Exam 1 - Principles of Biochemistry

Ionic Interactions

Electrostatic interactions between two fully charged atoms or groups with opposite charges

Hydrogen Bonds

Electrostatic interaction between hydrogen covalently bonded to an electronegative element (O,N) and nearby O or N

Van der Waals Interactions

Transient electrostatic interaction between permanent and/or induced dipoles

Hydrophobic Interactions

Association of nonpolar molecules or groups with each other in aqueous systems

How many hydrogen bonds can a water molecule form?

Up to four hydrogen bonds

Hydrophobic

Water-fearing

Hydrophlic

Water-loving

What do polar water molecules attract?

The negative and positive areas on the polar molecules (forming hydrogen bonds) which makes it dissolve in water

Which substances willingly dissolve in water?

Ionic and polar substances (hydrophilic)

Polar Groups

Contain electronegative atoms (O,N,S) that give rise to unequal sharing of electrons in the bonds

What is the result of unequal sharing of electrons?

Gives rise to partially charged poles on the bonds containing the electronegative atoms

What is the result of the polarity of the bonds?

The ability to hydrogen bond with other polar groups through partial charge attraction

What makes molecules not soluble in water?

Do no contain polar or ionizable groups

Are molecules that are in soluble in water, hydrophilic or hydrophobic?

Hydrophobic

Do water insoluble molecules share electrons equally or unequally?

Equally because they are nonpolar

Can nonpolar molecules dissolve in water?

No, meaning they cannot dissolve in water

Nonpolar Groups

Contain atoms with equal sharing of the bond electrons; the electronic charge density is essentially uniform

Can nonpolar groups interact with other groups?

No they cannot interact with other groups by forming hydrogen bonds or by strong dipole-dipole interactions

How do nonpolar groups act in aqueous environments?

They tend to cluster together via hydrophobic interaction

Amphiphilic (Amphipathic) Molecules

Contain both polar and nonpolar groups

What is an example of amphipathic?

Ionized fatty acids

In amphipathic molecules, which are water soluble: carboxyl group or the long carbon chain?

The carboxyl group is water soluble but the long carbon chain is not

What do amphipathic molecules form?

Tend to form micelles, colloidal aggregates with the charged “head” facing outward to the water and the nonpolar “tail” part inside

pH

The negative logarithm of the hydrogen ion concentration

What does pH measure?

Can measure the acidity conveniently without using large negative exponential numbers

What is an acidic pH?

Less than 7

What is a neutral pH?

Seven

What is a basic pH?

Greater than 7

What does the strength of an acid mean?

Its capability to release protons which can be determined by the acid dissociation constant

What does the value of the Ka mean in regard to acid strength?

Larger Ka = Stronger Acid

Smaller Ka = Weaker Acid