Amino Acids Flashcards

Question 1

Q

What are amino acids?

Answer

A

Amino acids are biologically important organic compounds made from amine (-NH₂) and carboxylic acid (-COOH) functional groups, along with a side-chain specific to each amino acid.
The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen, though other elements are found in the side-chains of certain amino acids.

Question 2

Q

What is the general structure of an amino acid?

Question 3

Q

How many naturally occuring amino acids are there?

Answer

A

There are 20 naturally occuring amino acids.

Question 4

Q

What are amino acids used for?

Answer

A

Amino acids function in:

Gastrointestinal function
Cellular energy production
Detoxification
Neurotransmitter metabolism
Muscle catabolism
Collagen
Nutritional markers
Vascular function

Question 5

Q

What disease processes are amino acid change in sequence implicated in?

Answer

A

Amino acid change in sequence has been implicated in:

Cardiovascular disease
Depression
Anxiety
Insomnia
Chronic Fatigue Syndrome
Multiple sclerosis
Congestive heart failure
Impotence/Erectile pain syndromes
Infertility

Question 6

Q

What does chirality mean?

Answer

A

An object or a system is chiral if it is not identical to its mirror image, that is, it cannot be superposed onto it. A chiral object and its mirror image are called enantiomers. A non-chiral object is called achiral and can be superposed on its mirror image.

Question 7

Q

How would you determine if an amino acid is an L or D isomer?

Answer

A

A rule of thumb for determining the D/L isomeric form of an amino acid is the “CORN” rule. The groups:

<dl>
<dd>
COOH, R, NH2 and H (where R is a variant carbon chain)</dd>
</dl>

are arranged around the chiral center carbon atom. Starting with the hydrogen atom away from the viewer, if these groups are arranged clockwise around the carbon atom, then it is the D-form. If counter-clockwise, it is the L-form.

Question 8

Q

What is the structure of the amino acid alanine?

Answer

A

Three letter abreviations: ala
One letter abreviation: A
pK_aa-carboxyl group, a-ammonium ion and side chain group: 2.34 & 9.69
Neutral, non-polar

Question 9

Q

What is the structure of arginine?

Answer

A

Three letter abreviation: arg
One letter abreviation: R
pK_{a of}_{a-carboxyl group, a-ammonium ion, and side chain group:}2.17, 9.04, and 12.48
Basic, polar

Question 10

Q

What is the structure of the amino acid Asparagine?

Answer

A

Three letter abreviation: asn
One letter abreviation: N
pK_a a-carboxylic acid & a-amine: 2.02 and 8.80
Neutral, polar

Question 11

Q

What is the structure of aspartic acid?

Answer

A

Three letter abreviation: asp
One letter abreviation: D
pKa carboxyl, amino, and R group: 2.10, 9.82, and 3.86
Acidic, polar

Question 12

Q

What is the structure of cystine?

Answer

A

Three letter abreviation: cys
One letter abreviation: C
pKa of a-carbon, a-amino, & R group: 2.05, 10.25, & 8.00
Neutral, slightly polar

Question 13

Q

What is the structure of glutamic acid?

Answer

A

Three letter abreviation: Glu

One letter abrevation: E

Polar (Charged)

Question 14

Q

What is the structure of glutamine?

Answer

A

Three letter abreviation: Gln

One letter abreviation: Q

Uncharged, polar

Question 15

Q

What is the structure of glycine?

Answer

A

Three letter abreviation: Gly

One letter abreviation: G

Nonpolar

Question 16

Q

What is the structure of histidine?

Answer

A

Three letter abreviation: His

One letter abreviation: H

Polar, + charge

Question 17

Q

What is the structure of isoleucine?

Answer

A

Three letter abreviation: Ile

One letter abreviation: I

Nonpolar

Question 18

Q

What is the structure of leucine?

Answer

A

Three letter abreviation: Leu

One letter abreviation: L

Nonpolar

Question 19

Q

What is the structure of lysine?

Answer

A

Three letter abreviation:

One letter abreviation:

Polar, + charge

Question 20

Q

What is the structure of methionine?

Answer

A

Three letter abreviation: Met

One letter abreviation: M

Nonpolar, hydrophobic

Question 21

Q

What is the structure of phenylalanine?

Answer

A

Three letter abreviation: Phe

One letter abreviation: F

Nonpolar

Question 22

Q

What is the structure of proline?

Answer

A

Three letter abreviation: Pro

One letter abreviation: P

Nonpolar

Question 23

Q

What is the structure of serine?

Answer

A

Three letter abreviation: Ser

One letter abreviation: S

Polar, uncharged

Question 24

Q

What is the structure of threonine?

Answer

A

Three letter abreviation: Thr

One letter abreviation: T

Polar, uncharged

Question 25

Q

What is the structure of tryptophan?

Answer

A

Three letter abreviation: Trp

One letter abreviation: W

Nonpolar

Question 26

Q

What is the structure of tyrosine?

Answer

A

Three letter abreviation: Tyr

One letter abreviation: Y

Nonpolar

Question 27

Q

What is the structure of valine?

Answer

A

Three letter abreviation: Val

One letter abreviation: V

Nonpolar

Question 28

Q

How do the carboxy and amino groups of amino acids exist at physiologic pH?

Answer

A

These groups are ionized at physiologic pH.

Question 29

Q

What is a Zwitterion?

Answer

A

These are molecules that bear charged grops at opposite polarities (Negative and positive groups).

Question 30

Q

How many major groups of amino acids are there?

Answer

A

Three: those with nonpolar R groups, those with uncharged polar R groups and those with charged polar R groups.

Question 31

Q

What are the nine (9) amino acids that have nonpolar R groups?

Answer

A

Glycine

Alanine

Valine

Leucine

Isoleucine

Methionine

Proline

Phenylalanine

Tryptophan

Question 32

Q

What are the six (6) amino acids with uncharged polar side chains?

Answer

A

Serine

Threonine

Asparagine

Glutamine

Tyrosine

Cysteine

Question 33

Q

What are the five (5) amino acids that have charged polar R groups?

Answer

A

Lysine

Arginine

Histidine

Aspartic acid

Glutamic acid

Question 34

Q

What makes cysteine unique among the 20 amino acids?

Answer

A

Cysteine has a thiol group that allows it to form disulfide bonds with another cysteine via an oxidation reaction. The disulfide bond has important implications for protein structure.

Question 35

Q

What is the isoelectric point (pI) of an amino acid?

Answer

A

This is the point where an amino acid carries no net electric charge.

At a pH below their pI, proteins carry a net positive charge; above their pI they carry a net negative charge.

The pI value can affect the solubility of a molecule at a given pH. Such molecules have minimum solubility in water or salt solutions at the pH that corresponds to their pI and often precipitate out of solution.

Question 36

Q

Why is the pK_a of acetic acid (4.76) higher than that of the amono acid glycine?

NOTE: Acetic acid is an alpha amino derivative of glycine.

Answer

A

This large pK_a difference is caused by the electrostatic influence of glycines positively charged ammonium group. That is, the -NH₃ ⁺ group repels the proton from its COOH group. Conversley, the COOH group increases the basicicity of the amino group.

Question 37

Q

What is a racemic mixture?

Answer

A

This is a mixture of chiral molecules that has equal amounts of an enantiomeric pair.