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PHGY 209 > Transport Mechanisms > Flashcards

Transport Mechanisms Flashcards

1
Q

In Transport Mechanisms, in which part of the cell are we particularly interested in?

A

The Cell Membrane

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2
Q

What are the Permeability Characteristics of the Cell Membrane?

A

Highly permeable to:

  • H20, Lipid-soluble substances, Dissolved Gases (O2, CO2) and small uncharged molecules

Less permeable to:

  • Larger molecules and charged particles

Impermeable to:

-Very large molecules

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3
Q

Describe the Cell Membrane.

A

It has a Phospholipid Bilayer with hydrophilic heads (polar, on the outside) and hydrophobic tails (non-polar, on the inside)

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4
Q

What are hydrophilic heads composed of?

A

Carboxyl and hydrogen

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5
Q

What are hydrophobic tails composed of?

A

Tricglycerides and cholesterol

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6
Q

What is cholesterol’s function for in the Cell Membrane?

A

Acts as a buffer to prevent lower/increase TEMPERATURES for inhibiting/increasing FLUIDITY.

Involved in formation of vesicles that pinch off the plasma membrane

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7
Q

There are 2 types of protein pertaining to the Cell Membrane. What are they and where are they located?

A

Integral proteins: Closely associated with phospholipids (Trans-membrane)

Peripheral proteins: loosely associated on the cytoplasmic side

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8
Q

What is glycocalyx and what are it’s main functions?

A

It’s a fuzzy coating surrounding the cell membrane formed of glycans, glycoproteins and glycolipids

Functions: Contributes to cell-cell recognition, communication, adhesion and protection. Helps control vascular permeability

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9
Q

What are the functions of Plasma Membrane Proteins?

A

They act as selective or enzyme transporter, cell surface receptor or identity marker and cell-cell adhesion or attachment to the cytoskeleton

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10
Q

What are the 2 transmembrane pathways?

A
  1. Via the phospholipid bilayer
  2. Via interaction with a transmembrane protein
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11
Q

There are 2 Cell Membrane Transport Mechanisms. What are they and by which mechanisms?

A
  1. Passive (energy indepedent): Diffusion, Facilitated Diffusion and Osmosis
  2. Active (energy dependent): Active Transport (primary,secondary) and Pino/Phagocytosis
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12
Q

What is Diffusion?

A

It’s the movement of molecules from one location to another as a result of random thermal motion.

It happens even in the presence of a mechanical partition (membrane) as long as it is permeable

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13
Q

How does diffusion flux and net flux work?

A

Diffusion flux: It’s the amount of particles crossing a surface per unit time

Net flux: Movement of particles from high to low concentration

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14
Q

What happens to diffusion flux and net flux at equilibrium?

A

Diffusion flux: They become equal

Net Flux = 0

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15
Q

How does diffusion relates in terms of time and distance?

A

Diffusion time increases in proportion to the square distance travelled by the solute molecules

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16
Q

What affects Cell Membrane Diffusion?

A
  • Mass of molecule
  • Concentration gradient
  • Lipid Solubility
  • Electrical charge
  • Ion Channels
  • Membrane carriers
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17
Q

How can diffusion happen at the cellular level and what is it related to?

A
  • Diffusion across the lipid bilayer
  • Diffusion of ions through channels

It is related to the concentration gradient

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18
Q

What are Ion Channels?

A

Transmembrane proteins that show ion selectivity

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19
Q

How is the movement of an ion is affected?

A

By the presence of an electrical gradient and it’s own concentration gradient = electrochemical gradient

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20
Q

Ion channels can exist in open or closed state and may be gated but in what ways?

A
  • Ligand gated (chemical messengers)
  • Voltage gated
    -Mechanically gated
21
Q

Name the different Voltage Gated Ion Channels

A

Na+ channels
K+ channels
Ca+ channels
Cl- channels

22
Q

Current flow through single ion channels depends upon what?

A
  1. Channel conductance
  2. Channel open time
  3. Frequency of channel opening
23
Q

What is Mediated Transport?

A

The movement of ions and other molecules by integral membrane proteins called transporters or carriers.

24
Q

What are the characteristics of Mediated Transport?

A
  • Specificity (1 type of molecule transported)
  • Saturation (Rate of transport when all binding sites are occupied - Transport max)
  • Competition (When similar substances compete for binding sites)
25
Q

What are the factors that determine Mediated Transport?

A
  • Solute concentration
  • Affinity of transporter for the solute
  • Numbers of transporters
  • Rate of transporter conformational change
26
Q

What are the Mediated Transport Systems?

A
  1. Facilitated Diffusion (Passive)
  2. Active Transport via:
    • Primary Active Transport
    • Secondary Active Transport
27
Q

Summarize the process of Facilitated Diffusion

A
  1. Transported Solute binds to Transporter Protein’s binding site
  2. Transporter binding site changes configuration as well as the protein
  3. Solute is delivered to other side of membrane
  4. Transporter resumes original configuration
28
Q

What are the Characteristics of Facilitated Diffusion?

A
  • Transporter Mediated
  • Passive
  • Net flux going from hight to low concentration
  • Hormones may increase the number and/or affinity of transporters in some membranes
  • Glut-4 transports glucose in muscle that increased by insulin
29
Q

What are the Characteristics of Active Transport?

A
  • Transporter-Mediated
  • Requires supply of chemical energy (enzymatic hydrolysis of ATP)
  • Susceptible to metabolic inhibitors
  • Can transport solute AGAINST it’s concentration gradient
30
Q

Explain Primary Active Transport

A

It involves the hydrolysis of ATP by a transporter.

Phosphorylation of the transporter changes the conformation of the transporter and it’s solute binding affinity

31
Q

Describe Na+/K+-ATPase transport process

A
  1. Na+/K+-ATPase - ATP binds 3Na+
  2. Phosphorylation of ATP–>ADP
  3. Conformational change exposing Na to ECF and releasing them
  4. Change increase K+ affinity and binds it to site
  5. Dephosphorylation + return to original conformation
  6. Release of K+ in ICF
32
Q

What are the other Active Transporters and their functions?

A
  • Ca2+-ATP-ase: Maintain low intracellular Ca2+ levels
  • H+-ATP-ase: Maintain low lysosomal pH
  • H+/K+-ATPase: Acidification of the stomach
33
Q

How does Secondary Active Transport work?

A

Movement of Na+ down its concentration gradient (High to low) is coupled to the transport of another solute molecule (Glucose or aa).

It uses the energy stored of the electrochemical gradient to move both molecules

34
Q

Summarize Na+/K+ pump

A
  1. Na+ binds to a transporter outside the cell allowing glucose or aa to also bind
  2. Change in conformation = release of both molecules into the cell
  3. Back to normal conformity and Na+ is extruded from cell by Na+/K+ -ATPase
35
Q

Describe the 2 Secondary Active Transport Mechanisms

A

Symport: When solute x is transported in the same direction as Na+

Antiport: When solute x is transported in the opposite direction as Na+

36
Q

Name examples of Symports and Antiports

A

Symports: Na+/HCO3- cotransporter, Na+/aa cotransporter, Na+/glucose cotransporter

Antiports: Na+/H+ exchanger, Na+/Ca2+ exchanger

37
Q

What is Endocytosis and Exocytosis?

A

They are an active transport mechanisms involving participation of the cell membrane itself

Endocytosis: Cell Membrane invaginates and pinches off to form a vesicle

Exocytosis: An intracellular vesicle fuses with the cell membrane and its contents are released into ECF

38
Q

What are the 2 types of Exocytosis?

A

Constitutive Exocytosis: Non-Regulated. Replace plasma membrane, deliver membrane proteins to CM and get rid of substances from the cell

Regulated Exocytosis: Tends to be triggered by extracellular signals and the increase of cytosolic Ca2+. Responsible for secretion of: Hormones, Digestive Enzymes and Neurotransmitters

39
Q

There are 3 types of Endocytosis. What are they?

A
  1. Pinocytosis (Fluid Encocytosis)
  2. Phagocytosis
  3. Receptor Mediated Endocytosis
40
Q

Explain Pinocytosis

A

Endocytotic vesicle that engulfs ECF including present solutes. Fuse with other vesicles like endosomes or lysosomes. Non-specific.

41
Q

Explain Phagocytosis

A

Pseudopodia fold around particle and form a phagosome that fuses with lysosomes. Specific and triggered

42
Q

Explain Clathrin-dependent receptor -mediated endocytosis

A
  • Ligands bind to receptor ie cholesterol
  • Clathrin recruited to PM and linked to ligand-receptor
  • Clathrin coated pit forms a vesicle
  • Clathrin released from vesicle and recycled to PM
  • Vesicles can: Fuse with organelle, endosomes, lysosomes or PM
43
Q

Explain Potocytosis

A

Molecules are sequestred and transported by tiny vesicles calle caveolae. They can:

  • Deliver contents in cell cytoplasm, endoplasmic reticulum, organelle or PM

Implicated in uptake of vitamins (low M.W molecule)

44
Q

What is osmosis?

A

The net diffusion of H2O accross a semipermeable membrane

45
Q

What is Osmotic Pressure?

A

The pressure required to prevent the movement of water across a semi-permeable membrane.

46
Q

Describe the capillary wall.

A

A single layer of flattened endothelial cells and a supporting basement membrane

47
Q

Describe Capillary Structure and Permeability.

A

Structure: Endothelial cell separated by narrow water filled pores called intercellular clefts.

Permeability: via intercellular clefts and endo-exocytosis

48
Q

How does transport happened across capillary wall?

A

Diffusion

Transcytosis (endocytosis)

Bulk Flow: Plasma<–ECF–>ISF

49
Q
A

PHGY 209 (3 decks)

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