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MEDICAL PHYSICS > WEEK 2 (Transport systems) > Flashcards

WEEK 2 (Transport systems) Flashcards

1
Q

Define ‘Passive transport’

A

The movement of molecules from an area of a high concentration to an area of a lower concentration until equilibrium is reached

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2
Q

Define ‘Active transport’

A

The movement of molecules against a concentration gradient and requires energy from the cell

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3
Q

What is the cell membrane?

A

A selective permeability barrier that maintains distinct internal and external cellular environments

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4
Q

What are examples of transport across a biological membrane?

A
  • Diffusion driven by a concentration gradient
  • Diffusion of hydrophilic or charged particles driven by a voltage gradient
  • Facilitated diffusion
  • Active transport against a concentration gradient
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5
Q

What are aquaporins?

A

Membrane water channels that play critical roles in controlling the water contents of cells

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6
Q

Who discovered aquaporins?

A

Peter Agre & Roderick McKinnon

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7
Q

Frick’s Law of Diffusion is correct for ______, ____________ molecules

A

small, uncharged

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8
Q

Diffusion of large or charged molecules depends on ____________________

A

membrane potential

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9
Q

What are the properties of Aquaporins?

A
  • Form tetramers (proteins with a quaternary structure of four subunits) in the cell membrane
  • Facilitate the transport of H2O & some solutes across the membrane
  • Completely impermeable to charged species
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10
Q

What type of process is water permeation through aquaporins?

A

A passive process that follows the direction of osmotic pressure across the membrane

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11
Q

What is an example of a sophisticated molecular mechanism that aquaporins have evolved to response to harsh conditions?

A

Aquaporins in plants close their channels in response to harsh conditions to the environments under which exchange of water can be harmful for the organism e.g drought & flooding

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12
Q

What does the osmotic pressure of a solution depend on?

A

Colligative property (the number of particles in solution)

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13
Q

What is the ‘Donnan-Gibbs effect’?

A

The Donnan-Gibbs effect describes the behaviour of charged particles across a semipermeable membrane

Donnan Effect states that when an ion on one side of a membrane cannot diffuse through, membrane distribution of other permeable ions across the cell membrane is affected in a permeable way due to the ions’ electrostatic presence

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14
Q

The glucose rate of diffusion is higher than calculated with which equation?

A

Frick’s equation

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15
Q

Concentration of glucose in blood plasma is much more higher than in ____________

A

erythrocytes

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16
Q

What is the Michaelis-Menten equation of enzyme activity?

A

V = Vmax/(1+Km/C)

Km is the measure of affinity to glucose

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17
Q

What is Einstein’s formula for Diffusion?

A

D = kT / 6πrn

k – Boltzmann constant
T – absolute temperature
r – molecular radius
n – viscmosity of the medium

18
Q

What is Frick’s Law of Diffusion?

A

J = - DA dc/dx
J = - DA (Co – Ci )/(Xo – Xi)

J Net rate of diffusion
proportional of concentration difference and
inversely proportional of distance
D – diffusion coefficient
A – area of membrane

19
Q

What is the equation that represents membrane as three compartment system?

A

J = - DAb (Co – Ci )/dx= - PA(Co – Ci )
P = Db/dx

b – partition coefficient
P - permeability

20
Q

What is Van’t Hoff’s law of osmotic pressure?

A

π = i R T c

π – pressure
i - number of ions
R – ideal gas constant
T – absolute Temperature
c – molar concentration

this concludes that pressure will increase if
- no. of ions
- temperature
- molar concentration
increases

21
Q

What do Voltage gated channels open specifically in response to?

A

A change in the electric field that exists across the plasma membrane of cells at rest

22
Q

What are the different properties of Voltage gated channels?

A
  • Responsible for the propagation of electrical impulses over long distances in nerve and muscle
  • Open specifically in response to a change in the electric field that exists across the plasma membrane of cells at rest
23
Q

What are the differences between Na+ and Ca2+ voltage-gated ion channels and the K+ voltage-gated ion channel?

A

Na+ and Ca2+ VG ion channels are constructed from a single large polypeptide chain and the interconnected domains are arranged as a tetramer surrounding the channel.

K+ VG ion channel consists of four identical subunits

24
Q

What are the different Gated channels in the membrane?

A
  • Trans membrane potential (ion channels)
  • Ligand gated channel (needs an external mediator e.g neurotransmitter)
  • Ligand gated channel (needs an internal mediator e.g ion or nucleotide)
  • Mechanically gated channel (movement of cytoskeletal filaments is controlled by cellular deformation)
25
Q

What is needed for active transport?

A

Membrane proteins and energy

26
Q

Which molecule is hydrolysed to facilitate active transport?

A

ATP

27
Q

What are the two types of active transport?

A

Primary active transport and Secondary active transport

28
Q

What are the properties of ‘Passive transport’?

A
  • Needs no energy
  • Always goes down the concentration gradient
  • Simple diffusion and facilitated diffusion
  • A result of active transport
29
Q

Why does active transport require energy?

A

Transport against a concentration gradient or there is an energy barrier for hydrophilic molecules in a hydrophobic environment

30
Q

Why do cells need active transport?

A
  • To create higher concentration of some substances
  • To move certain molecules into and across the bilayer
31
Q

What are the stages of Primary active transport?

A
  1. ATP and three Na+ ions binds with the channel
  2. Hydrolysis of ATP and phosphorylation of ATPase leads to conformational change which reduces the channel’s affinity for Na+ and increases the channel’s affinity for K+
  3. Na+ ions are released on the other side. Binding of two K+ ions induces dephosphorylation
  4. Reversion to original conformation so the channel once again has a reduced affinity for K+ and an increased affinity for Na+
32
Q

What does the P domain (P ATPases) contain?

A

Canonical phosphorylated aspartic acid

33
Q

What does Ca2+ ATPase do?

A
  • transfers Calcium after muscle contraction
  • Aids in nerve impulses, muscle relaxation, secretion and absorption in kidneys and absorption of nutrient in intestine
34
Q

What does K+/H+ ATPase do?

A

-It is a proton pump in the stomach
- Exchanges potassium from the intestinal lumen with cytoplasmic H+
- Main source of acidification of stomach content
- Activation of digestive ferment pepsin

35
Q

What does H+ ATPase do?

A
  • Plasma membrane pump in plants and fungi
  • Creation of electrochemical gradient
  • Drives secondary active transport
36
Q

What does the CPx ATPase do?

A
  • A heavy metal transporter membrane protein
  • Drives secondary active transport
37
Q

Which ATPase transport phosphatidylserine from the outer surface of membrane to the inner?

A

Flippase

38
Q

Secondary active transporters are always ___________ that are coupled with active transport

A

Co-transporters

39
Q

What is the difference between secondary active transport of Na+ and Glucose?

A

Na+ is actively transported using ATPase whereas Glucose is actively transported using Permease

40
Q

Diffusion coefficient depends on _________________

A

Size of particles

41
Q

The Donnan-Gibbs effect tends to cause ____________________

A

Water to flow into the cell

42
Q

Where does the energy come from for secondary active transport?

A

Concentration gradient

MEDICAL PHYSICS (13 decks)

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