BMSC11002 Lecture Notes - Lecture 2: Lipoprotein, Defecation, Deoxyribose
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WEEK 2: CHEMICAL LEVEL OF ORGANISATION
2.5 ORGANIC MOLECULES ARE LARGE CARBON-BASED MOLECULES
• Macromolecules – large organic molecules formed from smaller organic molecules
o They are usually polymers – a polymer is a large molecule formed by the covalent bonding of many
identical or similar small building-block molecules called monomers
o Usually the reaction that joins two monomers is a dehydration synthesis
▪ The hydrogen atom is removed from one monomer and a hydroxyl group is removed from the
other to form a molecule of water
o Macromolecules such as carbohydrates, lipids, proteins, and nucleic acids are assembled in cells via
dehydration synthesis reactions
2.6 CARBOHYDRATES ARE BUILDING
BLOCKS AND SOURCES OF ENERGY
• Carbohydrates include sugars,
glycogen, starches and cellulose
Carbohydrates can be represented by
the stoichiometric formula (CH2O)n,
where n is the number of carbons in
the molecule. Therefore, the ratio of
carbon to hydrogen to oxygen is 1:2:1
in carbohydrate molecules. The origin
of the term "carbohydrate" is based on
its components: carbon ("carbo") and
water ("hydrate"). Carbohydrates are
classified into three subtypes:
monosaccharides, disaccharides, and
polysaccharides.
Monosaccharides
Monosaccharides (mono- = "one";
sacchar- = "sweet") are simple sugars
. In monosaccharides, the number of
carbons usually ranges from three to
seven. If the sugar has an aldehyde
group (the functional group with the
structure R-CHO), it is known as an
aldose, and if it has a ketone group
(the functional group with the
structure RC(=O)R'), it is known as a
ketose. Depending on the number of
carbons in the sugar, they also may be known as trioses (three carbons), pentoses (five carbons), and
or hexoses (six carbons). Monosaccharides can exist as a linear chain or as ring-shaped molecules; in
aqueous solutions they are usually found in ring forms.
Monosaccharides
Monosaccharides are classified based on the position of their carbonyl group and the number of carbons
in the backbone. Aldoses have a carbonyl group (indicated in green) at the end of the carbon chain, and
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ketoses have a carbonyl group in the middle of the carbon chain. Trioses, pentoses, and hexoses have
three, five, and six carbon backbones, respectively.
Common Monosaccharides
Glucose (C6H12O6) is a common monosaccharide and an important source of energy.
During cellular respiration, energy is released from glucose and that energy is used to help
make adenosine triphosphate (ATP). Plants synthesize glucose using carbon dioxide and water, and
glucose, in turn, is used for energy requirements for the plant.
Galactose (a milk sugar) and fructose (found in fruit) are other common monosaccharides. Although
glucose, galactose, and fructose all have the same chemical formula (C6H12O6), they differ structurally
and stereochemically. This makes them different molecules despite sharing the same atoms in the same
proportions, and they are all isomers of one another, or isomeric monosaccharides. Glucose and
galactose are aldoses, and fructose is a ketose.
Disaccharides
Disaccharides (di- = "two") form when two monosaccharides undergo a dehydration reaction (also known
as a condensation reaction or dehydration synthesis). During this process, the hydroxyl group of one
monosaccharide combines with the hydrogen of another monosaccharide, releasing a molecule of water
and forming a covalent bond. A covalent bond formed between a carbohydrate molecule and another
molecule (in this case, between two monosaccharides) is known as a glycosidic bond . Glycosidic bonds
(also called glycosidic linkages) can be of the alpha or the beta type.
Disaccharides
Sucrose is formed when a monomer of glucose
and a monomer of fructose are joined in a
dehydration reaction to form a glycosidic bond.
In the process, a water molecule is lost. By
convention, the carbon atoms in a
monosaccharide are numbered from the
terminal carbon closest to the carbonyl group.
In sucrose, a glycosidic linkage is formed
between carbon 1 in glucose and carbon 2 in
fructose.
Common Disaccharides
Common disaccharides include lactose,
maltose, and sucrose. Lactose is a
disaccharide consisting of the monomers
glucose and galactose. It is found naturally in
milk. Maltose, or malt sugar, is a disaccharide formed by a dehydration reaction between two glucose
molecules. The most common disaccharide is sucrose, or table sugar, which is composed of the
monomers glucose and fructose.
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Polysaccharides
A long chain of monosaccharides linked by glycosidic bonds is known as a polysaccharide (poly- =
"many"). The chain may be branched or unbranched, and it may contain different types of
monosaccharides. Starch, glycogen, cellulose, and chitinare primary examples of polysaccharides.
Plants are able to synthesize glucose, and the excess glucose is stored as starch in different plant parts,
including roots and seeds. Starch is the stored form of sugars in plants and is made up of glucose
monomers that are joined by α1-4 or 1-6 glycosidic bonds. The starch in the seeds provides food for the
embryo as it germinates while the starch that is consumed by humans is broken down by enzymes into
smaller molecules, such as maltose and glucose. The cells can then absorb the glucose.
Common Polysaccharides
Glycogen is the storage form of glucose in humans and other vertebrates. It is made up of monomers of
glucose. Glycogen is the animal equivalent of starch and is a highly branched molecule usually stored in
liver and muscle cells. Whenever blood glucose levels decrease, glycogen is broken down to release
glucose in a process known as glycogenolysis.
Cellulose is the most abundant natural biopolymer. The cell wall of plants is mostly made of cellulose
and provides structural support to the cell. Cellulose is made up of glucose monomers that are linked by
β 1-4 glycosidic bonds . Every other glucose monomer in cellulose is flipped over, and the monomers are
packed tightly as extended long chains. This gives cellulose its rigidity and high tensile strength—which
is so important to plant cells.
Polysaccharides
In cellulose, glucose monomers are linked in
unbranched chains by β 1-4 glycosidic linkages.
Because of the way the glucose subunits are joined,
every glucose monomer is flipped relative to the next
one resulting in a linear, fibrous structure.
Carbohydrate Function
Carbohydrates serve various functions in different
animals. Arthropods have an outer skeleton,
the exoskeleton, which protects their internal body parts. This exoskeleton is made of chitin, which is a
polysaccharide-containing nitrogen. It is made of repeating units of N-acetyl-β-d-glucosamine, a
modified sugar. Chitin is also a major component of fungal cell walls.
Benefits of Carbohydrates
Biological macromolecules are large molecules that are necessary for life and are built from
smaller organic molecules. One major class of biological macromolecules are carbohydrates, which are
further divided into three subtypes: monosaccharides, disaccharides, and polysaccharides .
Carbohydrates are, in fact, an essential part of our diet; grains, fruits, and vegetables are all natural
sources of carbohydrates. Importantly, carbohydrates provide energy to the body, particularly through
glucose, a simple sugar that is a component of starch and an ingredient in many basic foods.
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Document Summary
Blocks and sources of energy: carbohydrates include sugars, glycogen, starches and cellulose. Carbohydrates can be represented by the stoichiometric formula (ch2o)n, where n is the number of carbons in the molecule. Therefore, the ratio of carbon to hydrogen to oxygen is 1:2:1 in carbohydrate molecules. The origin of the term carbohydrate is based on its components: carbon (carbo) and water (hydrate). Carbohydrates are classified subtypes: monosaccharides, disaccharides, and polysaccharides. three into. Monosaccharides (mono- = one; sacchar- = sweet) are simple sugars. In monosaccharides, the number of carbons usually ranges from three to seven. If the sugar has an aldehyde group (the functional group with the structure r-cho), it is known as an aldose, and if it has a ketone group (the the structure rc(=o)r"), it is known as a ketose. Depending on the number of carbons in the sugar, they also may be known as trioses (three carbons), pentoses (five carbons), and or hexoses (six carbons).
