Biological Molecules

The Chemical Basis of Animal Life
Naveed Akhtar
Assistant Professor of Zoology
Punjab Higher Education Department
Naveed Akhtar (Assistant Professor of Zoology) 1

Concepts
 Animals are made up molecules which are collection of
atoms bounded to one another
 Carbon is the key element of organic compound because it
has unique physical and chemical characteristics
 Carbohydrate and lipids are main compounds of energy
for most animals
 Protein, nucleotides and nucleic acids provide basic
structure, function, information storage, energy transfer
and genetic regulation for animal life

The Molecules of Life
 BIOMOLECULES
 Biomolecules are molecules that occur naturally in
living organisms.
 Biomolecules include macromolecules like
proteins, carbohydrates, lipids and nucleic acids.
 It also includes small molecules like primary and
secondary metabolites and natural products.
 Biomolecules consists mainly of carbon and
hydrogen with nitrogen, oxygen, sulphur, and
phosphorus.

Carbohydrates
 Carbohydrates are compounds of carbon, hydrogen, and
oxygen
 They are usually present in the ratio of 1 C: 2 H
 Hydrated Carbons
 The general formula Cx(H2O)y is commonly used to
represent many carbohydrates, which means “watered
carbon.”
 Carbohydrates are probably the most abundant and
widespread organic substances in nature, and they are
essential constituents of all living things
 A polyhydroxyaldehyde or polyhydroxyketone, or a
substance that gives these compounds on hydrolysis

Functions of Carbohydrates
 1.Source of Energy:
 Carbohydrates function in protoplasm mainly as structural
elements and as a source of chemical energy
 55-60% of our energy comes from carbohydrates
 Glucose is the most important of these energy storing
carbohydrates.
 Living organisms use carbohydrates as accessible energy to
fuel cellular reactions.
 They are the most abundant dietary source of energy
(4kcal/gram) for all living beings.
 Carbohydrates along with being the chief energy source, in
many animals, are instant sources of energy. Glucose is
broken down by glycolysis/ Kreb’s cycle to yield ATP.

 Serve as energy stores, fuels, and metabolic
intermediates. It is stored as glycogen in animals and
starch in plants.
 Stored carbohydrates act as an energy source instead
of proteins.
 2.Structural Components
 They form structural and protective components, like
in the cell wall of plants and microorganisms.
 Structural elements in the cell walls of bacteria
(peptidoglycan or murein), plants (cellulose) and
animals (chitin).

 Carbohydrates are intermediates in the biosynthesis of
fats and proteins.
 Carbohydrates aid in the regulation of nerve tissue and
is the energy source for the brain.
 Carbohydrates get associated with lipids and proteins
to form surface antigens, receptor molecules, vitamins,
and antibiotics.
 Formation of the structural framework of RNA and
DNA (ribonucleic acid and deoxyribonucleic acid).

 They are linked to many proteins and lipids. Such
linked carbohydrates are important in cell-cell
communication and in interactions between cells and
other elements in the cellular environment.
 In animals, they are an important constituent of
connective tissues.
 Carbohydrates that are rich in fiber content help to
prevent constipation.
 Also, they help in the modulation of the immune
system

Sources of Carbohydrates

Classification of Carbohydrates

(Types of Carbohydrates)
 Carbohydrates are usually categorized into the
following three classes;
 1. Monosaccharides
 2. Oligosaccharides
 3. Polysaccharides

Monosaccharides
 Simplest group of carbohydrates and often called simple sugars since
they cannot be further hydrolyzed.
 Colorless, crystalline solid which are soluble in water and insoluble in a
non-polar solvent.
 These are compound which possesses a free aldehyde or ketone
group.
 Sweet in taste
 They are reducing sugars
 The general formula is Cn(H2O)nor CnH2nOn.
 They are classified according to the number of carbon atoms they
contain and also on the basis of the functional group present.
 The monosaccharides thus with 3,4,5,6,7… carbons are called trioses,
tetroses, pentoses, hexoses, heptoses, etc., and also as aldoses or
ketoses depending upon whether they contain aldehyde or ketone
group.

Examples

D and L Sugars

 Monosaccharides in solution are in equilibrium
between the open-chain and ring forms, and exist
primarily in the ring form

Difference between Reducing and
Non reducing Sugars
Reducing Sugars Non Reducing Sugars
Reducing sugars are carbohydrates that
can act as reducing agents due to
presence of free aldehyde or ketone
group
Reducing sugars are carbohydrates that
can not act as reducing agents due to
absence of free aldehyde or ketone
group
Good Reducing Agents Non Reducing Agents
Give positive test towards the Benedict
Test
Give positive test towards the Benedict
Test
All monosaccharides and some
disaccharides including maltose ,
lactose, cellobiose
Most oligosaccharides and all
polysaccharides

Oligosaccharides
 An oligosaccharide (Oligo; "a few“) contains 2-10
monosaccharides units
 Joined together by as pacific bond call Glycosidic Bond or
Glycosidic Linkage
 On hydrolysis, give two to ten monosaccharides
 They are subdivided into different catagories based upon
number of monosaccharides produced on hydrolysis
 Disacchardies
 Trisacchardies
 Tetrasacchardies
 Pentasacchardies

Examples of Oligosacchardies

Disacchardies
 Two monosaccharides can combine to form a disaccharide
(di, two) by removing a molecule of water (dehydration
synthesis)
 Disaccharides all have the same molecular formula,
C12H22O11
 Compounds with the same molecular formula but different
structure are isomers.
 Examples:
 Sucrose = Glucose +Fructose
 Maltose= Glucose Glucose
 Lactose= Glucose+Glactose

Sucrose
 Sucrose (table sugar) is a disaccharide formed by
linking a molecule of glucose to a molecule of fructose

Maltose
 Maltose, two joined glucose subunits, gives barley
seeds a sweet taste
 It is a disaccharide formed from two units
of glucose joined with an α(1→4) glycosidic bond.
28
Naveed Akhtar (Assistant Professor of Zoology)

Lactose
 A glucose molecule bonds to another
monosaccharide, galactose, the resulting
disaccharide is lactose (commonly called milk
sugar).

Ploysaccharides
 Polysaccharides are composed of many molecules
of simple sugars (usually glucose) linked together
in long chains called polymers
 Their empirical formula is usually written
(C6H10O5)n, where n designates the number of
simple sugar subunits contained in the polymer
 They are tasteless
 Non reducing
 On hydrolysis yield many monosacchardies
30
Naveed Akhtar (Assistant Professor of Zoology)

Examples
 Starch is the common form in which sugar is stored in
most plants and is an important food for animals

Glycogen

Cellulose
 ellulose is the main substance in the walls of plant
cells, helping plants to remain stiff and upright

Chitin
 Other biologically important polysaccharides include
chitin (a major component of the exoskeleton of
insects and of crustaceans, such as lobsters and
crabs)

What are lipids?
 Lipids are a heterogeneous group of organic
compounds that are insoluble in water and soluble in
non-polar organic solvents like such as ether, alcohol,
and chloroform.
 They naturally occur in most plants, animals,
microorganisms and are used as cell membrane
components, energy storage molecules, insulation,
and hormones.

Functions of Lipids

Chemical Composition of Lipids
 Lipid molecules are composed primarily of carbon,
hydrogen, and oxygen atoms, although some may
contain small amounts of phosphorus and nitrogen
 They contain a much smaller proportion of oxygen
than do carbohydrates, as the formula for the fat,
tristearin, C57H110O6
 The building blocks of fat molecules are fatty
acids and glycerol.

 What are fatty acids?
 Fatty acids contain long hydrocarbon chains bonded to
carboxyl (±COOH) groups
 Types of Fatty Acids:

Saturated Fatty Acids

Unsaturated Fatty Acids
Two common unsaturated fatty acids are Oleic acid and Linoleic acid

Polyunsaturated fatty acids
 •
 They have at least two double bonds in the carbon
chain
 • Typically come from plants such as olives
 • Tend to be liquid at room temperature
 • It has so many bends that it starts to curve over onto
itself or twist around itself
 Omega-3 and omega-6 fatty acids

Conti…

Types of Lipids
 The three principal groups of lipids are;
 Neutral fats
 Phospholipids
 Steroids

1. Neutral Lipids (Triglycerides)
 Triglycerides are also known as triacylglycerols and
compose 95% of fat in the foods we eat.
 Triglycerides are also the main fats we store in our
body
 Three fatty acid molecules combine with one
glycerol molecule by joining to each of the three
carbon atoms in the glycerol backbone
 Because there are three fatty acids, the resulting fat
molecule is called a triglyceride neutral fat, or
triacylglycerol.

Beef fat, with three Stearic acids

 Although the glycerol portion of every fat molecule is the
same, there are many kinds of fatty acids and, therefore,
many kinds of fats.
 Fatty acid molecules differ in the length of their carbon
chains and in the ways the carbon atoms combine.
 The most common are even-numbered chains of 14 to 20
carbons
 Unsaturated fats have low melting points because
their chains bend at the double bonds and the fat
molecules cannot align closely with one another,
which would lead to solidiﬁcation.
 Consequently, the fat may be ﬂuid at room
temperature.

 A liquid fat is called an oil.
 Most plant fats are unsaturated.
 Animal fats, in contrast, are often saturated and
occur as hard or solid fats.

2. Phospholipid
 A phospholipid molecule is similar to a fat molecule in that
it contains a glycerol portion and fatty acid chains.
However, the phospholipid has only two fatty acid chains
 Phosphate (PO43) and nitrogen-containing groups replace
the third chain.
 The polar phosphate and nitrogen groups are soluble in
water (hydrophilic) and form the “head” of the molecule;
the insoluble (nonpolar, hydrophobic) fatty acid portion
forms the “tail.”
 The phospholipids are amphipathic .
 The hydrophilic end usually contains a negatively charged
phosphate group, and the hydrophobic end usually consists
of two "tails" that are long fatty acid residues.

 The first phospholipid identified in 1847 as such in
biological tissues was lecithin (the most abundant
phopholipid in cell membrane),
or phosphatidylcholine, in the egg yolk of chickens by
the French chemist and pharmacist Theodore Nicolas
Gobley.

 Function of Phospholipids
 Phospholipids are the major structural components of
cell membranes because of this tendency to be soluble
at one end and insoluble at the other.
 They can form lipid bilayers because of
their amphipathic characteristic.
 In eukaryotes, cell membranes also contain another
class of lipid, sterol, interspersed among the
phospholipids.
 The combination provides fluidity in two dimensions
combined with mechanical strength against rupture

3. Steroids
 Steroids are another class of lipid molecules, identifiable
by their structure of four fused rings.
 Although they do not resemble the other lipids structurally,
steroids are included in lipid category because they are also
hydrophobic and insoluble in water.
 Three of the rings are six-sided, and the fourth is ﬁve-sided.
The four rings contain a total of 17 carbons
 Many steroids also have an –OH functional group attached
at a particular site, as shown for cholesterol below; such
steroids are also classified as alcohols, and are thus called
sterols.

 Example:
 Cholesterol, the most common steroid, is mainly
synthesized in the liver and is the precursor to many
steroid hormones.
 These include the sex hormones testosterone and
estradiol, which are secreted by the gonads (testes and
ovaries).
 Cholesterol also serves as the starting material for other
important molecules in the body, including vitamin D and
bile acids, which aid in the digestion and absorption of
fats from dietary sources.
 It’s also a key component of cell membranes, altering their
fluidity and dynamics.

4. Waxes
 Waxes are another biologically important category of
lipids.
 Wax covers the feathers of some aquatic birds and the leaf
surfaces of some plants, where its hydrophobic (water-
repelling) properties prevent water from sticking to, or
soaking into, the surface.
 This is why water beads up on the leaves of many plants,
and why birds don’t get soaked through when it rains.
 Structurally speaking, waxes typically contain long fatty
acid chains connected to alcohols by ester linkages,
although waxes produced by plants often have plain
hydrocarbons mixed in as well.

PROTEINS: THE BASIS OF LIFE’S
DIVERSITY
 What are proteins?
 Proteins are large size and most abundant molecules
(macromolecules), polymers of structural units called
amino acids.
 Proteins always contain atoms of carbon, hydrogen,
nitrogen, oxygen, and sometimes, sulfur
 The individual building blocks of proteins are amino acids
 AminoAcids
 Amino acids always contain an amino group (±NH2), a
carboxyl group (±COOH), a hydrogen atom, and a
functional group, designated R, all bonded to a central
carbon atom:

Continue…
 The nature of the R group linked to the central carbon
atom determines the identity and unique chemical
properties of each amino acid.

Five of the twenty naturally occurring amino
acids

Peptide Bond
 Covalent bonds called peptide bondslink individual
amino acids in chains.
 In the formation of a peptide bond, the carboxyl group
of one amino acid bonds to the amino group of
another amino acid, with the elimination of water (a
dehydration synthesis reaction)
 When two amino acids bond, they form a unit called a
dipeptide; three bonded amino acids form a
tripeptide. When many amino acids bond, they form
a chain called a polypeptide

 In different proteins, the chain of amino acids can vary
from fewer than 50 to more than 2,000 amino acids.
 Each type of protein contains a speciﬁc number and
kind of amino acids arranged in a particular sequence.
 The protein molecule may be coiled and folded, or it
may interact with other protein molecules to form a
unique three-dimensional structure.
 Different kinds of protein molecules have different
shapes related to their particular functions in life
processes

Functions of Protein

Structural Levels of Protein
 A protein is not just a long string of amino acids; it is a
highly organized molecule.
 For convenience, biochemists recognize four levels of
protein organization called primary, secondary, tertiary,
and quaternary structures.
 1. Primary Structure:
 The primary structure is the linear sequence of amino acids
in the polypeptide chains comprising the molecule
 Amino acids are covalently linked by peptide bonds.
 Each component amino acid in a polypeptide is called a
“residue” or “moiety”
 Example: Insulin

2. Secondary Structure

3. Tertiary Structure

4. Quaternary structure

Biological Molecules

More Related Content

What's hot

Similar to Biological Molecules

More from NaveedAkhtar58

Recently uploaded

Biological Molecules