Lecture 2 - Jan. 25

Lecture 2 - Jan. 25 - Cell Biology 341 Last lecture: Weds.,...

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Cell Biology 341 Weds., January 25, 2012 The syllabus and all lecture slides are posted on our Sakai classroom. See the Cell Biology Interactive program on the DVD that came with your textbook for 5 videos for Chapter 1 showing examples of eucaryotic cells See Chapter 2 videos: 2.1 noncovalent interactions, 2.2 enzyme catalysis, 2.3 Brownian motion and the beginning of 2.5 citric acid cycle The text for the videos is in the Media Guide on the DVD Today: 4 types of noncovalent bonds or forces Fatty acids Proteins Last lecture: Reviewed syllabus Eucaryotic vs. procaryotic cells Organelles allow greater efficiency and regulation Chapter 2: nonpolar covalent bonds hydrophobic molecules Polar covalent bonds → hydrophilic molecules 4 types of noncovalent bonds
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1. Ionic bonds: one atom loses(donates;transfers) an electron to another see page 111 and fig. 2-5 Ionic bonds in salt crystals are very strong But ionic bonds are weak in aqueous solution, about 3 kcal/mol - Sodium gives up an extra electron and chlorine receives the extra electron – Both Na and Cl are filled. Electrostatic attractions - The ions will separate in solution, and each will be surrounded by a shell of water molecules (see fig 2-14) The δ - oxygen atom of “shell” water molecules will face the Na + ion - Hydrogens on water molecule repelled by positive charge on Na. - When Cl is put into a solution, O repels from the Cl that bonds with Na. Ions can pair with charged groups in macromolecules(e.g. Bonding of (+) substrate and (-) Enzyme) The ions in Na + Cl - exhibit electrostatic attractions
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2. Hydrogen bonds: a partially charged H atom (δ + ) is attracted to a partial negatively charged (δ - ) atom of another molecule Hydrogen bonds are weak, about 1 kcal/mol (1/20 strength of covalent bond) They occur only in molecules with polar bonds (hydrophilic molecules), and always involve a hydrogen atom with δ + Easily broken by heat Figure 2-15, also see page 108 H-bond contains regions of electrons being shared(covalent bond), and electrons not being shared. Strength of H-bond depends whether the bond is straight. - Bent bonds are weaker.
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Each water molecule can form up to 4 H-bonds with other water molecules, resulting in a latticework. The oxygen atom can form two H-bonds.
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Lecture 2 - Jan. 25 - Cell Biology 341 Last lecture: Weds.,...

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