2. INTRODUCTION
A gene is a specific sequence of DNAcontaining
genetic information required to make a specific
protein
Prokaryotic gene is uninterrupted.
In Eukaryotic gene the coding sequences (exon)are
seprated by non-coding sequences called introns.
In complex eukaryotes, introns account for more than
10 times as much DNA as exons.
3. What is a gene?
•The gene is the
Functional unit of
Heredity.
•Each gene is a segment of DNA that give rise to a
protein product or RNA.
•A gene may exist in alternative forms called alleles.
•Chromosome in fact carry genes.
•Each chromosome consists of a linear array of genes.
4. History of genes:
The classical principles of genetics were deduced by
Gregor Mendel in 1865 on the basis of breeding experiments
with peas. He assumed that each trait is determined by a
pair of inherited ‘factors’ which are now called gene.
Mendel’s work was rediscovered in 1900 by Hugo de
Vries,Correns and Tschermak
Wilhelm Johannsen coined the term ‘GENE’ in 1909.
William Bateson in 1905 coined the term genetics.
5. In 1972,Walter Fiers and his team determined the sequence
of a gene in bacteriophage MS2 coat protein.
Richard J Roberts and Phillip Sharp found the gene can
be split into segments making it possible that a single gene
might be coding for several proteins.
6. STRUCTURE OF GENE
• Genes are encoded within long strands of DNA strands.
• DNA consist of nucleotide monomers, which are
comprised of a pentose sugar (Deoxyribose), a
phosphate group, and either one of of the four
nitrogenous bases: Adenine (A), Thymine (T), Cytosine
(C), or Guanine (G).
• So, a gene is comprised of a code of an assortment of
ATCG nucleotides.
7. • Gene sequences are not entirely comprised of protein
coding; however, most of the gene is composed of repeats
and untranslated regions necessary for gene expression
regulation. These repeats are termed as introns, while
protein coding sequences of the gene are named exons.
8. PROKARYOTIC GENE STRUCTURE
• Prokaryotic gene structure is the organization of the
prokaryotic genes in the genome. The most significant
feature of the prokaryotic gene organization is the presence
of polycistronic operon, which are the clusters of genes with
related functions. Therefore, the genes responsible for a
particular function can be regulated altogether under a
single promoter in prokaryotes.
9. EUKARYOTIC GENE STRUCTURE
Eukaryotic gene structure the most significant feature is the presence of
introns between the ORF, breaking it into pieces called exons. Only exons
will remain in the mature mRNA as the removal of introns occurs during the
post-transcriptional modifications in a process called RNA splicing.
Generally, introns sequences are longer than exon sequences. Once spliced
out, the eukaryotic mRNA contains a single, continuous protein-coding
region. Apart from that, a 5’ cap and a 3’ poly A tail are added to the
eukaryotic mRNA to increase the stability.
10. Continued..
• Prokaryotes, eukaryotic genes do not form clusters
regulated by the shared regulatory elements. In addition,
each eukaryotic gene has its own promoter and other
regulatory elements. Therefore, the eukaryotic mRNA
always contains a single open reading frame.
11.
12. Similarities Between Prokaryotic and
Eukaryotic Gene Structure:
• Both are made up of DNA and in the double-
stranded molecule, one of the two strands
(sense strand) encodes the information of a
gene.
• Also, both types of gene structure contain
common elements due to the shared ancestry of
cellular life.
• in both, the open reading frame of the gene
structure runs in the 5’ to 3’ direction.
13. FEW GENE RELATED TERMS
Cistron:
It is the largest element in a gene which
encodes a polypeptide during protein
synthesis. The term “cistron” refers to a test
called cis-trans test, which is similar to a
complementation test. The term “cistron” is
a unit of function.
Recon:
They are locations within a gene which
participate in recombination. There is a
minimum distance between recons within a
gene, and recombination cannot occur
within a recon. The term “recon” is a unit
of recombination.
Muton:
They are elements within a gene that can
undergo a mutation and lead to the
production of mutant phenotype. The term
“muton” is a unit of mutation.
14. Functions of genes:
• Genes control the morphology or phenotype of individuals.
• Replication of genes is essential for cell division.
• Genes carry the hereditary information from one generation to the next.
• They control the structure and metabolism of the body.
• Reshuffling of genes at the time of sexual reproduction produces
variations.
• Different linkages are produced due to crossing over of genes.
• Genes undergo mutations and change their expression.
• Development or production of different stages in the life history is
controlled by genes.
• Genes consist of a particular set of instructions or specific functions. For
example, the globin gene was instructed to produce haemoglobin.
Haemoglobin is a protein that helps to carry oxygen in the blood.
