Lecture 3: Chemical Interactions in Biology

Of the known elements, how many are thought to be essential to sustain life?

20-25%

In order for an atom to hold a positive charge, it must have more of which type of sub-atomic particle vs the others?

Protons

Which of the following chemical interactions is the strongest in water?

Covalent Bond

True/False: Dipoles of like (the same) charge are likely to interact (ex: partial positive and partial positive).

False

True/False: Polarity results from differences in electronegativity of the atoms sharing an electron in a covalent bond.

True

Which two chemical interactions make salt bridges so strong (contributing to protein structure)?

• Hydrogen Bond

• Ionic Interaction

What is true of the hydrogen acceptor in a hydrogen bond?

It contributes unshared electrons to the hydrogen bond.

Define a nonpolar covalent bond.

A bond where electrons are shared equally due to the two atoms having the same electronegativity.

Define a polar covalent bond.

A bond where electrons are shared unequally due to a difference in electronegativity between the two atoms.

What are Chemical Bonds?

Interactions between atoms that keep them close together.

What is a Covalent Bond?

Interaction where two atoms share valence electrons.

What is an Ionic Bond?

Bond between positively and negatively charged atoms (full charges on atoms from electron exchange allow bonding) 

What is a Ion-Dipole interaction?

Ionic charges (cations and anions) and opposite partial charges (dipoles) interact.

What is a Hydrogen bond?

A noncovalent attraction between a hydrogen and an electronegative atom.

What part does the H-bond donor play?

Electronegative atom covalently bonded to hydrogen contributed to H-bond interaction.

What part does the H-bond acceptor play?

Electronegative atoms that contributes an unshared pair of electrons to the H-bond interaction.

What is a Dipole-Dipole Interaction?

• The electrostatic interactions between the permanent dipoles of different polar molecules.

  • These interactions align the molecules to increase the attraction.

What is a Dipole-Induced Dipole interaction?

A weak attraction that results when a polar molecule induces a dipole in an atom or in a nonpolar molecule by disturbing the arrangement of electrons in the nonpolar species.

What is a Induced Dipole-Induced Dipole interaction?

A weak, temporary interaction that occurs in all molecules (polar and non-polar).

Define Electronegativity.

The tendency for an atom to attract electrons towards itself (over other atoms in a chemical bond).

Define Polarity.

The unequal sharing of electrons in a chemical bond, resulting in partial charges on the involved atoms.

Define Dipoles.

Chemical bonds with positively charged parts (atoms).

Describe how a salt bridge is both hydrogen bonding and an ionic interaction?

Involves the electrostatic attraction between oppositely charged ions (ionic interaction) while also having a hydrogen bond component where a hydrogen atom from one charged group is positioned close enough to an electronegative atom on the oppositely charged group to create a weak attractive force.

How are the chemical interactions ranked?

1. Covalent Bond

2. Ionic Interaction (Ion-Ion)

3. Ion-Dipole

4. Hydrogen Bonding

5. Dipole-Dipole

6. Dipole-Induced Dipole

7. Induced Dipole-Induced Dipole