Proteins Flashcards
what does the term protein mean in Greek
first importance
what do proteins provide us with
Hydrogen, Carbon, Nitrogen, and Sulfur. Nitrogen and Sulfur are not available in fats or carbs
what are the most abundant macro molecules in the cell
proteins
______ are biological catalysts, and most of them are proteins. Reactions that would take days or weeks or require extremely high temperatures without these are completed in an instant.
enzymes
Defense proteins include ______ (also called _________)
antibodies
immunoglobulins
antibodies are are specific protein molecules produced by specialized cells of the immune system in response to foreign ______
antigens
foreign invaders include _____ and _____ that infect the body.
bacteria
viruses
Each antibody has regions that precisely fit and bind to a single _____, helping to destroy it or remove it from the body.
antigen
_________ carry materials from one place to another in the body.
transport proteins
The protein ________ transports iron from the liver to the bone marrow, where it is used to synthesize the heme group for hemoglobin.
transferrin
The proteins _____ and _______ are responsible for transport and storage of oxygen in higher organisms, respectively.
hemoglobin
myoglobin
__________ control many aspects of cell function, including metabolism and reproduction.
Regulatory proteins
For life to exist, ________, ________, and ________ must be carefully regulated.
body temp
pH of blood
blood glucose levels
Many of the hormones that regulate body function, such as ____ and _____, are proteins.
insulin
glucagon
__________ provide mechanical support to large animals and provide them with their outer coverings.
Structural proteins
Our hair and fingernails are largely composed of the protein _____.
keratin
__________ are necessary for all forms of movement.
Movement proteins
Our muscles, including that most important muscle, the heart, contract and expand through the interaction of ___ and ____ proteins.
actin
myosin
Sperm can swim because they have long ___ made up of ____.
flagella
proteins
_______ serve as sources of amino acids for embryos or infants.
Nutrient proteins
Egg ____ and ____ in milk are examples of nutrient storage proteins.
albumin
casein
The proteins of the body are made up of some combination of twenty different subunits called _______
α-amino acids
Nineteen of the twenty amino acids that are commonly isolated from proteins have this same general structure; they are _______ on the _____. The remaining amino acid, ______, is a secondary amine.
primary amines
α-carbon
proline
Notice that the α-carbon in the general structure is attached to a _______ (a carboxyl group that has ______, −COO−) and a ________ (an amino group that has _______, −N+H3).
carboxylate group
lost a proton
protonated amino acid
gained a proton
At _____, a condition required for life functions, you will not find amino acids in which the carboxylate group is _____(−COOH) and the amino group is ______(−NH2).
pH 7
protonated
unprotonated
Any neutral molecule with equal numbers of positive and negative charges is called a ____
zwitterion
Thus, amino acids in water exist as _____ called ______.
dipolar ions
zwitterions
The α-carbon of each amino acid is also bonded to a ______ and a side chain, or ______
Hydrogen atom
R group
In a protein, the R groups interact with one another through a variety of ___________
weak attractive forces
The interactions in the R groups participate in ____ the protein chain into a precise _____ that determines its ______.
folding
3D shape
ultimate function
The R group interactions also serve to maintain that 3D _____
conformation
The d-l notation is very similar to that discussed for carbohydrates, but instead of the −OH group we use the ____ group to determine which is d- and which is L-
N+H3
most oxidized part of protein
carboxyl group
Almost all of the α-amino acids isolated from proteins in nature are members of the
L-Family
The α-carbon is attached to four different groups in all amino acids except
glycine
The α-carbon of most α-amino acids is therefore
chiral
The α-carbon of most α-amino acids is therefore ____, allowing ______ forms, ______, to exist
chiral
mirror images
enantiomers
Glycine has two _____ attached to the α-carbon and is the only amino acid commonly found in proteins that is _____.
hydrogen atoms
not chiral
Because all amino acids have a carboxyl group and an amino group, all differences between amino acids depend upon their
side chain R groups
The side chains of some amino acids are _____. They prefer contact with one another over contact with water and are said to be ______ amino acids.
nonpolar
hydrophobic
where are hydrophobic amino acids found
in the interior of proteins, where they can associate with one another and remain isolated from water
list the 9 hydrophobic amino acids
“Grandma Always Visits London In May For Winston’s Party”
alanine, valine, leucine, isoleucine, proline, glycine, methionine, phenylalanine, and tryptophan.
The ____ of proline is unique; it is actually bonded to the α-amino group, forming a ______.
R group
secondary amine
The hydrophobic interaction between nonpolar R groups is one of the forces that helps maintain the
proper three-dimensional shape of a protein.
The side chains of the remaining amino acids are polar. Because they are attracted to
polar water molecules
The side chains of the remaining amino acids are polar. Because they are attracted to polar water molecules, they are said to be
hydrophilic amino acids
The hydrophilic side chains are often found
on the surfaces of proteins
The polar amino acids can be subdivided into three classes
polar neutral amino acids
Negatively charged amino acids
Positively charged amino acids
_____ is another weak interaction that helps maintain the proper 3D structure of a protein
Hydrogen bonding
the positively and negatively charged amino acids within a protein interact with one another to form ________ that also help to keep the protein chain folded in a precise way
ionic bridges
have R groups that have a high affinity for water but are not ionic at pH 7
Polar, neutral amino acids
examples of Polar, neutral amino acids
“Santa’s Team Crafts all grinches together”
serine, threonine, tyrosine, cysteine, asparagine, and glutamine
most of the amino acids that are polar neutral associate with one another by _____. but cysteine molecules form _______ with one another
hydrogen bonding
disulfide bonds
have ionized carboxyl groups in their side chains. At pH 7, these amino acids have a net charge of −1.
negatively charged amino acids
examples of negatively charged amino acids
Aspartate and glutamate
why are Aspartate and glutamate acidic amino acids
because ionization of the carboxylic acid releases a proton.
examples of positively charged amino acids
Lets argue here
lysine, arginine, and histidine
Positively charged amino acids._____ , lysine, arginine, and histidine have a net ___ charge because their side chains contain _______.
pH 7
positive
positive groups
positively charged amino acids are basic. why?
because the side chain reacts with water, picking up a proton and releasing a hydroxide anion.
Proteins are linear polymers of
L-α-amino acids
which groups are linked together in a protein
the carboxyl group of one amino acid is linked to the amino group of another amino acid.
the peptide bond is technically a ____ bond
amide
the peptide bond in a protein is formed between what
the −COO− group of one amino acid and the α-N+H3 group of another amino acid.
when glycine and alanine react what do they form
glycyl-alanine
what reaction do glycine and alanine undergo to form glycyl-alanine
condensation (removal of a water molecule)
The molecule formed by condensing two amino acids is called a
dipeptide
the amino acid with a free α−N+H3 group is known as
the amino terminal, or simply the N-terminal amino acid residue or N-terminus
the amino acid with a free −COO− group is known as
the carboxyl, or C-terminal amino acid residue or C-terminus.
structures of proteins are conventionally written with their N-terminal amino acid on the ___
left
The number of amino acids in small peptides is indicated by the prefixes di- (__units), tri- (___units), tetra- (__units), and so forth.
two units
three units
four units
Peptides are named as derivatives of the
C-terminal amino acid, which receives its entire name
For all other amino acids, the ending -ine is changed to
-yl
The dipeptide formed from alanine and glycine that has alanine as its _________ is named alanyl-glycine
N-terminal amino acid
the backbone of a peptide contains the repeating sequence
N-C2-C1-N-C2-C1-N-C2-C1
what do the three N, C2, and C1 represent
N=α-amino group
C2= awlays bonded to the hydrogen atom and the R group side chain
C1= carboxyl group
Pauling discovered that peptide bonds are
both planar (flat) and rigid and that the N−C bonds are shorter than expected.
Pauling concluded that the peptide bond has a partially
double bond character because it exhibits resonance.
This means that there is free rotation around only
two of the three single bonds of the peptide backbone
having free rotation around two of the three single bond of the peptide bonds limits what
the number of possible conformations for any peptide.
A second feature of the rigid peptide bond is that the R groups on adjacent amino acids are on
opposite sides of the extended peptide chain
The primary structure of a protein is the
amino acid sequence of the protein chain.
what does the primary structure result from
the covalent bonding between the amino acid residues in the chain (peptide bonds).
The primary structures of proteins are translations of information contained
genes
Each protein has a different ______ with different _______ in different _________. This sequence of amino acid residues is dictated by the sequence of the ___.
primary structure
amino acid residues
places along the chain
gene
Ultimately, it is the primary structure of a protein that will determine its
biologically active form
The interactions among the R groups of the amino acids in the protein chain depend on
the location of those R groups along the chain.
what do the interactions among the R groups of the amino acids govern
how the protein chain folds
how the protein chain folds dictates what
its final three-dimensional structure and its biological function.
Regions of the primary sequence of a protein, the chain of covalently linked amino acids, fold into regularly repeating structures that resemble designs in a tapestry. These repeating structures define the
secondary structure of a protein
The secondary structure is the result of ____ bonding between _______ and __________ of the peptide bonds.
hydrogen
the amide hydrogens
carbonyl oxygens
_______ are needed to maintain the secondary structure and thereby the overall structure of the protein.
many hydrogen bonds
Some regions of a protein chain may have a random or non regular structure; however, the two most common types of secondary structure are the ____ and the ______ because they _________ in the backbone.
α-helix
β-pleated sheet
maximize hydrogen bonding
The most common type of secondary structure is a coiled, helical conformation known as the
α-helix
a feature of α-helix is that Every amide hydrogen and carbonyl oxygen associated with the peptide backbone is involved in a
hydrogen bond when the chain coils into an α-helix.
what do the hydrogen bonds do to the α-helix (features of alpha helix)
lock it into place
Every carbonyl oxygen is ________ to an amide hydrogen ____ amino acids away in the chain.
(features of alpha helix)
hydrogen bonded
four
The hydrogen bonds of the α-helix are parallel to the
features of alpha helix
long axis of the helix
The polypeptide chain in an α-helix is
features of alpha helix
right handed
The repeat distance of the helix, or its pitch, is _____, and there are ________.
(features of alpha helix)
- 4 angstroms (A)
3. 6 amino aicds/ turn of the helix
are structural proteins arranged in fibers or sheets that have only one type of secondary structure.
fibrous proteins
The ____ are fibrous proteins that form the covering (hair, wool, nails, hooves, and fur) of most land animals.
α-keratins
Human hair provides a typical example of the structure of the
α-keratins
The proteins of hair consist almost exclusively of
polypeptide chains coiled up into α-helices.
A single α-helix is coiled in a bundle with two other helices to give a three-stranded superstructure called a
protofibril
A single α-helix is coiled in a bundle with two other helices to give a three-stranded superstructure called a protofibril that is part of an array known as a
microfibril
These structures, which resemble “molecular pigtails,” possess great ______, and they are virtually_________
mechanical strength
insoluble in water
Structure of the α-keratins. These proteins are assemblies of triple-helical ____ that are assembled in an array known as a _____. These in turn are assembled into _____. Hair is a collection of _____and hair cells.
protofibril
microfibril
macrofibril
macrofibrils
The major structural property of a coiled coil superstructure of α-helices is its
great mechanical strength
The second common secondary structure in proteins resembles the pleated folds of drapery and is known as the
β-pleated sheet
All of the carbonyl oxygens and amide hydrogens in a β-pleated sheet are involved in
hydrogen bonds
the polypeptide chain in β-pleated sheet is nearly _______
completely extended
The polypeptide chains in a β-pleated sheet can have
2 orientations
If the N-termini are head to head, the structure is known as a
parallel β-pleated sheet
And if the N-terminus of one chain is aligned with the C-terminus of a second chain (head to tail), the structure is known as an (β-pleated sheet)
antiparallel β-pleated sheet.
The structure of silk fibroin is almost entirely
aantiparallel β-pleated sheet
Some fibrous proteins are composed of β-pleated sheets. For example, the silk-worm produces _______, a protein whose structure is an ________
silk fibroin
antiparallel β-pleated sheet
The polypeptide chains of a β-pleated sheet are almost completely _____, and silk does not _____
extended
stretch easily
_____ accounts for nearly half of the amino acids of silk fibroin. ____ and ____ account for most of the others
glycine
alanine
serine
The ____ groups of alanines and the _____groups of serines lie on ____ sides of the sheet.
methyl
hydroxymethyl
opposite
Most fibrous proteins, such as silk, collagen, and the α-keratins, are almost
completely insoluble in water
the majority of cellular proteins, however, are soluble in the
cell cytoplasm
Soluble proteins are usually ________
globular proteins
Globular proteins have three-dimensional structures called the _______ of the protein, which are distinct from their secondary structure.
tertiary structure
Tertiary structure refers to the
3D shape of the entire peptide chain
The regions of secondary structure, α-helix and β-pleated sheet, further ____ on themselves to achieve the _____
fold
tertiary structures
We have seen that the forces that maintain the secondary structure of a protein are ______ between the _____ and the _____ of the peptide bond.
hydrogen bonds
amide hydrogen
carbonyl oxygen
The globular tertiary structure forms spontaneously and is maintained as a result of
interactions among the side chains, the R groups, of the amino acids.
name the molecular interactions that maintain the structure of globular tertiary proteins
van der Waals forces (London dispersion forces and dipole-dipole attractions)
Hydrogen bonds
Covalent bonds
Ionic bonds (salt bridges)
van der Waals forces (London dispersion forces and dipole-dipole attractions) between the
hydrophobic R groups
Hydrogen bonds between the
polar R groups
Ionic bonds (salt bridges) between the
oppositely charged R groups
Covalent bonds between the
thiol-containing amino acid residues. Two of the polar cysteines can be oxidized to a dimeric amino acid called cystine
The disulfide bond of cystine can be a _____ between different proteins, or it can _____ within a protein together
cross-link
tie two segments
it is the tertiary structure of the protein that defines its
biological function
Most of the time, ____ side chains of amino acid residues are buried, closely packed, in the ____ of a globular protein, out of contact with ____
non polar
interior
water
Polar and charged side chain amino acid residues lie on the _____ of globular proteins
surfaces
Globular proteins are extremely
compact
The tertiary structure can contain regions of ____ and regions of ________
α-helix
β-pleated sheet
_____- regions of random coil connect regions of α-helix and β-pleated sheet.
Hinge
Because of its ____ structure, ____ disrupts an _____. As a result, ____ is often found in these ____ regions.
cyclic proline α-helix proline hinge
For many proteins, the functional form is not composed of a single peptide but is rather an aggregate of
smaller globular peptides
For instance, the protein hemoglobin is composed of
four individual globular peptide subunits: two identical α-subunits and two identical β-subunits.
Only when the four peptides are bound to one another is the protein molecule
functional
The association of several polypeptides to produce a functional protein defines the ________ of a protein
quaternary structure
The forces that hold the quaternary structure of a protein are the same as those that hold the
tertiary structure
The forces that hold the quaternary structure of a protein are the same as those that hold the tertiary structure. These include _____ forces between hydrophobic R groups,_____ between polar R groups, ______ between oppositely charged R groups, and _______.
van der waals
hydrogen bonds
ionic bridges
disulfide bridges
In some cases, quaternary structure of a functional protein involves binding to a
nonprotein group
In some cases, quaternary structure of a functional protein involves binding to a nonprotein group. This additional group is called a
prosthetic group
For example, many of the receptor proteins on cell surfaces are
glycoproteins
For example, many of the receptor proteins on cell surfaces are glycoproteins. These are proteins with ___ groups ____ attached
sugar
covalently
Each of the subunits of hemoglobin is bound to an
iron containing heme group
The heme group is a_______________ with an ___ ion coordinated within it.
large unsaturated organic cyclic amine
iron
As in the case of hemoglobin, the prosthetic group often determines the
function of a protein
For instance, in hemoglobin it is the iron-containing heme groups that have the ability to
bind reversibly to oxygen
what is the prosthetic group in hemoglobin
heme group
The ____ structure of the protein is the amino acid sequence of the protein. The primary structure results from the formation of ______ between amino acids. Peptide bonds are ____ formed between the carboxylate group of one amino acid and the amino group of another.
primary
covalent peptide bonds
amide bonds
As the protein chain grows, numerous opportunities for _____ interactions in the backbone of the polypeptide chain become available. These cause regions of the chain to fold and orient themselves in a variety of _______ arrangements. The secondary level of structure includes the ____ and the _____, which are the result of ______ between the amide hydrogens and carbonyl oxygens of the peptide bonds. Different regions of the chain may be involved in different types of secondary structure arrangements; some regions might be α-helix and others might be a β-pleated sheet.
non covalent conformational α-helix β-pleated sheet hydrogen bonding
When we discuss tertiary structure, we are interested in the overall ___ of the entire chain. In other words, we are concerned with the ____ of the secondary structure. Both _____ interactions between the R groups of the amino acids and _________ play a role in determining the tertiary structure. The noncovalent interactions include _____, ______, and ______
folding further folding noncovalent covalent disulfide bridges Hydrogen bonding, ionic bonding, and van der waals forces (London dispersion forces and dipole-dipole attractions).
It is the tertiary and quaternary structures of the protein that ultimately
define its function
some of the tertiary and quaternary structures have _____ with great mechanical strength
fibrous structure
fibrous structures make up what
the major structural components of the cell and the organism. Often they are also responsible for the movement of the organism.
some of the tertiary and quaternary proteins fold into
globular shapes
Most of the transport proteins, regulatory proteins, and enzymes are
globular proteins
The very precise three-dimensional structure of each of these proteins allows each to carry out its
very specific function in the body
the change of even a single amino acid in the primary structure of a protein can have far-reaching implications, including
loss of function that can be life threatening
Our cells require a steady supply of oxygen, but oxygen is only slightly soluble in aqueous solutions. To overcome this solubility problem, we have an oxygen transport protein,
hemoglobin
where is hemoglobin found
in RBCs
what is hemoglobin
is the oxygen transport protein of higher animals.
myoglobin
is the oxygen storage protein of skeletal muscle.
The ___ ion in the heme group is the binding site for ___ in both myoglobin and hemoglobin.
Fe2+
oxygen
myoglobin has a _________for oxygen than does hemoglobin
greater attraction
Hemoglobin (Hb) is a ____ composed of ____ polypeptide subunits: two α-subunits and two β-subunits
tetramer
four
Because each subunit of hemoglobin contains a heme group, a hemoglobin molecule can bind
four molecules of oxygen
Oxygen diffuses from the region of _________ to the region of ________
high pO2 in the lungs
low pO2 in the blood.
Oxygen diffuses from the region of high pO2 in the lungs to the region of low pO2 in the blood. There it enters_____and binds to the _____ of the heme groups of ____, forming _____. This binding actually helps bring ____O2 into the blood.
RBCs Fe2+ ions deoxyhemoglobin oxyhemoglobin more
he fetus, however, has a unique type of hemoglobin, called
fetal hemoglobin
the fetal hemoglobin has _____ for oxygen ______
more affinity
than the mothers hemoglobin
he biosynthesis of fetal hemoglobin stops _____ when the genes encoding fetal hemoglobin are switched ____ and the genes coding for adult hemoglobin are switched ____
shortly after birth
off
on
is a human genetic disease that first appeared in tropical west and central Africa.
Sickle Cell Anemia
sickle cell anemia individuals produce a ___
a mutant hemoglobin known as sickle cell hemoglobin (Hb S).
Sickle cell anemia receives its name from the_____appearance of the _______ that form in this condition
sickled
red blood cells
The sickled cells are unable to pass through the small capillaries of the circulatory system, and circulation is
hindered
The sickled cells are unable to pass through the ______ of the circulatory system, and circulation is hindered. This results in damage to many organs, especially ___ and ____, and can lead to ____________
small capillaries
bone
kidney
death at an early age.
Sickle cell hemoglobin differs from normal hemoglobin by a
single amino acid
In the β-chain of sickle cell hemoglobin, what has replaced what
a valine (a hydrophobic amino acid) has replaced a glutamic acid (a negatively charged amino acid).
the replacement of glutamic acid by valine provides a basis for the
binding of hemoglobin S molecules to one another
When oxyhemoglobin S unloads its oxygen, individual deoxyhemoglobin S molecules ____________
bind to one another as long polymeric fibers
When oxyhemoglobin S unloads its oxygen, individual deoxyhemoglobin S molecules bind to one another as long polymeric fibers. This occurs because
the valine fits into a hydrophobic pocket on the surface of a second deoxyhemoglobin S molecule.
The fibers generated in this way radically alter the ___ of the red blood cell, resulting in the ____ effect.
shape
sickling
Sickle cell anemia occurs in individuals who have
inherited the gene for sickle cell hemoglobin from both parents.
Afflicted individuals with sickle cell anemia produce 90–100%
defective β-chains.
Individuals who inherit one normal gene and one defective gene produce
both normal and altered β-chains.
About 10% of African Americans carry a single copy of the defective gene, a condition known as
sickle cell trait
people with sickle cell trait Although not severely affected, they have a
50% chance of passing the gene to each of their children.
An interesting relationship exists between sickle cell trait and resistance to
malaria
In some parts of Africa, up to 20% of the population has
sickle cell trait.
The presence of sickle cell trait is linked to an
increased resistance to malaria because the malarial parasite cannot feed efficiently on sickled red blood cells.
People who have sickle cell disease ______ those without sickle cell trait have a high probability of succumbing to _______.
die young
malaria
people who have sickle cell trait do not suffer much from _______ and simultaneously resist ________
sickle cell anemia
deadly malaria
Because those with sickle cell trait have a greater chance of ____ and _____, the sickle cell hemoglobin gene is ______ in the population.
survival
reproduction
maintained
The blood plasma of a healthy individual typically contains _______ of protein.
60-80 g/L
This protein can be separated into
five classes designated α through γ
the seperation of proteins is based on the
overall surface charge on each of the types of protein.
The most abundant protein in the blood is ____, making up about ____ of the blood protein.
albumin
55%
Albumin contributes to the ______ of the blood simply because it is a ___ molecule.
osmotic pressure
dissolved
what does albumin also serve as
a nonspecific transport molecule for important metabolites that are otherwise poorly soluble in water.
Among the molecules transported through the blood by albumin are
bilirubin, Ca2+ , and fatty acids (organic anions).
bilirubin
a waste product of the breakdown of hemoglobin
________ make up 13% of the plasma proteins.
The α-globulins (α1 and α2)
The α-globulins include
glycoproteins (proteins with sugar groups attached), high-density lipoproteins, haptoglobin (a transport protein for free hemoglobin), ceruloplasmin (a copper transport protein), prothrombin (a protein involved in blood clotting), and very low density lipoproteins.
The most abundant α1-globulin is
α1-antitrypsin
what does α1-antitrypsin do
the inactivation of an enzyme that causes damage in the lungs
what is another inhibitor found the bloodstream
α1-Antichymotrypsin
α1-Antichymotrypsin along with ___ proteins is found in the _____________________
amyloid
amyloid plaques characteristic of Alzheimer’s disease (AD)
In the blood, α1-antichymotrypsin is also found complexed to ________
prostate specific antigen (PSA)
prostate specific antigen (PSA), the protein antigen that is measured as an indicator of
prostate cancer
Elevated PSA levels are observed in those with the
disease of prostate cancer
It is interesting to note that PSA is a
chymotrypsin-like proteolytic enzyme.
The β-globulins represent 13% of the blood plasma proteins and include
transferrin (an iron transport protein) and low-density lipoprotein.
a protein involved in coagulation of blood, comprises 7% of the plasma protein
Fibrinogen
IgG, IgM, IgA, IgD, and IgE, make up the remaining 11% of the plasma proteins.
the γ-globulins (antibodies)
The γ-globulins are synthesized by
B lymphocytes
most of the remaining plasma proteins are synthesized in the
liver
In fact, a frequent hallmark of liver disease is
reduced amounts of one or more of the plasma proteins
occurs when the organized structures of a globular protein, the α-helix, the β-pleated sheet, and tertiary folds become completely disorganized.
Denaturation
denaturation does not alter the
primary structure
The protein molecules are denatured as they lose their characteristic ______ and become completely _____
3D conformation
disorganized
occurs as the protein molecules then unfold and become entangled
coagulation
as the protein molecules then unfold and become entangled. At this point, they are no longer in solution; they have aggregated to
become a solid and will precipitate out of the solution
Many of the proteins of our cells—for instance, the enzymes—are in the same kind of viscous solution within the cytoplasm. To continue to function properly, they must remain in solution and maintain the correct
3D configuration
If the body temperature becomes too high, or if local regions of the body are subjected to very high temperatures, as when you touch a hot cookie sheet, cellular proteins become ____. They lose their ___, and the cell or the organism _____.
denatured
function
dies
The positively and negatively charged R groups on the surface of the molecule interact with ___ and ____ molecules, and these ____ keep the protein in ____ within the ____.
ions water interactions solution cytoplasm
When the pH of the solution is changed dramatically, the ___or ____ will change the _____ of the protein, interfering with the _____ and ______ that stabilize the tertiary structure.
acid base charge salt bridges hydrogen bonds
Polar organic solvents, such as ____________, denature proteins by disrupting __________ within the protein, in addition to forming hydrogen bonds __________
rubbing alcohol (2-propanol),
hydrogen bonds
with the solvent, water.
the _____ regions of these solvents interfere with _____________ in the interior of the protein molecule, thereby disrupting the conformation.
nonpolar
hydrophobic interactions
Traditionally, a 70% solution of rubbing alcohol was often used as a _________ or _________. However, recent evidence suggests that it is not an effective agent in this capacity.
disinfectant or antiseptic
Detergents have both a _________ and a ________
hydrophobic region (the fatty acid tail) a polar or hydrophilic region
When detergents interact with ____, they disrupt _____________, causing the protein chain to ____.
proteins
hydrophobic interactions
unfold
Heavy metals such as _______ may form bonds with ____________. This interferes with the _______ formed between amino acid R groups of the protein chain, resulting in loss of _______-.
mercury or lead
negatively charged side chain groups
salt bridges
conformation
Heavy metals may also bind to ______ of a protein.
sulfhydryl groups
Heavy metals may also bind to sulfhydryl groups of a protein. This may cause a profound change in the _____________ of the protein, accompanied by ________
3D structure
loss of function
Stirring, whipping, or shaking can disrupt the
weak interactions that maintain protein conformation.
Amino acids are also used in the biosynthesis of a large number of important molecules called the
nitrogen compounds
the nitrogen compounds includes
some hormones, the heme groups of hemoglobin and myoglobin, and the nitrogen-containing bases found in DNA and RNA.
Digestion of dietary protein begins in the
stomach
The stomach enzyme ____ begins the digestion by _____ some of the ______ of the protein. This breaks the protein down into __________
pepsin
hydrolyzing
peptide bonds
smaller peptides
Production of pepsin and other proteolytic digestive enzymes must be _________ because the active enzymes would ____ and ___ the _______
carefully controlled
digest
destroy
cell that produces them.
pepsin is actually synthesized and secreted in an inactive form called
pepsinogen
Pepsinogen has an additional __________ in its primary structure. These are removed in the stomach to produce ___________.
forty-two amino acids
active pepsin
Protein digestion continues in the _____ where the enzymes ____,______,_______, and others catalyze the hydrolysis of _________ at different sites in the protein.
small intestine
trypsin, chymotrypsin, elastase
peptide bonds
_______ cleaves peptide bonds on the carbonyl side of aromatic amino acids and _____ cleaves peptide bonds on the carbonyl side of basic amino acids. Together these __________ degrade large dietary proteins into amino acids that can be absorbed by cells of the ________.
chymotrypsin
trypsin
proteolytic enzymes
small intestine
Amino acids can be divided into two major nutritional classes. ________ are those that cannot be synthesized by the body and are required in the diet. __________ are those amino acids that can be synthesized by the body and need not be included in the diet
Essential amino acids
Nonessential amino acids
Proteins are also classified as
complete or incomplete
Protein derived from animal sources is generally
complete protein
complete protein provides all of the __________ in approximately the correct amounts for biosynthesis.
essential and nonessential amino acids
In contrast, protein derived from vegetable sources is generally _________ because it lacks a sufficient amount of _________
incomplete protein
one or more essential amino acids
Only a few _____ sources provide complete protein; among these are soy, quinoa, and buckwheat.
vegetable
People who want to maintain a strictly vegan diet or for whom animal protein is often not available have the problem that most high-protein vegetables do not have all of the
essential amino acids needed to ensure a sufficient daily intake.
Histidine and arginine are essential amino acids for _____ but not for ________
infants
healthy adults
Cysteine and tyrosine are considered to be ____________amino acids. They are required by ________________.
semiessential
premature infants and adults who are ill
list the essential amino acids
Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine
