Lecture 22: Transport Of Solutes Across Cell Membrane Flashcards
What is non mediated transport?
Transport across them membrane that does not directly use a protein
What is mediated transport?
Transport that moves material with the help of the protein
What is passive transport?
Transport that moves substances down their concentration gradients with only their kinetic energy
What is active transport?
Transport which uses energy to drive substances against their concentration or electrochemical gradient
What is vesicular transport?
Transport which moves materials across membranes in small vesicles either by exocytosis or endocytosis
What is a non polar molecule?
A molecule without electrical pores (does not have charge)
What is the process of non mediated transport?
Diffusion through the lipid bilayer
Why is non mediated diffusion important?
Because it’s used for the absorption of nutrients and the secretion of wastes
What type of molecules use non mediated transport and give examples
Many non-polar, hydrophobic molecules
E.g: oxygen, carbon dioxide, nitrogen, fatty acids, steroids, small alcohols, ammonia, fat-soluble vitamins (A, E, D and K)
Three properties of channels?
- Ion selectivity
- Gating
- Electrical current
What do channels do?
They form cores that span across the membrane but they do not bind to solutes
What are the channels made from?
Proteins that fold to form the core
What do the channels form?
A water-filled pore that shields the ions from the hydrophobic pore of the lipid bilayer
What does the channel allow through?
Ions and small molecules
What is the water filled pore of the channel lined with?
Hydrophilic amino acids
What is the outside of the folded protein lined with?
Hydrophobic amino acids
Is the channel the only way ions can get to the cell?
Yes, it’s the only way ions can pass through the hydrophobic core
What law is the channel governed by?
The laws of diffusion
Is ion channel transport rapid? How many ions pass through per second? Why is this?
Yes, about 1 million ions per second.
Fast because ions do not bind
How is the channel ion selective?
By having specific amino acids lining the core, in which the ion is determined by charge (eg a positively charged amino acid attracts negatively charged ions)
What does the channel selectivity allow for?
It allows the channel to harness the energy stored in the different ion gradients
What do ion gates do?
They control the opening and closing of the pore
What controls the opening/closing of the pore, and give examples?
Different stimuli, such as: voltage, ligand binding, cell volume (stretch), pH, phosphorylation
How do you measure the electrical current of the channel gate?
The patch clamp technique
What is the measurable current of the channel gate?
10^-12 amps
What do current fluctuations represent I’m regards to channel gates?
The opening/closing of a single ion channel (like pulses- no current when shut)
What do the current fluctuations represent?
The conformational changes in channel structure that are associated with channel gating
What are three types of passive transport?
- Diffusion through a lipid bilayer
- Diffusion through a channel
- Facilitated diffusion
What is carrier transport?
When the substrate to be transported directly interacts with the transporter protein
Is the carrier transport slower than channel transport?
Yes, because the transporter undergoes a conformational change
Is carrier transport active or passive?
It can be both (whereas channel transport is only passive)
What is the key difference between channels and carriers?
Binding.
What are two essential sequences for carrier transport?
- Molecule must bind to transport protein
2. Change in conformation , which opens a gate and allows molecule to move across the cell membrane
Can the protein carry any sized molecule in carrier transport?
No, it must fit in the binding pocket
What are carrier-mediated transport properties similar to?
Enzyme properties