Category: Biology Second Paper

All the genes present in a set of chromosomes are collectively called the genome. German botanist Hans Winkler first used the term genome in 1920. The human genome contains about 3000 million base pairs and 20,000-25,000 genes. In 2007, 2900 million nucleotides and about 30,000 genes were recorded in the human genome. 99.9 percent of human genomes (genes) are identical. Due to the difference in the structure of only 0.1% of the genes, there are different types of people in the world. Only 2% of human genes express the trait. The remaining 98% of genes are inactive. These inactive genes (98%) are called junk DNA. Mycoplasma genitalium has 517 genes, E. coli has 5416 genes and Arabidopsis thaliana has 25,000 genes.

Genes create new variations through mutation. A gene controls a trait. Sometimes more than one gene controls a trait. Gene expression can also be regulated by the environment. Mammalian cells may contain over 50,000 genes. Each gene contains a certain number of nucleotides. The smallest gene has 75 and the largest gene has 40,000 nucleotides recorded.
The coding part of a gene is called an exon and the non-coding part is called an intron. Exons synthesize proteins. Sometimes exons are non-coding like introns. Such a gene is called a speit gene.

The number of genes can range from a few thousand to several million depending on the species. Mammalian cells can contain over 50,000 genes. Human diploid cells have 30,000-40,000 genes. Human chromosome 1 has the highest number of 2968 genes and Y-chromosome 23 has the lowest number of 231 genes.

Gregor Johann Mendel called the carriers of heredity as particles or factors. In 1909 Johansen named this particle or factor as gene. In 1912, scientist Thomas Hunt Morgan proved that genes are located on chromosomes. Indian scientist Har Gobinda Khorana won the Nobel Prize in 1969 for discovering artificial genes.
In 1908, scientist Garrol first introduced the one gene, one enzyme theory. This was later called the one gene one polypeptide chain theory. In 1941, scientist Bidom and Tatum studied the fungus Neurospora crassa and said that specific genes produce specific enzymes.

The origin of the word gene is from the Greek word genes meaning born. The smallest piece of DNA that controls an organism’s characteristics and causes variation, mutation and evolution is called a gene. It is called the blue print of life. The location of a gene on a chromosome is called a locus. A locus on a chromosome contains two identical or different genes. Two genes are called alleles or allelomorphs of each other.

The importance of protein synthesis or protein in the living world is discussed.
1. As stored food: Protein acts as stored food in the body.
2. Energy production: Proteins produce energy as needed in the body. Each gram of protein in the body produces 4.10 kilocalories of energy through oxidation.
3. Body structure: Protein acts as the main structural component of the body. It forms the body of the organism.
4. Heredity: Histone proteins present in chromosomes play an important role in the inheritance of organisms.
5. Growth and Development: Growth and development of organisms are controlled by hormones. A hormone is a type of protein.
6. Transport: Proteins take part in the transport of various materials inside the cell. Hemoglobin protein transports O2 and CO2.
7. As an analgesic: Endorphin proteins produced in the brain act as pain relievers.
8. Immunity: Proteins produce antibodies in the body. Antibodies make the body immune to disease.
9. Regulation of reactions: Proteins control all types of reactions in the body.
10. Structure of Cell Membrane: Proteins form plasma membrane, nuclear membrane and membranes of various cellular organelles.
11. Prevention of viruses and cancer: A protein called interferon is used to prevent viruses and blood cancer.

Antibiotic drugs interfere with the translation process of disease-causing bacteria in the human body. Hence the human body gets rid of diseases. Antibiotics such as tetracyclines interfere with the attachment of tRNA to ribosomes. Erythromycin interferes with movement of mRNA to ribosomes. Streptomycin disrupts translation initiation. Chloromycin disrupts peptide bond formation. Neomycin interferes with the interaction of mRNA and tRNA.

Translation is a complex process. The steps in this process are translation initiation, polypeptide chain elongation and translation termination.
1 | Initiation
(i) mRNA enters the cytoplasm of the cell through nuclear pores. At this time tRNA is attached to the start codon of mRNA with methionine.
(ii) Small units of ribosome, tRNA and mRNA combine to form initiation complex.
(iii) The large unit of the ribosome binds to the initiation compound. Ribosomes have A site, P site, E site etc.
(iv) tRNA carries the amino acid to the A-site of the ribosome and initiates translation.
2. Elongation
(i) First the tRNA carries an amino acid to the A-site of the ribosome. Amino acids and tRNA are released there.
(ii) A code proceeds by scanning the ribosome. The amino acid remains at the A-site of the ribosome and the tRNA moves from the A-site to the P-site of the ribosome. At this point the second tRNA carries the amino acid to the A-site of the ribosome. There the second amino acid and tRNA are released.
(iii) Another code proceeds by scanning the ribosome. The first and second amino acids are added to the A-site of the ribosome and the second tRNA moves from the A-site to the P-site of the ribosome. The first tRNA moves from the P-site to the E-site of the ribosome. Meanwhile, the third tRNA carries the amino acid to the A-site of the ribosome. There the third amino acid and tRNA are released.
(iv) A further code proceeds by scanning the ribosome. At the A-site of the ribosome, the first, second and third amino acids join to form the chain. The third tRNA moves from the A-site to the P-site of the ribosome. The second tRNA moves from the P-site to the E-site of the ribosome and the first tRNA moves from the E-site of the ribosome to the cytoplasm.
(v) Thus one after the other amino acids come to the ribosome and join to the 5-3 carbon side of the mRNA to form a polypeptide chain. The presence of polyribosomes increases the speed of this process.
(vi) The polypeptide chain continues to form until the A-site of the ribosome reaches the stop codon of the mRNA.
(vii) Movement of tRNA from A-site to P-site and from P-site to E-site of ribosome is called translocation.
3. Termination
(i) A water molecule is added to the polypeptide chain when the A-site of the ribosome reaches the stop codon of the mRNA. As a result, the bond between the polypeptide and the ribosome is broken in the process of hydrolysis.
(ii) The newly formed polypeptide chain or protein molecule is released from the ribosome and translation ceases.

1. mRNA that acts as a template.
2. tRNA that carries specific amino acids.
3. Ribosomes that act as protein building sites. It has three binding sites. A-site, P-site and E-site.
4. Activating enzymes. These are called amino-acyl tRNA synthetase. It reacts with amino acids and ATP to form AA-AMP.
5. 64 types of codons for 20 amino acids.

The process in which mRNA joins numerous amino acids by peptide bonds to form protein molecules is called translation. mRNA copies information from DNA according to the code. The information is then translated into protein language. This is called translation.