Chapter 13 : Membrane Transport Flashcards
Membranes are impermeable to
ions and polar molecules
Cells use membrane proteins to
transport ions and molecules across the membrane
What are the two types of cellular transport ?
Active and passive
Passive Transport
Uses no energy and moves molecules from an area of high concentration to low concentration
Active Transport
Uses energy to move molecules from an area of low concentration to high concentration
Types of passive diffusion
Simple diffusion and facilitated diffusion
Simple diffusion
Molecules that move across the membrane without use of energy
Facilitated Diffusion
Molecules that move across the membrane with the aid of a membrane protein
What kind of curve does facilitated diffusion have
A logarithmic curve
What kind of curve does simple diffusion have
A linear curve
Channel proteins are used in
facilitated diffusion
Channel proteins can be used to transport ions such as
Na K, Mg , H20 , glycerol etc
Selectivity filter
A group of amino acid acid residues that select and bind to specific molecules
What does it mean if a channel is gated
A signal induces a conformational change to open a channel through ligand binding or a voltage change
Why are ion channels so important in the nervous system
They help to transport K and Na with electrical signals in serve cells
What are two essential structures of K+ channels
- A selectivity filter
- A gate that opens and closes
KcsA channel
channel found in Streptococcus lividans
- contains 3 α-helices
- gated by intracellular pH
What is the sequence of pentapeptides found in KcsA
TVGYG
What is the purpose of the KcsA backbone ?
the oxygens dehydrate the K+ ions by replacing the bonding with water with oxygen instead
Why is the K+ channel very selective for K+ over Na + ?
The smaller Na molecules cannot bind as favorably with oxygens
For every 2 K+ ions, how many Na+ ions are transported ?
3
By changing the selectivity filter , you can also change the
ions selected for transport.
Ex) substituting aspartic acid for tyrosine can change ion selectivity
How many helix segments are in a voltage gated K channel
4 , They serve as voltage sensors
When the paddles of a K channel lie in the down position , the channel is
closed
