DNA vs Chromosome
Nucleic acid constitutes the genetic material of all living organisms. These are polymers made up of sub -units called nucleotides. Nucleotide has three components, a five-carbon sugar, a nitrogen base and phosphoric acid. The nitrogen base is a cyclic compound that can be anyone of the two forms: purines or pyrimidines. There are two types of purines: adenine and guanine, and three types of pyrimidines : thyamin, cytosine and uracil. Different nucleotides are formed according to the sugars and bases used. There are two types of nucleic acids: DNA and RNA. A characteristic that differentiates DNA from RNA is that DNA contains all of the nitrogen bases except uracil. DNA is composed of a polynucleotide chain. Chromosomes, on the other hand, are compiled collections of DNA strands.
Like proteins, DNA can be regarded as having a primary structure, which is the sequence of nucleotides, and a three –dimensional structure. It was first discovered by James Watson and Francis Crick. They described a structure, with two helical antiparallel chains of polynucleotides, held together by pairing of bases through hydrogen bonds. Adenine pairs with thyamin, and guanine with cytosine. Because of this rule in base pairing, the sequence of one chain determines the other. The two chains are thus said to be complementary. This characteristic makes DNA unique and the nitrogen base sequence is capable of storing genetic information. Furthermore, a DNA strand has the capability to replicate itself to transmit the data into another cell.
The basic unit into which the DNA is packed in organisms is the chromosome. These are composed of DNA containing the genetic material and histone proteins which help package them. The DNA having an overall negative charge bonds with the positively charged histone proteins making a complex called chromatin. This process happens because of the lack of packaging space within the cell compared to the 2.2m overall length of DNA. Human chromosomes are on average about 6 µm long, a packing ratio of 8000:1. Eight histone protein molecules come together to form a nucleosome around which DNA wraps itself around for about 1.7 turns. This configuration is repeated to form a structure like a chain of beads. This structure further becomes super coiled to shorter thicker strands to form chromosomes. Hence the chromosomes contain only a single long DNA molecule and many genes along it. Human contains 24 chromosomes in their cells.
What is the difference between DNA and Chromosome?
• DNA and chromosomes are both storages of genetic material and would help determine the internal metabolism and external features of an organism.
• They are both similar in structure to a certain extent because the DNA strand is common to both.
• In a single cell, the number of both DNA and chromosomes are similar, but only chromosomes contain histone proteins.
• The DNA which is much longer (4.8 cm) than chromosomes (6 µm) has a less coiled structure than chromosomes.
• The DNA can replicate in its natural form, but the chromosomes have to unwind themselves to attach with transcriptase for the replication.
• All cells except red blood cells contain DNA and chromosomes. They both together are the basis of the fine function of the cell and through that the whole body. They are most importantly the mode of transmission of genetic material from one generation to another along with the hereditary traits and characters.