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Lecture 3

BIOL 2021 Lecture 3: L3 Chapter 10b

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BIOL 2021
Patricia Lakin- Thomas

Chapter 10 cont… Membranes - Figure 10-15 o Asymmetry of plasma membrane (PM) o Outside – Ptd-Cho, sphingos, all glycolipids o Inside – Ptd-Ser (- charge), Ptd-Etm  Charged inside o Cholesterol – evenly distributed, Flip-flip easily o Functions of asymmetry of PM  Signalling purposes  Proteins (protein kinase C) bind to specific lipids on cytosolic side  Lipid head groups generate signals o Inositol phospholipids as example  Ptd-Ser used in apoptosis o Death signal from outside so neighboring cells will come eat them - Membrane proteins (other half of membrane by weight… other half is lipids) o 30% of animal genome codes for membrane proteins o different membranes -> different proteins -> different functions o proteins can be from 25%-75% of membrane weight  myelin of neurons (ex)– electrical insulation, 25% protein  mitochondrial inner membrane (ex) – 75% protein  electron transport, ATP synthesis o protein association with membranes  Figure 10-17 (IMPORTANT FIGURE) –ways proteins associate with lipid bilayer  Association depends on function of protein  Membrane proteins (A) o 1, 2, and 3 are transmembrane proteins (goes through and sticks out of membrane)  have both hydrophobic and hydrophilic regions/domain o 4 is a protein alpha helix only on cytosolic side o 5 is a covalently attached lipid  Figure 10-18 -  Fatty acid chain attached to the protein o 6 has a covalent attachment to lipid  glycosyl phosphatidyl inositol (GPI)  anchor  Membrane associated proteins (B) o 7, 8 – non-covalent interactions with membrane proteins o functions of membrane proteins  transmembrane: function on both sides of membrane  ex: transport proteins –CHAPER 11 cell-surface receptors – CHAPTER 15  attached to cytosol side: signal relay  from transmembrane protein -> to cytosolic protein  ex: Protein kinase – CHAPTER 15  GPI anchors: for quick release in response to a signal  Membrane-associated proteins: subunits of complex o Transmembrane protein structure  Always asymmetric across the membrane = have unique orientation in membrane (different structure on both sides of lipid bilayer) *look at 10- 17*  CHAPTER 12 – create asymmetry while synthesizing protein  Figure 3-7  Alpha helix o Crosses through the membrane, if it does not then it would energetically un-favoured o Hydrogen bonds involved within the stand/chain of protein  Stabilizes the helix  Figure 10-17  1 = single-pass  2 = multipass transmembrane protein o stands can slide against each other -> conformational changes  figure 10-19  tran
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