Chapter 3 (Section 3.1)

Proteins are _____ of a-amino acids

linear heteropolymers

Amino acids have properties that are well suited to carry out a variety of biological functions:

Capacity to polymerize

Useful acid-base properties

Varied physical properties

Varied chemical functionality

The a-carbon always has ____ substituents and is ______

four, tetrahedral

All amino acids (expect proline) have an _____ group connected to the a-carbon and a _____ group connected to the a-carbon

acidic carboxyl, basic amino

All amino acids are _____ except for _____

chiral, glycine

Proteins only contain L or D amino acids?

L

What are the nonpolar, aliphatic (non-aromatic) amino acids?

Glycine, Alanine, Proline, Valine, Leucine, Isoleucine, Methionine

What are the aromatic amino acids?

Phenylalanine, Tyrosine, Tryptophan

What are the polar uncharged amino acids?

Serine, Threonine, Cysteine, Asparagine, Glutamine

What are the positively charged amino acids?

Lysine, Arginine, Histidine

What are the negativity charged amino acids?

Aspartate and Glutamate

Intentional modifications of uncommon amino acids can occur:

After protein synthesis

During protein synthesis

Briefly to change protein function

Amino groups, carboxyl groups, ionizarle R groups equal weak ____ and _____…..

Acids, Bases

What are Zwitterions and at what pH do they occur?

Zwitterions are molecules that contain both positive and negative charges but are overall neutral. They occur at a neutral pH

At least how many ionizable protons do amino acids contain?

Two

The _____ has a acidic pKa and will be protonated at a ___ pH. It will be _____ at a biological pH

carboxylic acid, acidic (low), deprotonated

The _____ has a basic pKa and will be deprotonated at a ___ pH. It will be _____ at a biological pH

amino group, basic (high), protonated

Amino acids with uncharged side chains have how many pka values?

Two

Explain the role of the amino acid Glycine as it acts as a buffer

Buffers prevent a change in pH that are close in values, so glycine can act as a buffer in two pH regions centered at 2.34 and 9.6

What is an Isoelectric Point (pI)

is the specific pH value where a molecule carries no net electrical charge and is electrically neutral

Amino acids carry a net charge of ____ at a specfic pH which is the ____

Zero, Isoelectric Point

Zwitterions predominate at pH values between the pKa values of the ____ and _____ groups

amino, carboxyl

Whats the difference between pH ans pKa vaues

pH values represent how acidic or basic a solution is while pKa values represent how tightly a molecule holds onto its protons

How do you find the isoelectric point (pI) of an amino acids without ionizable chains?

You take the average pKa values ((pK1 + pK2)/2)

At the point where pI = pH, the net amino acid charge is ____. This is the pH where the amino acid is ____ and _____

zero, least soluble in water, does not migrate in an electric field

Ionizable side chains add a ____ pKa value

third

How do you calculate the pI when the side chain is ionizable?

1) Find the species that has a net zero charge

2) Find the pKa value that defines the acid strength of this zwitterion (+1)

3) Find the pKa value that defines the basic strength of this zwitterion (-1)

4) Take the average of these two zwitterions