Acidity and pKa in Amino Acids

The video tutorial discusses carnosine, a dipeptide composed of beta-alanine and histidine, known for its antioxidant properties. It explains how to rank the acidity of protons in carnosine by examining their pKa values. The tutorial covers the pKa of carboxylic acids, amino groups, alpha protons, and the imidazole ring in histidine. It provides a detailed method for determining the order of proton acidity, from least to most acidic, in carnosine.

What is carnosine composed of?

• Beta-alanine and histidine

• Two histidine molecules

• Histidine and glycine

• Two beta-alanine molecules

What is the role of carnosine in foods?

• It resists glycation

• It acts as a preservative

• It provides color

• It enhances flavor

Why is it useful to label pKa values when ranking proton acidity?

• To identify the molecular weight

• To determine the boiling point

• To make it easier to rank acidity

• To calculate the density

What effect does an electronegative group have on the pKa of a carboxylic acid?

• It increases the pKa

• It decreases the pKa

• It has no effect

• It doubles the pKa

What is the typical pKa range for the carboxylic acid group in amino acids?

• 9 to 10

• 6 to 7

• 2 to 3

• 4 to 5

What is the pKa range for protonated amines in amino acids?

• 4 to 5

• 10 to 11

• 9 to 10

• 2 to 3

What is the pKa of the alpha hydrogen adjacent to the carbonyl group of an amide?

• 19

• 25

• 30

• 40 to 60

Which proton in carnosine is the most acidic?

• Alpha hydrogen next to the amide

• Carboxylic acid proton

• Ammonium proton

• Amidazole proton

What is the pKa range for the imidazole ring in histidine?

• 9 to 10

• 6 to 7

• 2 to 3

• 30

Which proton in carnosine is the least acidic?

• Proton B

• Proton D

• Proton A

• Proton C