Even if water is polar a small amount of it can sneak through the plasma

Even if water is polar a small amount of it can sneak

This preview shows page 4 - 8 out of 16 pages.

Even if water is polar, a small amount of it can sneak through the plasma membrane because of its small size. Water also moves freely and reversibly by aquaporins (AQP). Osmosis happens when the water
Image of page 4
concentration vary from the 2 sides of a membrane. -1mM NaCl = 2mOsmol/L -1mM glucose = 1 mOsmol/L - Hypertonic: Pull water out of swollen tissues. - Hypotonic: Rehydrate dehydrated patients. - Isotonic: Keep their normal shape, there’s no loss nor gain of water. Active transport It occurs whenever a cell use energy to move solutes across the membrane. Substance are usually unable to pass in the necessary direction by through passive transport. They may be too large to pass through channels, not able to dissolve in the lipid bilayer, or move against its concentration gradient. There are 2 different passage; Active transport (primary and secondary) and vesicular transport. - Primary active transport (antiport): The energy to do work comes directly from hydrolysis of ATP by transport proteins (pumps). It causes the protein to change its shape to pump the bound solute across the membrane. It includes calcium and hydrogen pumps. The pump protein is an enzyme called Na+ -K+ ATPase. For each molecule of ATP used, the Na+ and -K+ pump drives 3 Na+ out of the cell and pumps 2 K+ back in. As a result, the concentration of K+ inside the cell is higher than the outside, and vice versa for the Na+.
Image of page 5
- Secondary active transport (cotransport) (symport): Uses a cotransport protein to couple the downhill movement of one solute to the uphill movement of another solute. Its concentration gradient is created by the primary active transport. When moving sodium across the plasma membrane against its concentration gradient, the pump stores energy. A substance pumped across a membrane can do work as it goes back downhill along its concentration gradient. EX: When sodium moves back into the cell, other substances are dragged along or cotransported by the same protein. Some sugars, amino acids, and ions are cotransported into cells lining the small intestine. Vesicular transport •Fluids containing large molecules and macromolecules are transported across the cellular membrane in-side bubble-like membranous sacs (vesicles). Transports substances in and out of the cell, they are energized by ATP. - Exocytosis (out): Transport substances from the cell interior into the extracellular fluid. It is stimulated when binding of a hormone to a membrane receptor or a change in membrane voltage. It accounts for hormone secretion, neurotransmitter release, mucus secretion, and ejection of wastes. (1) substance is enclosed in vesicle moves to the plasma membrane. (2) Proteins at the vesicle surface (V- snares) bind with plasma membrane protein (T-snares). (3) The vesicle and plasma membrane combine together and a pore opens up. (4) The substance in the vesicle are released to the cell exterior.
Image of page 6
- Endocytosis (in): Transports bulk solids, macromolecules, and fluids into the cell. Begins with a coated pit (an unfolding of the membrane) that have a protein coating on the cytoplasmic face that deforms the membrane to produce the vesicle.
Image of page 7
Image of page 8

You've reached the end of your free preview.

Want to read all 16 pages?

  • Fall '08
  • CARNEGIE
  • axon terminal

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes
A+ icon
Ask Expert Tutors