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Lecture 3

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REVIEW CHECKPOINT

What we have covered so far
  • Dipole, polar vs non-polar molecules

  • Solubility (like dissolves like)

  • Significance of solubility

  • Ionic and covalent bonds

  • Hydrogen bonds 

  • Hydrophobic force

  • Molecular bonds, shapes, and functions

Chemical Bonds: Electronegativity, Polarity, and Solubility

Basis of Solubility

- Polar and non-polar compounds must move into, around and out of the body

- Polarity is the basis for several physiological processes, especially in nutrition (think hydrophobic and hydrophilic)

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  • "like" dissolves "like"

    • When solids and liquids interact there must be an attraction between the soluble (solid) particles and the solvent (liquid) â€‹â€‹

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Solubility

- Substances that have regions or zones of polarity can still dissolve in water

- Non-polar compounds dissolve in organic solvents (ex. fats dissolve in ethanol or benzene) 

- Ethanol can still dissolve in water due to the short C skeleton and polar OH group

  • Hydrophobic ("scared of water")

    • often molecules with a lot of Cs and Hs​

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Polarity of Water

- Makes an excellent solvent for other polar molecules, which is important since water takes up 60-70% of average body composition (many functions and nutritional interactions are based on ability to dissolve in water) â€‹â€‹

  • hydrophilic ("water loving")

    • an affinity for water​

    • hydrophilic molecules are either polar molecules or have polar side groups

    • permanent dipole moment

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Solubility in Water

- Molecules with functions groups including OH (glucose), COOH (amino acids) and NH2, and compounds such as NaCl are water soluble

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Dissociation: when an ionic compound like NaCl is placed in water

- Na+ interacts with more negative O

- Cl- interacts with more positive H

Emulsifiers

- Some molecules have both polar and non-polar regions (amphipathic)

- serve as detergents or emulsifiers, can make oil and water mix

- Ex. (bile acids, membrane lipids) 

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Significance of Solubility

Nutrients

- Digestion takes place in the watery environment of the small intestine

- Absorption of nutrients into the cells of the GI and later onto the blood depends on their solubility properties

- fat is treated specially (uses bile acid as a detergent)

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Nutrient Assimilation
- cell membrane is made up of lipid bilayer with proteins interspersed
- solubility can control what enters and leaves the cell
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Significance of Solubility

Getting compounds out of the body

- Kidneys excrete water soluble compounds

- Water soluble vitamins easily leave the body

- Fat soluble vitamins are usually stored in liver or fat so they are hard to get rid of

- Organic toxins deposit in our fat and are hard to get rid of (you are what you eat) 

- Hydrophilic compounds that dissolve in water do not readily cross membranes

- They need transporters to get across, sometimes require energy

- This is true for absorption and to get into and out of any cell (assimilation) 

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- Compounds that are hydrophobic must travel in blood with a carrier molecule, usually bound to a protein

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Consequences of Solubility

Cooking

- Salad dressing: due to polarity oil and vinegar don't mix

- Chicken soup: fat will separate and rise to the top

- Loss of water soluble nutrients

©2023 by Syracuse University Dr.Margaret Voss

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