Amino acids

Question 1

What are the two functional groups of an amino acid?

Answer 1

Amine group

Carboxyl group

Question 2

Amino acids are amphoteric, what does this mean?

Answer 2

They have both acidic and base properties

Question 3

How are amino acids amphoteric?

Answer 3

Their carboxyl group is acidic and can donate a proton

Their amino group is basic and can accept a proton

Question 4

What is the equation for the carboxyl group acting acidic?

Answer 4

-COOH -COO- + H+

Question 5

What is the equation for the amino group acting as a base?

Answer 5

-NH2 + H+ -NH3

Question 6

What is the equation for the amino group acting as a base?

Answer 6

-NH2 + H+ -NH3+

Question 7

What are the stages to naming amino acids?

Answer 7

1) find the longest carbon chain, including the carboxylic acid group and write down its name
2) Number the carbon in the chains, starting with the carbon in the carboxylic acid group as number 1
3) Write down the positions of any NH2 groups and show that they are NH2 groups with the word “amino”
4) Write down the names of any other functional groups and say which carbon they are on

Question 8

What are zwitterions?

Answer 8

Dipolar ion

Question 9

What does dipolar ion mean?

Answer 9

They have both a positive and negative charge in different parts of the molecule

Question 10

Where can zwitterions only exist?

Answer 10

Near an amino acids isoelectric point

Question 11

What is the isoelectric point?

Answer 11

The pH where the overall charge on the amino acid is zero and depends on the amino acid’s R group

Question 12

What are the different parts of an amino acid?

Answer 12

central carbon atom 
Variable R group 
Carboxyl group 
Amino group 
Hydrogen

Question 13

When does an amino acid become a zwitterion?

Answer 13

When its amino group is protonated to NH3+ and its COOH group is deprotonated to COO-

Question 14

What happens to the amino acid in conditions more acidic than the isoelectric point?

Answer 14

The -NH2 group is likely to be protonated but the -COOH is likely to be unchanged so the amino acid will carry a positive charge but not a negative

Question 15

What happens to the amino acid in conditions more basic than the isoelectric point?

Answer 15

The COOH group is likely to be deprotonated to -COO- but the -NH2 group will be unchanged so the amino acid will carry a negative charge but not a positive

Question 16

What can you use to separate amino acids?

Answer 16

Using thin layer chromatography

Question 17

Why can you separate amino acids?

Answer 17

They all have different R groups so they will all have different solubilities in the same solvent

Question 18

What do you have to do to the amino acids to make them visible in TLC?

Answer 18

Spray them with ninhydrin solution to turn them purple
or use a special plate with fluorescent dye attached to it and the dye glows in UV light where the amino acids will appear as dark spots

Question 19

What formula can use to calculate an Rf value to identify amino acids?

Answer 19

Rf = Distance travelled by spot / distance travelled by solvent