Chapter 12 Flashcards
Why do we need to be able to transport molecules and ions?
Transport nutrients and waste, maintain concentrations of ions, create gradients, control osmosis, electrical signaling of neurons
What are the factors that control rate of diffusion?
Size, solubility, and charge
Which molecules flow through membranes the easiest? Which molecules flow through membranes the slowest?
(size, polarity, charge)
1 Small hydrophobic (nonpolar)
2 Small charged
3 Large uncharged polar
4 Ions
How do transport proteins effect Ea?
Lower it by creating a hydrophilic environment
Differentiate between transporters and channels
Transporters undergo a conformational change that allows transport across membranes, they have binding sites similar to enzymes (non-covalent interactions). Transporters are also subject to competitive inhibition
Channels are tiny hydrophilic pores that can be opened or closed, they discriminate between ions based on size and charge.
Describe Simple Diffusion. Are specific proteins needed? What type of kinetics would you see in a graph of concentration vs rate of diffusion?
Certain molecules like H2O and CO2, pass directly through the membrane, no proteins needed. Linear kinetics
Describe Passive Transport/Facilitated Diffusion. Are specific proteins needed? What type of kinetics would you see in a graph of concentration vs rate of diffusion?
No energy required, molecules move through channels or transporters. Molecules follow their concentration gradients. Hyperbolic kinetics, has Vmax where the rate is limited by the number of transport proteins.
Describe Active Transport. Are specific proteins needed?
Requires energy, uses transporters but not channels.
Where could the energy used for active transport come from?
Light (bacteria), ATP hydrolysis, Coupled against another molecule that is transported across its gradient (that molecule has a negative deltaG)
Differentiate between Uniporters, Symporters, Antiporters
Uniporters = 1 solute, Symporters = 2 solutes, same direction, Antiporters = 2 solutes, different direction
They could all be passive or active
Describe the sodium potassium pump. Describe its purpose, the electrochemical gradient of each ion, which is on each side of the membrane, how it works and what it does.
Higher solute concentration inside the cell vs outside means water will move in by osmosis
Plant cells deal with this by tough cell walls, protozoans by contractile vacuole
Na+ has an electrochemical gradient heading inside the cell and K+ has an electrochemical gradient heading outside of the cell. This is because the inside of the cell has a negative charge, Na+ is more concentrated outside the cell, and K+ is more concentrated inside the cell.
The pump moves both Na+ and K+ against their concentration gradient by using ATP. The pump goes through a cycle of Na+ binding, ATP adding P, Na+ ejected outside of the cell, K+ binds, pump loses P, K+ ejected.
Na+’s electrochemical gradient can be used to do work.
Describe what the Glucose/Na+ Symporter does. Active or passive?
Active. Uses the Na+ gradient to move glucose against its concentration gradient, into the cell
Describe the Uniporter of Glucose. Active or passive?
“GLUT1”. Passive. Moves glucose along its concentration gradient (bidirectional). Has a Vmax, hyperbolic type curve. Similar to Michaelis-Menton enzyme kinetics.
Describe the Ca+2 pumps. What is its purpose? What is the purpose of Ca? Where are these pumps located?
Ca+2 can bind tightly to a variety of proteins and alter their activities.
An influx of that ion is used as an intracellular signal to trigger various cell processes
Lower concentration = more sensitive -> want to keep low
Pumps are in the plasma membrane and the endoplasmic reticulum membrane.
If only the ER pumps are working, they can keep calcium low by themselves
Describe aquaporins. What type of protein are they?
Helps to move H2O across the membrane, type of transporter protein
Describe how ion channels select their ions
Selectivity based on size and charge
Selectivity filter at smallest opening of channel
Lined with charges that will interact with ions
Too big -> won’t fit
Too small → won’t make proper connections to get through
Describe how ion channels can be gated
100% open or 100% closed
Voltage-gated, Ligand-gated (extracellular or intracellular), Stress-Gated
Auditory nerves are stress gated, move by force
Inside of cell has a slight negative charge = membrane potential
Which mutation causes cystic fibrosis, and how?
Cl- mutation causes cystic fibrosis
Cl- ions help keep mucus from getting too sticky by drawing in water
Many different mutations → no transport protein, misfolded, does not function, faulty, insufficient quantities
Describe Patch Clamp recording. How do we use it?
It is a technique used to monitor the activity of ions channels in a membrane by a tight seal between the tip of a glass electrode and a small region of cell membrane, and manipulation of the membrane potential by varying the concentrations of ions in the electrode.
Detect whether an ion channel is open/closed by current
Can take as few as one ion channel
Channels flicker between open and closed, can be more or less likely to be in one state
Describe how a membrane potential is established.
K+ leak channels allow ions to move outside of the cell and create a slight neg charge in cell
Not gated, randomly open or closed
Specificity by 4 subunits with protein loops lined with carbonyl groups
Follows gradient, keeps electrochemical gradient at 0
Resting membrane potential decided by Na+/K+ pumps and K+ leak channels.
What is action potential? Which channels are involved in its formation?
Change from resting state (~ -60) to equilibrium of Na+ (40+)
Activated by opening of voltage-gated Na+ channels
Voltage gated through 2 sets of + charged amino acids alongside
Describe the experiment that showed what was necessary for an action potential
Giant squids have large axons, replacing their axoplasm with solutions show that only Na+ and K+ are needed for action potential
Extracellular Na+ concentrations will affect max mV and temporal lagging
How is neural signaling strength maintained through an axon?
By the Voltage-gated Na+ channels opening in waves along axon
How does an action potential get changed into a chemical signal?
Action potential opens voltage-gated Ca+2 channels
Those trigger synaptic vesicles to move to the end of the cell and release neurotransmitters
Binding of neurotransmitter activates receptor (ligand-gated ion channel), allows Na+ in and continues the membrane potential
Inhibitory neurotransmitters cause influx of Cl-, further polarizing the cell and preventing another action potential from forming
