Protein denaturation usually refers to the disruption of which of the following types of molecular interactions? Select all that apply.
A.)Van der Waals attraction
B.)Covalent bonds
C.)Hydrogen bonds
D.)Hydrophobic interactions
Transcribed Image Text: Learn It: Explain the role of chemical
attractions in protein folding and
denaturation.
Every protein is a three-dimensional molecule that has a specific
shape. This shape, the structure of the protein, is essential to the
function of that protein. For example, if a protein functions as an
enzyme, catalyzing a reaction, it must have the right shape to take up
the reactants and allow them to be converted to products. The main
determining factor of the shape of a given protein is the sequence of
amino acids that make up the polypeptide chain(s) of the protein
itself. Each of the twenty amino acids that make up a protein has a
side chain, known as the R group, that gives it unique properties. The
way that these R groups interact with one another and the outside
environment causes the protein to fold into the specific structure that
enables its function.
The amino acids are grouped into four categories based on the
properties of their side chains. The largest of these groups is the
hydrophobic amino acids. The side chains of these amino acids are
nonpolar and are hydrophobic, or "water-fearing." The second-largest
group of amino acids are those that have electrically charged side
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Learn It: Explain the role of chemical
attractions in protein folding and
denaturation..
The interactions described are all relatively weak and are vulnerable
to a process called denaturation. During protein denaturation, a
protein loses its structure, and therefore cannot perform its function.
Conditions such as heat disrupt interaction like hydrogen bonds
between R groups, while high salt, acidic, or basic conditions can
disrupt the formation of salt bridges. These forces are usually not
strong enough to break the covalent bonds that join the amino acids
together. Denatured proteins are often marked for destruction so
that the amino acids can be recycled into new proteins.
One amino acid, cysteine, foims very strong, covalent bonds with
other cysteines. This is due to the presence of a sulfur atom in the
side chain of this amino acid. These sulfur groups are capable of
forming covalent bonds, known as disulfide bonds, with other sulfur
groups. These bonds are very difficult to break and are often found in
high numbers in proteins from organisms that live in high
temperatures because they are more resistant to denaturation in the
presence of high heat.
You may be wondering why proteins cannot just refold after
Learn It: Explain the role of chemical
attractions in protein folding and
denaturation.
group of amino acids are those that have electrically charged side
chairis at physiological pH. Some of these amino acids have a positive
charge, while others have a negative charge. The third group of
amino acids includes those whose side chains are polar, but not
electrically charged. Finally, there is a group of "special case" amino
acids, whose side groups have properties that don't fit into the other
groups. One of these amino acids, cysteine, plays a special role in
protein structure, and we will come back to it later.
The R groups of the polypeptide interact with one another according
to the rules of chemical bonding that you've already learned. 4
Opposite charges attract one another, so positive and negative side
chains may move toward each other, forming what are known as salt
bridges. Polar side chains tend to interact with water. Remember that
the cytosol is made of mostly water, so you will often find these
amino acids on the outside of a protein. Hydrophobic nonpolar side
chains tend to fold away from the cytosol, toward the inside of the
protein. Some side groups are also able to form hydrogen bonds with
other side groups, while others interact via Van der Waals attractions.
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Learn It: Explain the role of chemical
attractions in protein folding and
denaturation..
C
other cysteines. This is due to the presence of a sulfur atom in the
side chain of this amino acid. These sulfur groups are capable of
forming covalent bonds, known as disulfide bonds, with other sulfur
groups. These bonds are very difficult to break and are often found in
high numbers in proteins from organisms that live in high
temperatures because they are more resistant to denaturation in the
presence of high heat.
'
You may be wondering why proteins cannot just refold after.
denaturation because the amino acid sequence remains intact. This is
because proteins do not usually fold on their own in the cytosol,
During protein synthesis, specialized proteins, known as chaperones,
protect the protein and provide an environment that is conducive to
protein folding. Once the protein is in the cytosol, or whatever cellular
compartment that it is targeted to, the environment is no longer
folding-friendly, so once the protein loses its shape it is difficult, often
impossible, to refold.