Lecture 16: Movement Across Membranes Flashcards
Transmembrane domain (TMD) (3) is a…
- alpha helical peptide sequence that is largely hydrophobic and spans the membrane - consists of AA with hydrophobic side chains
- permanently attaches the protein to the PM - hydrophobic FA tai;s interact with hydrophobic TMD
- can facilitate protein-protein interactions
Example of a transmembrane protein is…
Glycoproteins A dimer
Lipid bilayers allow many compounds or molecules to pass through them freely
True or False?
False, they do not allow many compounds or molecules to pass through them
Which molecules are able to pass through membranes easily? (4)
Small, uncharged molecules (H2O, O2, CO2, NO)
Large, polar, charged compounds ______ pass through membranes easily
Cannot
- ex. Of these molecules are ions, glucose
Mechanisms for moving molecules across membranes (4)
- Simple diffusion
- Diffusion through a channel
- Facilitated diffusion
- Active Transport
Passive transport mechanisms are (3)
Simple diffusion, diffusion through a channel, facilitated diffusion
Active transport mechanisms are (1)
Active transport
Non mediated transport mechanisms are (2)
Simple diffusion, diffusion through a channel
Transporter mediated transport mechanisms are (2)
Facilitated diffusion, active transport
Passive Transport (simple diffusion) moves from..
- Relies on molecular concentrations of substances across membranes
- Moves from high to low concentration, down the concentration gradient
- Doesn’t require energy
Simple diffusion (passive mechanisms) works for only…
Very small and uncharged molecules
Aquaporins are…?
Specific water channels; H2O moves through aquaporin in single file down concentration gradient in passive mechanisms
Passive mechanisms: Channels
- channels (ion channels) are formed by integral membrane proteins - multiple subunits - that line aqueous pore
- mode is effective for small charged molecules
- ions move down concentration gradients
- channels are selective
- multiple ions at the same time go through
Ion channels
- gated, can be open or closed
- turned on/off
- gate is on the low concentration side of membrane
What are the two types of gated ion channels
- Voltage gated
- Ligand gated
Voltage-gated channels (Na+ and K+)
respond to changes in charge across membrane due to ions changing charge as they move across
Ligand-gated channels
Responds to binding of specific molecule on its surface - a ligand, this produces conformational change in the structure of the receptor/channel
- only responds to ONE type of ligand
Tetrodotoxin (TTX) is a…
Na+ channel blocker
Curare is a
Toxin that inhibits the receptors from working
Passive mechanisms: Carriers, facilitated diffusion
Compound binds to integral protein called facilitating transporter
Change in transporter conformation allows compound to be released on other side of membrane
Facilitation transport, steps:
- Transporter ready to accept glucose
- Glucose accepted
- Intracellular side of transporter opens
- Glucose is released
In some cases, cells need to move substances from a
Low to high concentration gradient (this is not the norm)
How can cells transport glucose from a low to a high concentration gradient?
Rely on chemical gradient of symporters and transport both molecules in the same direction
Na+ glucose symporter
Glucose being transported against [] gradient (low to high), and Na+ with [] gradient
Na Glucose symporter steps
- Binding of 2 Na+ and 1 glucose to transporter
- Causes conformational change in transporter
- Transporter adopts inward-facing conformation
- Dissociation of two Na+ molecules in cytosol, glucose gets pushed as well
- Return to outward-facing conformation - no ATP required
Antiporter
Two molecules being transported in opposite directions
What happens during antiportation?
Concentration gradient of one molecule is used to transfer a second molecule in opposite direction
Active transport
- compound binds to integral protein called active transporter
- change in conformation caused by hydrolysis of ATP molecule allows molecules release on other side of membrane
- using this mechanism, molecules move against [] gradient
- requires energy
