Exam 2: Membranes, Membrane Potentials, Diffusions, Tonicity, & Osmolarity

What charge does a cation have?

positive

What charge does an anion have?

negative

When the amount of positive and negative ions are equal, the solution is

electrically neutral

What types of forces act upon the movement of ions?

concentration and electrical

The concentration gradient moves from a

high to low gradient

In an electrical gradient, the charge moves () opposite charges

closer to

In an electrical gradient, the charge moves () alike/same charges

further away from

Opposite charges of ions…

attract towards one another

Similar charges of ions…

repels each other

The magnitude/strength of a concentration force is [] to the size of the concentration gradient.

proportional

The [] in concentration between the two sides of the membrane, [] the concentration force.

bigger the difference; the larger

How does one find the total concentration force?

look at the two forces, subtract the smaller amount from the bigger one= difference

How does one determine the direction of the concentration force?

if a side has more force, it will push towards the opposite direction

Ions are charges particles, meaning they require which mode of diffusion across the membrane?

facilitated diffusion via transport protein channels

The net force for each ion is the

combination of both the concentration and electrical forces acting on it

Forces going the same direction are [] to find the net force, while forces going the opposite direction are []

added together; subtracted from each other

What purpose(s) does the Na+/K+ (ATP) pump serve for the membrane potential?

establishes a concentration gradient of Na+ and K+ ions; establishes an electrical gradient

How does the Na”/K+ (ATP) pump establish an electrical gradient?

pumps 3 positive ions out of the cell, and only pumps 2 positive ions back in their place, cell has a net loss of +1 every time the pump breaks down a molecule of ATP

The electrical gradient across a cell membrane is known as the cell’s…

membrane potential (Em)

When the membrane potential is stable, it is called the…

resting membrane potential (RMP)

A typical cell (RMP) will have a resting membrane potential of

-70 mV

The [Na+] inside a typical cell (RMP) is…

15 mM

The [Na+] outside a typical cell (RMP) is…

150 mM

The [K+] inside a typical cell (RMP) is…

150 mM

The [K+] outside a typical cell (RMP) is…

5 mM

The [Cl-] inside a typical cell (RMP) is…

10 mM

The [Cl-] outside a typical cell (RMP) is…

150 mM

Depolarization means that the membrane potential…

moves closer to 0 mV (it becomes more postive)

Hyperpolarization means that the membrane potential…

moves farther from 0 mV (it becomes more negative)

If there is an influx of positively charged ions into the cell, the membrane potential is experiencing…

depolarization

If there is an efflux of positively charged ions out of the cell, the membrane potential is experiencing…

hyperpolarization

If there is an influx of negatively charged ions into the cell, the membrane potential is experiencing…

hyperpolarization

If there is an efflux of negatively charged ions out of the cell, the membrane potential is experiencing…

depolarization

If the current membrane potential is closer to zero than the equilibrium potential…

the electrical force is smaller than the concentration force (i.e. concentration force “wins”)

How many types of diffusions are there?

3

What is simple diffusion?

particles move from a high to low concentration gradient without any assistance

What is facilitated diffusion?

particles move from a high to low concentration gradient via a transport protein channel

What is active transport?

particles move from a low to high, against the concentration gradient, via a protein pump that requires ATP

What is osmosis?

water particles move from a high to low concentration gradient

What is osmolarity?

the total sum of all moving particles within a specific liter of water

Osmolarity is measured in units of…

milliosmole (mOsm)

Membrane potential is measured in units of…

milivolts (mV)

The concentration of specific particles are measured in units of…

milimoles (mM)

What is the typical osmolarity of a human cell?

300 mOsm

If a solution has the same osmolarity (300) as the typical human cell, it is considered…

iso-osmotic

If a solution has a higher osmolarity (400) compared to the typical human cell, it is considered…

hyper-osmotic

If a solution has a lower osmolarity (200) compared to the typical human cell, it is considered…

hypo-osmotic

What is tonicity?

how a solution affects the shape/tone of a cell

If the cell does not change its shape and there is no net movement of water, this is considered…

an isotonic solution

If the cell swells/lyse/burst and there is net movement of water into the cell, this is considered…

a hypotonic solution

If the cell shrivels/shrinks/cremate and there is net movement of water out of the cell, this is considered…

a hypertonic solution

Osmolarity measures [] in a solution and does not measure the []

only the concentration of dissolved solute particles; solvent (water) molecules themselves

If a solution causes the cell to shrink, it is considered

both hyper-osmotic and hypertonic

A solution of 300 mOsm of urea is considered

a iso-osmotic solution, but with a hypotonicity

Why does the 300 mOsm solution of urea cause cells to lyse?

despite being an iso-osmotic solution, urea is small and uncharged, meaning it can easily cross the cell membrane, which water will gradually follow when the ICF becomes hyper-osmotic compared to the hypo-osmotic ECF

Cells

When a molecule is not permeable to the cell, the solutions is always

hyper-osmotic and hypertonic or hypo-osmotic and hypotonic

K+ is at equilibrium at

-90mV

Cl- is at equilibrium at

-72mV

Na+ is at equilibrium at

+61mV

How much an ion will affect the membrane potential relative to other ions depends on the ____ of the ion relative to the other ions

permeability

(%) of energy is used power the Na+/K+ to just keep you alive

90%

How does the Na+/K+ pump create its gradients?

it pumps 3 Na+ out for every 2 K+ it pumps in

Ion’s equilibrium potential is when…

the membrane potential inside of the cell has an electrical force that cancels out the concentration force

The plasma membrane functions to

separate the intracellular fluid (ICF) and its contents from the extracellular fluid (ECF)

In short the plasma membrane serves to

keep the good stuff in and bad stuff out

The membranes of the cell have three basic components…

phospholipids, cholesterol, and proteins

The main component of the plasma membrane are the

phospholipids

Phospholipids are a class of molecule that have

a glycerol molecule attached to two fatty acids on one side and a phosphate group on the other

In phospholipids, the free fatty acids tails are

hydrophobic (water-fearing)

In phospholipids, the phosphate group (heads) are

hydrophilic (water-loving)

The glycerol and phosphate groups of phospholipids are referred to as the molecule’s

head

The free fatty acid tails of phospholipids are referred to as the molecule’s

tail

Phospholipids will form a stable configuration called a

bilayer

The cell membrane of all your cells are made form a

phospholipid bilayer

Cholesterol serves to

help keep the membrane fluid by making it easier for phospholipids to slide past one another

Membrane proteins are used for

structural elements, transporters and channels, enzymes, signalizing proteins, and receptors

Membrane proteins serves as structural elements by

connecting to the cytoskeleton and giving the cell its shape

Membrane proteins serves as transporter and channels by

moving substances across the membrane

Membrane proteins serves as enzymes by

catalyzing reactions (building or breaking molecules) at the cell’s surface [faster]

Membrane proteins serves as signaling proteins by

having a carbohydrate attached and signaling outgoing messages to the rest of the body

Membrane proteins serves as receptors by

detecting incoming signals in the form of chemical messengers in the ECF

Most biological molecules can not cross the plasma membrane without help due to two components…

size is too large or they are very charged

Only what molecules with what components can easily pass through the plasma membrane without help?

only hydrophobic molecules (not charged, weakly hydrophilic) can easily pass

What are three ways that molecules can get from one side of the membrane to the other

simple diffusion, facilitated diffusion, and active transport