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Bio Block 4 & 5 > Lecture 15. > Flashcards

Lecture 15. Flashcards

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1
Q

3 types of lipid molecules in the membrane

A

cholesterol
glycolipids
phospholipids

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2
Q

Phospholipids comprise __% of lipids

A

75

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3
Q

Fluidity is determined by:

A
  • Lipid tail length- the longer the tail the less fluid the membrane( won’t allow as many molecules through, more rigid, not as much diffusion)
  • Number of double bonds(in the lipid tails)- more double bonds increase fluidity
  • Amount of cholesterol-more decreases fluidity
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4
Q

The lipid bilayer is permeable to:

A

nonpolar, uncharged molecules( O2, N2, benzene)

lipid-soluble molecules( steroids, fatty acids, some vitamins)

small uncharged polar molecules: water, urea, glycerol, CO2

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5
Q

The lipid bilayer is impermeable to:

A

large uncharged polar molecules- glucose, AA

ions

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6
Q

Selective membrane permeability

A

The membrane will allow some molecules to pass, but not the others

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7
Q

membrane structure

A
  • 8 nm thick

- 50% lipid & 50 % protein( held together by Hydrogen bonds)

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8
Q

which part of the phospholipid is charged

A

hydrophilic head

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9
Q

membrane fluidity

A

membranes are fluid structures and lipids can move around within the plane of the membrane leaflet
membrane composition of the leaflet can be asymmetric

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10
Q

How can integral and peripheral proteins be removed?

A

integral- only by breaking the lipid bilayer( detergent)

Peripheral- by breaking H bonds, changing the conc. of other molecules. i.e Sodium

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11
Q

peripheral proteins can

A

change the shape of the membrane

-involved in the cytoskeleton

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12
Q

integral proteins:

A
  • amphipathic
  • have hydrophobic regions that span the hydrophobic core of the lipid bilayer(this region usually consists of non-polar AA coiled into helices)
  • Hydrophilic ends of the proteins interact with the aqueous solution
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13
Q

principles of diffusion

A
  • random mixing of particles as a result of particle’s kinetic energy
  • more molecules move away from an area of high concentration to the area of low concentration
  • the greater the difference in conc. between 2 sides of the membrane the faster the rate of diffusion
  • the higher the Temp the faster the rate of diffusion
  • the larger the size of the diffusing substance the slower the rate of diffusion
  • an increase in surface area( of the cell) increases the rate of diffusion
  • increasing diffusion distance slows the rate of diffusion
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14
Q

Diffusion: physical consequences

A
  • the rate of diffusion sets a limit on the size of a cell of about 20 um
  • to increase diffusion a cell can increase the membrane area available for exchange(diffusion) of a substance
  • the thicker the membrane the slower the rate of diffusion
  • diffusion is very fast over small distances
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15
Q

gradients across the cell membrane

A

-concentration gradient: uncharged molecules will diffuse down their conc. gradient( selective permeability enables a difference in conc across the membrane)

-electrical gradient: ions will be influenced by membrane potential in addition to their conc. gradient
(cells can maintain a difference in charged ions between inside & outside of the membrane- membrane potential) eg hydrophobic core does not allow ions to pass through

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16
Q

-movement of ions will be influenced by:

A

the electrochemical gradient

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17
Q

Gradients represent…

A

stored energy

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18
Q

cell used ~30 % of resting energy to…

A

maintain concentration and electrical gradients

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19
Q

osmosis

A

the net movement of water through a selectively permeable membrane from an area of high water concentration to the area of low water concentration

only occurs when the membrane is permeable to water but not the solute

in biological membranes- (the body wants to avoid cells swelling or shrinking)
so if an osmotic gradient exists water will eliminate it

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20
Q

Proteins that allow water to pass through

A

aquaporins( 9 isoforms)

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21
Q

membrane permeability to water

A

the rate at which water can move across the membrane

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22
Q

membrane permeability to water is determined by:

A
  • permeability through the membrane

- permeability through the water channels( aquaporins)

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23
Q

water permeability through membrane is

A
  • small
  • mercury insensitive
  • temperature dependant( increased temp increases fluidity)
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24
Q

water permeability through aquaporins

A
  • large
  • mercury sensitive( can be blocked by mercury)
  • temp independent
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25
why can cells have different Pw( water permeability)?
express different aquaporins isoforms( 9 isoforms) | * some can have none
26
Hypoosmotic solution
A lower concentration of solute will draw water into the cell( swelling)
27
Hyperosmotic solution
has a higher concentration of solute, will draw water from the cell
28
osmotic pressure
the pressure applied to a solution to prevent the inward flow of water across the semi-permeable membrane *pressure applied to oppose osmosis
29
non-mediated transport
does not use a transport protein diffusion through the lipid bilayer - always passive - important for nutrient absorption/excretion of waste - non-polar hydrophobic molecules ( oxygen, CO2, nitrogen, fatty acids, steroids, small alcohols, ammonia and fat-soluble vitamins(A, E, D, and K))
30
mediated transport
moves materials with the help of a transport protein
31
passive transport
moves substances down their concentration or electrochemical gradient with onyl their kinetic energy
32
active transport
uses energy to dirve substances against their concentration or electrochemical gradient
33
vesicular transport
move materials across the membrane in small vesicles by exocytosis or endocytosis
34
diffusion through ion channels
the channel forms a water-filled pore that shields the ions from the hydrophobic core of the lipid bilayer. -ions do not bind to channel pore. Transport is very rapid
35
what determines the selectivity of the ion channels
specific amino acids lining the pore the size of the channel by being selective to a particular ion the channel can harness the energy stored in the different ion gradients.
36
properties of ion channels: gates
- channels contain gates that control opening and closing of the pore - stimuli can control gate opening and closing
37
what stimuli can control gate opening and closing in ion channels
voltage, ligand binding, cell volume (stretch), pH, phosphorylation *can have multiple ways of controlling channel activity
38
how can ion channel function be measured
the patch clamp technique | isolates one channel to observe the electrical signals generated when the channel opens and closes
39
ion channels: electrical current
• The diffusion of over 1 million ions per second through a channel generates a measurable current (~10-12 amp) • Current fluctuations represent the opening and closing of single ion channels • The current fluctuations represent the conformational changes in channel structure that are associated with channel gating
40
Carrier mediated transport
•The substrate to be transported directly interacts with the transporter protein •Because the transporter undergoes a conformational change transport rates are slower than those obtained for channels transport proteins can allow passive and active passage, the mechanism requires the molecules to interact with the protein.
41
carrier-mediated transport properties
-properties similar to enzymes • They exhibit: Specificity( chemical/mopecule is specific to the binding pocket) Inhibition( something in the binding pocket can't get out) Competition( eg glucose and galactose) Saturation (transport maximum) all pockets are saturated - do not catalyse reactions, mediate transport across the cell membrane at a faster rate - transport can be passive or active
42
transport protein for glucose
GLUT
43
what is the normal level of glucose outside the cell
5mM
44
Facilitated diffusion of glucose
- ALWAYS DOWN THE CONC GRADIENT( can be coming into the cell or out of the cell depending on where the area of high conc is) - glucose binds to GLUT, transport protein changes shape - kinase enzyme reduces glucose concentration inside the cell by transforming glucose into glucose-6-phosphate!!
45
how is the glucose concentration gradient maintained
kinase enzyme reduces glucose concentration inside the cell by transforming glucose into glucose-6-phosphate!! VERY IMPORTANT FOR CELL FUCNTION THAT THE GRADIENT IS MAINTAINED
46
Active transport
requires energy | moves molecules against their concentration or electrochemical gradient
47
2 forms of active transport
primary energy is derived from ATP hydrolysis secondary energy stored in an ionic concentration gradient is used to drive the active transport of a molecule against its gradient
48
a typical cell uses__ % of its energy (ATP) on primary active transport
30
49
examples of primary active transport
Ca/K ATPase (Muscle SR) H/K ATPase (stomach) Na/KATPase
50
Na/K-ATPase primary active transport
* 3 Na+ ions removed from cell as 2 K+ brought into cell. | * Therefore the pump generates a nett current and is electrogenic.
51
The Na/K (low concentration of Na+ and | a high concentration of K+ in the cytosol) difference in ion concentrations is important for:
• Maintain resting membrane potential • Electrical excitability • Contraction of muscle • Maintenance of steady state cell volume • Uptake of nutrients via secondary active transporters • Maintenance of intracellular pH by secondary active transporters
52
Na pump( primary active)
establish the gradient that all other ion channels and secondary transporters are using for different processes
53
pump-leak hypothesis
Na and K are continually leaking back into the cell down their respective gradeints the pump works continuosly
54
secondary active transport
- uses energy stored in ion gradients created by primary active transporters - indirectly use energy of ATP hydrolysis - cells have many secondary transporters powered by the Na+ pump initially
55
Na+ antiporter or exchangers
Na+ ions rush inward, Ca2+ or H+ pushed out ]
56
Na+ symporters or cotransporters
Glucose or amino acids rush inward together with Na+ ions *each AA has its own transporter
57
Osmolarity
– If the solution has the same osmolarity it is isosmotic – If the solution has a lower osmolarity it is hyposmotic – If the solution has a higher osmolarity it is hyperosmotic
58
what is the osmolarity of the body fluids
~300 mOsmol -may have different ion compositions but the same number of particles -the osmolarity of the extracellular and intracellular fluids have to be equal(isoosmotic) so that no net water flow occurs
59
tonicity
• The effect a solution has on cell volume is termed tonicity • The tonicity of a solution depends on the membrane permeability of the solute
60
effect of tonicity on RBC
• Isotonic solution: no change in cell volume • Hypotonic solution: cause cell swelling and eventually cell lysis (hemolysis) • Hypertonic solution: causes cell shrinkage (crenation)
61
Affect of urea on cell
Iso-osmotic BUT can penetrate the membrane and increase cells osmolarity, drawing water into the cell, causing cell swelling and lysis, so is also hypotonic

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