description of dna structure

DNA molecule is a double helical structure made of deoxyribo nucleotides. RNA is also present in nucleus as well as cytoplasm. DNA is the major source of genetic information which is copied into RNA molecules (transcription). The sequence of nucleotides contains the '..

The most significant feature of DNA molecule is its capacity to make its own identical copies. This property is called replication. It occurs regularly during the synthetic phase of the cell cycle, every time a cell divides. During replication, the DNA molecule unwinds itself fr..

This is nothing but the double helical structure described by Watson and Crick. It has 10 base pairs in each tur..

Formation of Polynucleotide Each DNA molecule has two such polynucleotide chains joined to each other by hydrogen bonds. The hydrogen bonds are between the nitrogenous bases of the opposite nucleotides. If the polynucleotide chains are the sides of the ladder, the bonds can be compared to..

With the exception of a few viruses, DNA forms the genetic material in all living organisms. In the prokaryotic cells DNA occurs in the cytoplasm. In the eukaryotic cells it is confined largely to the nucleus and forms the main component of chromosomes. A small amount of DN..

It is a complex process and involves the participation of over a dozen enzymes and other protein factors. The intertwined DNA starts separating from a particular point and this is known as the origin of replication. The second step is that the two strands of DNA separate, before..

RNA molecule is a single stranded structure made of ribonueleotides. RNA contains the pyrimidine uracil instead of thymine in DNA. RNA is of 3 types, based on the cellular compositio..

fig. 19.3 Structure of Chromosomes The terminal end of a chromosome is called as telomere. It is functionally different from the rest of the chromosome. A chromatid may breakup into pieces and the pieces may rejoin, but no segment becomes connected to the telomere. Thus, the telomere show..

The chromatin material just before cell division forms into chromosomes. Each chromosome is made up of two longitudinal strands called the chromatids. Structure of Chromosome Each chromatid has a double helical DNA molecule. The two chromatids are held together by a structu..

>Plastids are spherical or oval cell organelles found only in plant cells. Plastids are of two types: leukoplasts without any colouring pigments and chromoplasts containing colouring pigments. The most familiar chromoplasts are the chloroplasts containing chlorophyll. Lysosomes are organelles bound..