Title: Physiology 2130 / Module 3: Human Cell

Header: Name the part of the cell membrane:

Header: Label the part of the cell:

Q: The cell membrane is [...].
A: selectively permeable
Extra: The cell membrane acts as a selectively permeable barrier, allowing some substances to cross easily, some to cross with difficulty, & other substances to not cross at all. This characteristic is due to the structure of the membrane, whose main feature is a bilayer of phospholipid molecules. Embedded within this lipid bilayer, among other things, are proteins that can act as channels, pores, transport carrier molecules, receptors, markers, & enzymes.

Q: Phospholipids have a hydrophilic [...] and hydrophobic [...].
A: head; tail

Phospholipid heads of a bilayer make up the surface of the outer and inner membrane, interacting with the outside and inside of the cell.

Q: Cholesterol helps keep the membrane [...] to some water-soluble molecules and [...] over a wide range of temperatures.
A: impermeable; flexible

Q: The associated protein (on the top of the membrane) is an [...] which helps [...]
A: enzyme; catalyze reactions.

Q: The associated enzyme protein can be attached to [...] but the [...] is usually on the intracellular surface of the membrane.
A: either the intracellular or eextracellular surface of the membrane; associated structural protein

Q: A glycocalyx is a [...] made up of carbohydrates.
A: protective layer on the membrane

Q: A glycocalyx plays a key role in the [...] and [...] in the body.
A: immune reponse; recognition of other cells

Q: The head group on a phospholipid is a [...] and the tail is a [...]
A: phosphate group; fatty acid chain.
Extra: The fatty acid tails are hydrophobic (water-resistant).
The phosphate heads are hydrophilic (water-loving).

Receptors, enzymes,ion channels/pores, membrane transport carriers, and cell identity markers are all types of membrane proteins.

Header: What is the function of the membrane protein?

The five major ways to cross a cell membrane are:
1. Endocytosis/Exocytosis/Pinocytosis; for smaller molecules);
2.Diffusion through the Lipid Bilayer for fat-soluble molecules;
3.  Diffusion through Protein Channels for water and water-soluble molecules;
4.  Facilitated Diffusion;
5.Active Transport.

Q: Diffusion is due to [...]
A: the molecules’ random thermal motion.

Q: Diffusion is the [...]
A: movement of molecules from an area of high concentration to low concentration.

Q: When molecules move from an area of high concentration to an area of low concentration this called the [...]
A: chemical concentration gradient.

Q: When there is no more concentration gradient, the [...] is 0.
A: net movement

Q: When net movement is 0, then [...] has been reached and [...] is 0.
A: chemical equilibirium; net diffusion

Q: Like charges [...] each other and unlike charges [...] each other.
A: repel; attract

Q: [...] molecules move towards areas of opposite charge, or down their [...]
A: Electrically charged; electrical gradient.

Q: Charged ions move down both their [...] and their [...], movement will stop once [...] is reached.
A: chemical concentration gradient; electrical gradient; electrochemical equilibirum

Q: Electrochemical equilibrium is reached when [...]
A: electrical foce is equal and in opposite direction to the chemical force.
Extra: That is, when both the chemical concentration gradient and the elecectrical charge gradient forces are equal in magnitude, there's not net movement.

Lipid-soluble substances include oxygen, carbon dioxide, fatty acids and some  steroid hormones.

Q: [...] substances can diffuse through the cell membrane directly.
A: Lipid-soluble

Q: Water soluble substances include [...] and [...]
A: water; many ions, ie. Na+ and K+.

Q: [...] cannot diffuse directly through the membrane, and require [...] or [...]
A: Water-soluble substances; protein channels; pores.

Factors that affect the rate of movement of diffusion are:
1. The size of protein channels
2. The charge on the molecule
3. The electrochemical gradient - the larger it is = greater rate of movement; and
4. The number of channels in the membrane.
Extra: Size of Protein Channels will limit the size of the molecule. Sugar molecules, for ex., are too large to diffuse through protein pores.
Charge on the Molecule (ex., Na+) will affect the rate of movement through channels because the proteins that make up the channels also have charges on them. Therefore, a positive ion will not go through a channel that has a positive charge.
The greater the Electrochemical Gradient of a molecule, the greater its rate of movement through the channels. Substances move down both their concentration & electrical gradients (opposite charges attract).
# of Channels in the Membrane affects the rate. Even if there’s a large concentration gradient for an ion, that ion will not move across the membrane unless there are channels for it. The more channels that exist, the more ions that will diffuse across the membrane.

Q: Facilitated diffusion is for [...] that cannot pass through simple diffusion or pores/channels.
A: large, water soluble molecules

Q: In [...] protein carriers are used to transport large, water soluble molecules and results in the [...] which will either pass or rotate the molecule through - this does not require energy.
A: facilitated diffusion; opening of a protein channel

Q: Facilitated diffusion does not require [...]
A: energy.
Extra: Energy = ATP

Q: The major difference between facilitated and simple diffusion is that facilitated diffusion's [...]
A: rate is limited by the number of avaliable proteins.

Q: When all carrier proteins are occupied they are [...]
A: saturated.
Extra: Consequently, the system cannot operate any faster. The speed at which the carrier can change shape or configuration is also limited.

Q: Chemical specificity and competitive inhibition is shown by [...] and [...]
A: facilitated diffusion; active diffusion.

Q: Active transport uses [...] and requires [...]
A: transmembrane proteins (more broadly, integral); ATP.

Q: Active transport requires energy because [...]
A: it moves molecules UP their conentration gradients, from low to high concentrations.
Extra: That is, it moves molecules against their concentration gradients.

Q: The [...] is an example of active transport.
A: sodium-potassium pump

Q: Like facilitated diffusion, active transport can be [...] and show [...] and [...]
A: saturated; chemical specificity; competitive inhibition.
Extra: Chemical Specificity (a given carrier protein will interact only with a specifically shaped molecule).
Competitive Inhibition (molecules that are very similar in shape will comptete in order to be transported by a carrier protein).

Q: When there is a net movement of water down its concentration gradient, this is called [...]
A: osmosis.

A solute is a substance being dissolved.
A solvent  does the dissolving.
You get a solution when you dissolve a solute in a solvent.

Q: A solution with a high concentration of solute will have [...] of water.
A: low concentration
Extra: Water is the solvent

Q: A solution with a low concentration of solute will have a [...] of water.
A: high concentration
Extra: Water is the solvent.

Q: In osmosis  [...] particles move from an area of [...] to [...]
A: solvent; high concentration; low concentration.
Extra: That is, osmosis is the movement of water down its concentration gradient.

Q: Osmosis across the cell membrane is affected by:
1. The [...] of the membrane to solutes in the intracellular and interstitial fluids;
2. The [...] of the solutes in the intracellular & interstitial fluids; and
3. The [...] across the cell membrane.
A: permeability; concentrations; pressure gradient

Q: A particle that causes osmosis is a [...]
A: osmotically active particle.

Na+, glucose, Cl- and K+ are osmotically active particles.

Q: An osmole describes [...]
A: the number of osmotically active particles in a solution.

Q: Units used to describe the concentration of a solution are:
1. Number of osmoles per [...]
2. Number of osmoles per [...]
A: kg of water; L of water

Q: [...] describes the ability of a solution to cause osmosis across a biological cell membrane.
A: Tonicity

An isotonic solution has the same concentration as body fluids, cell would remain same size.
A hypotonic solution has lower concentration of solute and would cause cell swelling.
A hypertonic solution has  higher concentration of solute and would cause cell shrinkage.

Q: The inside of the cell is [...] charged and the outside of the cell is [...] charged.
A: negatively; positively

Q: Most cells are not very permeable to Na+, Cl- and Ca++, they need [...] to pass, but they cannot move into the cell because there are few [...]
A: pores/channels; channels for them.
Extra: Just because they have a concentration gradient, doesn’t mean that they will diffuse in those directions. The cell membrane will determine just how many ions are allowed to move. The membrane, therefore, is permeable to a particular ion, & that permeability will vary depending on the ion & the particular type of cell.

Q: K+ can [...] down its concentration gradient due to membrane's permeability differences to different ions.
A: leak out
Extra: The membrane is more permeable to K+, so some will leak out down its concentration gradient.

Q: [...] is a charge difference between 2 points.
A: Electric potential

Q: Membrane potential is the [...]
A: charge difference between the innside (-) and outside (+) of the cell.

Different types of membrane potentials:
1. Equilibirum Potentials
2.Resting Membrane Potentials
3.Action Potentials
4.Excitatory and Inhibitory Postsynaptic Potentials
5.Generator Potentials

Q: The fluids inside and outside of the cell are [...] solutions, which means that they contain ions.
A: electrolytic

An electrical potential difference is established between the outside  and inside of the cell due to the accumulation of cations, outside and anions,inside.
Extra: Cations = Positively Charged Ions
Anions = Negatively Charged Ions

Q: Resting membrane potential is present in [...], and is due to the [...] difference between the inside and outside of the cell.
A: resting cells; electrical potential

Q: Resting membrane potential is [...]mV.
A: -70

Q: The equilibirum potential is the [...]
A: electrical potential that must be applied to the inside of the cell to stop the ion from moving down its concentration gradient.

Q: The [...] the concentration gradient, the [...] the equilibirum potential needed to stop the movement of an ion.
A: larger; larger

Q: Equilibirum potentials in vertebrate neurons for:
Na+ = [...]
K+ = [...]
Cl- =[...]
A: +60 mV; -90 mV; -70 mV
Extra: E(Na+) requires +60 mV. The cell membrane acts as a blockade preventing Na+ from leaking into the cell.
E(K+) requires -90 mV inside the cell to prevent it from leaking out.
E(Cl-) requires -70 mV outside the cell to keep it from leaking in (like charges repel).

The sodium-potassium pump pumps 3 Na+ ions out and 2 K+ ions in.

Q: An example of an integral membrane protein that is an electrogenic pump is the [...] pump.
A: sodium-potassium
Extra: It pumps 3 Na+ ions out & 2 K+ ions in. Since it contributes to the RMP by making the inside of the cell more negative (i.e., removes more positive Na+ from the cell than it replaces with K+), it’s called an electrogenic pump.

Q: Electrogenic is to [...]
A: produce a change in potential of a cell.

Q: The 2 types of excitable cells in the body are [...] cells and [...] cells.
A: nerve; muscle

Q: Excitable cells use [...] to do work and spontaneously [...] at their membrane.
A: membrane potential; regenerate electrical potentials

Q: The sodium-potassium pump prevents [...] and regulates [...]
A: cell swelling to the point of bursting; cell volume.

Na+ has a strong concentration gradient pushing it into the cell. To keep Na+ out, a  positive charge must be applied to the inside of the cell. Given the gradient for Na+ this charge must be +60mV.  Since the inside of the cell is actually -70mV there will be leakage. The sodium-potassium pump regulates this leakage.