Cell Bio Ch 11 Flashcards
2 main classes of membrane transport proteins
Transporters and channels
Without proteins in lipid bi-layer:
Membrane is highly impermeable to ions
Active vs passive transport
Passive transport- facilitated diffusion, uses concentration gradient to drive transport.
Active transport- requires energy to move solution against concentration gradient.
Factors determining electrochemical gradient
Chemical and electrical gradient
Common ways transport is couple to energy
Coupled transport
ATP-driven pump
Light-driven pump
Couple transport can be
Symport or antiport
Transporter moving one type of molecule
Uniport
3 classes of ATP-driven pumps
P-type pump - ion transport couple to ATP hydrolysis (ATPases)
F-type (and V-type) proton pump - transport of H+ ions coupled with ATP synthesis (ATP synthases)
ABC transporter - small molecule transport coupled to ATP hydrolysis (ATPases)
Ca2+ pump is this kind of pump
P-type ATPase
Na+/K+ pump
P-type ATPase
Important in almost cellular function and regulating cytotolic pH
Na+/K+ pump works in a cyclic manner
- Sodium from cytosol enters pump
- Pump phosphorylates with ATP
- Phosphorylation triggers conformational change, sodium is ejected out of cell
- Potassium from outside cell binds to pump
- Pump dephosphorylates
- Pump returns to original confirmation, potassium is ejected
ABC transporters are different in bacteria from eukaryotes
Bacteria- used for import and export
Eukaryotes- specialized in export
ABC transporters
Ancient protein
Transport many different types of small molecules
“Multi-drug resistant transporters” export drugs from the cell
ABC transporters and disease
Cancer cells- over-expression of ABC transporter multi-drug resistant (MDR) makes cancer cell immune to a variety of drugs
Malarial strain- amplified a gene coded for an ABC transporter that pumps chloroquine out of the cell
Cystic fibrosis- cystic fibrosis transmembrane conductance regulator protein (CFTR) is an ABC transporter that’s been mutated, regulates Cl-
Channels
100 million ions can pass through 1 channel in 1 sec, 10^5 times faster than any transporter.
No ATP
Types of channels
Voltage gated Ligand gated (Extracellular)- neurotransmitters Ligand gated (Intracellular)- ion or nucleotide gated Mechanically gated- linked to cytoskeleton
Membrane potential
Another name for the electrochemical gradient
More Na+ outside of cell, and more K+ inside the cell.
Parts of a neuron
Cell body (containing nucleus)
One long axon
Dendrites from body, to receive signals
Terminal branches on axon to send signals
Voltage gated ______ channels convert ________ signals to __________ signals.
Ca++, electrical signals to chemical signals
Neurotransmitters released to act on ligand gates of dendrites on next neuron (post synaptic)
Voltage gated _______ channels carry signal down the axon
Na+
Neuron activation
Resting potential -70 mV ligand gated Na+ channels open Depolarization occurs -50 mV At depolarization voltage gated Na+ channels open K+ gates open slowly \+50 mV reached K+ rushes out reestablishing -70 mV Na+/K+ pumps reestablish gradient
Neuromuscular junction activation
- Depolarization if nerve terminus opens voltage-gated Ca++ channels
- Higher Ca++ concentration triggers release of acetylcholine
- Acetylcholine released into synaptic cleft or synapse
- Acetylcholine acts on ligand-gated Na+ channels, Na+ flows in causing depolarization
- Voltage gated Na+ channels open, more Na+ pours in and spreads depolarization
- Depolarization is transmitted to the sarcoplasmic reticulum, releases Ca++ causing muscle contraction
