Lecture 14/02.19.25 Flashcards
(35 cards)
What does mechanism of transport depend on?
It depends on how permeable the membrane is to a specific molecule and the presence of appropriate transporter and an energy source.
How can free energy be calculated for a neutral charge?
By multiplying the gas constant and temperature times the natural log of the concentration in the C2/C1
How can we calculate the free energy for charged molecules?
The same as neutral except you add the charge of the molecule time the faradays constant times the difference in voltage across the membrane
How is passive transport defined for Gtrans?
If G is less than zero
How is active transport defined for Gtrans?
If G is greater than 0
What is true about ions and their permeability?
They have low permeability and need to have have water molecules removed before they enter
What is true about polar molecules and their permeability?
They have low permeability except for water which can be due to them being small
How do high selective permeable barriers work?
They work through protein pump and channels that are assigned to move certain ions across rapidly
What are the 3 classes of proteins for transports across membranes?
- membrane carriers/channels
- membrane pumps
- membrane cotransporters
What are membrane carriers/channels?
They are for passive transport or facilitated diffusion, provide selective pores, no use of ATP, can be sensitive to membrane polarization, and is when G is less than 0
How do membrane channels work?
They permit the movement of ions through the membrane down concentration gradient called facilitated diffusion or passive transport. It allows charged molecules to move across lipid bilayer
What are membrane pumps?
For primary active transport, when G>0, drive uphill reaction with ATP, different pumps use different strategies for transport and use of ATP
What are membrane co transporters?
They are secondary active transporters, when G>0, drive uphill reactions using chemical gradient, no use of ATP
What is aquaporin?
It is a membrane channel that is specific to water. Specifically, large amount of water. This is used in kidneys, erythrocytes, salivary glands, etc. They also have the shape of alpha helices.
What are membrane ion channels?
They are selective channels for specific ions such as sodium or potassium. They normally move ions from high to low
What is true about the structure of K channel?
It is a tetramer of 4 identical subunits forming a pore through lipid membranes
How does potassium work in the channel?
It work with the amino acids rather than water
Why does sodium not work in a K channel?
It is too small on its own and too big when it has water attached
What provides voltage gating?
It is provided by a positively charged domain at the bottom of the channel structure
What is the channel responsible for opening/closing?
It the domain S4
What is active transport?
It is when molecules(usually ions) are moved against their concentration gradient
What energy is used for active transport to move molecules?
ATP from hydrolysis
What is P-Type ATPase active membrane transport?
It is a type of transport that uses phosphorus for the process and moves molecules like potassium or sodium from low to high
What is ATP-Binding Casette(ABC) transporter pumps?
A type of transporter that removes substances(usually toxic) and uses ATP to do so because it works against concentration gradient.
