Biochem Unit 1 Lecture 4 Passive, Facilitated, and Active Transport

--- is a movement of biochemicals and other atomic or molecular substances across membranes that does not require an input of chemical energy.

Passive transport

--- is a transport process in which molecules or ions which would otherwise cross the membrane with great difficulty can use transmembrane protein channels to cross this membrane

Facilitated diffusion

Facilitated diffusion is a transport process in which molecules or ions which would otherwise cross the membrane with great difficulty can use --- to cross this membrane

transmembrane protein channels

--- is the movement of molecules across membranes by mechanisms that use some form of energy expenditure to accomplish movement.

Active transport

Active transport usually moves molecules --- their concentration or electrochemical gradient

against

The --- interior of a lipid bilayer prevents the passage of most polar molecules

hydrophobic

The hydrophobic interior of a lipid bilayer prevents the passage of most --- molecules

polar

The major classes of membrane transport proteins are known as --- (carriers or permeases) and ---.

transporters; channels

In the case of a single uncharged molecule, the --- on each side of the membrane drives passive transport and determines its direction.

concentration

In the case of a solute that carries a net charge, both its --- and the --- across the membrane, i.e., the membrane potential, influence transport.

concentration gradient; electrical potential difference

In the case of a solute that carries a net charge, both its concentration gradient and the electrical potential difference across the membrane, (the ---), influence transport.

membrane potential

Smaller, hydrophobic molecules diffuse --- across a bilayer.

faster

Give some examples of hydrophobic molecules

O2, CO2, N2, benzene

Give some examples of small uncharged polar molecules

H2O, urea, glycerol

Give some examples of large uncharged polar molecules

glucose, sucrose

Give some examples of ions

H+, Na+, K+, Ca2+, Cl-, etc

Put the following categories in order of MOST permeable to LEAST permeable in lipid bilayer.

Large uncharged polar molecules

Small uncharged polar molecules

Ions

Hydrophobic molecules

Hydrophobic molecules

Small uncharged polar molecules

Large uncharged polar molecules

Ions

Kinetics

For ---, the rate of transport is proportional to concentration of molecule being transported.

Simple Diffusion

Kinetics

For ---, the rate of transport reaches a maximum when transport protein is saturated.

Carrier Mediated diffusion

Kinetics

For Carrier Mediated diffusion, the rate of transport reaches a maximum when transport protein is ---.

saturated

List the 3 ways to drive active transport.

Coupled, ATP-driven, Light-driven pumps

Describe Coupled Active Transport.

When transport of one molecule against a concentration gradient is coupled to another molecule being transport down its concentration gradient

Describe ATP-driven Active Transport

involves energy derived from ATP hydrolysis to move a molecule against its concentration gradient

Describe Light-driven pumps (active transport)

found in bacteria, uses energy from light

List the 3 types of carrier-mediated transport.

uniport, symport, antiport

Which of the following types of carrier-mediated transport are coupled transport?

uniporter

symporter

antiporter

symporter

antiporter

Glucose Carrier is Driven by an --- Gradient

Na +

Glucose Carrier

Binding of Na + and glucose is ---; ie. when one binds this facilitates the binding of the other

cooperative

Glucose Carrier

The glucose carrier in the gut oscillates between 2 states (A and B).

In State A the extracellular Na + concentration is much --- than the cytosol concentration. When Na + binds to the carrier, this induces glucose to bind.

When both are bound this induces a --- that results in the release of glucose and Na + into the cytosol

higher; conformational change

Glucose Carrier

The glucose carrier in the gut oscillates between 2 states (A and B).

In State A the extracellular --- concentration is much higher than the cytosol concentration. When --- binds to the carrier, this induces --- to bind.

When both are bound this induces a conformational change that results in the release of glucose and Na + into the ---

Na +; Na +; glucose; cytosol

Intracellular K+ is high; Intracellular Na + is low compared to extracellular concentrations.

These concentrations are maintained by the ---

Na+ - K+ pump.

Na+ - K+ pump

Intracellular K+ is ---; Intracellular Na + is --- compared to extracellular concentrations.

high; low

Na+ - K+ pump

For every molecule of ATP that is hydrolyzed

3 Na + molecules are pumped --- and 2 K+ molecules are pumped -- cell.

out; into the cell

The Na+ - K+ pump is an example of an ---.

antiporter

Cell Junctions

Occluding junctions include --- junctions (vertebrates only) and --- junctions (invertebrates mainly).

tight; septate

Cell Junctions

--- junctions include tight junctions (vertebrates only) and septate junctions (invertebrates mainly).

Occluding

Cell Junctions: ANCHORING JUNCTIONS

Actin filament attachment sites include ---junctions (adherens junctions) and --- junctions (focal adhesions)

cell-cell; cell-matrix

Cell Junctions: ANCHORING JUNCTIONS

Actin filament attachment sites include cell-cell junctions (---) and cell-matrix junctions (---)

adherens junctions; focal adhesions

Cell Junctions: ANCHORING JUNCTIONS

--- attachment sites include cell-cell junctions (adherens junctions) and cell-matrix junctions (focal adhesions)

Actin filament

Cell Junctions: ANCHORING JUNCTIONS

Intermediate filament attachment sites include --- junctions (desmosomes) and --- junctions (hemidesmosomes).

cell-cell; cell-matrix

Cell Junctions: ANCHORING JUNCTIONS

Intermediate filament attachment sites include cell-cell junctions (---) and cell-matrix junctions (---).

desmosomes; hemidesmosomes

Cell Junctions: ANCHORING JUNCTIONS

--- attachment sites include cell-cell junctions (desmosomes) and cell-matrix junctions (hemidesmosomes).

Intermediate filament

Cell Junctions

--- junctions include gap junctions and plasmodesmata (plants only).

Communicating

Cell Junctions

Communicating junctions include --- and --- (plants only).

gap junctions; plasmodesmata

Cell Junctions

Signal- relaying junctions include ---

chemical synapses.

Cell Junctions

--- junctions include chemical synapses.

Signal- relaying

--- and --- create a barrier to the movement of molecules extracellularly between cells, creating the need for intracellular and/or transcellular transport

Tight junctions; adherens junctions

Cadherins

Cadherins are ---, meaning they are made up of two identical copies of the protein. They have a single --- domain, and a long extracellular domain. The intracellular domains are linked to the --- cytoskeleton.

homodimers; transmembrane; actin

Cadherins

The extracellular part of a cadherin is made up of --- cadherin repeats, with --- binding sites located between each pair of repeats.

5; Ca2+

Cadherins

When --- is not bound, the extracellular parts of the cadherin is floppy. As more --- binds, the structure becomes more rigid.

When enough --- is bound, the cadherin dimer extends from the surface and binds to a cadherin dimer on a neighboring cell.

Ca2+; Ca2+; Ca 2+

Cadherins

If --- is removed, the extracellular part of the protein becomes floppy and is degraded by proteolytic enzymes.

Ca2+

Cadherins

If Ca2+ is removed, the extracellular part of the protein becomes --- and is degraded by ---.

floppy; proteolytic enzymes

The cell is electrically ---

neutral

Gap Junctions are formed by ---.

connexins

--- are protein "tubes" composed of connexin monomers which connect two cells by penetrating the cell membranes of two adjacent cells.

Provides a fluid filled space (tunnel) for small materials to pass through between cells.

Gap junctions

Examples of materials transported via gap junctions are --- and ---

calcium and ATP

--- contribute to the electrical coupling of heart, neurons, and retinal tissues.

Gap junctions

True or false?

Gap junctions only exist in an open state.

False

Gap junctions can exist in a closed and in an open state.

Molecules of --- or less can pass thru gap junctions.

1000 MW or less

--- are monomers that form --- which are hexamers.

Connexins; connexons

Connexons can be ---, meaning they are made up of only one type of connexin.

Connexons can also be ---, meaning they are made up of multiple types of connexins.

homomeric; heteromeric

Humans have --- distinct connexins, each encoded by its own gene.

14

True or false?

Most cells express more than one type of connexin, making heteromeric connexons.

true