1.6 Plasma Membrane

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Biology

Cells

Last updated 12:41 AM on 1/20/24
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11 Terms

1
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Why Do Cells Need a Membrane?

  • Separate interior from exterior - protection, support

  • Very thin boundary

  • Allows some materials to cross more easily - selectively permeable

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What is it Made of?: Phospholipids*

  • Spontaneously arrange into bilayer (two parallel layers)

  • Amphipathic due to lipophilic and hydrophilic regions

  • Bilayer held together by weal hydrophobic interactions between tails

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What is it Made of?: Proteins (Pt. 1)*

  • Proteins may be permanently or temporarily attached

  • Diverse in structure, position, and function

  • Functions include: junctions, enzymes, transport, recognition, anchorage, and transduction

<ul><li><p>Proteins may be permanently or temporarily attached</p></li><li><p>Diverse in structure, position, and function</p></li><li><p>Functions include: junctions, enzymes, transport, recognition, anchorage, and transduction</p></li></ul>
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What is it Made of?: Proteins (the two types)*

Integral Proteins – permanently attached to membrane and are typically transmembrane (span across bilayer)

Peripheral Proteins – temporally attached to noncovalent interactions and associate with one surface

<p><strong><span style="color: blue">Integral Proteins</span></strong> – permanently attached to membrane and are typically transmembrane (span across bilayer)</p><p><strong><span style="color: purple">Peripheral Proteins</span></strong> – temporally attached to noncovalent interactions and associate with one surface</p><p><img src="https://knowt-user-attachments.s3.amazonaws.com/62d1ddfd-2d4d-4242-bacb-6df895a76df8.jpeg"></p>
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What is it Made of?: Proteins (location)*

  • Non-polar amino acids are located within membrane

    • Anchors protein into membrane

  • Polar amino acids located on outer surface of membrane

    • Extend into extracellular fluid & cytosol

<ul><li><p><mark data-color="blue">Non-polar amino acids</mark> are located <strong><span style="color: blue">within</span></strong> membrane</p><ul><li><p><em><mark data-color="blue">Anchors protein</mark></em> into membrane</p></li></ul></li><li><p><mark data-color="red">Polar amino acids</mark> located on <strong><span style="color: red">outer surface</span></strong> of membrane</p><ul><li><p>Extend into <em><mark data-color="red">extracellular fluid &amp; cytosol</mark></em></p></li></ul></li></ul><p><img src="https://knowt-user-attachments.s3.amazonaws.com/aefba973-9f95-4497-be28-6a7025d343ba.jpeg"></p>
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What is it Made of?: Carbohydrates*

Glycolipid

  • lipid with a carbohydrate chain attached

  • help cell to recognize other cells of body

Glycoprotein

  • protein with carbohydrate chain attached

  • help in cell to cell communication and transport

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What is it Made of?: Cholesterol*

  • Amphipathic molecule found in animal membranes

  • Immobilizes outer surface - reducing fluidity

  • Makes less permeable to small water-soluble molecules

  • Separates phospholipid tails - prevents crystallization

<ul><li><p><strong><span style="color: purple">Amphipathic</span></strong> molecule found in animal membranes</p></li><li><p><em><mark data-color="purple">Immobilizes outer surface - reducing fluidity</mark></em></p></li><li><p>Makes less permeable to small water-soluble molecules</p></li><li><p>Separates phospholipid tails - prevents crystallization</p></li></ul><p><img src="https://knowt-user-attachments.s3.amazonaws.com/0089fa95-90cd-4e40-926f-0b1676b39e00.jpeg"></p>
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Tell me about the Fluid-Mosaic Model

  • also called the Singer-Nicolson Model

  • Membranes are fluid - not fixed in position (can adopt

  • amorphous shapes)

  • Fluid - phospholipids can move

  • Mosaic - embedded with proteins

<ul><li><p>also called the <strong><span style="color: red">Singer-Nicolson Model</span></strong></p></li><li><p>Membranes are fluid - not fixed in position (can adopt</p></li><li><p>amorphous shapes)</p></li><li><p><strong><span style="color: blue">Fluid</span></strong> - phospholipids can move</p></li><li><p><strong><span style="color: yellow">Mosaic</span></strong> - embedded with proteins</p></li></ul><p><img src="https://knowt-user-attachments.s3.amazonaws.com/a3443b97-65ba-45c9-9ed8-3474239d01ec.jpeg"></p>
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Diagram of Plasma Membrane*

<h1 collapsed="false"><img src="https://knowt-user-attachments.s3.amazonaws.com/ca843346-39ed-42ef-b1ae-2fc525a5cb0c.jpeg"></h1>
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Tell me about Fluidity

Fluidity increases with temperature and shorter fatty acid tails - changes to kinetic energy and decreased viscosity

Fluidity increases with double bonds - harder to pack

At high temps cholesterol stabilizes membrane, at low temps it prevents clustering of phospholipids

<p>Fluidity <u><span style="color: red">increases</span></u> with<span style="color: red"> </span><strong><span style="color: red">temperature and shorter fatty acid tails</span></strong> - <em><mark data-color="red">changes to kinetic energy and decreased viscosity</mark></em></p><p>Fluidity <u><span style="color: red">increases</span></u> with <strong><span style="color: red">double bonds</span></strong> - <em><mark data-color="red">harder to pack</mark></em></p><p>At high temps <strong><span style="color: red">cholesterol stabilizes membrane</span></strong>, at low temps it<strong><span> </span><span style="color: blue">prevents clustering of phospholipids</span></strong></p><p><img src="https://knowt-user-attachments.s3.amazonaws.com/63296187-51e8-41fe-a74f-8f99433bf43e.jpeg"></p>
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Tell me about Davson-Danielli Model

Lipo-protein sandwich’, lipid layer sandwiched between two protein layers - trilaminar appearance

Falsification of this model led to Singer-Nicolson model

Proteins are embedded within lipid bilayer rather than existing as separate layer

<p>Lipo-protein sandwich’, lipid layer sandwiched between two protein layers - trilaminar appearance</p><p>Falsification of this model led to Singer-Nicolson model</p><p>Proteins are embedded within lipid bilayer rather than existing as separate layer<img src="https://knowt-user-attachments.s3.amazonaws.com/b598f9c9-5352-48cc-baba-f8e484dd9bfd.jpeg"></p>