{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

BIOL 141 Chapter 5 Membranes

BIOL 141 Chapter 5 Membranes - Chapter 5 Membranes 1...

Info icon This preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 5 . Membranes 1. Phospholipids 2. Lipid bilayer a. Fluid mosaic model b. Components of membranes 3. Transmembrane proteins a. Structure b. Functions c. Types of transmembrane proteins 4. Diffusion a. Basics of diffusion b. Osmosis i. Direction of osmosis ii. Osmotic balance 5. Bulk transport 6. Active transport a. Na + /K + pump b. Cotransport c. Proton pumps The membranes that encase all living things are made of lipids. The membranes are only 2 molecules thick, they are very thin 10,000 is the thickness of a sheet of paper. Phospholipids The lipid found in membranes is a phospholipid 3 parts to a phospholipid 1. Glycerol 2. Phosphate group (polar, hydrophilic) 3. Two fatty acid chains (non-polar, hydrophobic) When phospholipids are put into water they from a lipid bilayer. The bilayer is formed by hydrophobic exclusion, the non-polar tails align and the hydrophilic head align. The membrane forms spontaneously. Lipid bilayer is fluid The lipid bilayer is held together by hydrogen bonding from the water. Water continuously forms hydrogen bonds with the polar phosphate head of the molecule. 1
Image of page 1

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

View Full Document Right Arrow Icon
So the water keeps the bilayer together but it does not hold specific phospholipid molecules in place. Thus the individual phospholipid molecules are free to move around in the bilayer, the layer is fluid . Individual molecules are constantly moving around the membrane. This was shown using labeled proteins and watching two cell fuse, the labeled proteins spread out over the entire surface of the new cell. Some membranes are more fluid than others Similar to triglycerides, the fatty acid chains determine the fluidity of the membrane, chains with lots of double bonds typically are more fluid than chains without double bonds Fluid Mosaic Model The cell’s plasma membrane is composed of a lipid bilayer and several types of proteins. It was thought that the membrane was like a sandwich, with the bilayer in the middle and two layer of proteins on the inner and outer surface. If this were the case the lipid bilayer would break down. In 1972, the fluid mosaic model was proposed, In this model, proteins were inserted into the plasma membrane . The proteins float on the membrane (actually in the membrane) like boats on a pond Components of the a Cell Membrane Cell membranes are made of several parts; most membranes have similar basic structure 1. Lipid bilayer a. This is the basic membrane made of phospholipids 2
Image of page 2
2. Transmembrane Proteins a. These are proteins that are inserted in the membrane b. These have a huge variety of functions, ex i. Receptors ii. Channels iii. Enzymes 3. Supporting fibers a. These fibers are attached to transmembrane proteins, help cell maintain shape 4. Exterior proteins and glycolipids a. Membrane proteins are made in the ER and transported to the Golgi b. In the smooth ER special molecules are added to from the gylcocaylx c. This is a coating made of carbohydrate and lipids, has several functions i. Used for “self” recognition ii. Used to recognized other cell types Kinds of Transmembrane Protein The plasma membrane isn’t just a lipid bilayer. The
Image of page 3

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

View Full Document Right Arrow Icon
Image of page 4
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