mV, it will begin to move into the cell. At -93mV, it will move outside of the cell.

What will K+ do at any membrane potential more positive than -94mV?

Potassium will continue to move according to its chemical gradient as usual. Potassium will continue to flow outside the cell.

What will K+ do at any membrane potential more negative than -94mV?

Potassium will move against its chemical gradient and move according to the electrical gradient. Potassium will flow into the cell since it is so attracted to the positivity of the cell that the chemical gradient no longer matters.

What is the equilibrium potential of K+?

-94mV

When a cell is at rest, is K+ entering or leaving the cell?

leaving (chemical gradient in charge)

At -100mV, what will the net movement of K+ be?

into the cell, against chemical gradient

When a cell is at rest, the cell's charge is ___. Since there is more ___ on the outside of the cell and the charge of these ions are ___, both the ___ and ___ move these ions into the cell.

negative

sodium (Na+)

positive

chemical and electrical gradients

Both the chemical and electrical gradients of ___ encourage the ion to move into the cell when the cell is at rest.

Na+ (sodium)

What is the equilibrium potential of Na+?

+55mV

When the membrane potential of a cell is more positive than +55mV, what does Na+ do?

sodium goes out of the cell, against its chemical gradient

(whole reason electrical and chemical gradients wanted sodium to go into the cell is that the cell was very negative, if its more positive than its equilibrium potential sodium figures the cell is positive enough, no longer needed/attracted)

When the membrane potential of a cell is less positive than +55mV (like +54mV), what does Na+ do?

sodium continues to go into the cell, according to the desires of its electrical and chemical gradients

Most of the time, __ goes into a cell while __ comes out of the cell. In what situations does this change?

sodium

potassium

When equilibrium potential for sodium Na+ is more positive than +55mV, Na+ leaves the cell

When equilibrium potential for potassium K+ is more negative than -94mV, potassium enters the cell

When the equilibrium potential for Na+ is more positive than +55mV, Na+ ___ the cell.

leaves

When the equilibrium potential for K+ is more negative than -94mV, K+ ___ the cell.

enters

What happens at 0mV?

nothing, this is not special, things flow as they usually would with sodium entering the cell and potassium leaving the cell

At rest, the cell is always losing more __ than it is gaining ___.

potassium

sodium

Do the forms of membrane transport involve pumps or diffusion?

diffusion

Are pumps involved in membrane transport?

no

In __ transport, molecules move down their electrochemical gradient from a high to low concentration.

passive transport

In __ transport, molecules move up their electrochemical gradient from a low to high concentration.

active transport

In active transport, molecules move from a __ to __ concentration.

low

high

__ requires ATP to counteract diffusion?

Active transport 2

What are the two passive transport mechanisms?

simple diffusion

facilitated diffusion

__ is the movement of molecules as a result of random thermal motion.

Simple diffusion

During ___, molecules move freely across the membrane and net movement is down the electrochemical gradient.

simple diffusion

Leaving the classroom by floating straight through walls would be an example of what type of diffusion?

simple diffusion

During ___, molecules bind to specific protein carriers or transporters in the membrane that transport them down the electrochemical gradient.

facilitated diffusion

Leaving the classroom through doors is an example of what type of diffusion?

facilitated diffusion

During __, molecules flow through pores in the specific protein channels in the membrane down their electrochemical gradient.

diffusion through ion channels

Diffusion through ion channels is a form of ___ diffusion.

facilitated diffusion

The rate of simple diffusion is determined by ___, __, and __.

membrane permeability

driving force (aka concentration gradient)

membrane surface area

What four things determine membrane permeability?

size/shape of molecule

lipid solubility (can you pass right through the walls or do you have to go out a door?)

temperature (things move faster when hot)

membrane thickness

Does diffusion happen over long or short distances?

short (cells are small because of this)

What is the best way to increase the rate of diffusion?

increase membrane surface area

Diffusion through ___ is like going through a gate to get into an apartment complex. However, diffusion through a ___ requires a change in shape of a protein.

ion channel

carrier protein

A change in shape results in a change of ___.

function

During diffusion through a protein channel, what exactly requires energy?

diffusion doesn't require energy, but changing the shape of the carrier protein requires energy

What are the two forms of active transport?

primary active transport

secondary active transport

___ directly uses ATP to provide energy to move molecules against their electrochemical gradient.

Primary active transport

In ___, one molecule moves passively down its electrochemical gradient to provide energy for another molecule to move up its electrochemical gradient.

secondary active transport

What are the two forms of secondary active transport?

cotransport

countertransport

In ____ form of secondary active transport, the molecules involved move in the same direction.

cotransport

In ___ form of secondary active transport, the molecules involved move in opposite directions.

countertransport

If you help a toddler leave a hotel lobby's revolving door, this would be an example of what form of secondary active transport?

cotransport

If you go outside of a hotel lobby to help a toddler get back in through the revolving doors (you exiting allows him to enter at the same time), this is an example of what form of secondary active transport?

countertransport (because you two move in opposite directions)

The pumps of ____ prevent the equilibrium of Na+ and K+ in cells.

primary active transport

When sodium helps moves glucose into the cell as it enters the cell, this is an example of ___.

cotransport

When sodium helps move protons out of the cell as sodium enters the cell, this is an example of ___.

countertransport

__ is the transfer of water across a membrane from an area of low solute concentration to an area of high solute concentration, until their is an equal concentration of solute on both sides of the membrane.

Osmosis

During osmosis, water moves from an area of __ solute concentration to an area of __ solute concentration.

low

high

Is osmosis active or passive transport?

passive transport

The ___ solute you have, the more water you have.

less

If a 3M cell is put into a 15M environment, what will happen?

water leaves cell, cell loses mass and shrivels up

___ is the total solute particle concentration of a solution.

Osmolarity

If an intracellular solution and an extracellular solution have the same solute concentration, they are __.

iso-osmotic

The inside of a cell is ___ when the intracellular solution is higher than the extracellular solution.

hyperosmotic

If intracellular solution is hyperosmotic, will water flow into our out of the cell?

into the cell

If intracellular solution is hypoosmotic, will water flow into or out of the cell?

out of the cell

When is a cell hyperosmotic?

when there is more solute concentration (solution) inside the cell, water flows into it, cell swells up

When is a cell hypo-osmotic?

when there is less solute/concentration of solution inside the cell than extracellular, so water will flow out of it, cell shrivels up

When big molecules have to cross a membrane, they do so through the process of ___.

endocytosis

What are the three types of endocytosis?

phagocytosis

pinocytosis

receptor-mediated endocytosis

The process of ___ moves any big particle across the membrane. This is a form of __.

phagocytosis

endocytosis