Lecture 3
REVIEW CHECKPOINT
What we have covered so far
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Dipole, polar vs non-polar molecules
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Solubility (like dissolves like)
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Significance of solubility
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Ionic and covalent bonds
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Hydrogen bonds
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Hydrophobic force
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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"
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When solids and liquids interact there must be an attraction between the soluble (solid) particles and the solvent (liquid) ​​
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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
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Hydrophobic ("scared of water")
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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) ​​
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hydrophilic ("water loving")
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an affinity for water​
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hydrophilic molecules are either polar molecules or have polar side groups
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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)
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)
Nutrient Assimilation
- cell membrane is made up of lipid bilayer with proteins interspersed
- solubility can control what enters and leaves the cell
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
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