Flashcards in  Class 4: Transport Through Membrane 2 Deck (65)
Integral, polytopic membrane proteins
400 genes in human genome
Mediates Facilitated passive transport
Highly selective and specific for ions
1000X faster than pumps
Opening and closing channels shapes membrane potential
Why are transport ions 1000x faster than pumps?
They have efficient gates that can be voltage gated and not require the sequential steps of waiting for ATP binding and hydrolysis for the action to occur.
3 types of ion channels:
Respond to change in membrane potential
Respond to ligand such as neurotransmitters
Respond to mechanical stimuli, detect vibration, pressure. Stretch, touch, sounds, tastes, smell, heat, volume, and vision. Found in sensory neurons:
How was ion channeling proven by experiment?
Who was involved in first patch clamping experiment?
Erwin neher and Bert Sakmann
How long are ion channels open?
Current applied to patch clamping
S5 and S6 form:
The pore of the ion channel
S1-S4 form the:
Sodium, Ca+, K+ all homologous seem to be handed down in evo.
Model organism for Na+ channel testing:
260 kDa protein
4 terminal repeats
6 transmembrane domains
TM 4-voltage sensor
What is the basis of topical anesthetics:
Block sodium channels
Toxic substance from pufferfish that acts to inhibit Na+ channels:
Voltage sensor for K + channel
S5-s6 K+ channel:
Who determined structure of K+ channel and when?
Robert mackinnon; 1998
K+ direction of movement in tissue:
Move from inside out
HOw does selectivity filter work for K+ channel?
Hydrated K+ dehydrated when going through selectivity filter. Carbonyl bonds are forms w/ AA's in channel. Rehydrated exiting channel.
What is the signature of potassium channel?
Which is larger? Na+ or K+
Na+ = 0.95 å
K is 1.33å
Why cant Na+ pass through K+ channel if it is smaller than K+?
Na+ is rejected b/c of higher energetic cost of dehydrating sodium would not be recovered when passing through channel.
K+ resolvation energy > desolvation energy
How many binding sites for K+ channel?
Describe the fundamental reason that K+ ions continue through channel as opposed to remaining bonded to carbonyl of AA in pore:
D/t repulsion of like charges- K+ ions push each other along as more come into pore
Na+/ K+ channels are gated by:
membrane potential or voltage
What happens in voltage gated channels in response to changes in membrane potential?