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biochem lec > Amino acids, Peptides & Proteins > Flashcards

Amino acids, Peptides & Proteins Flashcards

1
Q

are biopolymers of varying size that are constructed from a set of 20 α-amino acids

A

Proteins

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2
Q

______ are the chief constituents of skin, bone, hair, and nails.

A

Collagen and keratin

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3
Q

Virtually all reactions in living systems are catalyzed by proteins called _________

A

enzymes

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4
Q

Muscles are made up of proteins called __________

A

myosin and actin

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5
Q

__________ transports oxygen from the lungs to cells, other proteins transport molecules across cell membranes.

A

Hemoglobin

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6
Q

Many hormones are proteins, among them:

A
  • insulin
  • oxytocin
  • human growth hormone.
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7
Q

______ in milk and _______ in eggs store nutrients for newborn infants and birds.

A
  • Casein
  • ovalbumin
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8
Q

Blood clotting involves the protein ________; the body used proteins called antibodies to fight disease.

A

fibrinogen

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9
Q

a protein in the liver, stores iron

A

Ferritin

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10
Q

Certain proteins not only control the ________, but also control when gene expression takes place.

A

expression of genes

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11
Q

Two major types of Proteins

A
  • fibrous proteins
  • globular proteins
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12
Q

insoluble in water and are used mainly for structural purposes

A

fibrous proteins

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13
Q

more soluble in water and are used mainly
for nonstructural purposes.

A

globular proteins

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14
Q

A compound that contains both an amino group and a carboxyl group.

A

Amino acid

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15
Q

they are chains of amino acids

A

proteins

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16
Q

An amino acid in which the amino group is on the carbon adjacent to the carboxyl group.

A

a-Amino acid

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17
Q

Although a-amino acids are commonly written in the un-ionized form, they are more properly written in the ___________ form.

A

zwitterion (internal salt)

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18
Q

With the exception of glycine, all protein-derived amino acids have at least _________ and are chiral.

A

one stereocenter (the a-carbon)

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19
Q

The vast majority of a-amino acids have the _______ at the a-carbon.

A

L-configuration

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20
Q

we can classify amino acids into four groups:

A
  • nonpolar
  • polar neutral
  • acidic
  • basic
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21
Q

non-polar side chains are

A

hydrophobic

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22
Q

polar neutral, acidic, and
basic side chains are ______

A

hydrophilic

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23
Q

Alanine

Shortcut

A

Ala

A

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24
Q

Arginine

Shortcut

A

Arg

R

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25
Q

Asparagine

Shortcut

A

Asn

N

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26
Q

Aspartic acid

Shortcut

A

Asp

D

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27
Q

Cysteine

Shortcut

A

Cys

C

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28
Q

Glutamic acid

Shortcut

A

Glu

E

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29
Q

Glutamine

Shortcut

A

Gln

Q

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30
Q

Glycine

Shortcut

A

Gly

G

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31
Q

Histidine

Shortcut

A

His

H

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32
Q

Isoleucine

Shortcut

A

Ile

I

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33
Q

Leucine

Shortcut

A

Leu

L

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34
Q

Lysine

Shortcut

A

Lys

K

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35
Q

Methionine

Shortcut

A

Met

M

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36
Q

Phenylalanine

Shortcut

A

Phe

F

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37
Q

Proline

Shortcut

A

Pro

P

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38
Q

Serine

Shortcut

A

Ser

S

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39
Q

Threonine

Shortcut

A

Thr

T

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40
Q

Tryptophan

Shortcut

A

Trp

W

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41
Q

Tyrosine

Shortcut

A

Tyr

Y

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42
Q

Valine

Shortcut

A

Val

V

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43
Q

Give all Non-Polar Amino Acids

A
  • Methionine
  • Leucine
  • Tryptophan
  • Proline
  • Phenylalanine
  • Alanine
  • Isoleucine
  • Valine
  • Glycine
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44
Q

Give all Polar Amino Acids

A
  • Threonine
  • Serine
  • Cysteine
  • Asparagine
  • Tyrosine
  • Glutamine
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45
Q

Give all Acidic Amino Acids

A
  • Aspartic acid
  • Glutamic acid
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46
Q

Give all Basic Amino Acids

A
  • Histidine
  • Lysine
  • Arginine
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47
Q

Amino Acids with sulfur

A
  • Cysteine
  • Methionine
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48
Q

Amino Acids with amide

A
  • Asparagine
  • Glutamine
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49
Q

Amino Acids with aromatic rings

A
  • Phenylalanine
  • Tyrosine
  • Histidine
  • Tryptophan
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50
Q

Amino Acid with non-aromatic ring

A

Proline

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51
Q

For 19 of the 20, the a-amino group is primary; for proline, it is ___________.

A

secondary

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52
Q

With the exception of glycine, the a-carbon of each is a _________.

A

stereocenter

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53
Q

Isoleucine and threonine contain a ____________.

A

second stereocenter

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54
Q

The __________ on an amino acid depends on the pH of the solution in which it is dissolved.

A

net charge

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55
Q

If we dissolve an amino acid in water, it is present in the aqueous solution as its ___________

A

zwitterion

56
Q

If we add a strong acid such as HCl to bring the pH of the solution to 0.0, the strong acid donates a proton to the -COO- of the zwitterion turning it into a __________.

A

positive ion

57
Q

If we add a strong base such as NaOH to the solution and bring its pH to 14, a proton is transferred from the NH3+ group to the base turning the zwitterion into a _____________.

A

negative ion

58
Q

The pH at which the majority of molecules of a compound in solution have no net charge.

A

Isoelectric point, pI

59
Q

Phenylalanine and tyrosine are precursors to _____________ and ______________, both of which are stimulatory neurotransmitters.

A
  • norepinephrine
  • epinephrine
60
Q

epinephrine The -SH (sulfhydryl) group of cysteine is easily oxidized to an ___________

A

-S-S- (disulfide).

61
Q

Hydroxylation (oxidation) of Tryptophan

A

5-Hydroxytryptophan

62
Q

Decarboxylation of 5-Hydroxytryptophan

A

Serotonin
(5-Hydroxytryptamine)

63
Q

oxidation of Phenylalanine

A

Tyrosine

64
Q

oxidation of Tyrosine

A

3,4-Dihydroxyphenylalanine
(L-DOP A)

65
Q

decarboxylation of 3,4-Dihydroxyphenylalanine
(L-DOP A)

A

Dopamine

66
Q

oxidation and methylation of dopamine

A

Epinephrine

67
Q

Hydroxylation (oxidation) of proline

A

Hydroxyproline

68
Q

Hydroxylation (oxidation) of Lysine

A

Hydroxylysine

69
Q

iodination of Tyrosine

A

Thyroxine

70
Q

In 1902, Emil Fischer proposed that proteins are long chains of amino acids joined by ___________.

A

amide bonds

70
Q

The special name given to the amide bond between the a-carboxyl group of one amino acid and the a-amino group of another.

A

Peptide bond (peptide linkage)

71
Q

A short polymer of amino acids joined by peptide bonds; they are classified by the number of amino acids in the chain.

A

Peptide

72
Q

A molecule containing two amino acids joined by a peptide bond.

A

Dipeptide

73
Q

A molecule containing three amino acids joined by peptide bonds.

A

Tripeptide

74
Q

A macromolecule containing many amino acids joined by peptide bonds.

A

Polypeptide

75
Q

A biological macromolecule containing at least 30 to 50 amino acids joined by peptide bonds.

A

Protein

75
Q

The individual amino acid units are often referred to as

A

“residues”

76
Q

Linus Pauling, however, discovered that there is about 40% ________ character to the C-N bond and that a peptide bond between two amino acids is ________, which Pauling explained using the concept of resonance.

A
  • double bond
  • planar
77
Q

By convention, peptides are written from the left to right, beginning with the free _____ group and ending with the free _______ group.

A
  • -NH3+
  • -COO-
78
Q

the amino acid at the end of the chain having the free -COO- group.

A

C-terminal amino acid

79
Q

The amino acid at the end of the chain having the free -NH3+ group.

A

N-terminal amino acid

80
Q

Other name for
C-terminal amino acid and N-terminal amino acid

A

C-terminus and the N-terminus

81
Q

At its ________, the protein has no net charge

A

isoelectric point

82
Q

At any pH above (more basic than) its pI, it has a ______

A

net negative charge

83
Q

At any pH below (more acidic than) its pI, it has a _________.

A

net positive charge

84
Q

pl of hemoglobin

A

6.8

85
Q

pl of Serum albumin

A

4.9

86
Q

Proteins are least soluble in water at their _________ and can be ________ from solution when pH = pI

A
  • isoelectric points
  • precipitated
87
Q

The sequence of amino acids in a polypeptide chain. Read from the N-terminal amino acid to the C-terminal amino acid.

A

Primary structure

88
Q

Conformations of amino acids in localized regions of a polypeptide chain. Examples are a-helix, b-pleated sheet, and random coil.

A

Secondary structure

89
Q

The complete three-dimensional arrangement of atoms of a polypeptide chain.

A

Tertiary structure

90
Q

The spatial relationship and interactions between subunits in a protein that has more than one polypeptide chain.

A

Quaternary structure

91
Q

The sequence of amino acids in a polypeptide chain.

A

Primary structure

92
Q

The number dipeptides possible from the 20 protein-derived amino acids

A

400

93
Q

The number tripeptides possible from the 20 protein-derived amino acids

A

8000

94
Q

The number of peptides possible for a chain of n amino acids is ___

A

20n

95
Q

For a small protein of 60 amino acids, the number of proteins possible is 20^60 =

A

10^78

96
Q

The hormone insulin consists of two polypeptide chains, A and B, held together by two ____________.

A

disulfide bonds

97
Q

Human insulin consists of two polypeptide chains having a total of ____ amino acids; the two chains are connected by two interchain disulfide bonds.

A

51

98
Q

Vasopressin and oxytocin are both __________ but have quite different biological functions.

A

nonapeptides

99
Q

Vasopressin is an __________ hormone.

A

antidiuretic

99
Q

affects contractions of the uterus in childbirth and the muscles of the breast that aid in the secretion of milk.

A

Oxytocin

100
Q

A type of secondary structure in which a section of polypeptide chain coils into a spiral, most commonly a right-handed spiral.

A

a-Helix

101
Q

A type of secondary structure in which two polypeptide chains or sections of the same polypeptide chain align parallel to each other; the chains may be parallel or antiparallel.

A

b-Pleated sheet

102
Q

In a section of a-helix
there are __ amino acids per turn of the helix.

A

3.6

103
Q

In a section of a-helix, The ________ of each peptide bond lie in the same plane.

A

six atoms

104
Q

In a section of a-helix, the _________ of peptide bonds point in the same direction, roughly parallel to the axis of the helix.

A

N-H groups

105
Q

In a section of a-helix, the ________ of peptide bonds point in the opposite direction, also roughly parallel to the axis of the helix.

A

C=O groups

106
Q

In a section of a-helix, the C=O group of each peptide bond is _________ to the N-H group of the peptide bond four amino acid units away from it.

A

hydrogen bonded

107
Q

In a section of a-helix, all ________ point outward from the helix.

A

R- groups

107
Q

a polypeptide derived entirely from alanine

A

polyalanine

108
Q

In a section of b-pleated sheet; The six atoms of each peptide bond of a b-pleated sheet lie in the _________.

A

same plane

109
Q

In a section of b-pleated sheet;
The C=O and N-H groups of the peptide bonds from adjacent chains point toward ________ and are in the same plane so that hydrogen bonding is possible between them.

A

each other

110
Q

All R- groups on any one chain ___________, first above, then below the plane of the sheet, etc.

A

alternate

111
Q

Many globular proteins contain all three kinds of secondary structure in different parts of their molecules:

A
  • a-helix
  • b-pleated sheet
  • random coil
112
Q

the overall conformation of an entire polypeptide chain.

A

Tertiary structure

113
Q

Tertiary structure is stabilized in four ways:

A
  • Covalent bonds
  • Hydrogen bonding
  • Salt bridges
  • Hydrophobic interactions
113
Q

for example, the formation of disulfide bonds between cysteine side chains.

Tertiary structure stabilization

A

Covalent bonds

114
Q

between polar groups of side chains, as for example between the -OH groups of serine and threonine.

Tertiary structure stabilization

A

Hydrogen bonding

114
Q

as for example, the attraction of the -NH3+ group of lysine and the -COO- group of aspartic acid.

Tertiary structure stabilization

A

Salt bridges

115
Q

as for example, between the nonpolar side chains of phenylalanine and isoleucine.

Tertiary structure stabilization

A

Hydrophobic interactions

115
Q

The arrangement of polypeptide chains into a noncovalently bonded aggregation.

A

Quaternary structure

116
Q

Two side chains with the same charge would normally repel each other, but they can also be linked via a metal ion.

Tertiary structure stabilization

A

Metal Ion Coordination

117
Q

Two alpha chains of 141 amino acids each, and two beta chains of 146 amino acids each.

A

Adult hemoglobin

118
Q

Two alpha chains and two gamma chains. Has a greater affinity for oxygen than does adult hemoglobin. Each chain surrounds an iron-containing heme unit.

A

Fetal hemoglobin

119
Q

______________ proteins form quaternary structures in which the outer surface is largely nonpolar (hydrophobic) and interacts with the lipid bilayer.

A

Integral membrane

120
Q

The process of destroying the native conformation of a protein by chemical or physical means.

A

Denaturation

121
Q

Denaturing agents include:

A
  • Heat
  • 6 M aqueous urea
  • Surface-active agents
  • Reducing agents
  • Heavy metal ions
  • Alcohols
122
Q

Heat can disrupt ___________

Denaturing agents

A

hydrogen bonding

123
Q

in globular proteins, it can cause unfolding of polypeptide chains with the result that coagulation and precipitation may take place.

A

Heat

123
Q
A
124
Q

6 M aqueous urea: Disrupts _________

A

hydrogen bonding

125
Q

Surface-active agents: Detergents such as _________________ disrupt hydrogen bonding.

A

sodium dodecylbenzenesulfate (SDS)

125
Q

Reducing agents: _______________ cleaves disulfide bonds by reducing -S-S- groups to-SH groups.

A

2-Mercaptoethanol (HOCH2CH2SH)

126
Q

Heavy metal ions: Transition metal ions such as Pb2+, Hg2+, and Cd2+ form ___________ with -SH groups; Hg2+ for example forms -S-Hg-S-.

A

water-insoluble salts

127
Q

Alcohols: 70% ethanol penetrates bacteria and kills them by _________ their proteins. It is used to sterilize skin before injections.

A

coagulating

biochem lec (10 decks)

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