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EOM 1 - Test 1 > Lecture 15: Membrane Transport > Flashcards

Lecture 15: Membrane Transport Flashcards

Membrane Transport

1
Q

What does the rate of diffusion through a lipid bilayer depend on?

A

Membrane Permeability Surface Area of Membrane Thickness of the Membrane Concentration Gradient

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2
Q

What is the equation for membrane permeability?

A

Membrane Permeability = Lipid Solubility / Molecular Size

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3
Q

What is Fick’s Law of Diffusion?

A

Rate of Diffusion = (Surface Area x Concentration Gradient x Membrane Permeability ) / Membrane Thickness

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4
Q

What is created as ions are out of balance across a membrane? What direction of movement does this promote?

A

Electrical Gradient (Membrane Potential Vm) Down the gradient towards equilibrium

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5
Q

What is the term for an out of balance concentration of chemicals and ions?

A

Electrochemical Gradient

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6
Q

What are the three major classes of membrane transport proteins?

A

Channels Transporters ATP-Powered Pumps

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7
Q

What is the function of Channel Proteins? Can any molecule pass? Are they always open? What form of transport are they considered?

A

Transport water, ions, and few small hydrophilic molecules No, they are selective Most are gated, only open to response to stimulus Facilitated Diffusion

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8
Q

What is the structure and function of Transporters (Carrier Proteins)? What is their speed compared to Channel Proteins?

A

Transporters bind the substrate with high specificity and undergo conformational change to move substances across the membrane Much slower, but can transport much larger molecules

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9
Q

Define the Following Transporters: Uniporter: Symporter: Antiporter: Which are Cotransporters? What is a Cotransporter?

A

Uniporter: Move single type of substrate, only occurs DOWN gradients Cotransporters are Symporter/Antiporter: Symporter: Move substrates in same direction Antiporter: Move substrates in opposite direction Cotransporters often transport a substrate against its gradient, by coupling to transport of substrate moving DOWN it’s gradient Termed “Secondary Active Transport”

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10
Q

What is the structure and function of ATP-Powered Pumps?

A

Use energy from hydrolysis of ATP to transport substances UP their concentration gradient. These are much slower, referred to as primary active transport.

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11
Q

What is an aquaporin?

A

Family of integral membrane channels that selectively transport water

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12
Q

What is primary route for movement of water into/out of cells?

A

Aquaporins

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13
Q

What molecules can/can’t pass through aquaporins?

A

Mainly water, but also small solutes such as glycerol Impermeable to charged particles

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14
Q

What is the structure and function of an ion channel? How are they gated? Are they selective?

A

Transmembrane protein that allows ions to flow DOWN their concentration gradient. Gated: 1) Membrane Voltage 2) Chemical Signals 3) Physical Forces Yes, selective to certain ions and gating

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15
Q

What are Leak Channels?

A

Ion Channel that is always open, ions pass through them continuously

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16
Q

What are Gated Channels? What methods do these gates operate?

A

Ion Channels that open/close in response to stimulus. 1. Voltage Gated (Membrane Voltage) 2. Ligand Gated (Chemical Signals) 3. Mechanically Gated (Physical Force)

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17
Q

How does a Ion Channel select for passage?

A
  1. Charge of Ion 2. Size of Ion 3. Amount of water attracted to and retained by ion (hydration shell)
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18
Q

Are all Ion Channels the same selectivity? What is a given exception from lecture?

A

Monovalent Cation Channels permit passage of Na and K

19
Q

What are Carrier-Mediated Transport proteins? What are their three major properties?

A

Proteins which bind to specific substrates, and Uber them across cell membranes. Operate by alternating between two conformational states. 1. Specificity 2. Competition 3. Saturation

20
Q

For Carrier-Mediated Transport proteins, what is an analogue to the three major properties and their rates?

A

Enzyme Kinetics Other similar passengers can “compete” and inhibit molecules from getting in their Uber. Once all the Ubers are taken up, there is saturation and the limiting step is release of substrate from protein (or other factor)

21
Q

What is Facilitated Transport (Facilitated Diffusion)? Example?

A

Movement of ion or molecule across membrane DOWN it’s concentration gradient at rate faster than simple diffusion Example is GLUT1

22
Q

What is the structure and function of the GLUT1 Transporter?

A

Exists in two conformations, T1 and T2. T1 binding site is exposed to outer surface of plasma protein. T2 binding site is exposed to the inner surface.

23
Q

What are the four steps of GLUT1 Transport? What is this an analogue to?

A
  1. Glucose in the interstitial fluid binds to site on T1 to form Glucose-out-T1, lowering Ea 2. Conformational change results in Glucose-in-T2, resulting in passage 3. Glucose is released from T2 into cytoplasm 4. Transporter returns to T1 conformation, ready to get back to work Analogous to enzyme-catalyzed reaction
24
Q

What regulates the GLUT4 transporter?

A

Insulin

25
Q

What is the result of Glucose being chemically unchanged during transport?

A

Glucose transport across the membrane by facilitated diffusion occurs in either direction

26
Q

For Glucose transport, when does 1/2 Vmax occur?

A

[Glucose]out = Kt

27
Q

What is the structure and function of SGLT1 (Na+/glucose cotransporter 1)? How many of each molecule does it transport? How are these molecules moving wrt their gradients? What provides any required energy?

A

Symporter in the small intestines and kidneys that transport glucose and sodium in the same direction. One glucose/two sodiums Glucose moves UP, Sodium moves DOWN Sodium flow provides energy, Na/K ATPase pump maintains gradient.

28
Q

What form of transport is the SGLT1 system? Why?

A

Secondary Active Transport because the electrochemical gradient for sodium movement is maintained by a Na/K ATPase

29
Q

What system does the SGLT1 system work with for exit?

A

GLUT2-mediated facilitated diffusion

30
Q

The Chloride-Bicarbonate Exchanged in RBCs is an example of what? What type of protein is this?

A

Antiporter Anion Exchange (AE) Protein

31
Q

What molecules are moved by the Chloride-Bicarbonate Exchanger?

What is the result?

What is the function of this system?

A

HCO3- and Cl-

HCO3- moved into cell

Cl- moved out of cell

– Electrochemically neutral

Function is icrease CO2 carrying capacity of blood

32
Q

What converts CO2 to HCO3- in systemic capillaries and pulmonary capillaries?

A

Carbonic Anhydrase

33
Q

What is the structure and function of P-Class Ion Pumps?

A

Undergo reversible phosporylation during transport process.

34
Q

How many molecules does the Na+/K+ ATPase move?

A

3 Na+ OUT

2 K+ IN

Per ATP

35
Q

What is the structure and function of ABC Transporters (ATP-binding cassette)?

Do they bring substrates in or out of cell?

A

Four core domains, two transmembrane domains span membrane in multipass fashion, forming a pathway for solutes to cross.

Other two ATP-bdining cassette (ABC) domains face the cytostolic surface.

Can function as importers or exporters

36
Q

In eukaryotic cells, what is a primary funtion of ABC Transporters?

What has this function led to for cancer treatments?

What disease are these class of transporters related to?

A

Exporters to empty toxic effects of various endogenous metabolites and xenobiotics

Multidrug resistant transporters are found in certain tumor cells, causing designed drugs to be exported from cell. Can be related to antibiotic resistance as well.

In Cystic Fibrosis, ABC transporter functions a a Cl- transporter.

37
Q

What type of compounds inhibity the Sodium Potassium ATPase?

A

Digoxin and Ouabain

38
Q

What are the two main conformations of the Sodium Potassium ATPase? *** review w/YouTube vids…

A

E1 : 3 high affinity Na, 2 low affinity K ; phosphorylation

E2 : Na is released, dephosphorylation

39
Q

What is the structure and function of V-class pumps?

A

Utilize energy from ATP-Hydrolysis to pump H+ against the gradient from the cytosol into the intracellular organelles

Major function to lower the pH

40
Q

What is the structure and function of F-class proton pumps?

A

Important in mitochondria, movement of protons DOWN gradient is used to generate ATP

Also called ATP Synthase

41
Q

What maintains the chemical and eletrochemical non-equilibrium in various biological tissues?

A

Transporters

42
Q

What substances are impermeable to phospholipid bilayers?

A

Ions, Amino Acids, Sugars, other water soluble molecules

43
Q

What molecules can diffuse across a phospholipid bilayer?

A

Small, liphilic molcules; certain gasses (CO2, O2), few small uncharged polar molecules

44
Q

Can water diffuse across a membrane? What impact does cholesterol have on this?

A

Yes, but not rapid

Low cholesterol content = more permeable to water

EOM 1 - Test 1 (16 decks)

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