Why DNA Is the Genetic Material Structure Function and Proof
The nucleic acids in living organisms are of two types. They are deoxyribonucleic acid and ribonucleic acid. The DNA is the genetic material in almost all living organisms except some viruses. In RNA viruses, RNA is the genetic material of a cell. The RNA carries the genetic information thus, it functions as a messenger. It also functions as an adaptor that picks up amino acids Sometimes, it also carries catalytic molecules.
The deoxyribonucleotides make up the DNA the genetic material. It is acidic in nature and is present in the nucleus of the cell. Mischer identified the DNA cell or the DNA in 1869 and he named it nuclein. After that, Altmann found out that they are acidic in nature therefore he named them nucleic acids. The number of nucleic acids helps in defining the length of the DNA. These nucleic acids are known as the base pairs. It is a characteristic of an organism. We will learn about the location in the cell of DNA and what is genetic material and more about DNA.
Structure of the Polynucleotide Chain
The DNA as genetic material is found in living organisms. The nucleotide is the basic unit of DNA. The nucleotides are composed of three units that are a nitrogenous base, a pentose sugar and a phosphate group. Pentose sugar is deoxyribose in nature. Two types of nitrogenous bases are present. They are:
Purines: They are heterocyclic in nature. They have a double ring structure. The double ring is 9-membered in nature. The nitrogen is present at positions 1,3,7 and 9. Examples of purines are Adenine and Guanine.
Pyrimidines: It is also heterocyclic in nature. It is a 6-membered ring structure. It is a single ring structure. The nitrogen is present at 1 and 3 positions. Cytosine, Thymine and Uracil are pyrimidines. In both DNA and RNA, cytosine is common whereas thymine is present in DNA and Uracil is present in RNA at the place of thymine.
The polynucleotide linkage shows two types of linkages, they are N-glycosidic linkage and Phosphodiester linkage. In N-glycosidic linkage, the nitrogenous base is linked to the pentose sugar with the help of an N-glycosidic linkage which then forms the nucleoside. In phosphodiester linkage, the phosphate group is linked to the 5’-OH of the nucleoside. This takes place with the help of phosphodiester linkage. By this, a nucleotide is formed. The polymer that is formed by this has a free phosphate moiety at the 5’-end of the sugar. Similarly, the other end has a 3’-OH free end. Sugars and phosphates form the backbone of the polynucleotide chain. The backbone is formed by the nitrogenous base that is linked to the sugar moiety.
Derivation of the DNA Structure
A question arises that “DNA is found in what part of the cell?” The DNA as genetic material is found in the nucleus of the cell. There were two methods that were followed for the derivation of the DNA structure. They are:
X-Ray Crystallography: Wilkins and Franklin did these studies. It was obtained from a very fine X-diffraction of the DNA. From these studies, they suggested that the structure of DNA is sort of a helix. But they were not able to produce a definitive model for the DNA.
Erwin Chargaff’s Rule: The studies were made on the basis of the base composition of the DNA. Some generalizations on the double-stranded DNA were put forward. The purines and the pyrimidines are produced in equal amounts. Adenine purine is equimolar to thymine pyrimidine.
Watson-Crick Model
The Double-helix model which is the most famous model of DNA was proposed by Watson and Crick. The main thing about their model was the base pairing that is present between the two strands of the polynucleotide DNA. This base pairing is a very unique property of the polynucleotide chains. The base pairs are complementary to each other. This means that if we know the base pairing of one strand then we can formulate the base pairing of the other strand also.
Adenine is always present complementary to thymine and Guanine is always present complementary to cytosine. The two chains of the DNA are always present or run in an antiparallel pattern to each other. The pairing between the two strands is done with the help of hydrogen bonds. Due to this, a purine always comes opposite to pyrimidine. Due to this, there is always a uniform distance between the two strands. The helical chain is twisted in a right-handed fashion.
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Functions of the DNA
The Functions of the Dna the Genetic Material are:
It carries hereditary information or it works as a tool for carrying the genetic material for carrying the genetic information.
It helps in carrying out the variations that occur at the time of meiosis.
It is useful in DNA fingerprinting technique.
The sudden mutations are present in the DNA.
They help in controlling the mutations.
The process of DNA replication is carried out with the help of DNA.
Packaging of DNA Helix
The prokaryotes do not have a defined nucleus but still, their DNA is not present in scattered form in the cell. It is found in the cytoplasm and is present in the supercoiled stage. No-histone basic proteins help in maintaining the coils. Protein polyamines have a positive charge and this helps in maintaining the coils. Nucleoid is the name given to the supercoiled structure. In eukaryotes, the coiling is done with the help of positively charged histone proteins. These histone proteins are rich in basic amino acid residues. The basic amino acid residues are lysines and arginines. Five types of proteins are present in it out of which four of them are present in pairs and they make octamer structures. Two types of chromatin are present that is:
Heterochromatin: This region is darkly stained in nature. The chromatin material in it is densely packed. This is inactive transcriptionally.
Euchromatin: This region is lightly stained in nature. It is transcriptionally active and has loosely packed chromatin.
FAQs on DNA as the Genetic Material in Living Organisms
1. What is DNA genetic material?
DNA is the genetic material that stores and transmits hereditary information in almost all living organisms. It is a molecule called deoxyribonucleic acid (DNA) that contains instructions for growth, development, reproduction, and functioning. These instructions are organized into segments called genes, which determine traits such as eye color, blood type, and enzyme production.
2. Why is DNA considered the genetic material?
DNA is considered the genetic material because it can replicate accurately and store biological information that is passed from parents to offspring. It fulfills key criteria of genetic material:
- It can undergo replication to produce identical copies.
- It carries information in the sequence of nitrogenous bases.
- It can mutate, allowing variation and evolution.
- It directs protein synthesis, which controls cell structure and function.
3. What is the structure of DNA?
The structure of DNA is a double helix made of two complementary strands twisted around each other. Each strand consists of repeating units called nucleotides, and each nucleotide contains:
- A deoxyribose sugar
- A phosphate group
- A nitrogenous base: adenine (A), thymine (T), guanine (G), or cytosine (C)
4. Where is DNA found in a cell?
In eukaryotic cells, DNA is mainly found in the nucleus, while in prokaryotic cells it is located in the cytoplasm. Specifically:
- In eukaryotes, most DNA is inside the nucleus, and small amounts are in mitochondria (and chloroplasts in plants).
- In prokaryotes, DNA is present in a region called the nucleoid.
5. How does DNA store genetic information?
DNA stores genetic information in the specific sequence of its nitrogenous bases. The order of A, T, G, and C forms a genetic code that:
- Defines genes
- Determines the sequence of amino acids in a protein
- Controls inherited traits
6. How does DNA replication work?
DNA replication is the process by which DNA makes an identical copy of itself before cell division. It occurs in the following steps:
- The double helix unwinds with the help of helicase.
- Each strand acts as a template.
- DNA polymerase adds complementary nucleotides (A–T, G–C).
- Two identical DNA molecules are formed, each with one old and one new strand (called semi-conservative replication).
7. What is the difference between DNA and RNA?
The main difference between DNA and RNA is that DNA stores genetic information, while RNA helps in protein synthesis. Key differences include:
- DNA contains deoxyribose sugar; RNA contains ribose sugar.
- DNA uses thymine (T); RNA uses uracil (U).
- DNA is usually double-stranded; RNA is usually single-stranded.
- DNA remains mostly in the nucleus; RNA moves to the cytoplasm.
8. What is the function of DNA in protein synthesis?
DNA controls protein synthesis by providing the instructions for making proteins. This occurs in two main steps:
- Transcription: A segment of DNA is copied into messenger RNA (mRNA).
- Translation: The mRNA sequence is used by ribosomes to assemble amino acids into a protein.
9. Can RNA be genetic material?
Yes, RNA can act as genetic material in some viruses known as RNA viruses. In these organisms:
- RNA stores genetic information instead of DNA.
- The RNA can replicate inside the host cell.
- Examples include influenza virus and coronavirus.
10. Why is DNA important for inheritance?
DNA is important for inheritance because it carries genes that are passed from parents to offspring. During reproduction:
- DNA is replicated.
- Genes are transmitted through gametes (sperm and egg).
- Offspring receive a combination of parental genes.
