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Chapter 12: Pathways to Biomolecules
____________________ are molecules such as fats and oils, carbohydrates,
proteins and nucleic acids that are found in all living things. They have
an essential role in the supply of energy to the body, the growth and
repair of organs and tissue, the ____________________ of muscles, the activity
of nervous and hormonal systems and the elimination of waste. Many
biomolcules are ____________________.
Fats
Humans can make their own fat ____________________. Though this is not
usually necessary as fat is readily available in the food we eat. Fat is a
name used to describe a large number of ____________________ compounds
belonging to an even larger class of biological molecules called
____________________. Fats and oils are the best known types of lipids.
Oil in food have very different ____________________ and properties from
hydrocarbon oils. Compounds such as ____________________ and steroids
(which include cholesterol) are also ____________________. Lipids are based
mainly on carbon and hydrogen. They also contain small amounts of
oxygen and sometimes some other elements. Most lipids are non-polar
and ____________________ in water.
Fats and oils have very similar chemical structures. They are simply
distinguished on the basis of their physical states at normal
temperatures:
–Fats are ____________________
–Oils are ____________________
Most fats and oils are formed by a ____________________ reaction between a
single molecule of ____________________ and three molecules of fatty acids.
Fatty acids contain a carboxyl functional group which reacts with the
hydroxyl groups in the glycerol. The –COO- groups in fat are
____________________ linkages. Three molecules of water are also produced
in this reaction. Fats and oils formed from this process are called
____________________. Most fats have two or three different fatty acids
attached to the glycerol molecule. Triglycerides are large,
____________________ -polar molecules and therefore are insoluble in
aqueous.
Draw an example of the production of a fat
Fats are distinguishable on the basis of the ____________________ acids from
which they are made:
–____________________ fats are made from fatty acids, such as palmitic acid,
that contain only single carbon-carbon bonds. Saturated fats are
generally unreactive and occur as waxy solids at room temperature.
–____________________ fats are made from fatty acids, such as oleic acid, that
contain one carbon-carbon double bond.
–____________________ fats are made from fatty acids, such as linoleic acid,
that contain more than one carbon-carbon double bond.
Polyunsaturated fats have lower melting temperatures than saturated
fats and often occur at liquids, oils, are room temperature. They are
more reactive than saturated fats.
The different physical states of ____________________ and polyunsaturated
fats are thought to arise because molecules of saturated fats can pack
more ____________________ together, resulting in stronger ____________________
forces between the molecules. The arrangement of the carbon chain
sections at the double bond sites of polyunsaturated fats do not permit
close ____________________. Consequently saturated fats have higher
____________________ points than unsaturated fats.
Chemical digestion of fat does not start until it reaches the small
____________________. There it is mixed with bile, from the gall bladder. Bile
contains ____________________ that convert the fats into an
____________________ of smaller fat globules. This increases the surface area,
meaning it is able to react more rapidly. Secretions from the pancreas
and the walls of the small intestine contain enzymes that
____________________ the hydrolysis of fat into fatty acids and glycerol;
reversing the condensation reaction from which fat was made. Enzymes
in the small intestine operate best under ____________________ conditions.
Once the fatty acids and glycerol have been absorbed into the body, they
are reassembled into triglycerides via condensation reactions. (see page
180).
Condensation and Polymerisation
The monomers used to make polymers by a ____________________
polymerisation reaction have a pair of functional groups that are able to
react together, producing a new functional groups that links
____________________ and also produces a small molecule such as water.
____________________ polymers such as nylon and polyester are formed in
this way, are proteins, DNA, cellulose and starch.
Carbohydrates
The main structural component of all plants is a polymer called
____________________. Cellulose belongs to a class of compounds called
____________________. Green plants in the presence of sunlight, convert
carbon dioxide and water into a number of substances including the
carbohydrate ____________________. CHOs are a source of energy in our
diets. CHOs are made from the element C, H and O and usually have the
formula Cx(H2O)y, where x and y are whole numbers.
CHOs range in size from small molecules, with Mr’s of between
____________________ and 200 to very large polymers with Mr greater than 1
____________________.
Monosaccharides
Are the smallest CHOs. They are white crystalline solids that highly
____________________ in water. Most monosaccharides have a sweet taste.
Monsaccharides together with another group of CHOs called
____________________ are often called sugars. The most abundant
monosaccharide is ____________________.
It has the molecular formula C6H12O6 and the atoms are arranged in a
ring. ____________________ and Galactose have similar structures. All three
of these molecules contain a number of ____________________ OH groups,
enabling them to form hydrogen bonds with water. As a results
monosaccharides are highly ____________________ in water.
Draw the structure of glucose, fructose and galactose
Glucose
Is the key ____________________ source in most forms of life. It is also a
major component of the larger CHOs. Glucose and its polymer, starch,
are more rapidly ____________________ than other forms of food.
Fructose & Galactose
Are not as abundant as glucose. ____________________ is not found in nature
as a free monosaccharide. It occurs frequently as a component of larger
CHOs. ____________________ is found in many fruit juices and honey.
Although fructose is a component of other large biological molecules, its
main role in the body is an energy source.
Disaccharides
Is the carbohydrate formed when ____________________ monosaccharides
undergo a ____________________ reaction. They too dissolve in water, taste
sweet and are called sugars. Maltose is formed when two glucose
molecules react, with the ____________________ of a water molecule. (a on
next slide) Notice how the hydroxyl functional groups react to form the
____________________ and water. The two rings are joined via an oxygen
atom. This linkage is called a ____________________ (or glycosidic) linkage.
Give an example of the production of a disaccharide
____________________ and Sucrose are two other disaccharides. Lactose is
made from a condensation reaction of glucose and ____________________. It
is not as sweet as glucose. Lactose is synthesised in the mammary
glands of mammals and is the main CHO in milk. Sucrose is formed from
a condensation reaction of glucose and ____________________. It is widely
used as a sweetener. It is found in the sap of trees and the juices of many
fruits.
Polysaccharides
Are ____________________ carbohydrates made by linking monosaccharides
into a chain. They are ____________________ of glucose molecules linked
together in different ways by condensation reactions. They are
generally ____________________ in water and have no taste. The three most
important polysaccharides are: glycogen, starch and cellulose.
Glycogen
Is found in animals, where it acts as a glucose ____________________
molecule. As glucose can be ____________________ to produce energy more
rapidly than fat, all glucose is polymerised to glycogen to be stored.
When there is no more storage space for glycogen, the glucose is
converted into fat. As energy is required, the glycogen is hydrolysed to
yield glucose for ____________________.
Starch
The glucose storage molecule in ____________________; the plants equivalent
of glycogen. The starch is stored and used at ____________________ to meet
the plant’s ongoing energy requirements when the glucose production
from ____________________ has ceased.
Digestion
During digestion, the ____________________ must be broken down to release
the glucose monomers. The polymers are first ____________________. This
hydrolysis is catalysed by enzymes; every 2nd glucose is hydrolysed to
produce ____________________. Another enzyme catalyses the hydrolysis of
maltose into glucose, which absorbed into the body. These can be
regarded as the reverse of condensation reactions.
Cellulose
The main ____________________ material in plants. It has a Mr ranging from
50,000 to 2.5 million. Its chemical structure differs from starch and
glycogen because of the ____________________ in the way the glucose
monomers are joined.
Draw the structures for starch and cellulose
Proteins
Proteins are found in every cell and are fundamental to cell
____________________ and operation. There are thousands of different types
of proteins and each has its own purpose.
Proteins are ____________________ built up from monomer molecules called
____________________ acids. Two of the simpler amino acids are glycine and
alanine. Every amino acid has an amine group and a ____________________
group. They have the general formula of H2N-CHZ-COOH. The major
difference between amino acid is the collection of atoms that make up
the ____________________ chain, known as the Z group.
Draw the general structure for an amino acid
As a consequence of the polar amino and carboxyl functional groups;
amino acids are ____________________ in water. In solution, the amino group
can acts as a ____________________, and the carboxyl as an acid. As a result,
the amino acid molecule in a solution at a particular pH will usually be
in the form of +H3N-CHZ-COO-. This sort of molecule is called a
____________________ or dipolar ion.
A proton has been lost from the acidic ____________________ group and the
basic amino group has gained a ____________________. The pH at which an
amino acid exists as a ____________________ depends on the structure of the
Z group. The ____________________ acidic and basic nature of amino acids
means that several different forms of an amino acid can be in
equilibrium in a solution. The predominant form depends on the
____________________ of the solution. In acidic solutions, the +H3N-CHZCOOH form is most abundant, whereas H2N-CHZ-COO- form is most
abundant in alkaline solutions.
The ability of amino acids to react with both acids and bases means that
they can act as ____________________. This means they minimise the effect
that the addition of H+ or OH- ions to a solution would have on acidity.
Protein Structure
When a molecule containing a ____________________ combines with a
molecule containing NH2, a condensation reaction occurs to form an
amide functional group – CONH2-. This links the two molecules.
____________________ is also formed.
Draw a reaction demonstrating an amide linkage
Proteins are ____________________ formed by condensation reactions
between amino acids. During these reactions the amino acids join and
form long unbranched chains. The ____________________ group of one amino
acid reacts with the ____________________ of another. A covalent bond is
formed and a molecule of water is eliminated.
Peptides
Molecules made from amino acids are often called ____________________.
When two amino acid molecules react together it is called a
____________________. When three molecules react and ____________________ is
formed. A polymer made from amino acids is known as a
____________________. Polypeptides built up of more than 50 amino acids
are usually called proteins. The group of atoms –CONH- that links the
amino acids is an amide group, referred to as a ____________________ linkage
in proteins.
The role that any protein fulfils is dependent on its shape. This is
regarded as being made up of a primary, secondary and tertiary
structure.
The order of the amino acids is known as the ____________________
structure. The entire shape of a protein is a consequence of the order in
which the AAs are joined.
Show Primary Structure
Parts of the chain can attract each other creating 3D shapes. This coiling,
folding or pleating of sections is described as the protein’s
____________________ structure.
Show Secondary Structure
The Z groups in the amino acid units of a protein influence the overall
3D shape of the molecule. The Z groups in some amino acids are
relatively large and their size can cause distortions in the protein
structure. Further, some of the side groups are capable of forming bonds
with side groups elsewhere on the protein chain. As a consequence of
such bonds, a variety of protein shapes exist. The overall 3D shape
adopted by the protein is called its ____________________ structure.
Show Tertiary Structure
Enzymes
Many chemical reactions occur more rapidly when a ____________________ is
present. The biological catalysts that accelerate the rate of chemical
reactions in living things are a type of protein called enzymes. Enzymes
control the manufacture of complex substances as well as breaking
down the ____________________ to provide energy.
They are usually more efficient than inorganic catalysts, because they
allow reactions to occur rapidly within the narrow band of temperature
in which life can survive. Compared to ____________________ catalysts:
–Enzymes produce much ____________________ reactions rates: they can
increase the rate of a reaction by as much as 1010 times.
–Enzymes operate under ____________________ conditions.
–Enzymes are more ____________________: The catalytic activity of many
enzymes is destroyed when they are heated strongly because their
delicate structure breaks down. The enzyme is then described as being
denatured.
–Enzymes are very ____________________.
The catalytic activity of an enzyme depends on its ____________________
structure. A slight change in its 3D shape can render an enzyme
inoperative. The active site of an enzyme is usually a flexible hollow or
cavity within the molecule. Some enzymes have small, non-protein parts
called ____________________, such as vitamins or metal atoms associated
with the active site. These cofactors are necessary for catalytic effect.
The Lock and Key Process
A reactant molecule, known as the ____________________, is manoeuvred
into the active site. Here, at the surface of the enzyme the reaction takes
place. The steps are as follows:
1.The ____________________ (substrate) enters the active site.
2.Bonds formed between the enzyme and substrate ____________________
bonds within the substrate, thus lowering the reaction’s activation
energy.
3.The substrate breaks or ____________________ into new products and
these products are released.
Draw a diagram the demonstrates the lock and key process
Typically reactions occur at a rate of 1000/second on an active site.
During respiration the enzyme catalyses the decomposition of 600000
____________________ acid molecules into carbon dioxide and water each
second. In many cases the substrate and enzyme bind together because
part of the substrate and active site are non polar and so dispersion
forces are significant.
In other cases, the substrate is held in place by the attraction between
positive and ____________________ charges, attraction of a metal ion in the
enzyme to a negative dipole in the substrate, or hydrogen bonding
between enzyme and substrate. The selectivity of enzymes is one of
their most important features. This selectivity arises because the shape
and ____________________ groups in the active site of the enzyme allow it to
bind only with certain substrates. (Thus the lock and key process).
Some of the bonds that can occur between the substrate and enzyme
include:
–Ion-____________________ interactions
–____________________ bonds
–Ionic interactions
–____________________ forces and dipole-dipole interactions may also be
involved as an enzyme-substrate complex forms.
Denaturation
The bonds responsible for holding the protein chains in particular
shapes are often weak, so slight changes can disrupt the attractions
between parts of the chain. This causes the chain to ____________________
and render the protein ineffective. A change that destroys the biological
ability of a protein is called ____________________. It may result due to an
increased temperature, a change in pH or the addition of chemicals.
____________________ activity is dependent on temperature. As temperature
____________________, the rate of reaction catalysed by the enzyme increases
because of increased collisions between enzyme and substrate, until an
optimum temperature of 40°C is reached. As there is further
temperature ____________________, the protein is denatured and the
reaction rate rapidly ____________________.
Enzymes operate effectively within a small ____________________ range. Not
all enzymes have the same optimum pH. The ionisation of amino acids is
depended on pH. The bonds that determine the ____________________
structure of the enzyme are altered as change in pH alter the ionisation
of the amino acid ____________________ in the protein.
Once a protein has been denatured, the unfolded chains tend to form
randomly looped structures which come into close contact. The chains
become ____________________ and bond with each other, often by disulfide
bridges, so that large clumps of protein molecules are formed. This
process is called ____________________.
Draw a picture the demonstrates both denaturation and coagulation
The body’s natural defences produce proteins called ____________________
in the fight against infection caused by bacteria or viruses. These
antibodies are specific to a particular disease. The cells in diseased or
damaged body organs may release specific proteins that are unique to
that ____________________.
A raised level of these marker ____________________ in a patient’s blood or
tissue can be used to:
–____________________ a disease at early or advanced stages of
development.
–____________________ the progress of the disease.
–____________________ the effectiveness of treatment.
–____________________ for the recurrence of the disease.
A heart attack is caused when the blood supply to a part of the heart
muscle is blocked by a clot in one of the cardiac arteries. The cardiac
cells are starved of oxygen and nutrients and are consequently injured
or die. The cells in the damaged part of the heart muscle release various
cardiac ____________________ into the bloodstream. Blood levels of these
enzymes increase within a few hours after a heart attack and drop back
to normal after several days.
Cancer is an uncontrolled growth of cells. It is initially diagnosed by
digital examination and by measuring the level of a protein in the blood.
Normally a small amount of this protein is present in the blood.
Abnormal cancerous or non-cancerous cell growths block the ducts in
the prostate, forcing more of this protein into the bloodstream. The
concentration of this protein in the blood is used as a marker for
possible prostate cancer.