Chapter 3: Amino Acids

Question 1

Proteins are __________ of amino acids residue joined to its neighbor

Answer 1

Polymers (residue meaning lost water when one animo acid joined to another)

Question 2

All 20 common acids share common ________ features

Answer 2

Structural

Question 3

All 20 common amino acids are ____ amino acids where they have a carboxyl group & an animo group bonded to the same carbon atom (the alpha carbon)

Answer 3

Alpha amino

Question 4

The difference in amino acids is based on their ________

Answer 4

Side chains (R groups)

Question 5

The alpha carbon is a __________ center

Answer 5

Chiral center

Question 6

Amino acids have sterisomers called _____________

Answer 6

enantiomers

Question 7

The absolute configuration of the 4 substituents of carbon atoms is the _________ system

Answer 7

D,L system

Question 8

The amino acid residues in proteins are ______ steroisomers

Answer 8

L

Question 9

Amino acids can be classified by their ___ group

Answer 9

R group

Question 10

Amino acids are group into groups based on their _____ which is the tendency to interact with water at pH= 7.0

Answer 10

Polarity

Question 11

What are the 5 R groups of animo acids?

Answer 11

1. Nonpolar aliphatic R groups
2. Aromatic R groups
3. Polar uncharged R groups
4. Positively charged (Basic) R groups
5. Negatively charged (Acidic) R groups

Question 12

What are the 6 uncommon amino acids?

Answer 12

1. 4-hydroxyproline
2. 5-hydroxylysine
3. 6-N-methyllysine
4. Y-carboxyglutamate
5. Desmosine
6. Selenocysteine & pyrrolysine

Question 13

Amino acids can act as ______ & ______

Answer 13

Acids & Bases

Question 14

The amino & carboxyl group of amino acids & the ionizable R group of some amino functions as weak _____ & ____

Answer 14

Acids & bases

Question 15

When an amino acid lacking an ionizable R group is dissolved in water a pH = 7 it exist in solution as the __________ which can act as either acid or base

Answer 15

dipolar ion (zwitterion)

Question 16

Substances having the dual (acid-base) nature are _______ & called _____

Answer 16

Amphoteric, ampholytes

Question 17

Titration curves can predict the __________ of amino acids

Answer 17

Electric charge

Question 18

Isoelectric pH (isoelectric point)(pI)

Answer 18

The concentration pH at which the net electric charge is zero

Question 19

Amino acids with an ionizable R group have a titration curve with ______ stages (or flat spots) & have 3 pKa values

Answer 19

3

Question 20

_________ are chains of amino acids

Answer 20

Peptides

Question 21

Two amino acid molecules can be covalently joined through a substituted amide linkage called _________ to make a dipeptide

Answer 21

Peptide bond

Question 22

To form a dipeptide the elements of water is removed from the ________& _________ group

Answer 22

alpha carboxyl group & alpha amino group

Question 23

Peptide bond formation is a ___________

Answer 23

condensation reaction

Question 24

3 amino acids can form a _________< 4 can form a tetrapeptide, 5 can form a pentapeptide, etc

Answer 24

Tripeptide

Question 25

When only a few amino acids are linked together (like 2 or 3) then its called an \_\_\_\_\_\_\_\_\_\_

Answer 25

Oligopeptide

Question 26

When many animo acids are joined (Like 5 or 6) then its called a \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Answer 26

Polypeptide

Question 27

In a peptide, the amino acid residue at the end with a free alpha-amino group is called _____________ residue

Answer 27

Amino-terminal (or N-terminal) residue

Question 28

In a peptide the free carboxyl group is called the _________ residue

Answer 28

Carboxyl terminal (r C-terminal) residue

Question 29

When an amino acids sequence of a peptide, polypeptide or protein is shown the amino-terminal end is placed on the _______ & the carboxyl-terminal end is on the \_\_\_\_\_\_\_

Answer 29

Left, right

Question 30

Peptides are named beginning with the _________ residue

Answer 30

Amino-terminal residue

Question 31

Acid-base behavior of a peptide can be predicted from its free ____________________ & its ionizable R group

Answer 31

alpha amino & alpha carboxy group

Question 32

Multisubunit proteins

Answer 32

Have two or more polypeptide associated noncovalently

Question 33

The individual polypeptide chains in a multisubunit protein may be __________ or \_\_\_\_\_\_\_\_

Answer 33

Identical or different

Question 34

If at least two polypeptides chains in multisubunit proteins are identical then they are called ________ & the different units are called \_\_\_\_\_\_\_\_

Answer 34

Oligomeric, protomers

Question 35

The average molecular weight of the 20 common amino acids is about \_\_\_\_\_

Answer 35

138

Question 36

The average molecular weight if protein amino acid is near \_\_\_\_

Answer 36

128

Question 37

Simple proteins

Answer 37

Contain only amino acids residues & no other chemical constituents

Question 38

Conjugated proteins

Answer 38

Proteins that have permanently associated chemical components & amino acids residues

Question 39

The non-amino acid part of a conjugated protein is usually called its \_\_\_\_\_\_\_

Answer 39

Prosthetic group

Question 40

Conjugated proteins can be classified on the basis of the chemical nature of their \_\_\_\_\_\_\_\_\_\_\_

Answer 40

Prosthetic group (ex. lipoproteins contain lipids)

Question 41

Proteins can be _________ & \_\_\_\_\_\_\_\_\_

Answer 41

Separated & purified

Question 42

The 1st step in an y protein purification procedure is to break open the microbial cells ( the source of a protein) & releasing their proteins into a solution called a \_\_\_\_\_\_\_\_\_\_\_\_\_\_

Answer 42

Crude extract

Question 43

Once the extract preparation is ready then the extract is subjected to \_\_\_\_\_\_\_\_\_\_\_\_\_

Answer 43

Fractionation

Question 44

Fractionation

Answer 44

Separating the proteins into different fractions on a property such as size or charge

Question 45

After a protein is fractionize then the solution or protein is _________ by adding salts to selectively precipitate some proteins (unwanted proteins) (ex. ammonium sulfate is an effective salt to salt out unwanted protons)

Answer 45

“Salt out”

Question 46

After a solution contains only the wanted proteins then its \_\_\_\_\_\_\_\_

Answer 46

Dialysis

Question 47

Dialysis

Answer 47

Procedure that separates proteins from small solutes (keeps large proteins & can get rid of the salt added)

Question 48

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ is a method used for fractionating proteins

Answer 48

Column chromategraphy

Question 49

Column chromatography is a method used for ______________ proteins

Answer 49

Fractioning

Question 50

Ion-exchange chromatography

Answer 50

Exploits difference in the sign & magnitude of the net electric charge of proteins at a given pH