BABA SAHEB BHIM RAO AMBEDKAR UNIVERSITY

GENE ORGANISATION IN MICROBEBY :- PRASHANT TRIPATHI

M.SC[INDUSTRIAL MICROBIOLOGY]BBAU

GENE ORGANISATION• The word “genome,” coined by German botanist

Hans Winkler in 1920, was derived simply by combining gene and the final syllable of chromosome.

• An organism’s genome is defined as the complete haploid genetic complement of a typical cell.

• In diploid organisms, sequence variations exist between the two copies of each chromosome present in a cell.

• The genome is the ultimate source of information about an organism.

IN CONTINUATION :-• The number of genomes sequenced in their entirety

is now in the thousands and includes organisms ranging from bacteria to mammals.

• The first complete genome to be sequenced was that of the bacterium Haemophilus influenzae, in 1995.

• The first eukaryotic genome sequence, that of the yeast Saccharomyces cerevisiae, followed in 1996.

• The genome sequence for the bacterium Escherichia coli became available in 1997 .

• The much larger effort directed at the human genome was also accelerating.

PROKARYOTES AND EUKARYOTES GENOME

Prokaryotes EukaryotesSingle cell Single or multi cell

No nucleus Nucleus

One piece of circular DNA Chromosomes

No mRNA post transcriptional modification

Exons/Introns splicing

CHROMOSOME DIFFERENCE [PROKARYOTIC AND EUKARYOTIC CELL]

PROKARYOTIC CELL Lacks a membrane bound nucleus. Circular DNA and supercoiled domain. Histones not present. Prokaryotic genomes generally contains one large circular

piece of DNA refered to as a CHROMOSOME. Some bacteria have linear chromosome. Many bacteria have small circular DNA str. Called PLASMIDS

which can be swapped between neighbours and across bacterial species.

PLASMIDo The term plasmid was first

introduced by the American molecular biologist Joshua Lederberg in 1952.

o A plasmid is separate form, and can replicate independently of, the chromosomal DNA.

o Plasmid size varies from 1 to over 1,000 (kbp).

Classification and types of PLASMID

• Plasmids can be broadly classified into conjugative plasmids and non-conjugative plasmids.•In the complex process of conjugation, plasmid may be transferred from one bacterium to another via sex pili encoded by some of the tra genes.• Non-conjugative plasmids are incapable of initiating conjugation, hence they can be transferred only with the assistance of conjugative plasmids.

Another way to classify plasmids is by function. There are five main classes:

• Fertility F-plasmids, which contain tra genes. They are capable of conjugation and result in the expression of sex pili.

• Resistance (R) plasmids, which contain genes that provide resistance against antibiotics or poisons.

• Col plasmids, which contain genes that code for bacteriocins, proteins that can kill other bacteria.

• Degradative plasmids, which enable the digestion of unusual substances, e.g. toluene and salicylic acid.

• Virulence plasmids, which turn the bacterium into a pathogen.

VIRAL GENOME

A virus has either a DNA or an RNA genome and is called a DNA virus or an RNA virus, respectively. The vast majority of viruses have RNA genomes. Plant viruses tend to have single-stranded RNA genomes and bacteriophages tend to have double-stranded DNA genomes.

IN EUKARYOTES :-The genome of different

eukaroytic cells contains different base pairs.A small fraction of the

total DNA encodes protein.• Many repeats of coding

& non-coding sequences.

All chromosomes are contained in a membrane bound nucleus.

Histone protein is present.

KARYOTYPEo The study of chromosomes, their structure and

their inheritance is known as Cytogenetics.o Each species has a characteristic number of

chromosomes and this is known as karyotype.

GENES – GENETIC INFORMATION• One gene : one enzyme

hypothesis: summarizes that a gene is a stretch of DNA coding for one or more isoforms of a single enzyme.

• One gene : one polypeptide hypothesis: a gene is responsible for the production of a single polypeptide.

• Many genes: one protein:• e.g. Hemoglobin requires

different globin genes.

THANK YOU