Cell Phys Exam 2

Intracellular Concentration of Na+

5-15 mEq/l, 5-15 mM

Intracellular Concentration of K+

140 mEq/l, 140 mM

Intracellular concentration of Mg2+

1.0 mEq/l, 0.5 mM

Intracellular concentration of Ca2+

2×10^/-4 mEq.l, 10^-4 mM

Intracellular concnetration of H+

7×10^-5 mM or pH=7.2

Intracellular concentration of Cl-

5-15 mEq/, 5-15 mM

Extracellular concentration of Na+

145 mEq/l, 145 mM

Extracellular concentration of K+

5 mEq.l, 5 mM

Extracellular concentration of Mg2+

2-4 mEq/l, 1-2 mM

Extracellular concentration of Ca2+

2-4 mEq/l, 1-2 mM

Extracellular concentration of H+

4×10^-5 or pH=7.4

Extracellular concentration of Cl-

110 mEq/l, 110 mM

Phospholipid membranes are most permeable to

small nonpolar molecules

Phospholipid membranes are moderately permeable to

small uncharged polar molecules

Phospholipid membranes are virtually impermeable to

large charged polar molecules and ions

Simple diffusion

• Potential energy is expended

• gradient driven, dissipates gradient

• includes partitioning and extraction

• Not saturable

Facilitated diffusion

• Passive, but regulated

• Potential energy is expended

• Gradient driven, dissipates gradient, saturable

Active transport

• Regulated

• primary or secondary

• generates or overcomes a gradient

• saturable

• Potential energy is required and expended

Simple diffusion is unsaturable

Rate of net flux will always be proportional to the magnitude of the gradient.

Facilitated diffusion is saturable

Substrate concentration will reach a point where all available binding sites will be occupied, turn-over will be at a maximum rate

Facilitated diffusion is inhibitable

Structurally related compounds compete for transport

Channels

Regulated, selective pathway. Open pore that allows selected solutes to permeate. High permeation and high saturation concentration.

Transporters

Bind a solute(s), undergo a conformational change, and then release the solute on the other side of the membrane. Saturated at low concentrations.

Uniporter

Transporter that transports one molecule

Symporter

Transporter that transports at least 2 molecules at the same time in the same direction.

Antiporter

Transporter that transports at least 2 molecules at the same time in opposite directions. Exchangers.

Pump

Uses ATP to move solute against a gradient

Ca2+ channels within the cell membrane and SR

Facilitated diffusion for Ca2+

Na+/Ca2+ Exchanger

Antiporter. Secondary active transport with respect to Ca2+. Facilitated diffusion of Na+

Ca2+ ATPase

Uniporter. Primary active transport with direct coupling to ATP hydrolysis.

Na+/K+ ATPase

Pumps both Na+ and K+ against electro-chemical gradients. 3 Na+ out for 2 K+ in.

Creates charge imbalance across the membrane (5-30% of the RMP)

Generates gradient used for secondary active transport.

Contributes to osmotic regulation

SGLT1

Na+/glucose co-transporter in the apical membrane

GLUT2

Glucose facilitated diffusion carrier in the basolateral membrane

Na+/K+ ATPase

Involved in glucose absorption in the basolateral membrane.

Concentration of water

55.56 M, moles/kg solvent

Osmosis

water flux across a semi-permeable membrane from the compartment in which total solute concentration is lower when compared to one in which the total solute concentration is higher

Osmotic pressure

exerted by the diffusive flow of water down its concentration gradient. Proportional to the number of particles in solution

Colligative property of osmotic pressure

solutions containing mixtures of molecular species have an osmotic pressure that is the sum of the individual pressures.

Tonicity

Uses red blood cells as the standard

Aquaporins

Allow for water permeability. Introduce extreme sensitivity to changes in extracellular osmolarity.

Solution electroneutrality

the sum of positive charges equals the sum of negative charges in a fluid compartment

Na+/K+ ATPase

Pumps 3 Na+ (out) and 2 K+ (in) against electrochemical gradient.

Substantial contribution to RMP

Inhibited by cardiac glycosides

Ohm’s Law

Net flux in Coulombs per unit of time is proportional to (the electrical potential across a resistive barrier x the size of aggregate pathway).

Nernst Equation

Used to determine the direction an ion will flow in non-equilibrium conditions. Used to determine membrane potential (IF MEMBRANE IS PREMEANT TO ONLY ONE ION)

Requirements for determining membrane potential

• Gradient

• Charge Carrier

• Conductive Pathway

• Power source

Goldman-Hodgkin-Katz (GHK)

defines the equilibrium conditions for multiple ion species where Px=permeability of ion ‘x’ relative to a benchmark ion

Microtubule Structure

• Hollow tubes

• Often centered around the nucleus and extends outward

• alpha and beta tubulin

• Polarized! Alpha exposed or beta exposed

Microtubule location

• general cytoplasmic organization

• mitotic spindle

• axons and dendrites

• cilia

Microtubule function

• Cell scaffolding and polarization

• Polarized movement of organelles, proteins, and DNA

• Resists compression

Microtubule transport

• Kinesin (toward +/beta end)

• Dynein (towards -/alpha end)

• Bind to cargo and walk down the tubules

Centrosomes

Allows anchoring on - end

gamma-tubulin

Basal Bodies

organizing center for cilia

Gamma-tubulin

Dynamic Instability

High concentrations of GTP-dimers in solution promote MT growth, stability

Low concentrations of GTP-bound dimers in solution promote MT catastrophe and collapse

Uses up energy but allows for rapid regulation

Microtubule Associated Proteins (MAPs)

• Stabilize/destabilize the MT structure

• Cause bundling of the MT structure

• Cause branching of the MT structure

• Cause interaction with other cytoskeleton fibers or cell junctions

• Move proteins or organelles along the MT

Microfilament Structure

• Double helix fibers ~7nm

• Found throughout the cell but especially toward periphery

• only one subunit (g-actin)

• Actin assembles (f-actin) into a polarized strand

Microfilament location

• Cell cortex

• microvilli and stereocilia

• lamellipodia, filopodia

• Muscle fibers

Microfilament functions

• cell membrane organization

• ameboid movement

• muscle contractions

• cytokinesis

• Resists stretching

Microfilament Motor proteins

Myoins

Microfilament Regulation

Treadmilling

Actin binding proteins:

• stabilize/destabilize MF

• encourage MF polymerization

• cap MF

• Cause bundling of MF

• crosslink MF

• Nucleate/cause branching of MF

• Bind MF to membrane/ECM

• Generate force along the MF
  
  

Intermediate Filament Structure

• No distinct monomer

• Made up of fibrous proteins

• long fibrous proteins twist together into rope like structures

• all have very similar structures

Intermediate Filament function

• mechanical strength

• Non-motile scaffolding network

• Resists shearing

Intermediate Filament Regulation

• Relatively permeant

• nuclear lamins support the nuclear membrane

• lamins are phosphorylated by lamin kinases during entry into prophase which destabilize the IF

• dephosphorylated on entry to telophase which allows for reassembly

Tight Junctions

Connects two cells together very tightly. Found in epithelial layers. Made of claudins and occludins

Claudins

Forms a fence-prevents diffusion exchange of basolateral and apical membrane proteins

Occludin

Forms a gate/barrier- regulates exchange between apical and basolateral extracellular compartments

Adherens

Junction that causes cells to adhere together and act as a mechanical unit. Made of cadherins.

Adheren Regulation

Interact with actin cytoskeleton. Stimulus through Rho/ROCK can cause contraction of the actin cytoskeleton leading to tension through the adherens junctions and tissue modeling

Desmosomes

Junction that causes cells to adhere to one another. Especially abundant in tissues exposed to mechanical stress. made of cadherins (desmoscollin and desmoglein).

Desmosomes Regulation

Relatively permanent. Regulate through PKC phosphorylation causing stronger or weaker binding. Mature complexes can enter hyperadhesive state in which they are Ca+ independent. PKC activity brings them back to a Ca+ dependent state (more dynamic).

Gap Junctions

Allow for direct communication between the cytoplasm of two cells. Made of connexin subunits. 6 subunits form 1 connexon (hemichannel)

Gap Junction Regulation

Permeability can be affected by several things, connexins can be added to or removed from the membrane.

Cadherins

• Calcium-sensitive adhesion protein.

• Homophilic.

• Important in anchoring junctions, initiation of anchoring junctions, tissue development and sorting

Immunoglobulin-superfamily cell adhesion molecules (IgCAMS)

• Not Ca+ sensitive

• Homophilic or heterophilic

• Important in tissue sorting and immune response

Selectins

• bind CHOs

• heterophilic-bind to CHOs or glycoproteins on the cell surface

• Important in inflammation/immune response and uterine implantation

Integins

• Primarily extracellular matrix binding proteins, some are involved in cell interactions

• Made up of a heterodimer or an a-subunit and B-subunit

• Bind heterophilically to ECM proteins or other cell-surface adhesion molecules

• Important in immune response

Leukocyte Adhesion

1. CHOs on their surface bind to P-selectin (sequestered inside endothelial cells

2. Inflammation causes P-selectin to be expressed on the surface of endothelium cells and this cell weakly binds and rolls along the surface

3. LFA is activated by inflammatory signals.

4. LFA strongly binds to ICAM-1 slowing the rolling and allowing diapedesis into the tissue.

Extracellular Matrix

Complex network of extracellular macromolecules that provides structural, mechanical, and biochemical support to the cells. Components: Protein fibers, complex CHOs, and adhesive glycoproteins

Collagen

Most abundant structural protein. Fibrous, helical protein that gives tensile strength and rigidity to extracellular matrix. Strength and rigidity influenced by: Type of collagen, amount of protein, crosslinking, and orientation. Resistant to proteases.

Elastin

Fibrous, relatively disordered protein. Relaxed state is highly coiled, tension causes the fibers to straighten, returning to relaxed state recoils the fiber. Highly crosslinked. Gives flexibility and elasticity to the ECM.

Glycosaminoglycans (GAGs)

long, branched polymers of repeating sugar units that are significantly negatively charged-repel each other, volume and resistance to compression. Very hydrated, greatly impacts the movement of water and solutes in tissue. Give cartilage its characteristics.

Proteoglycans

Core protein with covalently attached GAG chains. A large portion of the volume of ECM. Most GAGs are found in this form - except Hyaluronan.

GAGs as signaling molecules

Hyaluronic acid (HA) can act as a migration substrate and a signal for epithelial-mesenchymal transition for migratory cells. Production and signaling is controlled by hyaluronan synthases and hyaluronidases.

Laminins

glycoprotein-heterotrimers composed of a, B, and y chains associated through a long coiled-coil region. Binds to Collagen IV, some GAGs, and cell surface receptors. Collagen Weave, especially present in the basal lamina

Fibronectins

Glycoprotein-Made up of 2 strands. Binds to collagen, some GAGs, some proteoglycans, and to cell surface receptors. Crosslinks the matrix and connects to the cell.

Integrins

Membrane Protein- transmembrane receptors that bind to ECM proteins (fibronectin, laminin, and collagen). Can attach to the cytoskeleton through adapter proteins (MF, IF(hemidesmosomes)

Facilitate communication and cohesion between the cytoskeleton and the ECM

Focal Adhesion

Integrins bound to actin filaments. Similar to adherens junctions (integrins instead of cadherins) Especially prominent in migrating and mechanically active adherent cells (highly dynamic)

ECM Remodeling

Matrix Metalloproteases (MMPs) digest specific ECM components when activated by the cell. Expressed during wound healing, migration, etc.

Describe how DNA replication can be used in diagnostics.

Artificial replication is used in the form of PCR tests for diagnostics of DNA based diseases. PCR tests involve using a DNA sample from the patient, a few nucleotides, and primers. The components are mixed together, heated to separate the DNA strand, cooled to facilitate binding of the primers, and heated to ~70 C (the optimal temperature for the non-heat sensitive polymerase)

Interpreting a PCR

PCR are read by adding fluorophore into the solution. If the replication was successful, the fluorophore will fit between the DNA strands (away from water) and will cause an orange light-this is a positive result.