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
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
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
4
Q
All proteins contain the elements __, __, __, and __; most also contain sulfur
A
Carbon
Hydrogen
Oxygen
Nitrogen
5
Q
The presence of ___ in proteins sets them apart from carbohydrates and lipids, which most often do not contain it
A
NITROGEN
6
Q
The average nitrogen content of proteins is ___% by mass.
A
15.4
7
Q
Other elements, such as ____, are essential constituents of certain specialized proteins
A
phosphorus and iron
8
Q
___, the main protein of milk, contains phosphorus, an element very important in the diet of infants and children.
A
Casein
9
Q
___, the oxygen-transporting protein of blood, contains iron
A
Hemoglobin
10
Q
A protein is a naturally occurring, unbranched polymer in which the monomer units are
A
amino acids
11
Q
An amino acid is an ___ (organic/inorganic) compound
A
Organic
12
Q
Amino acids contains both an ___ (-NH2) group and a ___ (-COOH) group.
A
amino, carboxyl
13
Q
The amino acids found in proteins are always ___
A
a-amino acids
14
Q
An ___ is an amino acid in which the amino group and the carboxyl group are attached to it
A
α-amino acid
15
Q
A standard amino acid is one of the __ a-amino acids normally found in proteins
A
20
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
17
Q
A ___ amino acid is an amino acid that contains one amino group, one carboxyl group, and a nonpolar side chain
A
nonpolar
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
19
Q
How many amino acids are in the nonpolar amino acid?
A
9
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
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
22
Q
In solution at physiological pH, the side chain of a polar neutral amino acid is neither ____.
A
acidic nor basic
23
Q
How many polar neural amino acids are there?
A
6
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
25
A _____ is an amino acid that contains one amino group and two carboxyl groups, the second carboxyl group being part of the side chain
polar acidic amino acids
26
In solution at physiological pH, the side chain of a polar acidic amino acid bears a __ charge;
negative
27
POLAR ACIDIC AMINO ACID
the side-chain carboxyl group has lost its acidic __ atom.
hydrogen
28
How many polar acidic amino acids are there?
2
29
A ___ is an amino acid that contains two amino groups and one carboxyl group, the second amino group being part of the side chain.
polar basic amino acid
30
In solution at physiological pH, the side chain of a polar basic amino acid bears a __ charge
positive
31
POLAR BASIC AMINO ACID
the nitrogen atom of the amino group has __ a proton
accepted
32
How many polar basic amino acids are there?
3
33
What are the 9 nonpolar amino acids
Glycine
Alanine
Valine
Leucine
Isoleucine
Proline
Phenylalanine
Methionine
Tryptophan
34
What are the polar neutral amino acids?
Serine
Cysteine
Threonine
Asparagine
Glutamine
Tyrosine
35
What are the Polar acidic amino acids?
Aspartic acid
Glutamic acid
36
What are the Polar Basic Amino Acids?
Histidine
Lysine
Arginine
37
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.
glycine
38
In pure form, amino acids are __ crystalline solids with relatively high decomposition points. (Most amino acids decompose before
they melt.)
white
39
Most amino acids are not very soluble in water
because of strong __ forces within their crystal structures.
intermolecular
40
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?
Both an acidic group (—COOH) and a basic group (—NH2) are present on the same carbon in an a-amino acid
41
In neutral solution, carboxyl groups have a tendency to lose protons (H+), producing a ___ charged species
Negatively
42
In neutral solution, amino groups have a tendency to accept protons (H+), producing a ___ charged species
Positively
43
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
Internal acid-base
44
From the German term meaning “double ion”
Zwitterion
45
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.
zwitterion
46
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
zero
47
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.
Cysteine
48
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
disulfide
49
A _ is a molecule that is made up of two like subunits
dimer
50
The covalent disulfide bond of cystine is readily broken, using __ agents, to regenerate two cysteine molecules.
reducing
51
A ___ is an unbranched chain of amino acids, each joined to the next by a peptide bond.
peptide
52
Peptides are further Classified by the ___ of amino acids present in the chain.
number
53
A compound containing two amino acids is specifically called a ___; three amino acids
joined together in a chain constitute a ___; and so on.
dipeptide, tripeptide
54
The name ___ is loosely used to refer to peptides with 10 to 20 amino acid residues,
oligopeptide
55
The name __ is used to refer to longer peptides.
polypeptide
56
The bonds that link amino acids together in a peptide chain are called ___.
peptide bonds
57
There are __ peptide bonds present in a
pentapeptide
four
58
A carboxylic acid and an amine can react to produce an
amide
59
The products are a molecule of water and a molecule containing the two amino acids linked by an ___
Amide bond
60
A peptide bond is a __ bond between the carboxyl group of one amino acid and the amino group of another amino acid.
covalent
61
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
amino acid residue
62
What are the terminal end in amino acid?
N-terminal, C-terminal
63
The repeating sequence of peptide bonds and a-carbon —CH groups in a peptide is referred to as the ___ of the peptide
The backbone
64
Peptides that contain the same amino acids but in
different order are different molecules (constitutional isomers) with different properties
Isomeric peptides
65
True or False
The number of isomeric peptides possible increases
rapidly as the length of the peptide chain decreases
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
SMALL PEPTIDE HORMONES
The two best-known peptide hormones, both produced by the pituitary gland, are
Oxytocin & vasopressin
67
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
Cysteine
3 and 8
68
It regulates uterine contractions and lactation
Oxytocin
69
It regulates the excretion of water by the kidneys; it also affects blood pressure
Vasopressin
70
are pentapeptide neurotransmitters produced by the brain itself that bind at receptor sites in the brain to reduce pain.
Enkephalins
71
The two best-known enkephalins are ___ and ___,
Metenkephalin, Leu-enkephalin
72
Structure of Metenkephalin
Tyr-Gly-Gly-Phe-Met
73
Structure of Leu-enkephalin
Tyr-Gly-Gly-Phe-Leu
74
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.
enkephalin
75
The action of the prescription painkillers ____ is based on their binding at the same receptor sites in the brain as the naturally occurring enkephalins
morphine and codeine
76
The tripeptide ___ is present in significant
concentrations in most cells and is of considerable physiological importance as a regulator of oxidation–reduction reactions.
glutathione (Glu–Cys–Gly)
77
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)
antioxidant
78
A ___ is a peptide in which at least 40 amino acid residues are present.
protein
79
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
arbitrary
80
A ___ protein is a protein in which only one peptide chain is present. Large proteins, those with many amino acid residues, usually are multimeric.
monomeric
81
A ____ protein is a protein in which more than one peptide chain is present.
multimeric
82
The peptide chains present in multimeric proteins are called ____.
protein subunits
83
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.
True
84
Proteins with up to ___ subunits are known.
12
85
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
insulin
86
A ___ is a protein in which only amino acid residues are present.
simple protein
87
More than one protein subunit may be present in a simple protein, but all subunits contain only __
amino acids
88
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
conjugated protein
prosthetic groups
89
A ___ is a non-amino acid group present in a conjugated protein
prosthetic group
90
is the order in which amino acids are linked together in a protein.
Primary protein structure
91
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.
order of attachment
92
___, 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 ___
Insulin
Frederick Sanger
93
is the arrangement in space adopted by the backbone portion of a protein.
Secondary protein structure
94
The two most common types of secondary structure are the
alpha helix (α helix) and the beta pleated sheet (β pleated sheet
95
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.
alpha helix
96
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
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
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.
beta pleated sheet
98
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).
intrachain, interchain
99
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.
Tertiary protein structure
100
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
Quaternary structure
101
A ____ is a protein whose molecules have an elongated shape with one dimension much longer than the others.
fibrous protein
102
tend to have simple, regular, linear structures. There is a tendency for such proteins to aggregate together to form macromolecular structures.
Fibrous proteins
103
A ___ is a protein whose molecules have peptide chains that are folded into spherical or globular shapes.
globular protein
104
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
hydrophobic, hydrophilic
105
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
membrane protein
106
The functional versatility of proteins stems from
(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
Proteins are probably best known for
their role as catalysts.
Catalytic proteins.
108
Proteins with the role of biochemical catalyst are called __.
enzymes
109
___ participate in almost all of the metabolic reactions that occur in cells. The chemistry of human genetics.
Enzymes
110
These proteins, also called immunoglobulins are central to the functioning of the body’s immune system.
Defense proteins.
111
They bind to foreign substances, such as bacteria and viruses, to help combat invasion of
the body by foreign particles
Defense proteins
112
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.
Transport proteins.
113
The most well-known example of a transport protein is ___, which carries oxygen from the lungs to other organs and tissues.
hemoglobin
114
Another transport protein is ___, which carries iron from the liver to the bone marrow.
transferrin
115
High- and low-density ____ are carriers of cholesterol in the bloodstream
lipoproteins
116
These proteins transmit signals to coordinate biochemical processes between different cells, tissues, and organs
Messenger proteins.
117
A number of hormones that regulate body processes are ___, including insulin and glucagon. Human growth hormone is another example of it
messenger proteins
118
These proteins are necessary for all forms of movement.
Contractile proteins.
119
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
Muscles
120
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
Structural proteins.
121
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
Transmembrane proteins.
122
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.
Storage proteins.
123
is an oxygen-storage protein present in muscle; the
oxygen so stored is a reserve oxygen source for working muscle
Myoglobin
124
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.”
Regulatory proteins.
125
are often the molecules that bind to enzymes (catalytic proteins), thereby turning them
“on” and “off,” and thus controlling enzymatic action
Regulatory proteins
126
These proteins are particularly important in the early stages of life, from embryo to infant.
Nutrient proteins.
127
__, 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 __
Casein, ovalbumin
128
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.
Protein denaturation
129
does not affect the primary structure of a protein
Protein denaturation
