Amino Acids

Isoelectric Point

100

What is the definition of isoelectric point?

The pH at which the net charge on a molecule is zero!

200

How to calculate isoelectric point?

1. Find the pH range that the molecule has a net charge of 0

2. Add the pKa's at both ends of that range and divide by 2 (find the average)

300

What is the isoelectric point of glycine? Assume pKa of the amino group is 9 and pKa of the carboxyl group is 3.4

(3.4+9)/2 = 6.2

400

What is the isoelectric point of lysine?

pKa1=2.16

pKa2=9.06

pKa3=10.54

Lysine will have a net charge of 0 at a pH between pKa2 and pKa3 (COO-, NH2, NH3+). So, (9.06+10.54)/2=9.8

500

What is the isoelectric point of glutamate?

pKa1=2.10

pKa2=4.07

pKa3=9.47

Glutamate will have a net charge of 0 at a pH between pKa1 and pKa2 (COO-, COOH, NH3+). (2.10+4.07)/2=3.09

Peptide Bonds

100

What functional group is a peptide bond?

Amide!

200

How is a peptide bond formed?

At physiologic pH, the COOH of one amino acid is deprotonated (COO-) and the amino group of another amino acid is protonated (NH3+). A dehydration reaction combines these two and removes water, so one oxygen on the carboxyl is taken out as well as two hydrogens from the amino group. The peptide bond is thus an amide (and is the bond between the C and the N)

300

Identify the peptide bond in the amino acid sequence. (See Google Doc)

:D

400

How many peptide bonds are found in the following? (See Google Doc).

:D

500

Identify the amino acids (See Google Doc)

>:D

Amino Acid Structure

100

What amino acids are basic? What charge do they have?

Lysine, histidine, and arginine; positive charge

200

What amino acids are sulfur-containing?

Methionine, cysteine

300

What amino acids are aromatic?

Phenylalanine, tyrosine, tryptophan

400

Which of the following substitutions would be least problematic?

A) Phenylalanine --> Histidine

B) Glycine --> Aspartate

C) Valine --> Isoleucine

D) Lysine --> Glutamate

C; both nonpolar; think about structure

500

In sickle cell disease, a single point mutation in the b-globin gene changes a glutamic acid to another amino acid. What amino acid substitution would cause the most detrimental change?

A) Valine

B) Aspartate

C) Asparagine

D) Lysine

A) 

Amino Acid Structure 2

100

What is the basic structure of any amino acid?

Chiral carbon connected to a H, amino, carboxylic acid, and R group

200

What amino acids are negatively charged?

Glutamate, aspartate

300

What functional group is on cysteine's side chain?

Sulfhydryl

400

Which amino acid is not chiral?

Glycine

500

Which amino acids can be phosphorylated?

Serine, threonine, and tyrosine

Identify

100

See Google doc #1

Glycine

200

See Google doc #2

Proline

300

See Google doc #3

Tryptophan

400

See Google doc #4

Lysine

500

See Google Doc #5

Tyrosine