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Questions and Answers
What are the three mechanisms of membrane transport?
What are the three mechanisms of membrane transport?
passive, active, secondary active
What is true about passive transport?
What is true about passive transport?
- Molecules move against their concentration gradient
- It involves ions
- It is spontaneous (correct)
- It requires energy input
Active transport requires energy input.
Active transport requires energy input.
True (A)
_______ transport uses an ion gradient set up by an active transport protein to energize the transport of another ion/solute.
_______ transport uses an ion gradient set up by an active transport protein to energize the transport of another ion/solute.
What is responsible for nerve impulses?
What is responsible for nerve impulses?
What is the result of the opening and closing of Na and K channels?
What is the result of the opening and closing of Na and K channels?
Action potentials are changes in membrane potential.
Action potentials are changes in membrane potential.
Cystic fibrosis is caused by a defective ____ channel.
Cystic fibrosis is caused by a defective ____ channel.
Which type of transport involves carriers that bind solute and change shape to transport solutes across membranes?
Which type of transport involves carriers that bind solute and change shape to transport solutes across membranes?
What controls the presence of GLUT4 in the membrane?
What controls the presence of GLUT4 in the membrane?
Active transport moves ions with their concentration/charge gradients.
Active transport moves ions with their concentration/charge gradients.
Match the following components of an animal cell with their functions:
Match the following components of an animal cell with their functions:
Study Notes
Membrane Proteins and Membrane Transport
- Membrane proteins have various functions, including transport of molecules and ions across the cell membrane
- There are three mechanisms of membrane transport: passive, active, and secondary active transport
- Ion channels and pumps are involved in membrane transport and generate ion gradients that power secondary active transport
- Water can also move across membranes through osmosis
Integral Membrane Proteins
- Have alpha helices that span the membrane with hydrophilic residues facing the inside of the protein and hydrophobic residues facing the lipid bilayer
- Involved in various functions such as cell adhesions and cancer metastasis
Functions of Membrane Proteins
- Cell adhesions and cancer metastasis
- Enable cells to drive cancer cell invasion
- Involved in fibroblast-driven cancer cell invasion
Membrane Transport
- Permeability through the lipid bilayer: some molecules can pass freely, but many biologically important molecules cannot pass through at rates required by cells
- Proteins have evolved to allow cells to move these molecules in a fast and controlled manner
- Three mechanisms of membrane transport:
- Passive transport: molecules move down their concentration gradient; spontaneous and requires no energy input
- Active transport: ions move against their concentration/charge gradients; non-spontaneous and requires energy input
- Secondary active transport: uses ion gradients generated by active transport to energize the transport of another ion/solute
Passive Transport
- Two types:
- Simple diffusion: molecules move through the bilayer itself
- Facilitated diffusion: molecules move through transport proteins (channels/carriers)
- Osmosis: movement of water down its concentration gradient
- Aquaporins: proteins that facilitate water transport across the cell membrane
Active Transport
- Ions move against their concentration/charge gradients
- Energy input required
- Examples:
- Na+/K+ ATPase
- H+ ATPase
- Ca2+ ATPase
Secondary Active Transport
- Uses ion gradients generated by active transport to energize the transport of another ion/solute
- Example: Na+/glucose symporter in the kidney, which can move glucose against a 30,000-fold concentration gradient
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