Life as we know it began in water ~3 billion years ago.
We evolved to take the water with us.
Cells, organisms, us; all need water to survive.
Cells are made of 70%-95% water
Things can move freely in water (atoms, molecules, organelles, etc.)
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Structure of water
H2O
Electrons are not shared equally.
A molecule in which opposite ends have opposite electric charges is polar!
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Polar vs. Non-polar
Polar molecules
Molecules that have slight positive and negative ends.
Still a neutral charge overall
Hydrophilic
Non-Polar molecules
Electrons are equally shared across the molecule
Do not have charged ends.
Hydrophobic
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Lipids
Non-polar. Hydrophobic (water hating).
Long-term energy storage, insulation/protective coating.
PHOSPHO-Lipids make up cell membranes.
Made up of FATTY ACIDS.
Saturated vs. Unsaturated (Trans fats?)
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Polarity
Polar molecules do not share electrons equally. They work like magnets!
Opposite charges attract, same charges repel.
Polar molecules are hydrophilic (water-loving), non-polar are hydrophobic (water-hating).
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Hydrogen Bonds
Because of the partial charge, H2O molecules will be attracted to charged ions, and other water molecules!
This weak attraction between slightly negative oxygen and slightly positive hydrogen is known as a hydrogen bond.
It’s ironic: not actually a bond.
This bond is common in proteins and DNA.
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Properties of Water
Why is water so important?
Cohesion/Adhesion
Density
Temperature Moderation
Universal Solvent
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Cohesion
Tendency of water molecules to stick to one another. (Co-operate)
Hydrogen bonding
Surface Tension
Hydrogen bonds are like velcro.
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Adhesion
Tendency of water molecules to stick to other molecules (Adhesive).
Capillary Action
When Adhesive forces are stronger than Cohesive forces.
Allows water to move against gravity.
Allows plants to acquire water from the ground.
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Density of Ice
When water molecules cool down, they form a solid that is commonly known as ice.
Ice is less dense than liquid water, and floats on water.
Benefits -
Bodies of water freeze over the top. Insulates the lower water, allowing life to survive under the frozen top.
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Temperature Moderation
Hydrogen bonds are hard to break.
Temperature of large bodies of water stays relatively stable while air temperature varies from day to night. (Do you remember talking about this when we went to the brook?)
When water evaporates, the remaining liquid cools down: Evaporative cooling.
This is why we sweat.
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The Universal Solvent: Hydrate!
Organisms are water based.
Water can dissolve a large variety of substances.
Solute - Dissolves into something.
Solvent - Substance that dissolves things.
Allows chemical reactions to occur in the body. (Temperature Moderation!)
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Acids
Low pH (1-6)
Releases (H+) ions in water
Bases
High pH (8-14)
accepts (H+) ions in water
Neutral
pH of 7
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Buffers
Used to resist changes in pH.
Your blood has buffers!
(H2CO3) and (HCO3-), work in unison to keep the pH at a neutral 7.4.
Hemoglobin binds to H+ ions, removing them and raising the pH.