CELL Membranes

Competencies 1. describe the structural components of the cell membrane- STEM_BIO11/12-Ig-h-11 2. relate the structure and composition of the cell membrane to its function - STEM_BIO11/12 -Ig-h-12

Activity (10 mins) Q & A 1. What do you remember about Cell membrane? Describe the membrane 2. Differentiate Plant and Cell membranes? 3. What are common substances impregnated in Cell membrane and what are its functions?

Cell Membrane (Transport) Notes Cell Membrane and Cell Wall: ALL cells have a cell membrane made of proteins and lipids Cell Membrane lipid bilayer protein channel protein pump Layer 1 Layer 2 SOME cells have cell membranes and cell walls – ex: plants, fungi and bacteria Cell Membrane Cell Wall

Plant cells have a cell wall made of cellulose – that cellulose is fiber in our diet Bacteria and fungi also have cell walls, but they do not contain cellulose Cell membranes and cell walls are porous allowing water, carbon dioxide, oxygen and nutrients to pass through easily

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Membrane Structure The fluid mosaic model of membrane structure has two components: 1. Phospholipids arranged in a bilayer 2. Globular Proteins inserted in the lipid bilayer

Membrane Structure Cellular membranes have 4 components: 1. Phospholipid Bilayer 2. Transmembrane Proteins 3. Interior Protein Network 4. Cell Surface Markers

Membrane Structure Membrane structure is visible using an electron microscope. Transmission electron microscopes (TEM) can show the 2 layers of a membrane. Freeze-fracturing techniques separate the layers and reveal membrane proteins.

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1. Phospholipids Phospholipid Structure (Chapter 3) -glycerol – a 3-carbon polyalcohol acting as a backbone for the phospholipid -2 fatty acids attached to the glycerol -phosphate group attached to the glycerol

1. Phospholipids The fatty acids are nonpolar chains of carbon and hydrogen. -Their nonpolar nature makes them hydrophobic (“water-fearing”). -The phosphate group is polar and hydrophilic (“water-loving”).

1. Phospholipids The partially hydrophilic, partially hydrophobic phospholipid spontaneously forms a bilayer: -fatty acids are on the inside -phosphate groups are on both surfaces of the bilayer

1. Phospholipids Phospholipid bilayers are fluid: Hydrogen bonding of water holds the 2 layers together Individual phospholipids and unanchored proteins can move laterally through the membrane

1. Phospholipids Phospholipid bilayers are fluid: Saturated fatty acids make the membrane less fluid than unsaturated fatty acids Cholesterols make the membrane more rigid Warm temperatures make the membrane more fluid than cold temperatures

Fatty Acids 87

Lipids: Cholesterol Figure 2.22 H3C CH3 CH3 CH3 CH3 HO 2-83 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H3C CH3 CH3 CH3 CH3 HO Figure 2.22 2-83

Fluid Mosaic Model

2. Membrane Proteins Membrane proteins have various functions: 1. Transporters 2. Enzymes 3. Cell Surface Receptors 4. Cell Surface Identity Markers 5. Cell-to-Cell Adhesion Proteins 6. Attachments to the Cytoskeleton

Membrane Proteins Two types of membrane proteins Classified by how they are associated with the membrane Peripheral membrane proteins Integral membrane proteins

Membrane Proteins 1. Peripheral membrane proteins Anchored to a phospholipid in one layer of the membrane on the intracellular or extracellular face of the membrane Oossess nonpolar regions that are inserted in the lipid bilayer Free to move throughout one layer of the bilayer

1. Peripheral membrane proteins

Membrane Proteins 2. Integral membrane proteins Span the lipid bilayer (transmembrane proteins) Nonpolar regions of the protein are embedded in the interior of the bilayer Transmembrane Domain Polar regions of the protein protrude from both sides of the bilayer

2. Integral membrane proteins

Membrane Proteins Integral proteins possess at least one transmembrane domain Region of the protein containing hydrophobic amino acids Spans the lipid bilayer Usually alpha-helices Many receptors are integral proteins

Membrane Proteins Extensive nonpolar regions within a transmembrane protein can create a pore through the membrane. β sheets in the protein secondary structure form a cylinder called a β-barrel β-barrel interior is polar and allows water and small polar molecules to pass through the membrane

Membrane Transport Passive Transport Active Transport Motion of substances in and out of the cell Cell membranes are Selectively permeable Two Types of Transport Mechanisms: Passive Transport Active Transport

Membrane Transport Passive transport is movement of molecules through the membrane in which no energy is required from the cell Active transport requires energy expenditure by the cell

Video on Cell membrane and Cell Transport Guide Questions: 1. What is cell membrane and its composition based on the video? 2. Initially, what is Cell Transport? Describe each type.