BIO130 Final > Lecture 2 > Flashcards

Lecture 2 Flashcards

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1
Q

What is the permeability of an artificial lipid bilayer?

A

impermeable to most water-soluble molecules (simple diffusion = very slow)

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2
Q

What is the permeability of a cell membrane lipid bilayer?

A

membrane transport proteins to transfer specific molecules (facilitated transport)

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3
Q

What is permeability?

A

movement via simple diffusion through lipid bilayer
- high conc. to low conc. (down conc. gradient)

  • more hydrophobic or non-polar molecules (faster diffusion)
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4
Q

What are some examples of permeable molecules?

A
  • small, nonpolar molecules (O2, CO2, N2, steroid, hormones)
  • Small, uncharged polar molecules (only some like H2O, ethanol, glycerol)
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5
Q

What does impermeable molecules mean?

A

they require membrane transport proteins for transport

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6
Q

What are some examples of impermeable molecules?

A
  • Large, uncharged polar molecules (except glucose)
  • Ions (cannot pass through)
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7
Q

What kind of proteins are involved in membrane transport?

A

Transmembrane proteins, create a protein-lined path across the cell membrane, which transports polar and charged molecules

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8
Q

Why are transmembrane proteins involved in membrane transport?

A
  • each transport protein is selective, by transporting a specific class of molecules
  • different cell membranes have a different complement of transport proteins
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9
Q

What are the main types of membrane transport proteins?

A

Channel and transporter

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10
Q

How do channel proteins transport molecules?

A
  • form transient interactions as solutes pass-through
  • no conformational changes, open channels
  • only allows a specific size and electric charge to pass
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11
Q

How do transporter proteins transport molecules?

A
  • specific binding of solute
  • series of conformational changes for transport
  • solutes fit into binding sites
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12
Q

What is passive transport?

A

the movement of molecules across a cell membrane without the need for energy input, moving down their concentration or electrochemical gradient

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13
Q

What is a concentration gradient?

A

the difference in the concentration of a substance between two regions

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14
Q

How is a concentration gradient related to diffusion?

A

a factor in the process of diffusion, which is the movement of particles from an area of higher concentration to an area of lower concentration. This movement continues until equilibrium is reached, meaning that the concentrations become equal throughout the system

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15
Q

What is the electrochemical gradient?

A

concentration gradient + membrane potential

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16
Q

What is active transport?

A

process that moves molecules across a cell membrane from an area of lower concentration to an area of higher concentration. Requires energy, typically in the form of ATP.

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17
Q

What are channel proteins and what role do they play in passive transport?

A

integral membrane proteins that form hydrophilic pores across the cell membrane, allowing specific inorganic ions to pass through by transient interactions with channel walls. They facilitate passive transport, where substances move down their concentration gradient without the need for cellular energy

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18
Q

What are the two types of ion channels?

A
  • non-gated ion channels (always open)
  • Gated ion channel
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19
Q

What are the ways in which an ion channel can be gated?

A
  • mechanically-gated (signal - mechanical stress)
  • ligand-gated (extracellular ligand) (signal-ligand, neurotransmitter)
  • ligand-gated (intracellular ligand) (signal - ligand, ion, nucleotide)
  • voltage-gated (signal - change in voltage across membrane)
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20
Q

What is an example of a non-gated ion channel?

A

K+ Leak channels are always open, allowing K to move out of the cell. Plays a major role in generating resting membrane potential in plasma membrane of animal cells

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21
Q

What is a transporter protein?

A

binds to a specific solute and goes through conformational change to transport solute across the membrane

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22
Q

Which has a better rate of diffusion, transporter or channel proteins?

A

channel

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23
Q

What is a uniport?

A

a type of transporter that carries a single solute across the membrane. It facilitates the movement of molecules down their concentration gradient without the direct use of energy and does not require the co-transport of another solute

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24
Q

Is a uniport involved in active or passive transport?

A

passive transport down its electrochemical gradient, but the direction of transport is reversible

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25
What is an example of a uniport?
glucose transporter, transports glucose down the concentration gradient, can work in either direction (glucose in or out)
26
Does a uniport work with one or multiple solutes?
one
27
What are some examples of active transport pumps?
- gradient-driven pumps: 1 solute down its gradient (energy), 2 solute against its gradient - ATP-driven pumps: ATP hydrolysis moves solute against its gradient - Light-driven pumps: light energy moves solute against its gradient
28
What is a symport?
a type of transporter that moves two or more solutes across a cell membrane in the same direction. It is a form of coupled transport because the movement of one solute is directly coupled to the movement of another
29
What is an example of a symport?
glucose-Na+ symporter found in intestinal epithelial cells which allows these cells to absorb glucose from the gut lumen by coupling its uptake with that of sodium ions (Na+), which are moving down their concentration gradient into cells
30
How do gradient-driven pumps work?
by moving substances across a cellular membrane against their concentration gradient using energy stored in a pre-existing gradient of another substance. They do not directly use ATP; instead, they rely on the energy from the concentration gradient of ions like H+ or Na+ created by primary active transporters
31
What is an antiport?
moves two substances in opposite directions across the membrane. One substance is transported into the cell while another is transported out simultaneously
32
How does the Na+-H+ exchanger function as an antiport?
transports sodium ions (Na+) into cells while exporting hydrogen ions (H+) out of cells, using the electrochemical gradient of Na+ to drive the exchange against the concentration gradient of H+
33
Why are antiports important for cellular function?
crucial for maintaining homeostasis within cells by regulating pH levels, ion concentrations, and osmotic balance; they also play key roles in processes such as neurotransmission and muscle contraction
34
What would happen if an antiporter stopped functioning correctly?
it can disrupt ion gradients across membranes leading to impaired cell functions such as electrical signaling in neurons or muscle contractions; resulting in various diseases or health issues depending on which tissues are affected.
35
Why is an Na-H exchanger needed?
to regulate cytosolic pH for optimal enzyme function. But excess H+ occurs in the cytosol from acid forming reactions which ends up leaking out of lysosome
36
How is the Na+ electrochemical gradient maintained?
symports (Na-K pump for animal cells) and antiports which bring Na down its electrochemical gradient to provide energy
37
What is an ATP-driven pump?
a type of active transporter that moves ions or molecules across a cell membrane against their concentration gradient using energy derived from the hydrolysis of ATP
38
What are the different types of ATP-driven pumps?
- P-type pump - ABC transporter - V-types proton pump
39
What role do ATP-driven pumps play in maintaining cellular homeostasis?
by controlling concentrations of key ions and molecules inside cells, which is critical for processes such as nerve impulse transmission and muscle contraction
40
What are P-type pumps and how do they function?
proteins that transport ions across biological membranes against their concentration gradients using energy from the hydrolysis of ATP. They undergo phosphorylation during the transport cycle, which leads to a conformational change necessary for ion movement.
41
What is an example of a P-type pump?
- Na+/K+ pump found in animal plasma membrane - Plays a crucial role in maintaining cell potential by pumping three sodium ions out of the cell and two potassium ions into the cell against their concentration gradients for each molecule of ATP hydrolyzed
42
What is the Na+ gradient used for?
- transporting nutrients into cells (glucose) - maintaining pH
43
How does the pumping cycle of the Na-K pump work?
- 3 Na bind - phosphorylation from ATP - Phosphorylation triggers conformational change and NA is ejected - two K bind - dephosphorylation - pump returns to original conformation and K is ejected
44
What is an ABC transporter?
an ATP-driven pump that uses 2 ATP to pump small molecules across the cell membrane (pump toxins out of the cell)
45
What is a v-type proton pump?
a type of membrane protein that transports protons (H+) across biological membranes, creating an electrochemical gradient
46
Where are v-type proton pumps found?
found in the membranes of intracellular compartments such as lysosomes, endosomes, secretory vesicles, plant vacuoles
47
What is the function of v-type proton pumps?
to acidify the lumen of intracellular compartments by pumping protons from the cytoplasm into these compartments. This acidic environment is crucial for various cellular processes such as protein degradation, receptor-mediated endocytosis, and neurotransmitter storage.
48
How do v-type proton pumps work?
utilize energy from ATP hydrolysis to transport protons against their concentration gradient. They consist of multiple subunits that form a complex structure with a central rotor-like domain responsible for translocating protons across the membrane
49
What is the function of F-type ATP synthase?
to convert the energy stored in an electrochemical proton gradient into chemical-bond energy in the form of ATP
50
What happens when the head of ATP synthase is mechanically rotated?
it can produce ATP even in the absence of an H+ gradient
51
Where is F-types ATP synthase located?
in mitochondria, chloroplast and bacteria
52
How do transport proteins regulate critical cellular processes?
- transcellular transport of glucose by transporters - generation of membrane potentials
53
What is the role of active glucose symports in the transcellular transport of glucose?
Active glucose symports in epithelial cells take up glucose actively from the lumen, creating a high concentration of glucose in the cytosol.
54
How do passive glucose uniports function in the transcellular transport of glucose?
release glucose down its concentration gradient from areas of high concentration within epithelial cells to areas of lower concentration for use by other tissues
55
What prevents mixing between different types of membrane components involved in transcellular transport?
ight junctions around the apex of epithelial cells form a diffusion barrier that prevents mixing between different types of membrane components such as active symports and passive uniports.
56
Where is the Na+-glucose symporter located in transcellular transport?
apical membrane (top of the tight junctions)
57
Which membrane proteins are located on the basolateral plasma membrane?
- GLUT2 uniporter - Na+-K+ pump (bottom of tight junctions)
58
What does the Na+-K+ pump do in transcellular transport?
sets up the gradient so the symporter can properly function
59
What is membrane potential?
difference in electrical charge on two sides of the membrane
60
What is the importance of membrane potential?
- used by gradient-driven pumps to carry out active transport - electrical signaling
61
What is involved in generating membrane potential in animal cells?
- K+leaking channel - Na+-K+ pumps Na+ is low in cytosol: 3 in K+ is high in cytosol: 2 out Net 1 ion pumped out - More + on the outside of cell - more - on the inside of cell
62
What is considered a resting membrane potential?
equilibrum, a balance of electrical charges inside and outisde the cell
63
What is resting potential in animal cells?
vary from -20 mV to -200 mV (in the cytosol)
64
How is membrane potential generated in plant cells?
plasma membrane P-type pumps, to pump H+ out of the cell
65
What is the function of membrane potential in plant cells
- used by gradient drive pumps to carry out active transport - electrical signaling - regulating pH
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