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. List two essential roles of ribosome during translation. Solution: Two essential roles of ribosome during translation are: Ribosomes are sites where synthesis of proteins occurs from individual amino acids. It consists of two subunits – larger subunit serves as an amino acid binding site whereas smaller subunit attaches to the mRNA forming a protein synthesizing complex Since large subunit of ribosome has two different sites to attach to tRNA, it facilitates amino acids to come closer for peptide bond formation. Also, ribosome behaves as a catalyst for the formation of peptide bond. Example – 23s r-RNA acts as a ribozyme in bacteria 10. In the medium where E. coli was growing, lactose was added, which induced the lac operon. Then, why does lac operon shut down some time after addition of lactose in the medium? Solution: A segment of DNA which comprises three adjacent structural genes – a promoter gene, an operator gene, and a regulator gene is known as Lac operon. It is functional in a coordinated manner in order to metabolize lactose into galactose and glucose. Lactose serves as an inducer in lac operon which binds to the repressor, inactivating it. Once the lactose is bound to the repressor, RNA polymerase binds to the area of promoter. Therefore, the structural genes express their product, corresponding enzymes are yielded. Lactose is metabolized due to the action of enzymes into galactose and glucose. Later on, the level of inducer decreases as enzymes completely metabolize them which results in the synthesis of the repressor from the regulator gene. Thus, the repressor is bound to the operator gene, restricting RNA polymerase from transcribing the operon, subsequently transcription is ceased. This kind of regulation is termed as negative regulation. NCERT solutions class 12 biology Chapter 6 - 2 11. Explain (in one or two lines) the function of the followings: (a) Promoter (b) tRNA (c) Exons Solution: (a) Promoter The section of DNA which aids in initiating transcription process and serving as a binding site for RNA polymerase is the promoter (b) tRNA The transfer RNA or tRNA is a small clover shaped RNA which reads the genetic code that is located on mRNA. It conveys particular amino acids to the mRNA ribosome while proteins are translated. Specific tRNAs are present for specific amino acids. (c) Exons In eukaryotes, these are coding sequences of DNA which transcribe proteins. In between, exons comprise of long non-coding sections of DNA known as introns. 12. Why is the Human Genome project called a mega project? Solution: The Human genome project was ought to be a mega project as the scale and the goals of the project were humongous. It had goals to sequence every base pair located in the human genome which took around 13 years for completion and accomplished in 2003. This large scale project intended to develop new technologies and produce new information in the stream of genomic studies. Subsequently, it unlocked scope for several new areas and possibilities such as in the stream of biotechnology, genetics, medical sciences etc which hints at comprehending different aspects of human biology. 13. What is DNA fingerprinting? Mention its application. Solution: The technique of DNA fingerprinting is helpful in identifying and analyzing variations in different individuals at the DNA level. It is based on the principle of variability and polymorphism in DNA sequences. Its applications are as follows: To identify potential crime suspects in forensic science Helpful in establishing family and paternity relationships Useful in identifying and preserving the commercial varieties of livestock and crops Useful to discover and know more about the evolutionary history of an entity, thus tracing the linkages between different entities. 14. Briefly describe the following: (a) Transcription (b) Polymorphism (c) Translation (d) Bioinformatics Solution: (a) Transcription It is the process to synthesize RNA from DNA template. A section of DNA gets duplicated into mRNA in the process. The transcription process originates from the promoter region of the template DNA and ends at the terminator region. The section of DNA between these two regions is termed as transcription unit. The transcription process necessitates DNA template, RNA polymerase enzyme, four types of ribonucleotides and a few cofactors, namely Mg2+. Three significant events occurring during the transcription process are: Initiation Elongation Termination The process of transcription is initiated when the DNA-dependent RNA polymerase and several initiation factors bind at the promoter region of the template strand at the double stranded DNA. The RNA polymerase passes along the DNA, causing the DNA duplex to unwind to two distinct strands. One of the strands is known as sense strand, which serves as a template for mRNA synthesis. The RNA polymerase enzyme uses nucleoside triphosphates (dNTPs) as raw material to polymerize them for the formation of mRNA as per the complementary bases positioned in the template DNA. This phenomena of opening of helix and elongation of polynucleotide chain lasts until the enzyme arrives at the terminator region. Once the RNA polymerase arrives at the terminator section, the freshly produced mRNA transcripted in addition to the enzyme is liberated. Additionally, another factor known as terminator factor is essential for the transcription process to end. NCERT solutions class 12 biology Chapter 6 - 3 (b) Polymorphism It is a form of genetic variation wherein different nucleotide sequences can be present at different sites in a molecule of DNA. There is a high frequency of this heritable mutation to be observed in a population which emerges as a result of mutation either in the germ cells or somatic cells. The germ cell mutation can be passed from parents to the offsprings which leads to the accumulation of different mutations in a population causing variation and polymorphism in the population. This has a crucial role to play in the evolution and speciation process. (c) Translation It is the process wherein amino acids are polymerized for the formation of a polypeptide chain, a ribosome by reading mRNA molecule. In mRNA, the triplet sequence of base pairs defines the order and sequence of amino acids in a polypeptide chain. This phenomena includes three steps: Initiation Elongation Termination The tRNA gets charged during the initiation of the translation when the amino acids binds to it with the help of ATP. The initiation code – AUG that is located on the mRNA is identified only by the charged tRNA. For the process of translation, the ribosome acts as an actual site, containing two distinct sites in a large subunit to attach to the following amino acids. The smaller subunit of ribosome is bound to the mRNA at AUG (initiation code) subsequently by the large subunit. The process of translation is then said to be initiated. In the elongation process, the ribosome passes one codon downstream with the mRNA in order to leave some space to bind another charged tRNA. Amino acid brings tRNA which gets linked with the former amino acid via peptide bond. The process continues leading to the formation of a polypeptide chain. When the ribosome arrives, one or more STOP codon (UAA, UGA, and UAG). The phenomena of translation ends, polypeptide chain releases and the ribosomes get detached from mRNA. NCERT solutions class 12 biology Chapter 6 - 4 (d) Bioinformatics It is the application of statistical and computational methodologies to the molecular biology stream. It explains practical issues that arise from the analysis and management of biological data. The stream of bioinformatics developed after accomplishing human genome project as huge amount of data was produced during the process which has to be stored and managed for easy access and analysis for later use. Thus, bioinformatics includes creating biological databases which stores huge data of biology. It comes up with a few tools for efficient and easy access to data which can be used. Also, bioinformatics brought in new algorithms and statistical techniques to figure out the dynamics between data, to predict structure of protein and their functionalities and to group protein sequences into their associated families.