L2 - Physiology PDF Notes - Membranes are composed of...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Membranes are composed of lipids and proteins. Lipids: Lipids of biological membranes are all amphipathic molecules. That is they have a hydrophilic end and a hydrophobic end. During synthesis of the phospholipid, the carboxy end is linked to the glycerol backbone through an ester linkage . Saturated bonding leads to straight chains. Unsaturated chains contain double bonds which lead to the presence of kinks in the chain. Cholesterol is also an amphipathic molecule. The phospholipid bilayer is a sheet-like structure composed of two layers of phospholipid molecules whose polar head groups (hydrophilic) face the surrounding water and whose fatty acyl chains (hydrophobic tails) form a continuous hydrophobic interior of about 3 nm in thickness. Molecular Species Permeability of the Lipid Bilayer Lipid-soluble molecules (e.g., steroids) High permeability Some small polar molecules (e.g., water, urea, ethanol) High permeability The majority of large polar molecules (e.g., glucose, amino acids) Low permeability Large polar macromolecules (e.g., proteins, carbohydrates) Low permeability Ions (e.g., Na + , K + , Cl , Ca 2+ , Mg 2+ , etc.) Low permeability The proper way to state these features is to say that the membrane is highly permeable to lipid-soluble molecules, or that the membrane is not permeable to ions. It may also be said that membrane permeability is high for lipid-soluble molecules, and that membrane permeability is low for ions and polar molecules. Another way of stating this is that
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

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