WHAT IS DNA?

**the process of protein synthesis (translation).

**The length of DNA is usually defined as number of nucleotides (or a pair of nucleotide referred to as base pairs) present in it.

**A nucleotide has three components – a nitrogenous base, a pentose sugar (ribose in case of RNA, and deoxyribose for DNA), and a phosphate group. There are two types of nitrogenous bases – Purines (Adenine and Guanine), and Pyrimidines (Cytosine, Uracil and Thymine). Cytosine is common for both DNA and RNA and Thymine is present in DNA. Uracil is present in RNA at the place of Thymine.

**The backbone in a polynucleotide chain is formed due to sugar and phosphates.

**Also, in RNA the uracil is found at the place of thymine (5-methyl uracil, another chemical name for thymine).

**DNA as an acidic substance present in nucleus was first identified by Friedrich Meischer in 1869. He named it as ‘Nuclein’.

**It was only in 1953 that James Watson and Francis Crick, based on the X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin, proposed a very simple but famous Double Helix model for the structure of DNA. One of the hallmarks of their proposition was base pairing between the two strands of polynucleotide chains.

**a nanometre is one billionth of a metre, that is 10^-9 m.

**In prokaryotes, such as, E. coli, though they do not have a defined nucleus, the DNA is not scattered throughout the cell. DNA (being negatively charged) is held with some proteins (that have positive charges) in a region termed as ‘nucleoid’.

**In eukaryotes, this organisation is much more complex. There is a set of positively charged, basic proteins called histones.

**Histones are rich in the basic amino acid residues lysines and arginines.

**The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called nucleosome

**Euchromatin is said to be transcriptionally active chromatin, whereas heterochromatin is inactive.

**Streptococcus pneumoniae (bacterium responsible for pneumonia)

**some viruses, RNA is the genetic material (for example, Tobacco Mosaic viruses, QB bacteriophage.

**RNA is also now known to be catalytic, hence reactive.Therefore, DNA chemically is less reactive and structurally more stable

when compared to RNA.

**In fact, the presence of thymine at the place of uracil also confers additional stability to DNA.

**RNA was the first genetic material. DNA being double stranded and having complementary strand further resists changes by evolving a process of repair.

**The process of copying genetic information from one strand of the DNA into RNA is termed as transcription.

**Translation refers to the process of polymerisation of amino acids to form a polypeptide

**Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatoria, etc.

**Fungi are also known to form symbiotic associations with plants (mycorrhiza).

**Other bacteria can fix atmospheric nitrogen while free-living in the soil (examples Azospirillum and Azotobacter), thus enriching the nitrogen content of the soil.

**symbiotic association of Rhizobium.

**A biological control being developed for use in the treatment of plant disease is the fungus Trichoderma.

**An example of microbial biocontrol agents that can be introduced in order to control butterfly caterpillars is the bacteria Bacillus thuringiensis (often written as Bt ).

**These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium. These bacteria are also present in the rumen (a part of stomach) of cattle. A lot of cellulosic material present in the food of cattle is also present in the rumen. In rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle.

**Primary treatment : These treatment steps basically involve physical removal of particles – large and small – from the sewage through filtration and sedimentation. These are removed in stages; initially, floating debris is removed by sequential filtration. Then the grit (soil and small pebbles) are removed by sedimentation. All solids that settle form the primary sludge, and the supernatant forms the effluent. The effluent from the primary settling tank is taken for secondary treatment.

**Secondary treatment or Biological treatment : The primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and air is pumped into it. This allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments to form mesh like structures). greater the BOD of waste water, more is its polluting potential. The effluent is then passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment. This sediment is called activated sludge. The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters. Here, other kinds of bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge.

**Statins produced by the yeast Monascus purpureus have been commercialised as blood-cholesterol lowering agents.

**Lipases are used in detergent formulations and are helpful in removing oily stains from the laundry.

**Yeast (Saccharomyces cerevisiae) is used for commercial production of ethanol.

**acid producers are Aspergillus niger (a fungus) of citric acid, Acetobacter aceti (a bacterium) of acetic acid; Clostridium butylicum (a bacterium) of butyric acid and Lactobacillus (a bacterium) of lactic acid.

**Alexander Fleming while working on Staphylococci bacteria, once observed a mould growing in one of his unwashed culture plates around which Staphylococci could not grow. its full potential as an effective antibiotic was established much later by Ernest Chain and Howard Florey. This antibiotic was extensively used to treat American soldiers wounded in World War II. Fleming, Chain and Florey were awarded the Nobel Prize in 1945, for this discovery.

**the same yeast Saccharomyces cerevisiae used for bread-making and commonly called brewer’s yeast, is used for fermenting malted cereals and fruit juices, to produce ethanol.

**the large holes in ‘Swiss cheese’ are due to production of a large amount of CO2 by a bacterium named Propionibacterium sharmanii.

**Lactobacillus and others commonly called lactic acid bacteria (LAB) grow in milk and convert it to curd. During growth, the LAB produce acids that coagulate and partially digest the milk proteins. also improves its nutritional quality by increasing vitamin B₁₂.