Highly repetitive sequence:
The segments of DNA (deoxyribonucleic acid), which are repeated many times in genome, are known as highly repetitive DNA. Highly repetitive sequences are relatively short for each copy, they are ranging from few nucleotides to hundred in length. For example, in humans Alu family sequences found nearly 300bp (base pair) long.
They are very similar to satellite DNA. They are found in a group in a tandem array or mix together in genome. Highly repetitive sequences are do not code for proteins. While studying the DNA renaturation process the highly repetitive DNA renatures earlier due to high the presence of highly complementarity.
Prevalence of highly repetitive sequences seems rather strange to many geneticists:
It seems to be a strange the DNA has no clear function. It is a waste of energy. Maybe the function, we do not know about yet. The evolution also allows the bad things to build up within genomes like genes which cause the diseases.
May be it is another example of the negative consequences of evolution. By this way Prevalence of highly repetitive sequences seems rather strange to many geneticists.
Bacterial chromosome is short DNA (deoxyribonucleic acid) molecule but it lacks protein coat. The DNA is double helix and closed circular in nature. In bacteria chromosome size is
bp (base pairs). In bacterial chromosomal replication three major steps are involved they are initiation, elongation and termination.
Eukaryotes contain multiple pairs of linear chromosomes. In eukaryotes chromosomes are composed of DNA coiled and condensed around nuclear proteins known as histones. They consist of repeated units of chromatin known as nucleosomes. In eukaryotes chromatin not only allows large amount of DNA fit in to a small place, but also helps in regulate gene expression.
Advantages and disadvantages of bacterial and eukaryotic compact structure:
• Bacterial chromosomal DNA is folded in to compact structure, so it occupying relatively small part of the cell.
• Bacterial chromosome is organized into independently supercoiled loops known as domains. Domain allows the chromosomal DNA to undergoing structural changes in cellular process.
• In eukaryotic chromosomes consists complex made up of protein and DNA and organized in condensed manner, it permits the large amount of DNA storage in the nucleus of the cell.
Functions of chromosomes:
Chromosomes store the genetic code and they determine the sex. They control cell division. They are also formation of protiens and storagE.
Bacteria contain one long stranded DNA (chromosome), which is present in the cytoplasm. DNA is ranges from 139 kilo base pairs to 13,000 kilo base pairs. Like eukaryotes bacterial DNA is not packed with histones to form chromatins. It exists as highly compact and super coiled structurE.Two main mechanisms by bacterial DNA become compacted:
Bacterial DNA first mechanism is arranged loop domains and loops of DNA are anchored to DNA-binding proteins. Another mechanism of bacterial DNA is to forming DNA double helix; super coiled to make it more compact like twisting rubber banD.