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What are some reasons why water is important?
- Abundant
- Most reactions take place in water- "Solvent of life"
- Polarity
- Hydrogen bonds
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How is body heat regulated?
- By releasing water into the air by sweat
- Start sweating
- Get water on skin
- Heat on skin used to break the H bonds of water in sweat
- Water evaporates, releasing heat
- H bonds allow us to release heat through evaporation- EXOTHERMIC
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What effect does water have on the lungs of premature new born babies?
- Water in alveoli forms H bonds with each other
- If nothing done to interfere with them, H bonds too strong and lungs collapse
- Evolution created amphipathi substance called surfactant
- Surfactant interferes with H bonds in alveoli, weakening them so they don't collapse
- Premature new borns don't have surfactants, so their lungs are collapsed
- Have to artificially support them
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What are alveoli?
- Air sacs in lungs where the exchange of oxygen and carbon dioxide takes place
- Covered in water
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What does amphipathic mean?
Combination of polar and nonpolar
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What are the characteristics of water molecules?
- Each H atom shares an electron pair with an O atom
- The oxygen orbitals form an almost perfect tetrahedron (105°)
- Oxygen attracts the electrons more strongly than H+
- The electrons spend more time close to the oxygen atom, resulting in 2 electric dipoles
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What do the atoms in water molecules share with each other?
Each hydrogen atom shares an electron pair with an oxygen atom
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What shape do the orbitals of oxygen in water form?
Tetrahedron
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What is the angle between the O/H atoms in water?
About 105°
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Which atom(s) in water attract electrons more strongly?
Oxygen attracts more strongly than H+
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Electrons in a water molecule spend more time close to which atom(s)?
Oxygen atom
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What results from electrons spending more time close to the oxygen atom in a water molecule?
Two electric dipoles
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What kind of partial charge does hydrogen have?
Positive
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What kind of interactions do hydrogen bonds form because of their partial positive charge?
Electrostatic interactions
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Hydrogen atoms can form electrostatic interactions with what kind of atoms?
Atoms that have negative partial or total charge
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Why are H bonds electrostatic and not covalent or ionic?
- Not covalent- not sharing any electrons
- Not ionic- not taking or losing electrons
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What is polarity?
- Asymmetric distribution of charge/electrons
- No net charge
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Why do electrons spend more time around oxygen than hydrogen?
- Oxygen is more electronegative
- Attracts electrons more
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Are H bonds weak or strong?
- Relatively weak when just one
- But in large numbers, like in water, become stronger; create a significant barrier that needs to be broken with force
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How does water have dipole?
- Difference in charge distribution
- Negative charge around O
- Positive charge around H
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What crucial role do hydrogen bonds play in biological molecules?
Stabilization
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How are charges depicted around a water molecule?
Cloud of electron density with dipole
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Give a list of examples for why hydrogen bonds are extremely important.
- Source of unique properties of water
- Structure and function of proteins, DNA, polysaccharides, etc.
- Binding of subtrates to enzymes
- Binding of hormones to receptors
- Matching of mRNA and tRNA
- Every biological thing we can think of is surrounded by and interacting with water
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Water can serve as both a(n) ________ and a(n) ________.
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Up to four H bonds per water molecule gives water what kind of characteristics?
- High boiling point
- High melting point
- Large surface tension
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Water molecules can make up to how many H bonds?
4 H bonds
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Hydrogen bonding in water is __________.
cooperative
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Hydrogen bonds btwn neighboring molecules are weak relative to what kind of bonds?
H-O covalent bonds
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What is the difference in bond energy between hydrogen bonds and H-O covalent bonds?
- H bonds- 20 kJ/mol
- H-O covalent bonds- 420 kJ/mol
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Hydrogen bonds are formed with what kind of atoms?
Electronegative atoms
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What does electronegative mean?
"electron-pulling"
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What does electropositive mean?
"electron-pushing"
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What are some biologically important H bonds?
- Between hydroxyl group of an alcohol and water
- Between the carbonyl group of a ketone and water
- Between peptide groups in polypeptides
- Between complementary bases of DNA
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Which has greater entropy, liquid water at 0° C or ice at 0° C? Why?
- Liquid
- Molecules are moving around more = more disorder
- Isn't stable in its structure
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At room temperature, the thermal energyy of an aqueous solution is comparable to what?
The energy needed to break the hydrogen bonds
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What are flickering clusters?
Bonds constantly being made and broken
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In liquid water, H bonds are made with about how many other water molecules?
- About 3.4 molecules
- Always fluctuating btwn 3 and 4
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What is the most common crystal form of ice?
Hexagonal ice
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How is the structure/entropy of ice different from liquid water?
- Water has more entropy than ice
- Ice is more structured and doesn't move around
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About how many hydrogen bonds does each water molecule form in ice?
4
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Why does hexagonal ice have low entropy?
Hexagonal ice forms a regular lattice
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Which is more dense, ice or liquid water?
Liquid water
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Why is ice less dense than liquid water?
- The structure of ice forces larger distance btwn water molecules
- Not as tightly packed?
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Molecules with what kinds of bonds/interactions are soluble in water?
- Hydrogen bonds
- Ionic bonds/electrostatic interactions
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What kind of solutes does water form hydrogen bonds with?
Polar solutes
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What kind of solutes does water interact electrostatically with?
Charged solutes
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How does water interact with charged solutes?
- Water stabilizes the charged solutes
- Weakens the electrostatic interactions between different charged solutes
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How does entropy of a structured crystal change when it gets broken down and separated?
- Order → disorder
- Increase in entropy
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How does enthalpy of a structured crystal change when it gets broken down and separated?
Doesn't change
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What kind of energy is the reason salt dissolves in water?
All dat entropy
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How does the entropy of water change when a structured crystal dissolves in it?
Water decreases in entropy
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Why does the entropy of water decrease when a structured crystal like NaCl dissolves in it?
- Before, the water molecules were free to move around
- Now, some get stuck hydrating Na+ or Cl-
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What is the overall change in entropy for a system with a structured crystal dissolving in water?
Overall has a large increase in entropy
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Why is there almost no change in enthalpy when a structured crystal dissolves in water?
The breaking of ionic bonds is balanced almost completely by the hydration bonds
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What is generally poorly soluble in water?
- Lipids, fats, oil, etc.
- Non polar gases are also insoluble in water
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From a biological perspective, it is extremely important that Carbon dioxide and Oxygen are both ________.
Nonpolar gases
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How is oxygen transported in blood?
- Only 2% transported dissolved
- Majority is transported bound to hemoglobin
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How is carbon dioxide transported in blood?
Only 10% travels dissolved in blood
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What are some gases that are nonpolar/insoluble in water?
- Nitrogen
- Oxygen
- Carbon dioxide
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What are some gases that are polar/soluble in water?
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What happens to CO2 in water?
- CO2 forms carbonic acid
- This dissociates into H+ and bicarbonate
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The dissociation of carbonic acid into H+ and bicarbonate causes what kind of change?
A change in pH
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What's an example of the effects of the change in pH due to the dissociation of carbonic acid?
Ocean Acidification, b/c CO2 increaes in atmosphere
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What can happen to blood when there are high levels of CO2 present?
Blood becomes more acidic
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About 60% of CO2 travels in blood as what?
Bicarbonate
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How does about 30% of bicarbonate travel?
Bound to hemoglobin
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What are the different kinds of non-covalent interactions?
- Ionic (Coulombic) interactions
- Dipole interactions
- van der Waals interactions
- Hydrophobic effect
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What are ionic interactions?
- Electrostatic interactions between permanently charged species
- Or between the ion and a permanent dipole
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What are dipole interactions?
Electrostatic interactions between uncharged, but polar molecules
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What are van der Waals interactions?
- Weak interactions between all atoms, regardless of polarity
- Attractive (dispersion) and repulsive (steric) component
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What is the hydrophobic effect?
- Complex phenomenon associated with the ordering of water molecules around non-polar substances
- Not a force, just an observation; polar and non polar substances don't interact
- Nonpolar substaces aren't attracted to each other
- Water is moving away from nonpolar/oily substance because waters are attracted to each other
- Oil gets together as a result
- Entropically favored
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Any molecule placed in water will interfere with what?
The hydrogen bonds of water
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When a hydrophobic substance is placed in water, how does this affect the change in enthalpy?
- Any molecule placed in water will interfere with hydrogen bonds
- But hydrophobic substances don't compensate this change in enthalpy (unlike Na and Cl which balance with hydration bonds)
- Therefore, there is an increase in enthalpy
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When a hydrophobic substance is placed in water, how does this affect the change in entropy?
- Hydrogen bonding isn't completely random anymore
- They force water into a more organized structure/pattern
- Decreases entropy of system
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What shows that putting a hydrophobic substance in water is highly unfavorable?
- Increase in enthalpy; decrease in entropy
- ΔG = ΔH - TΔS > 0
- Not spontaneous
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What is clathrates?
A compound in which molecules of one component are physically trapped within the crystal structure of another
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Why is nonpolar substances in water considered clathrate?
Highly ordered water molecules form "cages" around the hydrophobic substance
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What did the American chemist Walter Kauzmann discover?
- Nonpolar substances, like fat molecules, tend to clump up together rather than distributing themselves in a water medium
- When separated, the fatty substances have higher surface area, increasing contact with water and forcing water to stop randomly interacting with all the other water molecules (enthalpy) and forcing them to stay in rigid structure (entropy)
- Clumping up allows the fat molecules to have minimal contact with water
- It is entropically favored
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Why is the hydrophobic interactions mostly an entropic effect?
- Originates from the disruption of highly dynamic hydrogen bonds between molecules of liquid water by the nonpolar solute
- Clumping of nonpolar solutes is entropically favored
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The hydrophobic effect is one of the main factors behind what?
- Protein folding
- Protein-protein association
- Formation of lipid micelles
- Binding of steroid hormones to their receptors
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What is the misconception about the hydrophobic effect?
It does NOT arise because of some attractive direct force between two non-polar molecules
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What are amphipathic compounds?
Compounds that contain a polar and a non-polar region
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What do amphipathic compounds tend to do in water?
Form micelles
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What do amphipathic compounds do when in water?
- Non-polar groups are first dispersed, decreasing entropy
- Then they're isolated from water
- The released water molecules increase the entropy
- Only polar "head groups" are exposed and make energetically favorable H-bonds
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What are micelles?
Look like balls where the hydrophillic/polar head groups are on the outside, and the inside of the ball has the hydrophobic/nonpolar tails
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Hydrophobic effect favors what kind of binding?
Ligand binding
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Why does the hydrophobic effect favor ligand binding?
- Facilitates interaction btwn hydrophobic substrates and its enzyme
- Binding sites in enzymes and receptors are often hydrophobic
- Such sites can bind hydrophobic substrates and ligands such as steroid hormones
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