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173 Cards in this Set
- Front
- Back
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what were we originally
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hydrogen and some helium
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6 elements essential for life
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sulfur
phosphorus oxygen nitrogen carbon hydrogen |
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what created heavier elements necessary for life
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star formation and supernova explosions nuclear fusion
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origin of life
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RNA world
metabolism world extraterrestrial source |
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protocells
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first cells
defines intracellular/extracellular space darwinian evolution |
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physical constraints on protocells
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-permeability of lipid bilayer
-internal calcium ions disrupt many cellular processes |
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what kind of membrane did the first cells have
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leaky membrane, low Ca+2 concentration
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less leaky membrane means what about the transporters
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more transporters
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what can u add on a solute to make it impermeable to lipid bilayer
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hydrophillic group
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what effects does internal calcium have
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-aggregation of nucleic acids and proteins
-disrupt membrane structure |
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minimal cellular physiological properties
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-regulate membrane permeability
-regulate internal calcium concen. -regulate internal pH -regulate cell volume-osmolarity |
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percent of total body weight that's water
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75%
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percent of total number of molecules that's water
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99%
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is pure water a conductor of electricity
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NO
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water molecule properties
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polar molecule
polar covalent bonds electronegativity dipole |
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what kind of bonding occurs between water molecules
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hydrogen bonding
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what is water an excellent solvent for
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salts, acids and bases
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what does table salt (NaCl) dissociate into in water
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ions Na+ and Cl-
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cell membrane
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barrier to diffusion of charged and polar molecules
-lipid bilayers -phospholipids |
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phospholipid regions
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polar (hydrophillic) interact with water molecules and nonpolar (hydrophobic) interact with other hydrophobic molecules
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describe lipid bilayer
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hydrophobic core like thin layer of oil
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another name for cell membrane, why
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fluid mosaic model- integral membrane proteins
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membrane thickness
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60A (6 nm) thick
(thin) |
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hydrophobic core thickness
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30A (3 nm) thick
(thin) |
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membrane proteins
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-peripheral membrane proteins
-cytoskeletal -glycoproteins |
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how do lipophilic (hydrophobic) molecules cross the cell membrane
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simple diffusion
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lipophilic molecules that diffuse through cell membrane
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oxygen, carbon dioxide, fatty acids, steroid hormones
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how polar and charged molecules cross the cell membrane
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using membrane proteins
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pumps
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require energy in the form of ATP to move ions up concentration gradients
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ion channels
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facilitate diffusion of ions by creating pores in the cell membrane
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transporters
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don't directly require metabolic energy, often linked to ion gradients that indirectly provide the energy
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example of active transport
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pumps= expend energy in the form of ATP
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examples of membrane pumps
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Na,K-ATPase
Ca-ATPase H-ATPase H,K-ATPase |
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what does phosphorylation/ dephosphorylation produce
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conformational changes
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intracellular and extracellular K+
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125, 5
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intracellular and extracellular Na+
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12, 120
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intracellular and extracellular Cl-
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5, 125
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intracellular and extracellular Ca+2
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1E-4, 2
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intracellular and extracellular A-
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108, 0
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what is A-
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the fixed anions, sum of all the proteins, amino acids, inorganic ions, nucleotides, DNA, RNA that are located inside the cell
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purpose of H-ATPase
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maintains intracellular pH (H+ ion concentration)
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purpose of H,K-ATPase
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acid secretion in stomach and kidneys
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ion gradients as sources of cellular energy
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-source of chemical energy (secondary active transport)
-source of electrical energy membrane potential |
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direction of net solute flux crossing in diffusion
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high concentration to low concentration
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direction of net solute flux crossing in facilitated diffusion
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high concentration to low concentration
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direction of net solute flux crossing in active transport
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low concentration to high concentration
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describe glucose transporter
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facilitated diffusion, movement of glucose from blood stream into cells
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what do Ca+2 ions function as
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second messengers; modulate the function of a large # of different proteins, neurotransmitter release, muscle contraction
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what does prolonged increase in Ca+2 ion concentration trigger
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cell death
-blockade of blood flow-ischemic tissue damage -metabolically active tissue, heart (heart attack), brain (stroke) -tissues poor at regenerating new cells |
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what does decreased O2 lead to
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decreased ATP->increased Ca+2
->cell death |
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what is the primary determinant of changes in cell volume
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the flow of water into and out of the cell across the cell membrane
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what is osmolarity
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a measure of the concentration of osmotically active particles in a solution
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how is osmolarity expressed
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osmoles of solute per liter of solution
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what is a 1 molar solution for molecules like glucose, sucrose and urea
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1osmole/liter solution
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for NaCl, a 1M NaCl solution is what
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2 osmole/1 solution
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for CaCl2, a 1M CaCl2 solution is what
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3 osmole/1 solution
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what is the osmolarity of extracellular solution kept in
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the range 275-295 mosmole/l
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concentration of H2O molecules in pure water
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55.5M
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in a 1M glucose solution, what is the water concentration
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54.5M
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what do water molecules flow down their concentration gradient like
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like membrane permeable solutes
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what direction will water flow from when there is pure water and water in solute
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from pure water to water in solute
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what do aquaporin channels allow for
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water to flow down concentration gradient
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what are electrochemical phenomena
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brain and muscle function
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what are voltages in cells less than
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100 millivolts
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what range are currents in
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nA (nanoamps) =TINY
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what is the main mediator of small currents
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ion channels
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ion permeation
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how ions move through channels
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ion selectivity
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how we distinguish the different sorts of channels from eachother
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what is more selective K+ or Na+
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K+, by 1:10,000
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K+ radius
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1.33 A
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Na+ radius
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.95 A
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what is throughput
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how many ions flowing through every second
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what is the throughput of K+
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10^8/second
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how is high selectivity achieved without compromising the high throughput of K ions?
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require resolution of crystal structure
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K channel structure
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2 membrane spanning domains (amino and carboxy terminal) and they assemble as a tetramer
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selectivity filter
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string on amino acids in straight line parallel to the pore
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2 components of space-filling model of K channel
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rigid pores & flexible sparse region (opens, closes, and gates channel)
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how do ions get across cell membranes
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can maintain inner hydration shell and can go 75% through the water
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TVGYG
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selectivity filter
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what atoms function as molecular mimic of water
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oxygen atoms (like in carbonyl)
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what does long channel mean about ion selectivity
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increasing selectivity of the channel
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what happens to the pore so that K can flow through
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the pore flips between 2 conformations
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what does energy barrier signify about ion flow
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no energy barrier=max flow
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what direction is net flux always through
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the channel
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how do K+ ions move in and out of the channel without encountering any large energy barriers
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because the 4-fold symmetry of the channel mimics the inner hydration shell of the ion
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what substitutes for similar rings within the hydration shell
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rings of 4 carbonyl oxygen atoms above and below the ion
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how do ions move through the pore
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due to constant flipping between 2 stable channel states
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why is it energetically less favorable when Na comes into the pore
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Na cant pop along the 4 sides (fit perfectly between the oxygen atom)
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what does a change in aa effect
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pore function
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how is electrical flow produced
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by movement of ions (diffusion)
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what are the primary electrical current carriers in the body
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dissociated ions
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electrolytes
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cations-positive charge
anions-negative charge |
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what is a solution of sodium and chloride ions considered as
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hydration shell
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solid NaCl+water forms what
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a hydration shell (solution of sodium and chloride ions)
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direction of electric current
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positive to negative (opposite of electron flow)
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what is a bulk solution with ions compared to
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a resistor
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ohm's law
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V=IR
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what does chemical energy allow
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secondary active transport
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what does electrical energy allow
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membrane potential
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resting membrane potential
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-60 to -90 mV
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what is the intracellular potential relative to extracellular potential
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negative
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what does the non-equilibrium distribution of ions provide?
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a source of energy that can be converted to electrical potential energy
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what are the 2 structural components that are necessary for the conversion of ions to electrical potential energy
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-ion-impermeant lipid bilayer which can produce a separation of charge
-ion channels, which provide a pathway for ions to carry electric charge across the membrane |
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which charges are highly reactive
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unshielded charges
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cell membrane
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thin non-conducting sheet separating 2 conducting surfaces (intracellular and extracellular)
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what makes the cell membrane a better capacitor
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the thinner it is
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principle of electroneutrality
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separation of charge capacitance
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what direction of K ions flow
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out of the cell, so there's excess positive charge outside of the cell (voltage difference)
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chemical potential difference
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concentration gradient
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electrical potential difference
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charged ion will be affected by electric field
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electrochemical equilibrium
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combine 2 forces (chemical and electrical potential difference)
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Nernst equation
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Ei=61.2/Z log 61.5 log ([C]o/[C]i) mV
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Ei
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equilibrium potential of ion i
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Z
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valence of the ion (+1 for Na and K, -1 for Cl)
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log
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log to the base of 10
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[C]o
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ion concentration outside the cell
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[C]i
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ion concentration inside the cell
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what temperature does the nernst equation apply to
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37 degrees
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log (1/10)
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-1
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log(1)
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0
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log(10)
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1
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log(100)
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2
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what is the equilibrium potential for K+ ions
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-61.5mV
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another name for Nernst potential
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equilibrium potential
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what is equilibrium potential meaning
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potential at which electrical driving force=chemical driving force
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how does the system maintain a constant net flux of energy
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ATP is used up by the Na/K pump to maintain gradients
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typical membrane potential
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-70mV
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what is the equilibrium potential drawn towards
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Na potential
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what does the goldman equation give
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the relationship between Vm ion concentrations and ion permeabilities
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what is the goldman equation
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Vm=61.5 log([K+]o+b[Na+]o/[K+]i+b[Na+]i)mV
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what is b equal to in the goldman equation
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pNa/pK=0.02
permeability of Na/K (permeability of K is higher) |
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factors that determine Vm: membrane potential
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1.ion concentrations-determine the equilibrium for each ion
2.relative ion permeabilities- determine the relative importance of each ion's contribution to the membrane potential |
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what does the cell become during depolarization
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more positive
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what does the cell become during hyperpolarization
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less positive
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how do u get a net flux of Na ions
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when the ion movement due to concentration gradient is different from the ion movement due to electrical gradient
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for a typical cell, are most ions at equilibrium
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NO
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what will happen to the ionic gradients without influx of energy
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it will eventually run down
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what prevents run down of ionic gradients
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Na,K-ATPase pump must expend energy to maintain the ion gradients
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what existed before the big bang
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JUST ENERGY, NO MATTER
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what must've happened before life formed
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meteorite bombardment
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is there a gap between when life could've existed and when life actually came to existence?
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YES
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what does the center mean in the archaea, bacteria and eukaryote circle
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that is where the core cell functionality is established
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what was established in the early phase (prior to multicellular organisms)
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all protein motifs
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what must've occurred before eukaryotes arrived(2000 mya)? why
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photosynthesizing bacteria occurred (3000 mya), it oxygenated the atmosphere
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what is RNA
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source of genetic information and ribozyme
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what is responsible for surface tension
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strong interactions between water molecules
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is dissociation of ions favorable
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YES
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what is the cell membrane a barrier to
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diffusion of charged molecules
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amphipathic
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mixed chemical properties in the same molecule
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how is the lipid bilayer structured
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hydrophobic heads stick out and the tails interact with eachother
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what gives the cell structural integrity
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cytoskeleton
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what are most of the integral membrane proteins
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glycoproteins (sugar group on protein)
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protease
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enzyme that breaks down protein
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are pumps efficient
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NO
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what do ion channels do
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open or close to let ions move up or down the gradient
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what is a common thread between all cells
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high concentration of internal K+
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why do cells have high concentration of extracellular Na+
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cuz we all came from marine environment so extracellular fluid mimics that
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what occurs when ATPase phosphorylates proteins
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a conformation changes allowing 3 Na+ to move out and 2 K+ to move in
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what drives the conformational changes
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phosphorylation
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what is the Na,K-ATPase pump also called
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electrogenic pump, cuz there's constant current flowing out of the cell
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purpose of Ca ATPase
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creates a pore to get Ca+ out of the cell
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what is the main way cell stores energy
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ATP
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what must the molecule be to cross the membrane
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lipophillic
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what does the molecule need if it cant cross the membrane due to charge
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protein intermediate (no energy requires)
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what does facilitated diffusion and active transport rely on
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protein
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can glucose easily cross the membrane? why or why not
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NO, because its POLAR
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Na-glucose symporter
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2 binding sites-one for Na and one for glucose, and they both bind and cross the membrane.
net overall movement is Na & glucose into the cell. |
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what kind of transport is involved to bring glucose into the cell
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secondary active transport or facilitated transport
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cotransport
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both ions move in the same direction
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countertransport
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both ions move in opposite directions
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what produces the energy in the Na-Glucose symporter
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Na+ gradient
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where can Ca-ATPase pump Ca+2 into
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mitochondria, ER, cytoplasmic reticulum
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when does Ca+2 become a great second messenger
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when there's a slight increase in Ca+2
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