Chap 7 PPT - CHAPTER SEVEN Membrane Structure and Function...

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon

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

View Full DocumentRight Arrow Icon

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

View Full DocumentRight Arrow Icon

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

View Full DocumentRight Arrow Icon

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

View Full DocumentRight Arrow Icon

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

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: CHAPTER SEVEN Membrane Structure and Function The plasma membrane separates the living cell from its surroundings It exhibits selective permeability , allowing some substances to cross it more easily than others Models • The “sandwich” model was the accepted between 1935 – 1972, it was proposed by Davson and Danielli. It proposed that the phospholipid layer was sandwiched between to protein layers. • The fluid mosaic model of membrane structure is currently accepted. It was proposed in 1972, by Singer and Nicolson stating that a membrane is a fluid structure (moves around) with a “mosaic” of various proteins embedded in it. The membranes are fluid mosaic of lipids and proteins. Cellular membranes are fluid mosaics of lipids and proteins • Phospholipids are the most abundant lipid in the plasma membrane • Phospholipids are amphipathic molecules , containing hydrophobic and hydrophilic regions • The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it Phospholipid bilayer Hydrophobic regions of protein Hydrophilic regions of protein Hydrophilic head WATER Hydrophobic tail WATER Phospolipids • Are the most abundant lipid in the membrane • Are amphipathic, containing both hydrophobic and hydrophilic regions • Forms a bilayer Freeze Fractionations: Scientific Inquiry • It is used to study the plasma membrane – it supports the fluid mosaic model A cell is frozen and fractured with a knife. The fracture plane often follows the hydrophobic interior of a membrane, splitting the phospholipid bilayer into two separated layers. The membrane proteins go wholly with one of the layers. Extracellular layer Cytoplasmic layer APPLICATION A cell membrane can be split into its two layers, revealing the ultrastructure of the membrane’s interior. TECHNIQUE Extracellular layer Proteins Cytoplasmic layer Knife Plasma membrane These SEMs show membrane proteins (the “bumps”) in the two layers, demonstrating that proteins are embedded in the phospholipid bilayer. RESULTS The Fluidity of Membranes • Phospholipids in the plasma membrane can move within the bilayer • Most of the lipids, and some proteins, drift laterally • Rarely does a molecule flip-flop transversely across the membrane The Fluidity of Membranes • Phospholipids can move within the bilayer Lateral movement (~10 7 times per second) Flip-flop (~ once per month) Movement of phospholipids Protein movement • Proteins can drift within the bilayer EXPERIMENT Researchers labeled the plasma mambrane proteins of a mouse cell and a human cell with two different markers and fused the cells. Using a microscope, they observed the markers on the hybrid cell....
View Full Document

This note was uploaded on 09/14/2011 for the course BIOL 2301 taught by Professor Staff during the Spring '11 term at Lone Star College System.

Page1 / 50

Chap 7 PPT - CHAPTER SEVEN Membrane Structure and Function...

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online