INTRODUCTION TO DIAGNOSTIC MOLECULAR BIOLOGY prepared by Mr. John Kimbe (BMLS)

1. INTRODUCTION TO DIAGNOSTIC
MOLECULAR BIOLOGY
MLT06105
John Kimbe (BMLS)

2. Definitions of terms
• Molecular Biology refers to study of biology at
molecular level
• Molecular diagnosis is a collection of
techniques used to analyze biological
markers in the genome and proteome, and
how their cells express their genes as proteins,
applying molecular biology to medical testing

3. • Molecular biology
This is the branch of biology that studies the molecular basis
of biological activities, including bio molecular synthesis,
modification, mechanisms and interactions.
• Genes
A gene is a basic physical and functional unit of heredity. They
contain information for making specific molecules and
proteins that allow human cells to function and that control
how the body grows and operates. Genes are made up of DNA
• Genome
The genome is the entire set of DNA instructions found in a
cell. In humans, the genome consists of 23 pairs of
chromosomes.

4. • Chromosomes
Chromosomes are thread like structures located inside the
nucleus of animal and plant cells. Each chromosome is made
up of protein and a single molecule of deoxyribonucleic
acid(DNA).
They all have a short arm and long arm separated by a
primary constriction called the centromere. The short arm is
designated as p and the long arm as q .
• Centromere
The centromere is the location of spindle attachment and is
an integral part of the chromosome. It is essential for the
normal movement and segregation of chromosomes during
cell division

5. Chromosomes come in three basic shapes and can be
categorized according to the length of the short and long
arms and also the centromere location:
i. Metacentric chromosomes have short and long arms
of roughly equal length with the centromere in the
middle.
ii. Sub metacentric chromosomes have short and long
arms of unequal length with the centromere more
towards one end.
i. Acrocentric chromosomes have a centromere very
near to one end and have very small short arms.
ii. Telocentric chromosome is a chromosome whose
centromere is located at one end. The centromere is
located very close to the end of the chromosome that
the p arms would not, or barely, be visible.

7. • Each species has a normal diploid number of
chromosomes. Cytogenetically normal humans,
for example, have 46 chromosomes (44
autosomes and two sex chromosomes
• Germ cells (egg and sperm) have 23
chromosomes: one copy of each autosome plus a
single sex chromosome. This is referred to as the
haploid number. One chromosome from each
autosomal pair plus one sex chromosome is
inherited from each parent

8. • Nucleic acids
Nucleic acids are biopolymers, macromolecules, essential
to all known forms of life. They are composed of
nucleotides made of three components; a 5 carbon sugar,
a phosphate group and a nitrogenous base. The two main
classes of nucleic acids are deoxyribonucleic acid and
ribonucleic acid.
• Nucleosome
Nucleosome is the basic structural unit of DNA packaging
in eukaryotes. The structure of a nucleosome consists of a
segment of DNA wound around eight histone proteins
and resembles a thread wrapped around a spool

10. • Nucleotide
Nucleotides are organic molecules consisting of a nucleoside
and a phosphate, they are the basic building blocks of nucleic
acids
• Nucleoside
Nucleosides are glycosylamines. They are nucleotides without
a phosphate group. They simply consists of a nitrogenous base
( purine or pyrimidine ) and a five-carbon sugar.( 2-
deoxyribose in DNA and Ribose in RNA )
• Oligonucleotide
Oligonucleotides are short, single strands of synthetic DNA or
RNA. The most common use of oligonucleotide is as primers
for PCR

13. • A nucleotide or a nucleoside phosphate is formed by the
attachment of a phosphate to the 5’ position of a nucleoside by an
ester linkage. Such nucleotide can be joined together by the
formation of the second ester bond by reaction between the
phosphate of one nucleotide and the 3’ hydroxyl of another, thus
generating a 5’ to 3’ phosphodiester bond between adjacent sugars;
this process can be repeated indefinitely to give long polypeptide
molecules.
• DNA has two such polynucleotide strands; however since each
strand has both a free 5’ hydroxyl group at one end and a free 3’
hydroxyl at the other end, each strand has a polarity and
directionality. The polarity of the two strands of the molecule is in
opposite direction, and thus DNA is described as an antiparallel
structure.

14. • DNA
Deoxyribonucleic acid is a polymer composed of two
polynucleotide chains that coil around each other to form
a double helix carrying genetic instructions for the
development, functioning, growth and reproduction of all
known organisms and many viruses.
• RNA
Ribonucleic acid is a nucleic acid present in all living cells
that has structural similarities to DNA. Unlike DNA, RNA is
most often single-stranded. An RNA molecule has a
backbone made of alternating phosphate groups and the
sugar ribose, rather than the deoxyribose found in DNA

15. • cDNA
Complementary DNA is a DNA synthesized from a
single stranded RNA template in a reaction
catalysed by the enzyme reverse transcriptase.
• bDNA
B-DNA is the term given to the conical right-handed
DNA helix that is the most common form of DNA.
Conical B-DNA is a double helix made of two
antiparallel strands that are held together via
hydrogen bonding in the AT and GT base pairs.

16. • Codon ( genetic code )
The genetic code is the set of rules used by living
cells to translate information encoded within
genetic material into proteins.
• Anti-codon
An anticodon is a trinucleotide located at one
end of a transfer RNA (tRNA) molecule, which is
complementary to a corresponding codon in a
messenger RNA (mRNA) sequence

17. • mRNA
Messenger RNA is a single stranded molecule of
RNA that carries codes from the DNA in the
nucleus to the site of protein synthesis in the
cytoplasm (the ribosomes).
• tRNA
Transfer RNA is a small RNA molecule that
serves as the physical link between the mRNA
and the amino sequence of proteins.

18. SIGNIFICANCE OF DIAGNOSTIC
MOLECULAR BIOLOGY