Cell Bio 10 Flashcards
Types of Integral Membrane Proteins that Move Molecules/ions across the membrane
Channels Transporters -Uniporter -Symporter -Antiporter ATP-Powered Pumps
Driving Force of Facilitated Transport
Concentration Gradient
No energy required
Types of Facilitated Transporters
Pores: a hole through the plasma membrane
Channels: gated version of the pore
Gates
Movement of ______ substances through a ______-_____ pathway so they don’t come in contact with ______ ______ of the membrane
hydrophilic
protein-lined
hydrophobic interior
Facilitated diffusion is
Faster than predicted by passive diffusion
Specific
Saturable: Glucose can only get through this channel at a certain rate; even if there is a lot of glucose not all of it will transport at a certain rate
Facilitated Transport Example
Glucose Uniporter
Pores and Channels
Integral membrane proteins creat holes in the membrane, large enough for solutes to pass through.
Sized-Based Exclusion
Specificity
Size Selectivity
The channel contains hydrophilic amino acids lining the channel, these proteins have residues in them that can bind to the specific molecule that is passing through.
K+ is surrounded by oxygen atoms in water in solution.
The oxygen in the K+ resting channel has the same spacing as water surrounding K+ ion.
K+ will favourably pass through but Na+ will not.
K+ Resting Channel
Plasma membrane freely permeable to K+ due to open resting channels, not permeable to Na+ or Cl-
Selectivety of the transporter can lead to significant electric potential across the membrane without any input of energy beyond the inherent concentration gradient.
Electrical charge present on membranes due to the potassium resting channel.
All cells have a negative charge on the plasma membrane because of the potassium resting channel.
Gates
Normally closed bu open when needed
Ligand gated/Voltage gated
Ligands opens channel by a change in gate conformation.
Specific, saturable, can be ligand or voltage gated, rely on a concentration gradient.
Primary Active Transport
ATP-powered pumps
Classifed by subunit composition, molecules transported, mechanism of action.
Types of ATP-Pumps
P-Class: H+, Na+, K+, Ca++
V-Class: H+ only
F-Class: H+ only
ABC-Type: Many small molecules
ATP binding cassette
Na+/K+ pump
P-class Pump
Responsible for the Na+/K+ concentration gradient
3 Na+ out + 2 K+ in per ATP
Muscle Ca++ ATPase
P-class Pump
Reversible phosphorylation = conformational change
Calcium is pumped out of the cytosol into the sarcoplasmic reticulum
working against a concentration gradient.
2 Ca2+ out /ATP
ABC-class pumps
ATP-Binding Cassette
Not restricted to ions
Move very large molecules into the cell, flippases move things across the PM by flipping them in.
Moves molecules between leaflets
Move against the concentration gradients
Secondary Active Transport
Co-transporter
Antiporter, symports
Coupled transport between two different molecules.
- one with gradient
- one against gradient
Use ion gradients generated by ATP-powered pumps, then couple the free energy associated with these ions going back along their concentration gradient to the import or export of other molecules against their concentration gradient.
Na+ Glucose Symporter
Energy availably following Na+/K+ ATPase and K+ resting channel functions: concentration/electrical gradient
Harness this energy for other uses
2 Na+ down gradient, 1 glucose against concentration gradient
Use the free energy of sodium moving down its concentration gradient, glucose can move in with it.
Co-transport in Epithelial Cells
Apical surface (luminal side)
Basal Surface (sitting on the extracellular matrix)
Epithelial gut cells are stuck together, gap junctions and tight.
Gap junctions allow ions to flow between the cell, tight junctions prevent movement the things between the cell.
All cells have a Na+/K+ pump, because of the potassium resting channels some K+ leaks out giving the PM a negatve charge on the inside of the cell.
These charges and ion concentration are continuous across of the epithelial cells due to the gap junctions
Move glucose from the gut into the cell.
Na+ can move glucose into the cell against its concentration gradient, high levels of glucose in the cell, facilitated transport is used on the basal side of the cell to move glucose and allow it to move down its concentration gradient.
