BIO130H1 Lecture Notes - Lecture 4: Epithelium, Uniporter, Cooperative Binding
Membrane Proteins and Transport Across Membranes
Proteins Involved in Membrane Transport:
- Multipass transmembrane proteins-
o Create a protein-lined path across cell membrane
o Transport polar and charged molecules
o Ions, sugars, amino acids, nucleotides, various cell metabolites
- Each transport protein is selective-
o Transports specific class of molecules
- Different cell membranes-
o Have a different complement of transport proteins
Passive and Active Transport:
- Transporter proteins= carrier proteins
Resting Membrane Potential:
- Red- assuming there are channels, will go from high concentration to low concentration.
- Blue- same as red but will move faster because positive charge will be attracted to
negative.
- Green- same as red but will move against the concentration gradient because negative
repel.
Concentration Gradient and Membrane Potential:
- Generally in a cell, concentration gradient plays a bigger role than the electrochemical
gradient.
Passive and Active Transport for Molecules with a Net Charge:
- Both concentration gradient and
electrochemical gradient play an
important role in molecular transport.
- Recall that active transport requires
energy and goes against the gradient.
Passive transport goes with it and thus,
does not require energy or a carrier
protein.
There is no electrochemical
gradient here.
Membrane is slightly
more negative on the
inside. Charges are
additive.
Charges work against
each other.
Concentration gradient + Membrane potential (electrical gradient) = Electrochemical gradient
Overview of Transport Proteins:
- Channel proteins (passive transport)
- Transporter proteins
1. Passive transport by transporter proteins.
o Uniporter
2. Active transport by transporter proteins
A. Cotransport/secondary active transport
o Symporter
o Antiporter
B. ATP-driven pumps (transport ATPases)
o P-type ATPase
o F-type and V-type ATPase
o ABC Transporters
Channel Proteins:
- Hydrophilic pore across membrane
- Most channel proteins are selective. Ex: Ion channels transport a specific ion.
- Passive transport
o Weak interactions with solute
o Faster transport by channels than transporters
o Several molecules pass through when open
Ion Channels:
- Found in animals, plants and microorganisms
- Two types:
1. Non-gated- always open. Ex: K+ leak channels. Major role in generation of resting
membrane potential in animal cells.
2. Gated- chemical or electrical signal required for channel opening. Some type of
signal is required.
Non-Gated Ion Channels:
1. Non-gated ion channels. Ex: K+ leak channels
o Always open
o K+ moves out of the cell
- Important in the plasma membrane of animal cells;
involved in the resting membrane potential.
- From the cytosol we go from high concentration to
low concentration (down the concentration
gradient) If potassium is leaking out, then the
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Document Summary
Multipass transmembrane proteins: create a protein-lined path across cell membrane, transport polar and charged molecules, ions, sugars, amino acids, nucleotides, various cell metabolites. Each transport protein is selective: transports specific class of molecules. Different cell membranes: have a different complement of transport proteins. Red- assuming there are channels, will go from high concentration to low concentration. Blue- same as red but will move faster because positive charge will be attracted to negative. Green- same as red but will move against the concentration gradient because negative repel. Membrane is slightly more negative on the inside. Concentration gradient + membrane potential (electrical gradient) = electrochemical gradient. Generally in a cell, concentration gradient plays a bigger role than the electrochemical gradient. Passive and active transport for molecules with a net charge: Both concentration gradient and electrochemical gradient play an important role in molecular transport. Recall that active transport requires energy and goes against the gradient.
