Chapter 4- Amino Acids

Question 1

pKa of primary amine

Answer 1

~9

Question 2

pKa of the carboxyl group

Answer 2

~2

Question 3

Aliphatic hydrocarbon side chains are typically:

Answer 3

Non polar

Question 4

Characteristics of Met

Answer 4

• first amino acid in proteins
• participates in hydroponic interactions
• involved in metal binding

Question 5

Proline is conformationally

Answer 5

constrained (No movement)

Question 6

nonpolar amino acids are typically found in the ____ of proteins

Answer 6

interior (not exposed to water)

Question 7

AA’s that have maximum absorbance of 280 nm

Answer 7

Trp and Tyr

Question 8

Why do Phe, Tyr and Trp absorb strongly in the UV/Vis spectrum?

Answer 8

Their phenyl group

Question 9

UV/Vis spectroscopy is an

Answer 9

absorption technique (transition from ground state to excited state)

Question 10

Fluorescence is:

Answer 10

emission of a photon from an excited state to the ground state (shows up in higher wavelengths) (typically lower energy than absorption)

Question 11

The amino acids in the middle of the protein typically participate in _____ with other side chains

Answer 11

H-bonds

Question 12

The OH in side chains is

Answer 12

Very reactive
common in enzyme active sites
sites of protein modification

Question 13

Disulfide bond formation requires an

Answer 13

oxidizing agent (O2, H2O2)

Question 14

Reducing agents often contain a

Answer 14

Thiol group (SH)

Question 15

Why can His act as a proton donor and an acceptor?

Answer 15

The pH is so close to the physiological pH

Question 16

Characteristics of His:

Answer 16

• Can be buried in the protein fore or exposed to solvent
• involved in many enzymatic acid-base reactions

Question 17

Charged amino acids generally prefer to be on the _______ of proteins in an aqueous environment

Answer 17

surface

Question 18

Charged amino acids can form

Answer 18

electrostatic interactions (salt bridges)

Question 19

at physiological pH, the -COOH and -NH2 are

Answer 19

Overwhelmingly ionized

Question 20

Isoelectric point (pI)

Answer 20

pH where no net electric charge

Question 21

KI and Kj are

Answer 21

dissociation constants of the 2 ionizations flanking the pI

Question 22

Deprotonation of amino acids is ordered by

Answer 22

the lowest pKa to the highest pKa

Question 23

Increased distance from the alpha carbon results in

Answer 23

more basicity (electrostatic influence decreases)

Question 24

Stabilization/ destabilization is caused by

Answer 24

electrostatic interactions

Question 25

Hydrophobic interactions can ________ the pKa of acidic residues

Answer 25

raise

Question 26

Hydrophobic interactions can ________ the pKa of basic residues

Answer 26

Lower

Question 27

Amino acids are optically active because

Answer 27

the alpha carbon is chiral

Question 28

All amino acids derived from proteins are in the ___ conformation

Answer 28

L

Question 29

Post-translation modifications

Answer 29

modification of a standard amino acid happens after the polypeptide chain has been synthesized