Genome organization:
The word " genome," coined by German botanist Hans Winkler in 1920, was derived simply by combining gene and the final syllable of chromosome.
The genome include both the genes and non coding sequences of DNA. An organism's genome is defined as the entire collection of genes and all other functional DNA sequence in a haploid set of chromosomes. It includes structural genes, regulatory genes and non-functional nucleotide sequence. The genome is the ultimate source of information about an organism.
Genes are units of genetic information present on the DNA in the chromosomes and chromatin.
Genome is the entirety of an organisms hereditary organization. It is encoded either in DNA, or for many types of viruses, in RNA.
The number of genome sequenced in their entirety is now in the thousands and includes organism 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, fallowed in 1996. The genome sequence for the bacterium Escherichia coli became available in 1997. The much larger effort directed at human genome was also accelerating.
Prokaryotic Genome:
Prokaryotes are unicellular, one piece of circular DNA without definite nucleus, and there is no post transcriptional modification in prokaryotes.
The genome of E.coli contains amount of base pairs 4x 106 base pairs. Less than 90% of DNA encode protein. lacks a membrane bound nucleus. Circular DNA and suspended domain and there is no histone protein. Prokaryotic genomes generally contain one large circular piece of DNA referred to as a Chromosome( not true chromosome in the eukaryotic sense). Some bacteria have linear chromosomes, but many have small circular, double stranded extra chromosomal self replicating structures called Plasmids which can be swapped between neighbors and across bacterial species.
Plasmids:
The term plasmid was first introduced by the American molecular biologist Joshua Lederberg in 1952.
A plasmid is separate from, and can replicate independently of, the chromosomal DNA. They vary size from 1 to over 1000kbp.
Eukayotic Genome:
The genome of yeast cells contains 1.35x 107 base pairs. A small fraction of the total DNA encodes protein. Many repeats of non-coding sequences. In eukaryote all chromosome contained in a membrane bound nucleus. And DNA is devided between two or more chromosomes. A set of five histone protein help in DNA packaging and gene expression regulation.
It contains fallowing
1.Nuclear DNA :
Nuclear DNA is a DNA contained within the nucleus of the Eukaryotic organisms. It is double stranded and linear and is made up of 3.3 billion DNA base pairs and only two copies of nuclear genome per somatic cells.
It has 20,000-25,000 genes including mitochondrial genes and codes for all proteins required for its function.
Nuclear genome has introns or non-coding DNA and accounts for 93% of total DNA and is inherited equally from both parents.
2. Mitochondrial DNA:
Mitochondrial DNA is a DNA located in mitochondria, that convert chemical energy from the food into the form of that cells can use, ATP. Each mitochondria is estimated to contain 2-10 mt DNA and there are many mitochondria in each of the cells. This DNA is similar to prokaryotic DNA. There are no histones or any other proteins associated with mitochondrial DNA. There is no introns and maternal inheritance. The genome of mitochondria only code for mitochondrial ribosomes and RNAs and some genes code for polypeptide sub units of the electron transport chain common to all mitochondria.
Chloroplast DNA:
Chloroplast DNA are circular, double stranded DNA molecule located in stroma of chloroplast. It is typically 1,20,000-170,000 base pairs long, there is more than one copy of genome in each chloroplast. The chloroplast DNA is not associated with true histone, but a histone chloroplast protein(HC) coded by the chloroplast D
NA that tightly packs chloroplast DNA ring into a nucleoid.
Chloroplasts genomes typically contain 100-200 genes and encode proteins essential for photosynthesis. Post trascriptional RNA processing plays an important role in chloroplast gene expression can also influence the expression of nuclear gene.