Membrane Transport + Nucleus and Cytoplasm

very small hydrophobic molecules (O2 , CO2 )

membrane permeable

small uncharged polar molecules (H2 O, urea)

Mostly membrane permeable

large uncharged polar molecules (glucose)

Mostly membrane impermeable

Ions (Na + , K+ , Cl‐, Ca 2+ )

Completely impermeable

ONLY pass through by facilitated diffusion or active transport.

Completely impermeable

can pass through by facilitated diffusion or active transport.

Mostly membrane impermeable

some pass through by osmosis or diffusion, others don't

Mostly membrane permeable

Pores are __ __

non selective

Channels and carrier proteins are both __ __

highly selective

form aqueous tunnels across the lipid bilayer allowing specific solutes to pass through and cross the membrane.

Channel Proteins

Fast Transport

Channel Proteins

bind to specific solutes and undergo conformation changes in structure to transfer bound solutes across the membrane.

Carrier Proteins

Slow Transport

Carrier Proteins

Trans‐membrane proteins that permit the selective passage of ions through the membrane establishing an electrical current.

Ion Channels

Ion channels have __ transport

passive

1. Channels show __ __

2. Channels are __

Ion selectivity, gated

transient, rapid rise and fall of the membrane voltage

Action Potential

The net difference in charges between two locations (e.g., outside the cell membrane versus inside the cell)

Membrane Potential

Equilibrium voltage = __mV

‐70

voltage across a cell membrane when that cell is "at rest," __mV

Resting Membrane Potential, -70mV

K+ equilibrium voltage = __mV

‐94

Na + equilibrium voltage = __mV

+60

when the membrane potential moves back toward the resting potential in either direction.

Repolarization

when the membrane potential moves away from the resting potential in a more positive direction. (e.g. ‐70mV to ‐50mV)

Depolarization

when the membrane potential moves away from the resting potential in a more negative direction. (e.g. ‐70mV to ‐90mV)

Hyperpolarization

1. Membrane at __ voltage

2. A region of the membrane __ as Na+ flow into membrane

3. Adjacent regions of the membrane become __ initiating the __ __ along the axon

4. __ occurs as K + ions flow out resulting in repolarization of the initial region

5. __ continues down the axon and process is repeated propagating the electrical signal

resting, depolarizes, action potential, Hyperpolarization, repolarization, Depolarization.

__ voltage gated ion channels function in the release of neurotransmitters at synapses.

Calcium

__ voltage gated ion channels, the largest and most diverse, has its most important function as opposing sodium channels to generate Resting Membrane Potential.

Potassium

Channels present in neurons; control excitability.

Chloride

Transmembrane ion channel proteins which open to allow ions such as

Na+, K +, Ca 2+ , and/or Cl− to pass through the membrane in response to the binding of a chemical messenger.

Ligand Gated Channels

Acetylcholine Receptors are __ gated channels that release __ into the cytoplasm by accepting the __.

ligand, sodium, acetylcholine

ATP driven movement of molecules across a membrane against their gradient.

Primary Transport

Uses an electrochemical gradient generated by Active Transport as an energy source to move molecules against their gradient.

Secondary Transport

__ transport moves molecules against their gradient using either ATP or a generated electrochemical gradient.

Active

Primary transport: grouped based on their ability to catalyze auto (self) phosphorylation to drive the reaction.

P‐type ATPase Superfamily

Primary transport:

- Unidirectional

- Two NBD domains & two TMD domains

- Transport multiple substrates (i.e. amino acids, sugars, vitamins, proteins, lipids, etc.

- ATP‐hydrolysis driven transport

ABC Transporter Superfamily

Direction of transport is the same for both driving and driven molecule. Symport.

Co-transport

Direction of transport is opposite for the driving and driven molecule. Antiport.

Exchange

- Solutes move through open channels

- Fast passage rates (10,000 mol/sec)

- Passive Transport (open or closed)

- Water soluble solutes

Channel

- Solutes bind on one side of membrane and released on the other

- Slow passage rates (100 mol/sec)

- Active Transport (solute is facilitated across the membrane)

- Water soluble AND insoluble molecules

Carrier

Channels are always __

gated

Carrier proteins bind specific solutes and transfer them across

the lipid bilayer by undergoing __ changes

conformational

Evolutionary Origins of Eukaryotic Cells "the __ model"

autogenous

Eocyte used plasma membrane extensions to engulf bacteria. Lead to topographically different organelles like mitochondria and lysosomes compaired to the cytoplasm or nucleus.

inside out theory

nucleus & cytoplasm are topographically __

Similar

mitochondria or lysosome & cytoplasm are topographically __

Different

Continuous stretch of AA, typically 15-60 residues used to signal.

Signal sequences

3D conformation of AA forming a specific fold used to signal.

Signal patches

selective “gates” between compartments that actively transport specific macromolecules into topographically similar spaces.

Gated Transport

makes use of membrane-bound protein complexes to directly move specific proteins from one compartment to a topographically different compartment.

Transmembrane Transport

membrane enclosed transport intermediates from one compartment to another. Topographically different compartments.

Vesicular Transport

Gated transport into topographically similar spaces, between Nucleus and Cytoplasm, occurs via __ __ that act as selective gates.

nuclear pores

__ form the nuclear pore

nucleoporins

__ nucleoporins form the nuclear rings

membrane

__ nucleoporins form the central transporter

FG

__ nucleoporins form the spoke ring assembly, nuclear cage, and nuclear basket.

structural

The nuclear cage and basket extends into the __

nucleus

The spoke ring assembly extends into the __

Cytoplasm

Proteins <__nm enter the nucleus by free diffusion, all else via active transport.

5

Selectivity of nuclear pore complex model theory:

- Thermodynamic exclusion of cargo into the pore

Virtual Gate Model

Selectivity of nuclear pore complex model theory:

- FG filaments interact and form a selective 3D sieve

to exclude cargo by a 3D sieve

Selective Phase Model non saturated

Selectivity of nuclear pore complex model theory:

- FG filaments form the maximum number of interactions

resulting in a highly ordered mesh with even pore size

Selective Phase Model saturated

- Short – 5 residues

- Basic – (i.e. KKKRK)

- Can be located “anywhere” in the primary structure

- In some cases relies on a signaling patch

Nuclear Localization Signal

Transportins: Importin-alpha and Importin-beta

1. Importin-__ recognizes and binds to cargo with NLS.

2. Importin-__ binds to importin-__.

3. Importin-__ is the actual transport factor through the NPC.

alpha, beta, alpha, beta

Nuclear Import:

1. Nuclear Import Receptors (Importins) associate with Ran-__ and the cargo having a NLS and bring them to the NPC.

2. Somehow the cargo moves through the NPC

3. Once in the nucleus, Ran-__ displaces the cargo from the import receptor.

4. Receptor/Ran-__ complex moves back through the NPC to the cytoplasm.

5. Once back in the cytoplasm, Ran-__ is hydrolyzed to Ran-GDP by the action of Ran-__ and the process repeats.

GDP, GTP, GTP, GTP, GAP

Ran-__

- Distinct from Ran and causes Ran to release GDP and bind to GTP in the nucleus.

- Promotes the exchange of Ran-GDP with GTP.

GEF

Ran-__

- A separate protein that causes Ran to hydrolyze GTP in the cytoplasm.

- Promotes the conversion of Ran-GTP to Ran-GDP (hydrolysis)

GAP

__ GDP outside of the nucleus, __ GDP the nucleus (compared to the cytosol).

More, less

__ GTP outside of the nucleus, __ GTP the nucleus (compared to the cytosol).

Less, more

Nuclear Export:

1. Nuclear Export Receptors associate with Ran-__ and the cargo having a NES and bring them to the NPC. (NES - LxxxLxxLxL)

2. Somehow the cargo moves through the NPC

3. Once in the cytosol, Ran-__ is hydrolyzed from the complex causing release of the cargo.

4. Ran-__ dissociates from receptors.

5. Process is repeated.

GTP, GTP, GDP

Ran-__ associates with cargo containing a NES.

GTP

Ran-__ associates with cargo containing a NLS.

GDP

nuclear export receptors __ directly bind to RNA

dont

__ processing occurs during Co-Transcriptional Regulation

RNA

__ Proteins (Transcription/Export) - adaptor for nuclear export of mRNA

TREX

__ Proteins (Serine/Arginine-rich) - adaptor for nuclear export of mRNA

SR

Tap-p15 is a __ __ __ protein

nuclear export receptor

Travel of the hnRNA through the NPC is an __ dependent process

ATP

__ complex is formed by TREX, SR, and Tap-p15 proteins.

mRNP

Nuclear Export of hnRNA:

1. mRNP complex moves to the NPC.

2. Once in the channel of the NPC, the __ complex proteins are removed.

4. This prevents sliding of the mRNA back through the NPC to the nucleus.

5. mRNA goes through __ by the ribosomes

mRNP, Tap-p15, translation

Proteins containing nuclear localization signals are __ transported inward through the nuclear pore complex.

actively

The __ __, provides directionality for nuclear

transport.

GTPase Ran

Proteins like ribosome subunits and RNPS associated with RNA molecules contain nuclear __ signals that direct their active transport __ through the pore complexes.

export, outward

Proteins containing nuclear __ signals are actively

transported __ through the nuclear pore complex.

localization, inward