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The subcomponents of biological molecules & their
sequence determine the properties of that molecule:
The structure of macromolecules determine their function; as such, differently
shaped proteins or lipids etc have different functions in the body. If a
macromolecule changes its structure, its function may also be altered.
CARBOHYDRATES:
The subcomponents of starch and cellulose are both glucose. Yet their sequence, or
the way they’re linked, makes them very different. In starch, the glucose monomers
all have the same orientation; the glucose is alpha-linked. In cellulose, the glucose is
beta-linked, meaning that each glucose molecule is “upside down” from its
neighbors (with beta-ringed structures, the hydroxyl group is reversed with the
hydrogen).
This difference makes starch molecules helical, and cellulose straight. Plants use
starch as their food storage, and cellulose as the tough cells that enclose their cells.
Their different structures allow for different functions.
LIPIDS:
A saturated fatty acid is different from an unsaturated fatty acid in both their
structure and their properties. A saturated fatty acid is ‘saturated’ with hydrogens;
are there are no double bonds in the fatty
acids. Their tails don’t have kinks and are
straight. An unsaturated fatty acid has
one+ double bonds, with one less hydrogen molecule for each double bond
occurring. Each double bond creates a kink in the hydrocarbon chain tail. Saturated
fatty acids  saturated fat = animal fats (ex: lard/butter) and are solid at room
temperature. Unsaturated fatty acids  unsaturated fat = fats from plants or fish,
and usually liquid at room temperature (ex: vegetable oil/cod liver oil). This is
because the kinks in the hydrocarbon tails prevent the molecules from packing
tightly together and solidifying at room temperature.
On the other hand, a phospholipid has two fatty acids and a phosphate group
joined to the glycerol head. The phosphate group is electronegative, and small polar
molecules can link to the phosphate group to create a variety of phospholipids.
PROTEINS:
Proteins are composed of a string of amino acids (20 possible amino acids).

During primary structure, the amino acids are bonded covalently. If one amino
acid is substituted for another, the molecule could be different and may fold
differently.

In secondary structure, the carboxyls and amines bind and form a backbone
through hydrogen bonds between oxygen and hydrogen molecules.
Secondary protein structure can take the form of either an alpha-helix or
beta-pleated sheet. Primary structure can impact the form proteins take in
secondary structure.

Hydrogen bonds between polar side chains (from secondary structure) affect
tertiary structure. In tertiary structure and ionic bonds form between positively
& negatively charged side chains and disulfide bridges form between cysteine
groups. Additionally hydrophobic interactions form between hydrophobic
molecules, held together by van der Walls interactions.
o IF the primary structure is different, the amino acids that are
hydrophobic might turn out hydrophilic, or there might be another
hydrophobic amino acid somewhere else on the polypeptide chain. It
would cause the protein to fold differently.
o IF in secondary structure, the hydrogen bonds form differently
o THIS ALSO AFFECTS quaternary structure. An incorrectly/differently
folded protein in tertiary cannot fold with other proteins the same way
in quaternary structure.
For sickle cell disease, a glutamine is substituted with a valine. This causes the
protein to fold incorrectly, and it’s function is therefore affected.
NUCLEIC ACIDS:
Replacing one nitrogenous base with another means replacing its complementary
base too because A always bonds with T/U and C with G. Since DNA codes for
proteins through mRNA, changing a base will result in a change in the proteins
structure and/or function. EXAMPLE: Hemophilia, where a mutation on the Xchromosome causes the lack of a coagulation factor in the person’s blood.
Interactions between molecules affect their structure
and function
Different molecules have separate properties, so it makes sense that interactions
between molecules affect each molecule’s structure and function. Interactions
between reactive molecules affect their structure as they bond, and their function as
they become a compound. Interactions between molecules in our body fuel
metabolism through the processes of releasing and/or utilizing energy. A great
example to demonstrate and thoroughly explain how interactions between
molecules affect their structure and function is the activity of enzymes and
their substrates.
An enzyme’s purpose is to catalyze chemical reactions in an organism so they can
perform all their necessary processes quickly enough to survive. Below (right) is a
picture from the textbook explaining the interaction between enzymes and
substrates – the enzyme turns the substrates into different products with different
functions. If there is no enzyme to interact with the substrate and catalyze reactions,
the rate of the reaction would be much slower (below left: textbook picture
displaying a graph of enzyme versus no enzyme in reaction).
There are multiple factors that affect the interaction between enzymes & substrates,
each affecting the structure & function of both; under different conditions the
interactions between the two occur differently. There are seven scenarios that will
be discussed in this blog post; the first two address interactions but not structure
and function as much (they’re more of a background to explain the process of
enzyme-substrate activity), while three through seven address the main question
(both).
ONE
In conditions where enzyme concentration is greater, the rate of substrates being
catalyzed increases, because there are more enzymes for substrates to interact with.
Products Produces vs
Time (One Enzyme)
24
21
18
15
12
9
6
3
0
0
10
20
30
40
Total # of Products Made
Total # of Products Made
Products Produced vs
Time (Two Enzymes)
24
19
14
9
4
-1
Time (sec)
0
10
20
30
40
Time (sec)
Likewise, if there are fewer enzymes present, less substrates will get converted into
products. Even in the amount of substrates present is at the maximum level, an
enzyme can only work so fast. Differences in reaction rate can be observed below:
TWO
If there are more substrates, more of them will interact with the enzyme, resulting in
a faster rate of reaction, up to a point where the amount of substrates are at the
maximum level and an enzyme cannot work faster.
Reaction Rate (products/s)
Reaction Rate vs Time as Substrate
Concentration Increases
1000
900
800
700
600
500
400
300
200
100
0
0
1
2
3
4
5
6
7
8
Time (sec)
THREE
Increasing the temperature of a solution/within an environment where enzymes and
substrates react affect both their interaction and the structure and function of the
enzyme. Increased temperature facilitates greater kinetic energy, which makes
collisions of enzymes and substrates more likely. As such, the rate of reaction will
increase. Enzymes have optimal temperatures that they work best in. However, an
enzyme will denature if the temperature is too high; their structure will change and
make their active sites unsuitable to binding enzymes. Their ability to turn reactants
into products will decrease. As seen in the graph below, higher temperatures are
favorable until the point of denaturation, when the temperature is high enough to
alter the shape of the enzyme.
Reaction Rate (products/sec)
Reaction Rate vs Temperature
600
500
400
300
200
100
0
23
28
Temperature (˚C)
33
FOUR
Increasing the pH of the environment also changes the way enzymes interact, and
their structure and function. Similarly to temperature, different types of enzymes
have different optimal pH levels. Usually, if a solution/the environment is too acidic
or basic, the enzyme’s structure will change (denaturation), resulting in a worse
ability to catalyze reactions. A neutral pH (pH 7) is usually suitable; however, as the
earth’s ancient oceans are speculated to be slightly acidic, a pH level between 5-7
can be optimal too. The more acidic pH could alter the active sites to bind better to
substrates (an example would be the peroxidase enzyme, which seems to work best
at a slightly acidic pH). In the graph below, the enzyme works best at pH7, and is
denatured to a point where they are less effective when out of the range of pH 5-8.
FIVE
Competitive inhibitors do not change the structure of the enzymes themselves, but
are imitate the structure of the substrate. Its function is to inhibit the substrates
from attaching to the active site. Examples are toxins/poisons such as sarin. The
Rate of Reaction vs Time
with Inhibitors
30
25
20
15
10
5
0
0
2
4
6
8
Total # Products Made
Total # of Product Made
Rate of Reaction vs Time
Without Inhibitors
Time (sec)
interaction between competitive inhibitors affect the
structure of an enzyme; now, substrates can no
longer bind because there is only one active site,
now taken up by the inhibitor. It also affects the
function; the enzyme is no longer able to act as a
catalyst for reactants for the while the inhibitor is
stuck on the active site. Increasing the number of
substrates can help increase the reaction rate, as
there are more substrates to compete with the
competitive inhibitors for an active site. Competitive
inhibitors slow the rate of reaction.
SIX:
Allosteric inhibitors regulate the amount of
products enzymes catalyze from reactants. They are
especially useful for metabolic pathways that
30
25
20
15
10
5
0
0
5
Time (sec)
10
involve multiple products being generated, which are used for reactants in the next
step of the pathway. Allosteric inhibitors ensure that there is the right amount of
reactants and products to ensure maximum pathway efficiency. A picture from the
textbook on the right shows how they work. Interactions of enzymes with allosteric
inhibitors affect their structure; they change their shape so they are stabilized and
don’t need a substrate in their active site for that purpose. Their function alters too;
they can no longer catalyze substrates due to their stable form and shape. Their
active sites are occupied. They can only take up substrates when inhibitors dissociate
from the enzyme. This slows the rate of reaction. Refer to the graphs above to
compare reaction rate; the rate for competitive and allosteric regulators compare
approximately equally to the rate of reaction without inhibitors.
SEVEN
Cofactors are nonproteins assisting the process of catalytic activity. They can be
inorganic or organic; examples are vitamins. They can either bind tightly and
permanently (covalently) to enzymes or loosely and reversibly to substrates with
weaker bonds; either way of interacting with these two will have the same results.
They serve to increase the rate of reaction; for example, their interaction with
substrates may involve shifting the substrates to be in cloze proximity to enzymes,
and their interaction with enzymes helps the enzyme better recognize and
attract/repulse a substrate.
Rate of Reaction With
Cofactors
50
40
30
20
10
0
0
2
4
Time (sec)
6
8
Total # of Products Made
Total # of Product Made
Rate of Reaction Without
Cofactors
50
40
30
20
10
0
0
2
4
Time (sec)
6
8