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BIOCHEM (LEC) > PROTEINS > Flashcards

PROTEINS Flashcards

1
Q

A typical human cell contains about ___ different kinds of proteins, and the human body contains about ___ different proteins.

A

9000, 100,000

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2
Q

are needed for the:

  • Synthesis of enzymes, certain hormones, and some blood components
  • Maintenance and repair of existing tissues
  • Synthesis of new tissue; and sometimes for energy
A

Proteins

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3
Q

Next to water, proteins are the most abundant substances in nearly all cells— they account for about __% of a cell’s overall mass and for almost half of a cell’s dry mass.

A

15

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4
Q

All proteins contain the elements __, __, __, and __; most also contain sulfur

A

Carbon
Hydrogen
Oxygen
Nitrogen

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5
Q

The presence of ___ in proteins sets them apart from carbohydrates and lipids, which most often do not contain it

A

NITROGEN

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6
Q

The average nitrogen content of proteins is ___% by mass.

A

15.4

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7
Q

Other elements, such as ____, are essential constituents of certain specialized proteins

A

phosphorus and iron

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8
Q

___, the main protein of milk, contains phosphorus, an element very important in the diet of infants and children.

A

Casein

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9
Q

___, the oxygen-transporting protein of blood, contains iron

A

Hemoglobin

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10
Q

A protein is a naturally occurring, unbranched polymer in which the monomer units are

A

amino acids

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11
Q

An amino acid is an ___ (organic/inorganic) compound

A

Organic

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12
Q

Amino acids contains both an ___ (-NH2) group and a ___ (-COOH) group.

A

amino, carboxyl

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13
Q

The amino acids found in proteins are always ___

A

a-amino acids

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14
Q

An ___ is an amino acid in which the amino group and the carboxyl group are attached to it

A

α-amino acid

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15
Q

A standard amino acid is one of the __ a-amino acids normally found in proteins

A

20

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16
Q

What are the 4 categories of amino acids

A

▪ (1) nonpolar amino acids,
▪ (2) polar neutral amino acids,
▪ (3) polar acidic amino acids,
▪ (4) polar basic amino acids

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17
Q

A ___ amino acid is an amino acid that contains one amino group, one carboxyl group, and a nonpolar side chain

A

nonpolar

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18
Q

When incorporated into a protein, such amino acids
are hydrophobic

They are generally found in the interior of proteins, where there is limited contact with water.

A

Nonpolar amino acid

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19
Q

How many amino acids are in the nonpolar amino acid?

A

9

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20
Q

Nonpolar amino acid

___ is a borderline member of this group because water can weakly interact through hydrogen bonding with the NH ring location on tryptophan’s side-chain ring structure.

A

Tryptophan

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21
Q

A ___ is an amino acid that contains one amino group, one carboxyl group, and a side chain that is polar but neutral.

A

polar neutral amino acid

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22
Q

In solution at physiological pH, the side chain of a polar neutral amino acid is neither ____.

A

acidic nor basic

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23
Q

How many polar neural amino acids are there?

A

6

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24
Q

These amino acids are more soluble in water than the nonpolar amino acids as, in each case, the R group present can hydrogen bond to water

A

Polar neutral amino acids

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25
Q

A _____ is an amino acid that contains one amino group and two carboxyl groups, the second carboxyl group being part of the side chain

A

polar acidic amino acids

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26
Q

In solution at physiological pH, the side chain of a polar acidic amino acid bears a __ charge;

A

negative

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27
Q

POLAR ACIDIC AMINO ACID

the side-chain carboxyl group has lost its acidic __ atom.

A

hydrogen

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28
Q

How many polar acidic amino acids are there?

A

2

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29
Q

A ___ is an amino acid that contains two amino groups and one carboxyl group, the second amino group being part of the side chain.

A

polar basic amino acid

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30
Q

In solution at physiological pH, the side chain of a polar basic amino acid bears a __ charge

A

positive

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31
Q

POLAR BASIC AMINO ACID

the nitrogen atom of the amino group has __ a proton

A

accepted

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32
Q

How many polar basic amino acids are there?

A

3

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33
Q

What are the 9 nonpolar amino acids

A

Glycine
Alanine
Valine
Leucine
Isoleucine
Proline
Phenylalanine
Methionine
Tryptophan

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34
Q

What are the polar neutral amino acids?

A

Serine
Cysteine
Threonine
Asparagine
Glutamine
Tyrosine

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35
Q

What are the Polar acidic amino acids?

A

Aspartic acid
Glutamic acid

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36
Q

What are the Polar Basic Amino Acids?

A

Histidine
Lysine
Arginine

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37
Q

Four different groups are attached to the a-carbon atom in all the standard amino acids except __, where the R group is a hydrogen atom.

A

glycine

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38
Q

In pure form, amino acids are __ crystalline solids with relatively high decomposition points. (Most amino acids decompose before
they melt.)

A

white

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39
Q

Most amino acids are not very soluble in water
because of strong __ forces within their crystal structures.

A

intermolecular

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40
Q

Such properties are those often exhibited by compounds in which charged species are present.

Studies of amino acids confirm that they are charged species both in the solid state and in solution

Why so?

A

Both an acidic group (—COOH) and a basic group (—NH2) are present on the same carbon in an a-amino acid

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41
Q

In neutral solution, carboxyl groups have a tendency to lose protons (H+), producing a ___ charged species

A

Negatively

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42
Q

In neutral solution, amino groups have a tendency to accept protons (H+), producing a ___ charged species

A

Positively

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43
Q

In the neutral solution, the —COOH group of an amino acid donates a proton to the —NH2 of the same amino acid. We can characterize this behavior as an ___ reaction

A

Internal acid-base

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44
Q

From the German term meaning “double ion”

A

Zwitterion

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45
Q

A ___ is a molecule that has a positive charge on one atom and a negative charge on another atom, but which has no net charge.

A

zwitterion

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46
Q

Note that the net charge on a zwitterion is __ even though parts of the molecule carry charges. In solution and also in the solid state, α-amino acids exist as zwitterion

A

zero

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47
Q

is the only standard amino acid that has a side chain that contains a sulfhydryl group. The presence of this sulfhydryl group imparts to __ a chemical property that is unique among the
standard amino acids.

A

Cysteine

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48
Q

Cysteine, in the presence of mild oxidizing agents, readily dimerizes, that is, reacts with another cysteine molecule to form a cystine molecule. In cystine, the two cysteine residues are linked via a covalent ___ bond

A

disulfide

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49
Q

A _ is a molecule that is made up of two like subunits

A

dimer

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50
Q

The covalent disulfide bond of cystine is readily broken, using __ agents, to regenerate two cysteine molecules.

A

reducing

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51
Q

A ___ is an unbranched chain of amino acids, each joined to the next by a peptide bond.

A

peptide

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52
Q

Peptides are further Classified by the ___ of amino acids present in the chain.

A

number

53
Q

A compound containing two amino acids is specifically called a ___; three amino acids
joined together in a chain constitute a ___; and so on.

A

dipeptide, tripeptide

54
Q

The name ___ is loosely used to refer to peptides with 10 to 20 amino acid residues,

A

oligopeptide

55
Q

The name __ is used to refer to longer peptides.

A

polypeptide

56
Q

The bonds that link amino acids together in a peptide chain are called ___.

A

peptide bonds

57
Q

There are __ peptide bonds present in a
pentapeptide

A

four

58
Q

A carboxylic acid and an amine can react to produce an

A

amide

59
Q

The products are a molecule of water and a molecule containing the two amino acids linked by an ___

A

Amide bond

60
Q

A peptide bond is a __ bond between the carboxyl group of one amino acid and the amino group of another amino acid.

A

covalent

61
Q

An ____ is the portion of an amino acid structure that remains, after the release of H2O, when an amino acid participates in peptide bond formation as it becomes part of a peptide chain

A

amino acid residue

62
Q

What are the terminal end in amino acid?

A

N-terminal, C-terminal

63
Q

The repeating sequence of peptide bonds and a-carbon —CH groups in a peptide is referred to as the ___ of the peptide

A

The backbone

64
Q

Peptides that contain the same amino acids but in
different order are different molecules (constitutional isomers) with different properties

A

Isomeric peptides

65
Q

True or False

The number of isomeric peptides possible increases
rapidly as the length of the peptide chain decreases

A

False

The number of isomeric peptides possible increases
rapidly as the length of the peptide chain INCREASES

Let us consider the tripeptide Ala–Ser–Cys as another example. In addition to this sequence, five other arrangements of these three components are possible, each representing another isomeric tripeptide: Ala–Cys–Ser, Ser–Ala–Cys, Ser–
Cys–Ala, Cys–Ala–Ser, and Cys–Ser–Ala. For a pentapeptide containing 5 different amino acids, 120 isomers are possible

66
Q

SMALL PEPTIDE HORMONES

The two best-known peptide hormones, both produced by the pituitary gland, are

A

Oxytocin & vasopressin

67
Q

Oxytocin and vasopressin

Each hormone is a nonapeptide (nine amino acid
residues) with six of the residues held in the form of a loop by a disulfide bond formed from the interaction of two __ residues.

Structurally, these nonapeptides differ in the amino acid present in positions __ and __ of the
peptide chain.

In both structures an amide group replaces the C terminal single-bonded oxygen atom

A

Cysteine

3 and 8

68
Q

It regulates uterine contractions and lactation

A

Oxytocin

69
Q

It regulates the excretion of water by the kidneys; it also affects blood pressure

A

Vasopressin

70
Q

are pentapeptide neurotransmitters produced by the brain itself that bind at receptor sites in the brain to reduce pain.

A

Enkephalins

71
Q

The two best-known enkephalins are ___ and ___,

A

Metenkephalin, Leu-enkephalin

72
Q

Structure of Metenkephalin

A

Tyr-Gly-Gly-Phe-Met

73
Q

Structure of Leu-enkephalin

A

Tyr-Gly-Gly-Phe-Leu

74
Q

The pain-reducing effects of ____ action play a role in the “high” reported by long-distance runners, in the competitive athlete’s managing to finish the game
despite being injured, and in the pain-relieving effects of acupuncture.

A

enkephalin

75
Q

The action of the prescription painkillers ____ is based on their binding at the same receptor sites in the brain as the naturally occurring enkephalins

A

morphine and codeine

76
Q

The tripeptide ___ is present in significant
concentrations in most cells and is of considerable physiological importance as a regulator of oxidation–reduction reactions.

A

glutathione (Glu–Cys–Gly)

77
Q

Glutathione functions as an ___, protecting cellular contents from oxidizing agents such as peroxides and superoxides (highly reactive forms of
oxygen often generated within the cell in response to bacterial invasion)

A

antioxidant

78
Q

A ___ is a peptide in which at least 40 amino acid residues are present.

A

protein

79
Q

The defining line governing the use of the term protein — 40 amino acid residues — is an ___ line.

The terms polypeptide and protein are often
used interchangeably; a protein is a relatively long polypeptide

A

arbitrary

80
Q

A ___ protein is a protein in which only one peptide chain is present. Large proteins, those with many amino acid residues, usually are multimeric.

A

monomeric

81
Q

A ____ protein is a protein in which more than one peptide chain is present.

A

multimeric

82
Q

The peptide chains present in multimeric proteins are called ____.

A

protein subunits

83
Q

True or False

The protein subunits within a multimeric protein MAY all be identical to each other OR different kinds of subunits may be present.

A

True

84
Q

Proteins with up to ___ subunits are known.

A

12

85
Q

The small protein ___, which functions as a hormone in the human body, is a multimeric protein with two protein subunits; one subunit contains 21 amino acid residues and the other 30 amino acid residues

A

insulin

86
Q

A ___ is a protein in which only amino acid residues are present.

A

simple protein

87
Q

More than one protein subunit may be present in a simple protein, but all subunits contain only __

A

amino acids

88
Q

A ___ is a protein that has one or more nonamino acid entities present in its structure in addition to
one or more peptide chains.

These non-amino acid components, which may be organic or inorganic, are called

A

conjugated protein

prosthetic groups

89
Q

A ___ is a non-amino acid group present in a conjugated protein

A

prosthetic group

90
Q

is the order in which amino acids are linked together in a protein.

A

Primary protein structure

91
Q

Primary protein structure always involves more than just the numbers and kinds of amino acids
present; it also involves the ____ of the amino acids to each other through peptide bonds.

A

order of attachment

92
Q

___, the hormone that regulates blood-glucose levels, was the first protein for which primary structure was determined; the “sequencing” of its 51 amino acids was completed in 1953, after 8 years of work by the British biochemist ___

A

Insulin

Frederick Sanger

93
Q

is the arrangement in space adopted by the backbone portion of a protein.

A

Secondary protein structure

94
Q

The two most common types of secondary structure are the

A

alpha helix (α helix) and the beta pleated sheet (β pleated sheet

95
Q

An ___ structure is a protein secondary structure in which a single protein chain adopts a shape that resembles a coiled spring (helix), with the coil configuration maintained by hydrogen bonds.

A

alpha helix

96
Q

True or False

Proteins have varying amounts of a-helical secondary structure, ranging from a few percent to nearly 100%. In a helix, all of the amino acid side chains (R groups) lie inside the helix; there is not enough room for them in the interior

A

Proteins have varying amounts of a-helical secondary structure, ranging from a few percent to nearly 100%. In a helix, all of the amino acid side chains (R groups) lie OUTSIDE the helix; there is not enough room for them in the interior

97
Q

A ___ structure is a protein secondary structure in which two fully extended protein chain segments in the same or different molecules are held together by hydrogen bonds.

A

beta pleated sheet

98
Q

Hydrogen bonds form between oxygen and hydrogen peptide linkage atoms that are either in different parts of a single chain that folds back on itself ( ___ bonds) or between atoms in different peptide chains in those proteins that contain more than one chain (____bonds).

A

intrachain, interchain

99
Q

is the overall three-dimensional shape of a protein that results from the interactions between amino acid side chains (R groups) that are widely separated from each other within a peptide chain.

A

Tertiary protein structure

100
Q

The three-dimensional shape of a protein consisting of two or more independent peptide chains,
Which results from non covalent interactions between R groups

Electrostatic interactions
Hydrogen bond
Hydrophobic interactiond

A

Quaternary structure

101
Q

A ____ is a protein whose molecules have an elongated shape with one dimension much longer than the others.

A

fibrous protein

102
Q

tend to have simple, regular, linear structures. There is a tendency for such proteins to aggregate together to form macromolecular structures.

A

Fibrous proteins

103
Q

A ___ is a protein whose molecules have peptide chains that are folded into spherical or globular shapes.

A

globular protein

104
Q

The folding in such proteins is such that most of the amino acids with ___ side chains (nonpolar R groups) are in the interior of the molecule and most of the___ side chains (polar R groups) are on the outside of the molecule.

Generally, globular proteins are water-soluble substances

A

hydrophobic, hydrophilic

105
Q

A ____ is a protein that is found associated with a membrane system of a cell. ___ structure is somewhat opposite that of globular proteins, with most of the hydrophobic amino acid side chains oriented outward

A

membrane protein

106
Q

The functional versatility of proteins stems from

A

(1) their ability to bind small molecules specifically and strongly to themselves

(2) their ability to bind other proteins, often other like proteins, to form fiber-like structures

(3) their ability to bind to, and often
become integrated into, cell membranes

107
Q

Proteins are probably best known for
their role as catalysts.

A

Catalytic proteins.

108
Q

Proteins with the role of biochemical catalyst are called __.

A

enzymes

109
Q

___ participate in almost all of the metabolic reactions that occur in cells. The chemistry of human genetics.

A

Enzymes

110
Q

These proteins, also called immunoglobulins are central to the functioning of the body’s immune system.

A

Defense proteins.

111
Q

They bind to foreign substances, such as bacteria and viruses, to help combat invasion of
the body by foreign particles

A

Defense proteins

112
Q

These proteins bind to particular small biomolecules and transport them to other locations in the body and then release the small molecules as needed at the destination location.

A

Transport proteins.

113
Q

The most well-known example of a transport protein is ___, which carries oxygen from the lungs to other organs and tissues.

A

hemoglobin

114
Q

Another transport protein is ___, which carries iron from the liver to the bone marrow.

A

transferrin

115
Q

High- and low-density ____ are carriers of cholesterol in the bloodstream

A

lipoproteins

116
Q

These proteins transmit signals to coordinate biochemical processes between different cells, tissues, and organs

A

Messenger proteins.

117
Q

A number of hormones that regulate body processes are ___, including insulin and glucagon. Human growth hormone is another example of it

A

messenger proteins

118
Q

These proteins are necessary for all forms of movement.

A

Contractile proteins.

119
Q

are composed of filament-like contractile proteins that, in response to nerve stimuli, undergo conformation changes that involve contraction and
extension

Actin and myosin are examples of such proteins.

Human reproduction depends on the movement of sperm. Sperm can “swim” because of long flagella
made up of contractile proteins

A

Muscles

120
Q

These proteins confer stiffness and rigidity to otherwise fluid like biochemical systems. Collagen is
a component of cartilage and a keratin gives mechanical strength as well as protective
covering to hair, fingernails, feathers, hooves, and some animal shells

A

Structural proteins.

121
Q

These proteins, which span a cell membrane help control the movement of small molecules
and ions through the cell membrane.

Many such proteins have channels through which molecules can enter and exit a cell. Such protein channels are very selective, often allowing passage to just one type of molecule or ion

A

Transmembrane proteins.

122
Q

These proteins bind (and store) small molecules for future use.

During degradation of hemoglobin the iron atoms present are released and become part of
ferritin, an iron-storage protein, which saves the iron for use in the biosynthesis of new hemoglobin
molecules.

A

Storage proteins.

123
Q

is an oxygen-storage protein present in muscle; the
oxygen so stored is a reserve oxygen source for working muscle

A

Myoglobin

124
Q

These proteins are often found “embedded” in the exterior surface of cell membranes. They act as sites at which messenger molecules, including messenger proteins such as insulin, can bind and thereby initiate the effect that the messenger “carries.”

A

Regulatory proteins.

125
Q

are often the molecules that bind to enzymes (catalytic proteins), thereby turning them
“on” and “off,” and thus controlling enzymatic action

A

Regulatory proteins

126
Q

These proteins are particularly important in the early stages of life, from embryo to infant.

A

Nutrient proteins.

127
Q

__, found in milk, and ___, found in egg white, are two examples of such proteins.

The role of milk in nature is to nourish and provide immunological protection for mammalian young. Three-fourths of the protein in milk is __. Over 50% of the protein in egg white is __

A

Casein, ovalbumin

128
Q

is the partial or complete disorganization of a protein’s characteristic three-dimensional shape as a result of disruption of its secondary, tertiary, and quaternary structural interactions.

Because the biochemical function of a protein depends on its three- dimensional shape, the result of denaturation is loss of biochemical activity.

A

Protein denaturation

129
Q

does not affect the primary structure of a protein

A

Protein denaturation

BIOCHEM (LEC) (6 decks)

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