Description of Nucleic Acids in

relation to Molecular Biology

Definition of terms
Amos Reuben

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Molecular Biology
• Is the branch of biology that studies the molecular basis of biological
activity. or

• Is the discipline of biological sciences that emphasizes on the DNA (gene)

as the focal point (driver) for all cellular characteristics or behaviors.

• Is a branch of biology which concerns the molecular basis of biological

activity between biomolecules in the various systems of a cell, including
the interactions between DNA, RNA, and proteins and their biosynthesis,
as well as the regulation of these interactions

• It has borrowed the concepts from Biochemistry and Genetics.

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Importance of studying diagnostic molecular
biology for a Health Laboratory Personnel
• Early detection of infectious agents.
• Typing of infectious agents
• Improve cases confirmation eg. Infectious agents
• Improve disease surveillance
• Prognosis
• Molecular epidemiology
• Phylogenetic analysis
• Detection of medical conditions – genetically coded e.g.
Cancers, SCD etc.
• In development of molecular based therapy
• In development of vaccines
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Genome
The genome is often described as the information repository
of an organism.

The genome is the entire set of DNA instructions found in a cell.

In humans, the genome consists of 23 pairs of chromosomes

located in the cell’s nucleus, as well as a small chromosome in
the cell’s mitochondria.

A genome contains all the information needed for an individual

to develop and function.

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Gene
• A gene is a basic physical and functional unit of heredity
(inheritance).

• 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

• A unit of heredity which is transferred from a parent to

offspring and is held to determine some characteristic
of the offspring.
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• Genes are passed from parents to offspring and contain the
information needed to specify physical and biological traits.

• If you alter the gene the behavior must also be altered.

• If gene is deleted or knocked out the behavior must also

disappear.
• If the gene is inserted the new behavior must appear.
• If the gene is amplified or duplicated the behavior must
also be duplicated.

• So, Molecular Biology experiments involves a lot of gene

manipulations, such as, gene knock outs, gene insertions, gene
duplication, etc, to study behaviors of cells.
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 Gene transmit
traits to offspring

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Chromosomes
• Are threadlike structures made of protein and a single
molecule of DNA that serve to carry the genomic
information from cell to cell.
• Humans have 22 pairs of numbered chromosomes
(autosomes) and one pair of sex chromosomes (XX or
XY), for a total of 46.
• Each pair contains two chromosomes, one coming from
each parent, which means that children inherit half of
their chromosomes from their mother and half from
their father.

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• The chromosome is located inside the nucleus of animal
and plant cells

• They all have a short arm and a long arm separated by

a primary constriction called centromere.

• The short arm is designated as “p” and the long arm as

“q”

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 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.
iii. Acrocentric chromosomes have a centromere very
near to one end and have very small short arms.
iv. Telocentric chromosome

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• 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.
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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.

• A major function of nucleic acids involves the storage

and expression of genomic information.
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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

• A single nucleosome consists of about 150 base pairs of DNA

sequence wrapped around a core of histone proteins.

• In forming a chromosome, the nucleosomes repeatedly fold in on

themselves to tighten and condense the packaged DNA.
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A nucleotide
• Is the basic building block of nucleic acids (RNA and
DNA).
• A nucleotide consists of a sugar molecule (either ribose
in RNA or deoxyribose in DNA) attached to a phosphate
group and a nitrogen-containing base.
• The bases used in DNA are adenine (A), cytosine (C),
guanine (G) and thymine (T).
• In RNA, the base uracil (U) takes the place of thymine.
• DNA and RNA molecules are polymers made up of long
chains of nucleotides.
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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 )

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• 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.

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• DNA has two such polynucleotide strands; however
since each strand has both a free 5’ phosphate 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.

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Oligonucleotide
• Oligonucleotides are short, single strands of synthetic
DNA or RNA.
• The most common use of oligonucleotide is as primers
for PCR

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A codon
• Is a DNA or RNA sequence of three nucleotides (a trinucleotide) that
forms a unit of genomic information encoding a particular amino acid
or signaling the termination of protein synthesis (stop signals).

• There are 64 different codons: 61 specify amino acids and 3 are used
as stop signals.

• A codon is a DNA or RNA sequence of three nucleotides (a

trinucleotide) that forms a unit of genetic information encoding a
particular amino acid.

• It can also be referred to as the genetic code

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An anticodon
• Is a trinucleotide sequence located at one end of a
transfer RNA (tRNA) molecule, which is complementary
to a corresponding codon in a messenger RNA (mRNA)
sequence.

• Each time an amino acid is added to a growing

polypeptide during protein synthesis, a tRNA anticodon
pairs with its complementary codon on the mRNA
molecule, ensuring that the appropriate amino acid is
inserted into the polypeptide.

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Deoxyribonucleic acid (DNA)
• 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.

• DNA is made of two linked strands that wind around each

other to resemble a twisted ladder — a shape known as a
double helix.

• Each strand has a backbone made of alternating sugar

(deoxyribose) and phosphate groups.
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Cont’d
• Attached to each sugar is one of four bases: adenine
(A), cytosine (C), guanine (G) or thymine (T).

• The two strands are connected by chemical bonds

between the bases: adenine bonds with thymine, and
cytosine bonds with guanine.

• The sequence of the bases along DNA’s backbone

encodes biological information, such as the instructions
for making a protein or RNA molecule.
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Ribonucleic acid (RNA)
• Is a nucleic acid present in all living cells that has
structural similarities to DNA.

• Unlike DNA, however, 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.

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Cont’d
• Attached to each sugar is one of four bases: Adenine
(A), Uracil (U), Cytosine (C) or Guanine (G).

• Different types of RNA exist in cells: messenger RNA

(mRNA), ribosomal RNA (rRNA) and transfer RNA (tRNA).

• In addition, some RNAs are involved in regulating gene

expression. Certain viruses use RNA as their genomic
material.

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Messenger RNA (mRNA)
• Is a type of single-stranded RNA involved in protein
synthesis.

• mRNA is made from a DNA template during the process of

transcription.

• The role of mRNA is to carry protein information from

the DNA in a cell’s nucleus to the cell’s cytoplasm
(watery interior), where the protein-making machinery reads
the mRNA sequence and translates each three-base codon
into its corresponding amino acid in a growing protein chain.
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Transfer RNA (tRNA)
• Is a small RNA molecule that plays a key role in protein
synthesis.

• Transfer RNA serves as a link (or adaptor) between the

messenger RNA (mRNA) molecule and the growing chain of
amino acids that make up a protein.

• Each time an amino acid is added to the chain, a specific

tRNA pairs with its complementary sequence on the mRNA
molecule, ensuring that the appropriate amino acid is
inserted into the protein being synthesized.
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cDNA

• Is synthetic DNA that has been transcribed from a

specific mRNA through a reaction using the enzyme
reverse transcriptase.

• While DNA is composed of both coding and non-coding

sequences, cDNA contains only coding sequences.

• Scientists often synthesize and use cDNA as a tool in

gene cloning and other research experiments.

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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.

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Illustrations

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TASK
• What is a DNA ?
• What is an RNA ?
• What are the differences between the DNA and an
RNA ?

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