Lehninger: Chapter Three

Question 1

What happens at a neutral pH in a basic amino acid structure?

Answer 1

At neutral pH 7, the carboxyl groups gets deprotonated (loses an H+) because its normal range is from 0-2, the amino group is in its ionic state as well (NH3+)

Question 2

What are zwitterions?

Answer 2

At neutral pHs, both amine and carboxylic acid are charged ( NH3+), (COO-)

Question 3

What links amino acids?

Answer 3

Ribosomes link amino acids by peptide bonds in a condensation or dehydration reaction during translation

Question 4

What poor leaving group have you seen in the slide examples?

Answer 4

OH is poor leaving group

Question 5

True or false: The chiral alpha carbon produces two enantiomers, explain reasoning

Answer 5

True; Because it is chiral it produces L and D stereochemistry, but in nature the only bioloigically active form are L-amino acids in which the amino group is on the left of the molecule.

Question 6

Describe the nomenclature in amino acids

Answer 6

1. the chiral carbon is the alpha position and all the other carbons in the R group ( if any ) are designated beta, gamma, delta and epsilon
2. The carboxylate carbon (COO-) is designated #1 and the remaining numbers are numbered accordingly

Question 7

At around how many nanometers do aromatic amino acids absorb light?

Answer 7

The absorb light at around 280 nm.

Question 8

which of the three aromatic amino acids absorbs light most strongly?

Answer 8

W ( tryptophan)

Question 9

Which amino acid’s sidechain can ionize and form disulfide bonds?

Answer 9

Cysteine, refer to slide # 14

Question 10

Which groups are the most hydrophilic?

Answer 10

The charged ones ( negative and positive)

Question 11

True or false: amino acids are weak acids/bases

Answer 11

TRUE

Question 12

What is an isoelectric point (PI) ???

Answer 12

The pI is the pH in which a compound has a zero net charge

Question 13

How to calculate PI from structure

Answer 13

1. Draw structure of amino acid
2. Completely protonate the amino acid
3. Place all the pKa values ranging from smallest to largest
4. Figure out the overall charge on what each structure would look like
5. Find the zwitterion, the one that has no overall charge
6. Add the pKa values that give that structure and divide by 2

Question 14

Which is the lightest amino acid? How much does it weigh?

Answer 14

The lightest amino acid is glycine, it weighs 75 Da

Question 15

What is the heaviest amino acid?

Answer 15

The heaviest amino acid is tryptophan, which weighs 204 Da

Question 16

What is the average MW of amino acids

Answer 16

110 Da