BIOCHEM: amino acids: chirality, pKa's and pI's

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1

top

In determining the chirality of an amino acid, you should position the alpha-carboxylate group where? top, bottom, right, or left?

2

D

Once you've correctly rotated the amino acid, let's say the alpha-amino group is on the right; which isomer is it? L, D, R, or S?

3

glycine

This is the only amino acid that is not chiral.

4

L

Natural amino acids exist as: L or D (isomers)?

5

aliphatic

Leu and Val have only C and H in their side chains and are thus described as _____________.

6

Ile

The 3 letter code of isoleucine

7

aromatic

A cyclic side chain is also described as:

8

H, K, R

Using one-letter abbrev., list the 3 amino acids that are basic, such as X,Y,Z (in alphabetical order)

9

nitrogen

A guanidinium group contains 3 elements of ___________.

10

Asp, Glu

Using their 3-letter abbrev., list the two amino acids that have an extra carboxyl group. (separate with a comma and space)

11

Asn, Gln

Using their 3-letter abbrev., list the two amino acids that have an amide group. (separate with a comma and space)

12

cystine

Two cysteines bonded together:

13

COOH

In an amino acid, which functional group loses a proton first? COOH, NH3, or side chain

14

zwitterion

This "species" of amino acid is neutral (equal number of + and - charges).

15

triprotic

Histidine is: monoprotic, diprotic, or triprotic?

16

side COOH

In aspartate and glutamate, the second proton comes off the: alpha-COOH, NH3, or side COOH

17

isoelectric point

The pH value at which the amino acid has a net zero charge (2 words).

18

+1

In the fully protonated form, most amino acids have an electrical charge of +2, +1, 0, -1, -2?

19

NH3, COO

At pH 7, amino acids have a + charge on the _______ group and a - charge on the _______ group. (Write as, for example: CH3, OH)

20

2.95

Aspartic acid has the following pKa values: 2.0 (alpha-carboxyl), 9.9 (amino), and 3.9 (side chain). What is its pI (to two decimal places)?

21

10.75

Arginine has the following pKa values: 1.8 (alpha-carboxyl), 9.0 (amino), and 12.5 (side chain). What is its pI (to two decimal places)?

22

5.7

Tyrosine has the following pKa values: 2.2 (alpha-carboxyl), 9.2 (amino), and 10.5 (side chain). What is its pI (to one decimal place)?

23

+2

In the fully protonated form, the 3 basic amino acids have an electrical charge of +2, +1, 0, -1, -2?