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
When the paddles on the K channel lie in the up position , the channel is
open , from depolarization
The ball and chain model has been used to describe which voltage gated channel ?
K+ and Na+
What are some of the kinds of gates that open channels ?
ligand, voltage, pH gated
What is the most common forms of energy input in active transport ?
- ATP hydrolysis
- light energy
- ion gradients
How do ATPases provide energy
Through coupled phosphoylation
Examples of secondary transport molecules
Lactose or permease which can be used as energy
All cells expel ___ ions and uptake ____ ions
Na + ions are expelled and K+ ions are uptaken
ATPase is used as a ___ to transport sodium and potassium
pump
The sodium ATPase can be inhibited by
cardiac glycosides
Examples of cardiac glycosides
oubain and digitalis .
Both can help to treat CHF but are poisonous at high amounts
The Ca2+ ATPase is primarily found in which types of cells ?
muscle cells
An enzyme that uses light instead of ATP as energy source
bactiorhodopsin
Gastric H+ or K+ ATPase enzymes are found primarily in
the stomach
How does phosphorylation play a role in the function of the Na+ K+ ATPase ?
Phosphorylation of a protein adds a large negative charge to it which changes the shape and affinity for the substrate when converting
What other kinds of energy besides ATP do proteins use to actively transport molecules ?
Concentration gradient, electrical gradient,light
