PHSC 2301: exam 2

contact-dependent signaling

requires cells to be in direct contact, membrane-membrane contact

paracine

signals released and act upon neighboring cells

synaptic

signals release in synaptic space

endocrine

endocrine cells release signals operating through whole organism

causes resistance to ligands

1. change in receptors

2. loss of receptors

3. exhaustion of mediators

4. increased metabolic degradation

5. physiological adaptation

types of receptor regulation

1. down regulation

2. up regulation

4 types of signal transduction

1. lipid soluble

2. kinase-linked

3. ion channel

4. g protein coupled receptors

intracellular receptors

1. steroid ligands

2. receptors

3. gene activation depends on cell type and ligand

hormones involved in steroid receptor signal

cortisol, progesterone, estradiol, testosterone, retinoic acid

nuclear initiated steroid signaling steps

1. steroid ligand diffuses through membrane

2. binds to soluble receptor in cytoplasm or nucleus

3. activate nuclear dna-ligand binding domain (HRE)

type 1 steroids

corticosteroids, mineralocorticoids, sex steroids

type 2 steroids

vitamin A, vitamin D, retinoid, and thyroid hormones

action time of lipid soluble

hours-days

membrane initiated steroid signaling steps

1. membrane receptors located on outer membrane surface in caveola

2. rapid action due to steroid receptors on plasma membrane

number of encoding receptor proteins in human genome

1500

concentration that extracellular signal can be detected at

10^-8 (low)

other signals cells respond to

1. mechanical force

2. osmolarity

3. temperature

4. light

receptor downregulation

long term usage leads to decreased sensitivity

receptor upregulation

increased sensitivity to drug after not using for a long time

kinase linked receptors

ligand affects outside of cell, phosphorylation occurs inside the cell, attaches phosphate group, energy provided

action time of kinase linked

minutes

common architecture of receptor in kinase-linked

large extracellular binding domain

cytoplasmic enzyme domain in kinase-linked

tyrosine kinase, serine kinase, or guanylyl cyclase

the kinase-linked receptor is involved in

cell growth and differentiation

ion channel linked receptor

ligand affect receptor outside cell, ionic channel opens, ions flow through

action time of ion linked

seconds-miliseconds

5 subunits

2 alpha, 1 beta, 1 sigma, 1 gamma

in ion linked channel mw weight ranges from

43000-50000

cylindrical structure of ion linked channel width

8 nm diameter

g protein coupled receptors

ligand affect receptor, receptor affect g protein, beta moves laterally to enzyme, turns ATP to cAMP which makes Pk, opens channel, lets ions move througha

action time of gpcr

seconds-ms

transmembrane receptor - insulin

alpha and beta subunits connected by disulfide bonds, ligand attaches to alpha subunit, signal transmitted, phosphorylation occurs in beta subunit, affects DNA/RNA synthesis, can affect glut4 transporters

g protein couples receptors ligands

epinephrine, norepinephrine, opioids

typical MW of drug

100-1000 g/mol

stimulatory g protein family

increase adenylate cyclase, increase cAMP, opens Ca2+ channel

inhibitory g protein family

inhibits AC, inhibits Ca2+ channel

stimulates PLA2, activates K+ channel

adenylate cyclase

membrane bound enzyme, turns ATP → cAMP, low ATP needed, resembles certain channel proteins

cAMP

universal second messenger, major intracellular target (protein kinase a), enzyme phosphodiesterase converts cAMP to 5’-AMP

second messengers

• adenylate cyclase, cAMP, PkA

• guanylate cyclase, cGMP, PkG

• phospholipase C, DAG, PkC

kind of protein that protein phosphorylation controls

intracellular proteins

what reverses phosphorylation

phosphatases

types of passive transport

1. simple diffusion

2. facilitated diffusion

3. osmosis

4. filtration

types of transport

1. passive

2. active

3. coupled

4. endocytosis

amount of substance crossing membrane

flux

flux movement

high to low

simple diffusion

diffusion without energy

fick’s law

calculates rate of diffusion

RT = DS (C0 –Ci)/ ∆x

diffusion coefficient

stokes-einstein equation

D=kBT/6πηr

diffusion coefficient = (Boltzmann's constant absolute temperature)/(6π viscosity * molecular radius)

units of simple diffusion

D: cm^2/sec or micrometers^2/milliseconds

dC/dx: mol/cm^3/cm

S: cm^2

RT: mol/sec

permeability definition and formula

speed of diffusion

P=KD/diffusion distance -> velocity (cm/s)

permeability coefficient = dimensionless partition coefficient * diffusion coefficient / distance of diffusion

substances with high permeability

oxygen, carbon dioxide, water, anesthetic gases

water, oxygen, and carbon dioxide P (cm^2/s) and time

10^-4 - 10^-6, 0.5-5 seconds

urea P (cm^2/s) and time

10^-6, 10 minutes

glucose and amino acids P (cm^2/s) and time

10^-7, 1.4 hours

Cl- P (cm^2/s) and time

10^-11, 1.6 yrs

K+ and Na+ P (cm^2/s) and time

10^-13, 160 yrs

Simple Diffusion - nonpolar (lipid-soluble)

oxygen, co2, fatty acids, lipid-soluble -> diffuse directly across phospholipid bilayer

Simple Diffusion - Polar/ionized (water-soluble)

ions, glucose, amino acids
pass through selective ion CHANNELS formed by integral proteins
- similar design
- proteins configured to create a transmembrane water-filled channel
- water-filled pore allow ions to diffuse across membrane

What membrane channels are formed with

integral proteins

Types of membrane channels

1. selective ion channels (H+, Na+, K+, Ca2+, Cl-, HCO3-)
2. porins (larger MW)
3. aquaporins (water)

how ion channels work

ligand bind to receptor, conformational change, open ion channel

Three types of selective ion channels

1. voltage-gated: action potential
2. ligand-sensitive
3. mechanosensitive

What is the charge inside membrane

negative

selective ion channels charge at channel entrance

negative

What is the selectivity filter size for K+?

0.3 nm

transport rate for ion channels

10^6-10^8

Porins specificity and size of channel

less specific, bigger channel (1.2nm)

What passes through porins?

hydrophilic solutes: anions, cations, ATP, cAMP (>1.0nm), IP3

porins gating controlled by

Ca2+, H+, voltage, and anethetics

size of pore limits size of ___

solute (<1000)

Porins transport rate

10^3 molecules/sec

what does not have aquaporins

prokaryotes

Aquaporins channel diameter

0.3 nm

what is on inside aqp channel

hydrophilic side chain

transport rate of aquaporins

10^9

pore (AQP1) H2O transit rate

10^9/s

channel Na+ transit rate

10^8/s

channel K+ transit rate

10^7/s

channel Cl- transit rate

10^6/s

facilitated diffusion

passive transport across membrane with the help of transporters (integral proteins) without energy/ATP

Characterization of facilitated diffusion

1. receptor site by chemical specificity
2. binding receptor site on transporter by competition
3. facilitated diffusion by saturation kinetics

transport rate facilitated diffusion

10^2 molecules/sec

Facilitated diffusion positions

ligand binds to receptor, transporter changes form and shape, substance released inside cell , transporter returns original position

Rate of transport plateau

reached saturation-> used all transporters

What facilitated diffusion transports

polar, large molecules

Osmosis

mvmt of water to higher concentration of salt

Water diffusion methods

1. lipid bilayer

2. aquaporins 10^9 mol/sec

Osmotic pressure

increased volume, increased pressure -> prevent water entry

filtration

movement of protein-free plasma across capillary wall

What drives filtration

hydrostatic and osmotic pressure

Where filtration occurs

All capillaries

Inside capillaries pressure

hydrostatic =35mmHg

Plasma proteins blood vs. interstitial

blood> interstitial ->water moves toward higher salt concentration
- creates osmotic pressure

what filtration is determined by

MW of solutes, type of capillaries, type of tissue, size of pores in capillary

Pressure osmotic

25mmHg

net pressure difference/Pressure filtration

10mmHg

active transport

ions and molecules movement (positively charged ions)
low to high concentration

what is necessary for active transport

ATP/energy

active transport pathway

ligand binds to receptor of carrier protein, breaks down atp, phosphorylation of protein

examples of active transport

Na+/K+ ATPase, Ca2+ATPase