RNA and DNA are the special compounds, produced in the nucleus of cell. These are composed of Carbon, Hydrogen, Nitrogen and Phosphorus.
There are two types of nucleic acid:
It is produced from the DNA in the nucleus, and is then transferred into the cytoplasm. RNA contains ribose sugar. It takes part in protein synthesis. The DNA and RNA are composed of small units, called nucleotides. These nucleotides are composed of three parts.
- A pentose sugar i.e. consisting of 5-carbon atoms. DNA contains Deoxyribose and RNA contains ribose
- A phosphate group (Phosphoric Acid).
- Nitrogen Base.
Nitrogen Bases are of different Types:
In RNA, Thymine is replaced by another nitrogen base, called Uracil.
Functions of RNA:
RNA is formed in the nucleus by the DNA and then transferred into cytoplasm. It takes part in protein synthesis.
The polymers of ribonucleotides are called RNA. The RNA molecule has single strand. Sometimes, this strand may fold back to give double helical characteristics. The nitrogen bases form complementary pairings.
Ribonucleic Acid have nitrogenous base Uracil in place of Thymine. Cytosine (C) forms pair with Guanine (G) and Uracil (U) forms pair with Adenine (A). DNA synthesizes Ribonucleic Acid. The process of synthesis of Ribonucleic Acid from DNA is called Transcription.
Types of RNA:
There are three main types of RNA. These are messenger RNA (mRNA), transfer RNA (tRNA) and ribosomal RNA (rRNA). All three types of RNA are synthesized from DNA in nucleus. After their synthesis they are transferred to cytoplasm. All three RNA (mRNA, tRNA and rRNA) interact with each other. They synthesize proteins from the genetic information (gene).
a) Messenger RNA (mRNA)
The mRNA brings genetic message from nucleus to the ribosome. The mRNA is about 3% to 4% of the total RNA in the cell. The ribosomes are present in the cytoplasm for the synthesis of the particular protein. DNA transfers its genetic information to mRNA.
Now, this mRNA has genetic information for the synthesis of protein. The mRNA consists of single strand of variable length. Its size depends on size of gene (on DNA) for the specific protein. For example, the mRNA has 3,000 nucleotides for a protein of 1,000 amino acids.
b) Transfer RNA (tRNA)
The tRNA reads message (code) on mRNA and transfer specific amino acid to the ribosome. These amino acids are linked to form polypeptide chain of the protein. There is one specific tRNA for each amino acid. So, the cell contains 20 types of tRNA. It forms about 10% to 20% of the total cellular RNA. The tRNA has small size. Its chain is composed of 75 to 90 nucleotides.
c) Ribosomal RNA (rRNA)
The rRNA combines with ribosomal proteins and forms ribosome. Ribosome is made up of rRNA and protein. The rRNA forms 50% of the ribosome. It forms a large part, about 80% of total RNA. It acts as machine for the synthesis of protein.
RNA as a carrier of Information:
Ribonucleic acid (RNA) acts as carrier of information from DNA to ribosome for protein synthesis. The genetic information is transferred from DNA to mRNA and the due to cytoplasm for protein synthesis in TWO Steps:
The first step of protein synthesis is called transcription. It takes place in the nucleus. In this process the DNA produced a single strand RNA molecule from its one strand. This molecule is called messenger RNA (mRNA), because it carries the genetic message from DNA.
The messenger Ribonucleic Acid (mRNA) carries the message out of the nucleus to the ribosome in the cytoplasm. This message indicates the formation of a particular type of protein. The mRNA is attached to the ribosome, which is a site of protein synthesis.
In this step two types of Ribonucleic Acid, tRNA (Transfer RNA) and rRNA (Ribosomal RNA) take part. rRNA is attached to the ribosome. tRNA is present in the cytoplasm. It transfers specific amino acids to the ribosome to translate the information of mRNA. By this process the amino acids are arranged to prepare a particular type of protein.
“The compounds formed by the combination of two different types of molecules are called conjugated molecules or compounds”.
“When bio-molecule of two different groups is combined together, conjugated molecules are formed”.
Different types of Conjugated molecules are as follow:
- Glycolipids (conjugate compounds of carbohydrates)
- Nucleoproteins (conjugate compounds of Nucleic Acids)
Carbohydrates may combine with protein or lipid and form glycoprotein or glycolipids. Most of the cell secretions (like hormones) are glycoprotein. Both glycoprotein and glycolipids forms an important component of the cell membrane. They form the basic structural framework of all types of membranes in the cell.
When fatty acids and carbohydrates are combined with each other, these are called glycolipids. These compounds also contain nitrogen. These are the derivatives of carbohydrate glycosides. Glycolipids and Sulpholipids are found in chloroplasts. Glycolipids are also found in brain, called cerebrosides.
When carbohydrates and proteins are joined with each other, glycoproteins are formed. These are commonly found in animal and plant cells. For Example: Albumin of Egg and Gonadotrophic hormone. Some amount of glycoproteins is present in cell membrane.
Nucleoproteins (conjugate compounds of Nucleic Acids)
These are the combination of proteins with nucleic acid of nucleus. These are less acidic and soluble in water.
When lipids and proteins are linked, lipoproteins are formed. For Example: cholesterol and lecithin. Lipids are linked with simple proteins. These compounds take part in the transportation of lipids in blood plasma.
The lipoproteins are found in membrane of endoplasmic reticulum, nuclei and mitochondria. These are also present in sheath of nerves, chloroplast and bacterial membrane.