BIO 317 - Lec 2

BIO 317 - Lec 2 - BIO 317: Lecture 2! Prof. William...

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1 Prof. William Collins OfFce: 534 Life Sciences Building OfFce Hours: Mondays, 4:00 – 5:00 PM or by appointment Recommended Reading: BIO 317: Lecture 2 Asymmetry of the Lipid Bilayer is ±unctionally Important Phosphatidylserine is important for binding of protein kinase C to cytosolic surface of plasma membrane. Glycolipids are located exclusively in the noncytosolic lea²et - may play important roles in cell protection and cell recognition.
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2 Glycolipid Molecules Lipid Bilayers are Composed of Different Types of Lipids
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3 Cholesterol in a Lipid Bilayer Cholesterol molecules orient themselves with their hydroxyl groups close to the polar heads of the phospholipid molecules. The steroid ring region partly immobilizes the Frst CH 2 groups of the hydrocarbon chains. •Decreases membrane permeability •Decreases membrane ±uidity •Inhibits possible phase transitions Structure of the Plasma Membrane Phospholipid Bilayer – Additional components (cholesterol, glycolipids) Properties of lipid bilayer due to the shape and amphipathic nature of phospholipids – ²luidity – “Prohibition against free edges” • Spontaneous closure to form sealed compartment • Self-healing – Effective diffusion barrier against hydrophilic substances Inside and outside lea±ets of lipid bilayers are different (asymmetry) However, the bilayer structure alone does not explain how charged substances cross the plasma membrane?
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4 Relative Permeability of Lipid Bilayer Permeability coefFcients (cm/sec) Membrane Transport Cells need to transport speciFc water-soluble molecules across the plasma membrane • Ingest essential nutrients • Excrete waste products • Regulate intracellular ion concentrations How? Membrane Transport Proteins: • Carrier Proteins • Channel Proteins
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5 Membrane Transport Proteins Passive Transport (Diffusion) • Channel proteins create aqueous pores through the plasma membrane • A solute diffuses through the aqueous pore down its concentration gradient • The driving force is the concentration gradient of the solute Note, if a solute carries a net charge, then • both the concentration gradient and the membrane potential
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BIO 317 - Lec 2 - BIO 317: Lecture 2! Prof. William...

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