Permeability of Membranes

what kinds of molecules can easily move across plasma membrane

hydrophobic molecules (O2, CO2, N2, steroid hormones)

small uncharged polar molecules (water, urea, glycerol)

what kinds of molecules can not easily move across plasma membranes

large uncharged polar molecules (glucose and sucrose)

ions

_____ (polar/non-polar) molecules are strongly prevented from diffusing across plasma membrane

polar

what are the four main types of transport

1. simple diffusion

2. facilitated diffusion via channels

3. facilitated diffusion via carriers

4. active transport

what type of transport requires energy to proceed

active transport

what types of transport does not require energy to proceed

passive transport (simple diffusion, osmosis, facilitated diffusion)

what is simple diffusion

unassisted movement of solute molecules from areas of high concentration to low conentration

what is osmosis

solvent (ex water) moves from area of high solvent (low solute concentration) to low solvent (high solute concentration)

when does osmosis occur and not simple diffusion

osmosis occurs when the solute itself cannot move across the membrane but water (solvent) can

compare hypertonic vs isotonic vs hypotonic solutions

hypertonic - Water flows out of the cell and into the surrounding solution because higher solute concentration (lower water concentration) outside the cell

isotonic - Water flows in and out at the same rate because there’s equal solute and water concentration inside and outside the cell

hypotonic - Water flows into the cell from the surrounding solution because lower solute concentration (and higher water concentration) outside the cell.

what happens to animal cells in isotonic, hypertonic, and hypotonic solutions?

hypertonic - shriveled cell

isotonic - normal cell

hypotonic - lysed cell

what happens to plant cells in isotonic, hypertonic, and hypotonic solutions?

hypertonic - plasmolyzed cell

isotonic - flaccid cell

hypotonic - turgid cell

what drives simple diffusion

entropy (concentration gradient - ie disorder)

what kinds of molecules is simple diffusion limited to

non polar molecules and steroid hormones

why does water flow slower through membrane via simple diffusion

water is a polar molecule trying to pass through the hydrophobic (water-fearing) lipid core of the phospholipid bilayer

what is facilitated diffusion

a type of passive transport where substances move across a cell membrane from an area of high concentration to an area of low concentration with the help of specialized transport proteins

can most substances diffuse across the membrane at a reasonable rate? why?

no - The interior of the membrane blocks polar and charged molecules from passing freely

what are uniporters

integral membrane proteins (carriers or channels) that transport a single type of molecule across a cell membrane down its concentration gradient through facilitated diffusion

why is simple diffusion linear and facilitated not

Simple diffusion - linear because molecules pass directly through the lipid bilayer without a limit on how many can cross at once

facilitated diffusion - not linear because it relies on a fixed number of proteins that can become saturated (ie have a set rate of transport)

what are the three types of carrier proteins

• uniports

• symports

• antiport

compare uniports, symports, and antiports

uniport - Binds and moves a single specific solute down its concentration gradient that relies on passive transport

symport - Moves two different solutes simultaneously in the same direction across the membrane that relies on ion gradients (secondary active transport)

antiport - Moves two different solutes in opposite directions—one enters the cell while the other exits that relies on ATP hydrolysis or ion gradients

what are carrier protein also known as

permeases

explain how the passive glucose transporter works

1. A glucose molecule binds to a specific binding site on the exterior-facing conformation of the carrier protein

2. The binding of glucose triggers a physical shape change in the protein

3. this shape shift opens the binding pocket toward the inside of the cell, releasing the glucose molecule into the cell

4. After releasing the glucose, the protein returns to its original shape, ready to bind another molecule

what kind of channels do channel proteins form

hydrophilic channels

are protein channels passive or active

passive

what are three stimuli that can act as gated protein channels

• voltage gated channels

• light gated channels

• ligand gated channels

what happens to an ions hydration shell as it moves along a channel protein

As an ion enters and moves through a channel protein, its surrounding hydration shell is partially or completely stripped away and replaced on the other side of the membrane

what are porins

specialized channel proteins forming hydrophilic channels that allow water and large molecules in and out of cell

how are porins important for antibiotic resistance

allow hydrophilic molecules, like many antibiotics, to cross into the bacteria cell, the porins mutate leading to antibiotic resistance

compare direct and indirect active transport

direct - Uses ATP hydrolysis directly to transport ions across membrane

indirect - Uses the stored energy of an ion gradient across membrane

what is the direction ions are pushed in active transport

against their concentration gradient—moving from an area of lower concentration to an area of higher concentration

compare P-type ATPases, V-type ATPases, F-type ATPases

P-type ATPases

• does form a temporary phosphorylated intermediate

• consumes ATP to pump protons

V-type ATPases

• Does not form a phosphorylated intermediate

• consumes ATP to pump protons

F-type ATPases

• Does not form a phosphorylated intermediate

• produces ATP to pump protons

what is an example of P-type ATPases

sodium-potassium pump (3 Na+ and 2 K+)

how many molecules of ATP are required to move 3 Na+ ions in P-type ATPases

1 molecule of ATP to transport 3 Na⁺ ions

compare the pH level inside and outside the cell via V-type ATPases

lowers the pH inside the cell (pH 5) compared to outside the cell (pH 7)

describe the F-type ATPases

rotary molecular engines that primarily synthesize ATP from ADP and inorganic phosphate using a proton-motive force

what type of ATPase is ATP synthase

F-type ATPase

what is a function of F-type ATPase

uses proton gradient to drive ATP synthase

what is a function of V-type ATPase

keeps pH of compartments low = activates enzymes

what is a function of P-type ATPase

potassium/sodium pump

what are ABC transporters

membrane proteins that use energy from breaking down ATP to move a wide variety of molecules across cell membranes

describe the four domains of ATB transporters

2 ATP binding cassettes

2 membrane spanning domains

what transporters play an important rule in multidrug resistance of cancers

ABC transporters

what is an important kind of ABC transporter

CFTR (Cystic Fibrosis Transmembrane Conductance Regulator)

how does CFTR work

• channel that moves negatively charged chloride ions out of cells

• When chloride moves outside the cell, it attracts a thin layer of water. This keeps mucus thin and freely flowing.

• The watery layer allows cilia to sweep back and forth, clearing mucus and trapped germs out of the lungs

is CFTR a passive or active transporter

passive

what are three consequences of mutations in CFTR

1. pancreatic ducts get clogged so digestive enzymes can’t reach gut

2. bacteria accumulate in airways

3. skin CFTR reabsorbs salt before reaches skin (overly salty sweat)

what are two types of CFTR mutations

1. pores not working - Cl ions cannot pass through the channel

2. the protein is made but doesn’t embed into the membrane (just free floating)

what is indirect active transport

the energetically unfavorable transport of one solute is linked to the energetically favorable transport of another

what kind of transporter is the Na/glucose system

symporters - secondary active transporters

compare Bacteriorhodopsin vs channelrhodopsin vs halorhodopsin

Bacteriorhodopsin

• Light-driven proton pump

channelrhodopsin

• Light-gated ion channel

halorhodopsin

• Light-driven chloride pump