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MEDICAL BIOPHYSICS > MEMBRANES AND POTENTIALS > Flashcards

MEMBRANES AND POTENTIALS Flashcards

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USMLE® Step 1 flashcards
1
Q

WHAT ARE THE SPECIALIZED FUNCTIONS OF THE CELL?

A

-gas transport
-contraction
-energy storage
-hormone production
-action potential transmissions

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2
Q

WHAT MAKES THE MEMBRANE SELECTIVELY PERMEABLE?

A

-lipids and proteins

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3
Q

WHAT ARE THE FUNCTIONS OF THE CYTOPLASMIC MEMBRANE / PLASMALEMA?

A

-selective transport
-cell communication and signaling
-maintain homeostasis
-compartmentalize the cell
-energy storage and transfer
-chemical reactions
-separate external environment

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3
Q

WHAT ARE GLYCOCALYX?

A

-protective cover of some cells formed of oligos
-protects against chemical and mechanical damage

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4
Q

WHAT ARE THE DIFFERENT TYPES OF PROTEINS IN THE MEMBRANE?

A

-integral / intrinsic (embedded in membrane)
-transmembrane (extend all through membrane = alpha/beta sheets)

-peripheral membrane / extrinsic (bound to outer surfaces of membrane by covalent bonds to integral proteins)

-carrier proteins (undergo conformational changes to allow the passage of molecules through membrane)

-channel proteins (gated proteins that open and close to allow material in and out of the cell)

-transport proteins (carrier proteins and channel proteins)

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5
Q

WHAT IS ACTIVE TRANSPORT?

A

-solute moved against concentration gradient
-proteins pump solutes across membrane
with ATP
-indirect hydrolysis = secondary active transport

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6
Q

WHAT IS PASSIVE TRANSPORT?

A

-semipermeable membrane separates 2 compartments of different solute concentrations, over time the solute will diffuse until equilibrium is reached
-spontaneous phenomenon that increases the entropy and decreases the free energy

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7
Q

WHAT ARE ANCHORING PROTEINS?

A

-proteins (integrin) anchor the cell to
extracellular matrix/micro filaments

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8
Q

WHAT IS SIGNAL TRANSDUCTION?

A

-receptors bind molecules (hormones)
to transmit information

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9
Q

WHAT IS CELL RECOGNITION?

A
  • glycoproteins or other proteins that act as
    an identification tag
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10
Q

WHAT IS AN INTERCELLULAR JUNCTION?

A
  • adhesion of proteins that attach cells
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11
Q

WHAT IS DIFFUSION?

A

-a type of passive transport
-free transport of small non-polar molecules across the membrane

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12
Q

WHAT IS OSMOSIS?

A

-a type of passive transport
-solvent molecules go through a semi permeable membrane from low concentration to high concentration

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13
Q

WHAT IS A MEMBRANE CHANNEL?

A

-a type of passive transport
-transmembrane protein that does not need additional energy and can regulate whether it is open or closed
-cell specific

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14
Q

WHAT IS ENDOCYTOSIS?

A

-molecules are taken into the cell by invagination of molecules

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15
Q

WHAT IS EXOCYTOSIS?

A

-molecules are expelled from the cell through fusion of membranes

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16
Q

WHAT IS THE CHARGE OF THE MEMBRANE?

A

-inside is negative and outside is positive

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17
Q

WHAT IS THE MEMBRANES POTENTIAL AT REST?

A

range from -50 to -100mV

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18
Q

WHAT IS THE ROLE OF THE SODIUM-POTASSIUM PUMP?

A

-actively transports sodium out of the cell and potassium into the cell in the ratio of 3Na to 2K
-energy provided via ATP

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19
Q

WHY IS THE RESTING POTENTIAL ON THE MEMBRANE?

A

-maintain equilibrium during electro-chemical activity
-channels
-osmosis
-permeability
-active transport

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20
Q

WHAT IS VOLTAGE?

A

-measure of the potential of separated charges for doing work

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21
Q

WHERE IS POTASSIUM HIGH IN THE CELL?

A

-inside

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22
Q

WHERE IS SODIUM HIGH IN THE CELL?

A

-outside

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23
Q

WHAT DOES THE GIBBS DONNAN EQUILIBRIUM SAY?

A

-when 2 solutions containing ions are separated by membranes that are permeable to some of the ions and not to other, an electrochemical gradient is established
-electrical and chemical energies on either side of the membrane are equal and opposite to each other

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24
Q

WHAT IS THE NERNST EQUATION?

A

-allows us to predict the magnitude of an equilibrium diffusion potential from a particular distribution of ions

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25
Q

IF ONLY UNIVALENT IONS AND CONSTANT TEMPERATURE WHAT IS THE VOLTAGE FOR A CATION?

A

V = -59 log ([Xi]/[Xo]) for a cation

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26
Q

IF ONLY UNIVALENT IONS AND CONSTANT TEMPERATURE WHAT IS THE VOLTAGE FOR AN ANION?

A

V = +59 log ([Xi]/[Xo]) for a anion

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27
Q

EXPLAIN THE PROCESS OF SIGNAL TRANSMISSION, NERVE IMPULSE AT A SYNAPSE

A
  1. The resting membrane is polarized (PUMP)
  2. Stimulus initiates local depolarization (VOLTED GATED SODIUM OPEN)
  3. Depolarization and generation of an action potential
  4. Propagation of the action potential
  5. Repolarization (VOLATAGED GATED POTASSIUM OPEN)
  6. Initial ionic conditions restored
28
Q

WHAT IS THE ABSOLUTE REFRACTORY PERIOD?

A

-axon membrane is incapable of producing another AP
-> shorter in neurons than in cardiomyocytes

29
Q

WHAT IS THE RELATIVE REFRACTORY PERIOD?

A

-Voltage-gated channel shape alters at the molecular level
-Voltage-gated K+ channels are open
-Axon membrane can produce another action potential,
but requires stronger stimulus

30
Q

WHAT IS AN ACTION POTENTIAL?

A

-a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory
-action potential begins at the axon hillock as a result of depolarisation
-During depolarisation voltage-gated sodium ion channels open due to an electrical stimulus.
- As the sodium ions rush back into the cell, their positive charge changes potential inside the cell from negative to more positive.
-Potassium channels are then activated, and there is an outward current of potassium ions, returning the electrochemical gradient to the resting state
-refractory period (1-5ms) prevents action potential from traveling backwards

30
Q

WHAT IS THE THRESHOLD POINT?

A

-the potential which must be reached to form an action potential

31
Q

WHAT IS THE FUNCTION OF NEURONS?

A

-generation of action potentials
-integration of input signals
-thresholding of input signals

32
Q

WHAT IS HYPERPOLARISATION?

A

-repolarisation overshoots the resting membrane potential, making the membrane potential more negative

33
Q

WHERE DO ACTION POTENTIALS OCCUR AND WHY?

A

-the nodes of ranvier the gaps between myelin sheaths as they contain lots of ion channels

34
Q

HOW DOES MYELIN SPEED UP NERVE CONDUCTIONS?

A

-increasing the membrane resistance and reducing the membrane capacitance

35
Q

WHAT IS SALTATORY CONDUCTION?

A

-If the depolarisation exceeds the threshold, it initiates another action potential which is conducted to the next node.
-In this manner, an action potential is rapidly conducted down a neuron.

36
Q

WHAT CONTAINS A HIGH CONCENTRATION OF CALCIUM IONS?

A

-sarcoplasmic reticulum

37
Q

EXPLAIN MUSCLE CONTRACTION

A

-occurs when an action potentials reaches the neuromuscular junction and a chemical message is released by the motor neuron
-the chemical message, a neurotransmitter called acetylcholine, binds to receptors on the outside of the muscle fiber. That starts a chemical reaction within the muscle.
-Open channels allow an influx of sodium ions into the cytoplasm of the muscle fiber.
-The sodium influx also sends a message within the muscle fiber to trigger the release of stored calcium ions.
-The calcium ions diffuse into the muscle fiber.
-The relationship between the chains of proteins within the muscle cells changes, leading to the contraction.
-When the stimulation of the motor neuron providing the impulse to the muscle fibers stops, the chemical reaction that causes the rearrangement of the muscle fibers’ proteins is stopped. This reverses the chemical processes in the muscle fibers and the muscle relaxes.

38
Q

WHAT ARE THE COMPONENTS OF THE PLASMA MEMBRANE?

A

-Phospholipid
-Cholesterol
-Glycolipid
-Sugar
-Polytopic protein (transmembrane protein)
-Monotopic protein (e.g. a glycoprotein)
-Monotopic protein anchored by a phospholipid
-Peripheral monotopic protein (e.g. a glycoprotein)

39
Q

EXPLAIN THE THERMODYNAMIC FLOW OF SUBSTANCES.

A

-If the exchange of substances occurs in the
direction of the gradient (in the direction of decreasing potential) there is no requirement for an input of energy
-If the transport is against the gradient (in the direction of increasing potential) it will require the input of energy

40
Q

WHEN WILL AN EQUILIBRIUM POTENTIAL BE REACHED?

A

-a membrane which is permeable to potassium but not to sodium

41
Q

HOW ARE ACTION POTENTIALS IN NEURONS MOST COMMONLY INITIATED?

A
  • initiated by excitatory postsynaptic potentials from a presynaptic neuron, typically by release of neurotransmitter molecules which are consequently bind to receptors on the postsynaptic cell
42
Q

WHAT IS THE “ALL OR NOTHING PRINCIPLE”?

A

-the amplitude of an AP is independent of the amount of current that produced it. The frequency of APs is correlated with the intensity of a stimulus.

43
Q

WHAT IS THE WATER WEIGHT CONTENT OF THE HUMAN BODY?

A

60%

44
Q

WHAT HAPPENS TO BODY WATER CONTENT WITH AGE?

A

it decreases

45
Q

EXPLAIN THE FLUID-MOSAIC MODEL.

A

it states the the plasma membrane is more of a fluid structure than a rigid structure

46
Q

WHAT ARE TYPICAL MEMBRANE COMPONENTS?

A

phospholipid
cholesterol
glycolipid
sugar
transmembrane polytopic protein
glycoprotein monotropic protein
monotropic protein anchored by phospholipid
peripheral glycoprotein monotropic protein

47
Q

EXPLAIN THE PHOSPHOLIPIDS AMPHIPHATIC PROPERTIES

A

arranged that hydrophilic heads face the external environment while the hydrophobic heads face each other and the internal environment

48
Q

WHAT ARE CARRIER PROTEINS?

A

a type of transport protein
-undergo a conformational change in order for molecules to go through the membrane

EG: ABC transports which utilize ATP to do this

49
Q

WHAT ARE CHANNEL PROTEINS?

A

transport proteins which are gated
-triggered by stimuli in order to allow molecules to pass

50
Q

WHAT IS THE DIFFERENCE IN GOING ALONG CONCENTRATION GRADIENT OR GOING AGAINST IT?

A

ALONG IT: direction of gradient, no requirement for energy input, decreasing potential

AGAINST: direction opposite to gradient, input of energy required, increasing potential (DIALYSIS IS AN EXCEPTION)

51
Q

EXPLAIN THE MECHANISM OF DIALYSIS

A

-semipermeable membrane separates 2 solutions of different concentrations of the same solute
-if membrane allows passage of water but not solute, the water moves into the area with the greatest solute concentration to establish an equilibrium in which the energy is at of the system is at a minimum
-takes place as water moves from a high solvent concentration to a low one, and as the water is moving along the gradient it does not need external energy

52
Q

UNIPORTER

A

A uniporter is a membrane transport protein that transports a single species of substrate (charged or uncharged) across a cell membrane. It may use either facilitated diffusion and transport along a diffusion gradient or transport against one with an active transport process.[1] Uniporters include both carriers and ion channels,[2] and are referred to as facilitated transporters, suggesting movement down a concentration or electrochemical gradient.

53
Q

ANTIPORTER

A

-An antiporter (also called exchanger or counter-transporter) is a cotransporter and integral membrane protein involved in secondary active transport of two or more different molecules or ions across a phospholipid membrane such as the plasma membrane in opposite directions, one into the cell and one out of the cell. Na+/H+ antiporters

54
Q

SYMPORTERS

A

an integral membrane protein that is involved in the transport of two (or more) different molecules across the cell membrane in the same direction

55
Q

WHAT CAUSES THE MEMBRANE TO HAVE A NEGATIVE CHARGE?

A

resting potential is influenced by non diffusable ions such as proteins which have a net negative charge

56
Q

HOW WILL AN EQUILIBRIUM BE ESTABLISHED?

A

if the membrane is permeable to potassium but not to sodium
-forces acting on potassium are in different directions
-forces acting on sodium are in the same direction

57
Q

NA/K PUMP

A

-pumps 3Na in
-pumps 2K out
-30:1 ratio
-resting cell -70mV
-resting potential primarily potassium diffusion potential
-more permeable to potassium
-unequal distribution of ions
-at a steady state there is a balance between ions

58
Q

EXCITATORY SYNAPSE

A

-binding increases voltage
-depolarizes membrane

59
Q

INHIBITORY SYNAPSE

A

-binding decreases voltage
-hyperpolarizes membrane

60
Q

ABSOLUTE PHASE

A

Na channels cannot be opened by a stimulus irrespective of applied voltage

61
Q

RELATIVE PHASE

A

Spikes can be initiated since Na channels are reactivated but the threshold is greater
-causes by slight hyperpolarization due to higher than resting value for potassium
-higher threshold and more voltage needed

62
Q

HOW LONG DO DEPOLARIZATION AND REPOLARIZATION PHASES LAST?

A

1 ms

63
Q

RESOLUTION OF OPTICAL MICROSCOPES

A

200nm

64
Q

RESOLUTION OF ELECTRON MICROSCOPES

A

0.2nm

65
Q

WHAT IS THE RESTING MEMBRANE POTENTIAL OF CARDIOMYOCYTES?

A

-80 TO -90 mV

66
Q

SURFACE TENSION

A

delta = f/ l
measured by stalagometer

67
Q

WHAT IS THE BOILING POINT OF A SOLUTION IN COMPARISON TO THE PURE SOLVENT?

A

it is greater than the pure solvent

MEDICAL BIOPHYSICS (9 decks)

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