Cell Membrane Structures and Signaling Pathways

membranes

sheet-like structures that are two molecules thick (lipid bilayer), consisting mainly of lipids and proteins

polar

membrane lipids form barriers to the flow of __________ molecules

unsaturation, asymmetry

____________ and ____________ enhance membrane fluidity

non-covalent hydrophobic

membrane bilayers are held together by __________________________ interactions

proteins

specific __________ in membranes serve as pumps, channels, receptors, and enzymes

7TM (7 Transmembrane Receptors) and receptor tyrosine kinase

membrane proteins responsible for transmitting signals (hormones, neurotransmitters) initiated by various stimuli (light, odor, taste, pressure)

Ex: G protein-coupled receptors and insulin receptors

porin

membrane proteins that are tube-like protein channels that control the passage of water molecules in and out of cell

membrane bound enzymes

membrane protein enzyme that is attached to cell membrane by a set of hydrophobic alpha-helices

Ex: cyclooxygenase

COX (cyclooxygenase)

membrane-bound enzyme that catalyzes the biosynthesis of prostaglandins from arachidonic acid

ion channels

membrane proteins that allow for the passage of ions to produce some response

Ex: Na+/K+ ATPase, nicotinic acetylcholine receptor, ATP synthase

Na+/K+ ATPase

enzyme that generates the sodium/potassium gradient through ATP hydrolysis to provide energy to pump the sodium (3) out of the cell and bring the potassium (2) in

nicotinic acetylcholine receptor

ion channel membrane protein that is closed when no signal is present, but when acetylcholine binds, a conformational change is triggered that opens the aqueous pore and allows Na+ to flow into the cell

ATP synthase

an enzyme, molecular motor, and ion channel located in the mitochondrial membrane. Hydrogen ions flow inward from the mitochondrial intermembrane space and into the matrix, causing the central rotator to turn and phosphorylate ADP into ATP

150

ATP synthase central rotor part turns about __________ times every second during ATP synthesis; resulting in conformation changes in the catalytic site of the enzyme

molecular circuts

signal transduction pathways

primary messenger

signal molecule in which the release is triggered by a stimulus (light, sound, etc)
Ex: epinephrine

membrane recpeotors

receives primary messengers and transfers information to the cell interior (receptor-ligand complex)

second messenger

relays information from the receptor-ligand complex to different cell areas. Amplifies the signal
Ex: cAMP, Ca2+, phosphatidate, inositol, nitric oxide

G-protein coupled receptors

signal transduction pathway in which the primary signal binds to its receptor (ex: epinephrine w/ B-adrenergic receptor) causing the detachment of the beta and gamma subunits of the G-protein and phosphorylation of the GDP on the alpha subunit. The active G-protein activates adenylate cyclase which converts ATP into cyclic AMP (second messenger). cAMP activates protein kinase A

adenylate cyclase

enzyme activated by an active G-protein that converts ATP into cAMP

GTPase

the receptors for the alpha subunit of G-proteins have intrinsic _________ activity (a deactivation clock)

slow

GTP hydrolysis is relatively _________ to allow downstream components of the pathway to be activated (takes seconds to minutes)

insulin

the binding of __________ results in the cross-phosphorylation and activation of the insulin receptor

IRS-1

phosphorylated sites on the receptor act as binding sites for insulin-receptor substrates such as ____________

phosphoinositide 3-kinase (PI 3-kinase)

binds to phosphorylated sies on IRS-1 and converts PIP2 to PIP3

PDK1 (PIP3 dependent protein kinase)

enzyme activated by the binding of PIP3, which phosphorylates and activates kinases such as akt (protein kinase B)

Akt (protein kinase B)

an activated _______ can diffuse throughout the cell to continue the signal-transduction pathway (Ex: activation of GLUT and/or glycogen synthase) --> increases glucose transporter on the cell surface

nuclear recpetors

intracellular cytoplasmic receptors (transcription factors); ket in inactive form by binding to chaperone protein before binding ligand - after the ligand binds the chaperone detaches and the receptors dimerize

dimer

the nuclear receptor ____________ enters the nucleus, binds to DNA, and protein expression ensues

ligands

cortisone, vitamin D, vitamin A, and triiodothyronine are nuclear receptor ______________