Introduction to Molecular Cell
Biology
Molecules of Life
Dr. Fridoon Jawad Ahmad
HEC Foreign Professor
King Edward Medical University
Visiting Professor LUMS-SSE
Rules
No Talking & Phone Usage
Questions Welcome During & After Lecture
One hour lecture
Animation
Building Blocks of Life
Macromolecules
Macromolecules are polymers constructed by the
formation of covalent bonds between smaller
molecules called monomers
Monomers are joined by
condensation reactions,
which release a molecule
of water for each bond
formed.
Hydrolysis reactions use
water to break polymers
into monomers.
Condensation and Hydrolysis
Proteins: Polymers of Amino Acids
The functions of proteins include support,
protection, catalysis, transport, defense, regulation,
and movement.
The side chains, or R groups, of amino acids may be
charged, polar, or hydrophobic; there are also
special cases, such as the —SH groups of cysteine,
which can form disulfide bridges.
The side chains give different properties to each of
the amino acids
Proteins: Polymers of Amino Acids
Amino acids are
covalently bonded
together into
polypeptide chains
by peptide linkages,
which form by
condensation
reactions between
the carboxyl and
amino groups
Partial double bond
Amino Acids
Proteins: Structure
Primary Structure: the sequence of amino acids
bonded by peptide linkages (Diversity 20n)
Secondary Structure: α helices and β pleated sheets
(maintained by hydrogen bonds between atoms of
the amino acid residues)
The Relative Size
of the Visible
Universe
Proteins: Structure
Tertiary Structure: Generated by bending and folding
of the polypeptide chain
1) Covalent disulfide bridges, 2)Hydrophobic
interactions 3) van der Waals forces 4) Ionic bonds
Proteins: Structure
Weak chemical interactions are important in the
three-dimensional structure of proteins and in their
binding to other molecules
Proteins: Denaturation
Proteins are denatured by heat, alterations in pH, or
certain chemicals lose their tertiary and secondary
structure as well as their biological function.
Renaturation is not often possible.
Carbohydrates: Sugars and Sugar
Polymers
They act as source of energy that can be
transported
They also have structural role
Monosaccharides
Disaccharides
Oligosaccharides (3-20)
Polysaccharides
Monosaccharides
Produced by plants, all living cells have glucose
Glucose exists in two forms (ring more stable 99%)
Glycosidic linkages
Covalently link monosaccharides into larger units
such as disaccharides, oligosaccharides, and
polysaccharides (either α or β orientation in space).
Digestible
Polysaccharides
Starch: Glucose polysaccharide α Linkages, (Hydrophilic)
Glycogen: Glucose polysaccharide Branched (storage)
Cellulose: Glucose polysaccharide β Linkages
(chemically more stable because of β-glycosidic
Linkages can withstand harsh enviornments)
Polysaccharides
Modified Carbohydrates
Lipids: Diverse Hydrocarbons
Water insoluble due to nonpolar covalent bonds
Hydrophobic molecules aggregate together (by
hydrophobic and Van der Waals force)
1) Store energy
2) Phospholipids form cell membranes
3) Carotenoids help plants capture light energy
4)Steroids are hormones and vitamins
5) Animal fat is thermal insulator
6) Insulation of nerves
7) Water repellant for skin, fur and feathers
Lipids: Synthesis
Fats and oils are triglycerides, composed of three
fatty acids covalently bonded to a glycerol molecule
by ester linkages.
Lipids: Saturated and unsaturated
Saturated fatty acids have a
hydrocarbon chain with no
double bonds.
The hydrocarbon chains of
unsaturated fatty acids have
one or more double bonds
that bend the chain, making
close packing less possible.
Phospholipids
Lipids in Aqueous Cell Environment
The interactions of the hydrophobic tails and
hydrophilic heads of phospholipids generate a
phospholipid bilayer that is two molecules thick. The
head groups are directed outward, where they
interact with the surrounding water. The tails are
packed together in the interior of the bilayer.
Lipid Vitamins Signals
Nucleic
Acids
The DNA Polymer
DNA Double Helix has Uniform Width
Information in Sequence not Shape
RNA Genetic Material and Enzyme
There are a number of RNA-dependent RNA
polymerases that use RNA as their template for
synthesis of a new strand of RNA.
A number of RNA viruses (such as poliovirus) use
this type of enzyme to replicate their genetic
material
Hydroxyl groups make RNA less stable than DNA
because it is more prone to hydrolysis
RNA Genetic Material and Enzyme
Many viruses use RNA as their hereditary material
RNAs can achieve chemical catalysis, like enzymes
e.g. in ribosome the active site is composed entirely
of RNA (peptide bond formation)
RNA Can Have
Information in
Sequence and
Shape