Lecture 2--Transport of Solutes and Water. Flashcards
T/F: The cell membrane is a selective barrier
True
List the major components of the cell membrane
-Phospholipids (25%)
-Cholesterol and other lipids (17%)
-Carbohydrates (3%) - glycoproteins and glycolipids
-Proteins (55%) - integral and peripheral
What factors contribute to a substance’s ability to cross the membrane?
solubility and permeability
Describe functions of cell membrane:
Contain or exclude substances: size, solubility and polarity important
Allow some substances to cross membrane: solubility and permeability important (fig. 4.1)
Maintain electrical potential (inside negative) across the cell membrane
Inside- high K+ and low Na+ with impermeant anions
Outside - High Na+ and low K+
The purpose of ion and molecule movements across membrane: (2)
To maintain the steady state
To disturb the steady state
Describe the electrical potential across cell membrane (aka inside vs out)
Inside- high K+ and low Na+ with impermeant anions
Outside - High Na+ and low K+
Describe Diffusion
Occurs down a concentration gradient.
Random movement (fig. 4.3)
Through lipid bilayer or involves a protein “channel” or “carrier”
No additional energy required
Physical/Chemical Factors that effect Diffusion Rates (4)
Concentration gradients increases DR
Temperature increases DR
Distance decreases DR
Decrease in molecular mass DR
Membrane composition…permeability ??
Add infor from slide 6
What factors determine lipid soluble compounds rate of movement across membrane?
Solubility, size and concentration determine rate of movement
Ions move through channels…rate of movement determined bu
–Size, charge, concentration
–Permeability of membrane (i.e., number of open channels)
Provide **specificity and function to a membrane. There are more than 300 different ___ in cell membranes involved in transport.
membrane proteins
Sodium Selective Channel: Selectivity based on _____
size and charge
Sodium Selective Channel: Sodium channels are lined with ____ that literally pull the sodium ion away from its water shell. The smaller unhydrated sodium ion can then diffuse through the channel.
negatively charged amino acids (glutamate)
Sodium Selective Channel: Unhydrated (dehydrated) potassium ions are____ for sodium specific channels
too large
(Sodium Selective Channel) Variation in conductance controlled by:
number of channels open
(Potassium Selective Channel)
_______ in the selectivity channel essentially strip water molecules from the potassium molecule (but not the sodium molecule). So, only potassium ions can permeate
Carbonyl oxygens (C=O)
T/F: Proteins are selective about the molecules they bind
true
- the ability of a protein to bind to a particular molecule
Specificity
- degree to which a protein is attracted to a ligand
Affinity
the effectiveness of the P/L interaction to provoke a response
efficacy
T/F: Protein-Binding (P/L) Reactions Are Reversible
true
Describe Law of mass action
when protein binding is at equilibrium, the ratio of the bound and unbound components remains constant.
Keq = Equilibrium constant, the dissociation constant (Kd) is a specific type of Keq
Increasing affinity, decreases Kd, decreases concentration to saturation
Describe Allosteric Modulators
(binds away from binding site)
____ act as enhancers that bind to a protein causing a conformational change in the protein, typically increase binding affinity (e.g. Hb-CO2/O2)
Allosteric activators
____, act as antagonists, decrease binding site affinity and/or deactivate protein
Allosteric Inhibitors
_________ increase and decrease binding affinity similar to allosteric modulators, but instead are “permanent”. E.g. protein phosphorylation
Covalent modulators
Describe Competitive inhibition
*Reversible antagonists that compete for a binding site
Decreases affinity for ligand and/or blocks ligand docking
Describe Irreversible inhibition
Binds tightly and/or causes permanent structural change. E.g. Aspirin.
Four Basic Principles of P/L Interactions:
Specificity
Affinity
Competition
Saturation
[Facilitated Diffusion}
–no energy req
–_____ is necessary for substrate crossing
–Diffusion Rate is limited by carrier protein _____ aka saturation
–protein
–Vmax
[Facilitated Diffusion}
T/F: Adding more carriers does NOT affect Vmax
True….just how FAST you approach Vmax aka DR bc rate of diffusion is divided by number of protein carriers
Na+/K+ ATPase…… is a carrier protein loctated on the ___ of all cells
–maintains high ____ inside and ___ outside
–requires one to two thirds of cells energy
1) Plasma membrane
2) K inside and NA outside
Ca2+ ATPase ……present on the ____ and ____
–maintains ____ cytosolic Ca2+ conc
1) cell membrane and sarcoplasmic reticulum
2) low
H+ ATPase…..found in ________ and ______
1) parietal cells of gastric glands and intercalated cells of renal tubules
Properties of Ion Channels:
–have conducting states and non-conducting states
–gating
Permeability of cell memb to ion channels is determined by:
number of open ion channels
3 types of ion channel gating
voltage
chemical
mechanical
opening of channel when depolarized
activation
closure of channel when repolarizes
deactivation
inactivated channels do not pass any ions :
inactivated
[Leak or ungated ion channels]
ion passage is determined by ____
size, shape, distribution of charges
GLUT transporter is an example of ____
passive facilitated diffusion
SGLT Transporter is an example of ____
secondary active transported
3 Major types of cell junctions:
1) anchoring
2) communicating junctions
3) occluding junctions
T/F: Transcytosis utilizes endo and exocytosis
True
Osmolarity is based on the ____ in solution
concentration of solute
the amount of pressure to counter osmosis
Osmotic Pressure….greater osmolarity=greater osmotic pressure
Major determinant of Osmotic Pressure =
number of particles (density)
Time Course of a change in cell volume is dependent on the ____
membrane permeability of the particle
_____ looks at both penetrating and non-penetrating particles to determine
osmolarity
_____ is always greater than or equal to ____
Osmolarity; tonicity
Particles that can pass freely do not count towards _____
Osmotic Pressure
Tonicity tells what will happen to ______
cell’s volume at equilibrium
What is hypernatremia?
What are the causes?
–increased plasma sodium–
-inc water loss
-exc sweat
-central or nephrogenic diabetes insipidus dec ADH sec of responsiveness to ADH
What is hyponatremia?
What are the causes?
–decreased plasma sodium–
-large water ingestion
-syndrome of inappropriate ADH secretion (SIADH)– too much ADH leads to water retention, hyponatremia, and excretion of concentrated urine
–response takes s/min (quick)
–triggers rapid changes in ion channels
–changes in ion permeability
–return to normal cell volume
short term volume flux
–response takes hr/days (slower)
–hyperosmolarity triggers the accumulation of intracellular osmolytes (ex: sorbitol)
–cell shrinkage induce aldose reductase synthesis
–increases intracellular osmolarity, restores cell volumes
Long term osmolarity change
