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Biochemistry > Amino Acids > Flashcards

Amino Acids Flashcards

1
Q

Important biological functions of protein

A
  1. Enzymes, the biochemical catalysts
  2. Storage and transport of biochemical molecules
  3. Physical cell support and shape (tubulin, actin, collagen)
  4. Mechanical movement (flagella, mitosis, muscles)
  5. Decoding cell information (translation, regulation of gene expression)
  6. Hormones or hormone receptors (regulation of cellular processes)
  7. Other specialized functions (antibodies, toxins etc)
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2
Q

Under normal cellular conditions amino acids are dissociated ——-

A

zwitterions

Amino group = NH3+
Carboxyl group = COO-

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3
Q

Fischer projections

A

horizontal bonds from a chiral center extend toward the viewer, vertical bonds extend away from the viewer

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4
Q

Non-Polar Amino Acids

A

Ala-Gly-Val-Phe-Trp-Pro-Leu-Ileu-Met

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5
Q

Polar Charged Amino Acids

A

Basic (His-Arg-Lys)
Acidic (Asp-Glu)

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6
Q

Polar Un-charged Amino Acids

A

Ser-Cys-Tyr-Thr-Asn-Gln

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7
Q

Amino acids exhibit ————— (mirror image)

A

Stereoisomers

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8
Q

———– compounds that have the same molecular formula but differ in the arrangement of atoms in space

A

Stereoisomers

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9
Q

———— non-superimposable mirror images

A

Enantiomers

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10
Q

——— have four different groups attached

A

Chiral carbons

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11
Q

Clockwise path: absolute configuration —-

A

R

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12
Q

Counterclockwise path: absolute configuration

A

S

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13
Q

chemical synthesis of chiral molecules leads to a ———

A

racemic mixture (equal amount of L and D isomers)

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14
Q

All amino acids present in proteins are of —configuration

A

L-configuration

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15
Q

The (?) enantiomer is effective against morning sickness but the (?) is teratogenic and causes birth defects.

A

R
S

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16
Q

Importance of Cystine in proteins

A

Particularly important in protein folding and structural stability.

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17
Q

Over —- different amino acids are found in nature

A

200

Most are precursors to common amino acids or chemically modified derivatives

Some amino acids are chemically modified after incorporation into a polypeptide

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18
Q

Free standard amino acids undergo a number of reactions leading to modified free amino acids designated as ——————————————–

A

biologically active free non standard amino acids

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19
Q

The 21st amino acid ———————- is incorporated into a few proteins

A

Selenocysteine

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20
Q

Ionizable groups in amino acids:

A

(1) a-carboxyl
(2) a-amino
(3) some side chains

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21
Q

Each ionizable group has a specific pKa

AH <—-> B + H+

For a solution pH below the pKa, the ———- form predominates (AH)
For a solution pH above the pKa, the ———– form predominates (B)

A

protonated
un-protonated

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22
Q

Hydropathy

A

the relative hydrophobicity of each amino acid

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23
Q

The larger the hydropathy, the ——– the tendency of an amino acid to prefer a hydrophobic environment

A

greater

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24
Q

Hydropathy affects protein folding:

A

hydrophobic side chains tend to be in the interiorhydrophilic residues tend to be on the surface

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25
Q

——— linkage between amino acids is a secondary amide bond

A

Peptide bond

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26
Q

Peptide bond are formed by ————- of the a-carboxyl of one amino acid with the a-amino of another amino acid

A

condensation

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27
Q

Aspartame

A
  • is a dipeptide methyl ester (aspartylphenylalanine methyl ester)
  • About 200 times sweeter than table sugar
  • Used in diet drinks
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28
Q

Amino acids are named that way because each one _____________.
a. Is a unique carboxylic acid.
b. Has a standard configuration.
c. Is a carboxyl derivative of an amide acid.
d. Is an amino derivative of a carboxylic acid.

A

d. Is an amino derivative of a carboxylic acid.

29
Q

If the R group of an amino acid is –CH3, then the name of this compound is _______.

a.	Methyl amino acid
b.	2-aminopropanoic acid
c.	Alanine
d.	All of the above
e.	b and c
A

e. b and c

30
Q

Amino acids are zwitterions ions in general when they are ____________.
a. In any solution
b. At physiological pH, pH = 7.4
c. In acidic solutions only
d. In alkaline solutions only
e. All of the above

A

At physiological pH, pH = 7.4

31
Q

Glycine is not a stereoisomer because ________.
a. It has no chiral carbon
b. It does not form enantiomers
c. It does not exist in two superimposable forms
d. All of the above
e. a and b only

A

d. All of the above

32
Q

An amino acid with two chiral carbon atoms _______.
a. Is unstable
b. Can exist in 4 forms all of which are superimposable
c. Can form three possible stereoisomers
d. Can form four possible stereoisomers
e. Can form five possible stereoisomers

A

d. Can form four possible stereoisomers

33
Q

The RS system of nomenclature describes _____.
a. Amino acids not easily described by the DL system
b. The way the R groups are arranged
c. The chiral carbon centers of amino acids
d. The strength of the chemical groups in amino acids

A

c. The chiral carbon centers of amino acids

34
Q

The R group of an amino acid determines if it is _______.
a. Hyrophilic or hydrophobic
b. Polar or nonpolar
c. Charged or uncharged
d. An acid or a base
e. All of the above

A

e. All of the above

35
Q

Proline is distinct among the 20 commonly found amino acids because ____________.
a. It is a cyclic compound
b. It is hydrophilic and ionic
c. The alpha-nitrogen of the amino group is in a ring
d. The carbon of the carboxyl group is in a ring
e. It has little effect on protein structure

A

c. The alpha-nitrogen of the amino group is in a ring

36
Q

Tyrosine and tryptophan are less hydrophobic than phenylalanine because ______________.
a. Phenylalanine has an indole group
b. Phenylalanine has no polar group in the side chain
c. Phenylalanine is a phenol
d. Tyrosine and tryptophan have smaller R groups
e. All of the above

A

b. Phenylalanine has no polar group in the side chain

37
Q

Ultraviolet (UV) light can be used to estimate protein solution concentrations because ___________.
a. Phenylalanine absorbs at 260 nm
b. All the amino acids absorb UV light
c. Aromatic amino acids absorb at 280 nm
d. Tryptophan and tyrosine absorb at 280 nm
e. All of the above

A

d. Tryptophan and tyrosine absorb at 280 nm

38
Q

The amino acids in polypeptide chains which contain sulfur (S) are ______________.
a. Cysteine, cystine, and methionine
b. Cystine
c. Methionine only
d. Cysteine only
e. Cysteine and methionine

A

e. Cysteine and methionine

39
Q

Disulfide bridges can form in proteins ___________.
a. Between cysteine residues always close together
b. Between cysteine residues not necessarily close together
c. Between cystine residues in proteins
d. Between any S containing amino acids

A

b. Between cysteine residues not necessarily close together

40
Q

Although the hydroxyl groups in serine and threonine are uncharged, they can react within active sites of some enzymes because ________.
a. The hydroxyl group is uncharged
b. The hydroxyl group can be polar
c. The hydroxyl group can fit into the site
d. All of the above

A

b. The hydroxyl group can be polar

41
Q

Basic amino acids are ______ (positive, negative) at pH 7 and acidic R group amino acids are ______ (positive, negative) at pH 7.
a. Negative; positive
b. Negative; negative
c. Positive; negative
d. Positive; positive

A

c. Positive; negative

42
Q

Arginine is the most basic of the 20 amino acids because its side chain is _________ under most cell conditions.
a. highly charged
b. Hydrophobic
c. Titrated
d. Protonated
e. Negatively charged

A

d. Protonated

43
Q

A sequence of amino acids with a relatively high hydropathy are very likely to function by _____.
a. Being at the active site of an enzyme
b. Being embedded in a cell membrane
c. Making a protein soluble
d. Being on the protein surface

A

b. Being embedded in a cell membrane

44
Q

Amino acids which are not incorporated into polypeptides are converted into ________.
a. Neurotransmitters
b. Methyl donors
c. Antibiotics
d. Blood flow controllers
e. All of the above

A

e. All of the above

45
Q

Proteins can be modified by adding _________ to protein residues.
a. Sugars and phosphate groups
b. Hydroxyl and formyl groups
c. Cystine
d. a and b
e. All of the above

A

e. All of the above

46
Q

At the isoelectric pH of an amino acid which has two pKa values the net charge is ___________.
a. 0.5
b. 1
c. 0
d. -1

A

c. 0

47
Q

Histidine has pKa values of 6.0, 9.3 and 7.65. At pH 7.0, the net charge on histidine is ___________.
a. Positive
b. Negative
c. Neutral (uncharged)
d. Insufficient information to tell

A

c. Neutral (uncharged)

48
Q

All 20 common amino acids have an amino group and a carboxyl group bonded to the same carbon atom.
a. True
b. False

A

a. True

49
Q

All amino acids have two mirror-image pairs designated D and L.
a. True
b. False

A

b. False

50
Q

Uncharged R groups of amino acids are not polar.
a. True
b. False

A

b. False

51
Q

Ultraviolet (UV) light can be used to estimate concentrations of proteins in solutions because tryptophan and tyrosine absorb light at a wavelength of 280 nm.
a. True
b. False

A

a. True

52
Q

Asparagine and glutamine are amides of aspartic acid with uncharged side chains. Therefore these amino acids are nonpolar and often found on the interior of proteins.
a. True
b. False

A

b. False

53
Q

The hydropathy of amino acids can help determine the folding of protein chains.
a. True
b. False

A

a. True

54
Q

Amino acids and amino acid derivatives can be used to modify proteins.
a. True
b. False

A

b. False

55
Q

The isoelectric point of amino acids is the average of the values pKa1 + pKa2.
a. True
b. False

A

b. False

56
Q

Amino acids are neutral at the isoelectric pH.
a. True
b. False

A

a. True

57
Q

The twenty standard amino acids are the only amino acids found in living organisms.
a. True
b. False

A

b. False

58
Q

Most proteins contain an approximately equal amount of each of the standard amino acids.
a. True
b. False

A

b. False

59
Q

The pKa’s of arginine’s Alpha-Carboxyl group, Alpha-Amino group and side chain are 1.8, 9.0 and 12.5, respectively. Calculate the isoelectric point.
a. 7.8
b. 7.2
c. 10.8
d. 5.4

A

c. 10.8

60
Q

The pKa’s of isoleucine’s alpha-Carboxyl group and alpha-Amino group are 2.3 and 9.8, respectively. Calculate the isoelectric point.
a. 2.3
b. 6.0
c. 9.8
d. The isoelectric point cannot be calculated without the pKa value for the side chain.

A

b. 6.0

61
Q

The pH inside cells is normally near pH 7. At pH 7 which statement is true about the charges (ionization state) of the alpha-Carboxyl and alpha-Amino groups of an amino acid?
a. The alpha -Carboxyl group is 1- and the alpha -Amino group is 1+.
b. The alpha -Carboxyl group is 1+ and the alpha -Amino group is 1-.
c. The alpha -Carboxyl group is 1- and the alpha -Amino group is uncharged.
d. Both groups are uncharged (not ionized) at pH 7.

A

a. The alpha -Carboxyl group is 1- and the alpha -Amino group is 1+.

62
Q

Which structure below is appropriate for glycine at neutral pH?
a. H2NCH2COOH
b. H2NCH2COO-
c. H3+NCH2COO-
d. H3+NCH2COOH

A

c. H3+NCH2COO-

63
Q

The pKa of a certain weak acid is 4.0. Calculate the ratio of proton acceptor to proton donor at pH 7.0.
a. 1000:1
b. 20:1
c. 3:1
d. 1:1
e. The ratio cannot be calculated without knowing the structure of the weak acid.

A

a. 1000:1

64
Q

The pKa’s of the side chain group and the alpha-carboxyl group of glutamate are 4.1 and 2.1, respectively. Which statement accounts for this difference?
a. The side chain has more possible resonance structures.
b. The alpha-carboxyl group has less steric hindrance and is therefore ionized more easily.
c. The side chain is a different functional group than the alpha-carboxyl group.
d. The alpha-carboxyl group is closer to the alpha-amino group than the side chain is.

A

d. The alpha-carboxyl group is closer to the alpha-amino group than the side chain is.

65
Q

How do the pKa values of an ionizable side chain compare when the amino acid is free versus when it is in a polypeptide chain?
a. The pKa of the side chain is independent of whether the amino acid is in a polypeptide chain or is free.
b. The pKa of the side chain is always lower for the free amino acid.
c. The pKa of the side chain may be lower or higher in a polypeptide chain due to weaker inductive effects and differences in their microenvironments.
d. The pKa of the side chain is usually higher in a polypeptide chain due to stabilization from nearby residues in the three-dimensional structure.

A

c. The pKa of the side chain may be lower or higher in a polypeptide chain due to weaker inductive effects and differences in their microenvironments.

66
Q

The primary structure of a protein describes the _____________________.
a. number of each type of amino acid (percent composition)
b. linear sequence of amino acids
c. overall three-dimensional shape
d. Phi and Psi angles for each amino acid

A

b. linear sequence of amino acids

67
Q

The peptide bond is which of the following?
a. an amide bond
b. an ester bond
c. an ether bond
d. an amine bond

A

a. an amide bond

68
Q

Which amino acids are linked in phenylalanylglycine?
a. phenyline, alanine and glycine
b. phenol, alanine and glycine
c. phenylalanine and glycine
d. phenol, adenine and glycine

A

c. phenylalanine and glycine

69
Q

What is the N-terminal for the pentapeptide
Val-Ile-Glu-Arg-Tyr?
a. the NH3+ group on the side chain of Arg
b. Valine
c. Tyrosine
d. Tryptophan

A

b. Valine

Biochemistry (10 decks)

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