Chapter 4: Amino Acids

Question 1

What are proteins?

Answer 1

Natural products containing nitrogen

Question 2

All proteins are composed of what?

Answer 2

20 Amino Acids

Question 3

The building blocks of protein?

Answer 3

Amino Acids

Question 4

The common amino acids are known as? Why? Which are an exception to this?

Answer 4

-α-amino acids

-because they have a primary amino group (—NH2 ) as a substituent of the α carbon atom

-The sole exception is Proline, which has a secondary amino group
(—NH—), although for uniformity we will refer to proline as an α-amino acid.

Question 5

How do amino acids differ?

Answer 5

Different side chains also known as R groups

Question 6

Draw and describe the general structure of an amino acid?

Answer 6

R
I
H2N—–C—–COOH
I
H

Question 7

Why are Amino Acids Dipolar Ions?

Answer 7

Have at least 2 charges. Amino(NH3+) and Carboxyl (COOH-) are charged
=neutral

Question 8

An amino acid can act as both? Why

Answer 8

Acid and Base,
Because at physiological pH (∼7.4), the amino groups are protonated and the carboxylic acid groups are in their conjugate base (carboxylate) form

Question 9

What is a dipolar ion/zwitterion?

Answer 9

amino acids that bear charged groups of opposite polarity

Question 10

Structure of a dipolar amino acid?

Answer 10

R
I
H3N+—–C—–COO-
I
H

Question 11

amino acid is pos or neg?

Answer 11

positive

Question 12

carboxyl pos or neg?

Answer 12

neg

Question 13

low pH =
(3 names)

Answer 13

cationic, (+), acidic, fully pronated

Question 14

high pH=
(3 names)

Answer 14

anionic, basic, unpronated

Question 15

The process of amino acids forming chains with a peptide bond is known as?

Answer 15

condensation reaction

Question 16

What is a condensation reaction?

Answer 16

bond formation with the elimination of a water molecule

Question 17

The bond between amino acids?

Answer 17

Peptide bond

Question 18

3 steps in condensation reaction

Answer 18

take oh from carboxyl group in one amino acid
take h from amine group in other amino acid
creating elimination of water

Question 19

3 types of amino acids side chains?

Answer 19

Nonpolar, Uncharged polar, and charged polar R groups

Question 20

Why do the pK values of ionizable groups differ between free amino acids and amino acid residues in polypeptides?

Answer 20

they depend on environment

Question 21

all amino acids but _____ are chiral

Answer 21

glycine because it has 2 Hydrogens

Question 22

What is a polarimeter?

Answer 22

device used to measure optical rotation

Question 23

which amino acids recovered from polypeptides are optically active?

Answer 23

all except glycine

Question 24

is optically active asymmetric or symmetric?

Answer 24

asymmetric

Question 25

what does chiral mean

Answer 25

-when four different groups are bonded to the a-carbon atom
-chiral compounds have non superimposable (non identical) mirror images

Question 26

what are the two mirror image forms of a chiral called?

Answer 26

L isomer
D isomer
or called enantiomers

Question 27

Glycine has how many H atoms attached to its a-carbon atom?

Answer 27

2, making it superimposable/mirror image/not optically active

Question 28

Fischer convention is used for what

Answer 28

to describe the different forms of chiral molecules or asymmetric centers

Question 29

Chrirals rotate

Answer 29

the plane of polarized light

Question 30

Fischer projections

Answer 30

simpler ways to represent the complex chiral 3D molecules

Question 31

horizontal bonds extend ?

Answer 31

above/out the plane of the paper,

Question 32

vertical bonds extend?

Answer 32

below/in the plane of the paper

Question 33

Modified amino acids occur when?

Answer 33

after protein has been made “post translational modification”

Question 34

Amino acid modification include the simple additions of what?

Answer 34

additions of small chemical groups to certain amino acid side chains: hydroxylation, methylation, acetylation, carboxylation, and phosphorylation.

Question 34

Amino acid modification include the simple additions of what?

Answer 34

additions of small chemical groups to certain amino acid side chains: hydroxylation, methylation, acetylation, carboxylation, and phosphorylation.

Question 35

what’s unique about Individual amino acids and their derivatives?

Answer 35

they have diverse physiological functions. Such as gluthiaone which plays a role in cellular metabolism.

Question 36

What is an isoelectric point?

Answer 36

The pH at which a molecule carries no net electric charge

Question 37

pk1= what group? pH around?
pk2= what group? pH around?

Answer 37

pk1=carboxylic group pH around 2.2
pk2=α-amino groups pH around 9.4

Question 38

free amino acids in solution at neutral pH?

Answer 38

dipolar ions/zwitterions

Question 39

cysteine can form what kind of bonds

Answer 39

disulfide bonds (SH-) is attached to the side chain

Question 40

protein(peptide) chain starts with what and ends with what?

Answer 40

starts with amino end
ends with carboxylate

Question 41

What is the RS system?

Answer 41

In the Cahn–IngoldPrelog or RS system, the four groups surrounding a chiral center are ranked according to a specific, though arbitrary, priority scheme: Atoms of higher atomic number rank above those of lower atomic number (e.g., —OH ranks above —CH3).

Question 42

What is the RS system?

Answer 42

configuration classification Atoms of higher atomic number rank above those of lower atomic number (e.g., —OH ranks above —CH3).

Question 43

Amino acids are chiral molecules. Only blank-amino acids occur in proteins (some bacterial peptides contain D-amino acids).

Answer 43

L