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Bio notes section 5

Bio notes section 5 - Biology Notes Section 5 Lecture 5...

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Biology Notes Section 5: Lecture 5 + Chapter 4 Plasma Membrane A very thin (~10 nm diameter) semi-permeable material with 2 major functions: - All cells separation from environment - Eukaryotes compartmentalization (e.g. endoplasmic reticulum, Golgi body, etc.) 4 major components of plasma membrane: a. Phospholipid bilayer the phosphate group heads, which are polar + hydrophilic, face outwards, while the fatty-acid lipid tails (nonpolar + hydrophobic) face inwards. i. Consequences: cell can interact w/its fluid environment but stay separate from it because of the hydrophobic region created by the inward sets of fatty-acid tails. ii. The membrane itself has a fluid nature. iii. Only hydrophobic substances can pass through it w/o help, because “like dissolves like” a nd the membrane itself is hydrophobic (despite the charge of the heads). iv. Phospholipids are amphipathic = both water soluble + non-soluble e.g. like detergents, which can be dissolved in water but also attach to grease they contact. Phospholipids in water: They spontaneously form certain structures: - 1. Micelle a sphere with hydrophilic heads outside and hydrophobic tails inside. o This is the form taken by detergent- grease gets trapped inside the circle. - 2. Phospholipid bilayer, like in cell membranes. b. Cholesterol has a large hydrophobic tail (as it is also a lipid) w/ an attached hydrophilic hydroxyl group. i. It acts as a “patching substance” on the bilayer, keeping some small molecules from getting through. ii. By interacting w/ the fatty acid bilayer, cholesterol helps keep the membrane at an optimum level of fluidity.
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c. Proteins 2 types of membrane-related protein: o 1. Integral membrane proteins proteins bound to membrane’s hydrophobic interior. o 2. Peripheral proteins proteins lying on either side of membrane but not bound to it; usually attached to integral proteins at the surface with hydrogen/ionic bonds. - Because of this binding nature, to break down a membrane and remove peripheral proteins we must lower the pH (end up w/ protons) or raise salt concentrations (end up w/ ions). - To remove integral proteins we must dissolve the membrane entirely (using detergents). d. Glycoproteins integral proteins w/ added sugar groups called glycocalyx. i. Function in cell lubrication, adhesion, and signaling. ii. Signaling aspect: e.g. blood type depends on which of 3 sugar groups is present on the surface of red blood cell integral proteins.
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