Cells and Processes - Transport Across Cell Membranes Flashcards
What are the 5 different transport methods?
Non-Mediated Transport Mediated Transport Passive Transport Active Transport Vesicular Transport
What is the difference between non-mediated and mediated transport?
Non-mediated transport = Transport protein used
Mediated Transport = NO transport protein
What is non-mediated transport?
Does not directly use a transport protein
Molecules are permeable across the hydrophobic corse of the phospholipid bi-layer
What is mediated transport?
Moves materials with the help of a transport protein
Passive transport
Moves substances down their concentration or electrochemical gradients with only their kinetic energy
Ie: ALWAYS going from a high to low gradient
What is a passive transport scenario?
When the ball rolls down the stairs of the lecture theatre
This is because it just rolls down its gradient using the kinetic energy
Active Transport
Uses energy to drive substances against their concentration or electrochemical gradients
What is a scenario of active transport?
The process of walking the ball up the stairs of the lecture theatre requires energy
This is because kinetic energy is used to bring the ball up the stairs
What is the definition of vesicular transport?
The movement of materials across membranes in small vesicles either by exocytosis or endocytosis.
What is non-mediated transport important for?
Absorption of nutrients, excretion of wastes
What types molecules undergo non-mediated transport?
Non-polar, hydrophobic molecules
Ie: They can interact with the hydrophobic core
What is the function of ion channels?
Mediate the movement of ions down their electrochemical gradient
What is formed in the centre of an ion channel and what are its functions
A water filled pore that shield the ions from the hydrophobic core of the lipid bi-layer
What determines what ions can pass through an ion channel (ionic selectivity)
Certain amino acids lining the pore determine this
What is ionic selectivity?
Ion channels only allow certain ions to flow through
What is the result of channels being ion selective?
The channel can harness the energy stored n the different ion gradients.
Why can ion channels NOT be open all the time?
It would diminish the ion gradient
What do ion channels contain to control the passage of ions?
Gates
Examples of stimuli that control channel gate opening and closing
Voltage, ligand binding, cell volume (stretch), pH, phosphorylation
What is a patch clamp?
A sensitive voltage clamp method that permits the measurements of ionic currents flowing through individual ion channels
Number of ions that are able to diffuse through one ion channel per second?
1 million
The current through a single ion channel
10^-12 amps
How does carrier mediated transport work?
The substrate to be transported directly interacts with the transporter protein
Is carrier mediated transport faster or slower than ion channels and why
Slower
Because the transporter undergoes a conformation change
What is the general function of carrier mediated transport?
To take one molecule from one side of the membrane to the other
Carrier proteins exhibit these 4 properties?
Specificity
Inhibition
Competition
Saturation
Is carrier mediated transport active or passive?
It can be both
What does saturation mean for carrier mediated transporters?
They only have a certain number of binding pockets so they cannot intake anymore molecules than their binding pockets allow
Does increasing concentration increase uptake with carrier mediated proteins?
To a point, eventually, a point is reached where uptake is saturated
Name of protein that uptakes glucose?
Glucose Transporter Protein (GLuT)
Amount of glucose in blood?
5
Process of glucose moving into a cell?
Glucose BINDS to the the transport channel protein
Binding causes a conformational change in the shape of the protein
Allows glucose to then move into the cell
Does glucose move down its concentration gradient in facilitated diffusion?
Yes
What is glucose converted into in the cell by a kinase enzyme?
Glucose-6-phosphate
Why is glucose converted into glucose-6-phosphate?
To maintain the glucose concentration gradient
What cells do facilitated diffusion of glucose?
Muscle, nervous, fat cells
What is Glut NOT called?
Do NOT call this a glucose channel that is doing passive diffusion.
Glut is a carrier protein and undergoes passive, facilitated diffusion
Process of sodium and potassium ATPase
- Na+ binds
- ATP is split and Na+ is pushed out of the cell
- K+ binds and phosphate is released
- K+ is pushed in
With a Na/KATPase, how many Na+ are removed?
3 Na+ ions are removed from the cell
With a Na/KATPase, how many K+ are brought into the cell?
2 K+ ions are brought into the cell
What is the result of a Na/KATPase?
Pump generates a net current and is electrogenic
