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The Importance of Weak and Strong Chemical Bonds

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Erika LaTorre

on 28 February 2014

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Transcript of The Importance of Weak and Strong Chemical Bonds

The Importance of Weak and Strong Chemical Bonds
Free Energy (G)
-The change in energy during bond breaking and bond forming.

- At equilibrium, there is no further change in the amount of free energy.

- The free energy lost as equilibrium is approached is either transformed into heat or used to increase the amount of entropy.

- The equilibrium constant is exponentially related to free energy.
-The stronger the bond, the greater the change in free energy.
deltaG=-RT(lnKeq)
Weak Bonds in Biological Systems
van der Waals
Ionic Bonds
Hydrogen Bond
Conclusion
Characteristics of Chemical Bonds
-What is a Chemical Bond?
-It is an attractive force that holds atoms together.
-Characteristics:
-Valence
-Bond Angle
-Freedom of Rotation
Donating Molecules are Unstable
Catalyst and Strong Bonds
-Since covalent bonds have lost energy during formation, they do not have the energy to break apart thus they need help from a catalyst.

-The energy supplied to break the bonds is the activation energy.
-The least amount of energy is needed because a collision of the molecules occurs at the activated state.

-Enzymes catalyze reactions by lowering the activation energies; some reactions will not occur without the help of an enzyme.
Types of Bonds
-van der Waals: attractive force originating when two atoms come close together. All molecules exhibit van der Waals and it is the weakest of the weak bonds; it depends heavily on the distance between the interacting groups.
Chemical Bonds and Energy
-The formation and breakage of bonds converts energy from one form to another.
-The amount of energy that must be added to break a bond is exactly equal to the amount that was released upon formation of the bond
More Weak Bonds
-Organic Molecules that tend to from hydrogen bonds are water soluble.
-Hydrophobic: water fearing
-Hydrophilic: water loving

-Hydrophobic "bonds" stabilize macromolecules.

-Weak bonds attach enzymes to substrates.
-If enzymes were bound to their substrates, or to their products, by more powerful bonds, they would act much more slowly.

-Weak bonds mediate most protein-DNA and protein-protein interactions.
A+B-->AB + ENERGY
AB+ ENERGY--> A+B
- Equilibrium: number of bond making equals the number of bond breaking.
Polar and Nonpolar
-A combination of separated positive and negative charges is called an electric dipole moment.
- Molecules that have a Dipole moment are Polar molecules.
- Molecules not having a Dipole moment are Nonpolar molecules.
-Main types of Weak Bonds:
-van der Waals, Hydrophobic bonds, Hydrogen bonds, and Ionic bonds.

-They have energies between 1 and 7 kcal/mol.

-They are constantly made and broken at phisiological temperatures.

Hydrogen Bonds
Ionic Bonds
-The electrostatic forces acting between the oppositely charged groups.

-Many organic molecules possess ionic groups that contain one or more units of net positive or negative charge.

-One or more electrons from one atom are removed and attached to another atom, resulting in positive and negative ions which attract each other.

Hydrogen Bonds: are formed between a donor hydrogen atom with some positive charge and a negatively charged acceptor atom.

-Both the donor hydrogen atom and the negative acceptor atoms have a less than a unit of charge.

-The most important hydrogen bonds involve hydrogen atoms covalently bound to oxygen or nitrogen.
-Molecules linked by weak bonds posses a greater amount of free energy than those linked by strong bonds.
-Molecules linked by weak bonds do not require a catalyst to convert into other molecules and are unstable
-They are converted to more stable compounds.
Strong Bonds
-In order for molecules with strong bonds to convert to other molecules they need the help of a catalyst.
-Strong bonded molecules have lost a large amount of free energy in the process of forming.
High Energy Bonds
-Were thought to violate the laws of thermodynamics.

-Upon superficial examination, they were thought to increase free energy upon formation.

-Was found that they do not violate the laws but are based on different reactions than the ones originally thought.

-Precursors are first enzymatically converted to high-energy activated molecules, and in the presence of an enzyme then convert to the desired product.
Biosynthetic Processes
-ATP is the primary energy source of the cell, formed from ADP and inorganic phosphate.

-ATP contains several high-energy bonds.

-Groups linked by high-energy bonds are considered high-energy groups; these high energy groups can be transferred to other molecules by group-transfer reactions.
-Weak and Strong bonds are IMPORTANT
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