Molecular Basis of Inheritance Chapter 6 PDF

MOLECULAR BASIS OF INHERITANCE.00000 CHAPTER – 6 MOLECULAR BASIS OF INHERITANCE At the time of Mendel the nature of those factors regulating RNA (Ribonucleic Acid). In most species, DNA serves as...

MOLECULAR BASIS OF INHERITANCE.00000 CHAPTER – 6 MOLECULAR BASIS OF INHERITANCE At the time of Mendel the nature of those factors regulating RNA (Ribonucleic Acid). In most species, DNA serves as the pattern of inheritance was not clear, over the next 100 genetic material. In other creatures, such as viruses, RNA also years the nature of the putative genetic material was serves as genetic material and as a messenger. It serves as an investigated culminating in the realisation that DNA is the adaptor, structural molecule, and in certain situations a genetic material at least for the majority of organisms. catalytic molecule. DNA is a lengthy polymer of deoxyribonucleotides. Base pairs DNA and RNA are the two types of nucleic acids found in are another name for a pair of nucleotides. The length of DNA living systems, DNA acts as the genetic material in most of the is often defined as the number of nucleotides present. Human organisms while RNA though acts as genetic material in some DNA has a haploid content of 3.3x109 bp, while Escherichia virus mostly functions as a messenger. coli has 4.6 x 106 bp. Deoxyribonucleic acid: The two kinds of nucleic acids present in living beings are DNA (Deoxyribonucleic Acid) and The polynucleotide Chain: A nucleotide is made up of three parts: a nitrogenous base a pentose sugar (ribose in the case of RNA and deoxyribose in the case of DNA), and a phosphate group. Purines (Adenine and Guanine) and Pyrimidines (Cytosine, Uracil and Thymine) are the two kinds of nitrogenous bases. A polynucleotide Chain Cytosine is found in both DNA and RNA, whereas Thymine is dinucleotide, two nucleotides are connected together via a 3'- found in DNA. Uracil is found in RNA in place of Thymine. 5' phosphodiester bond. More nucleotides combine to produce polynucleotide. A nucleoside is formed when a nitrogenous base is connected to a pentose sugar via an N-glycosidic bond. Nucleotide is Salient Features of DNA: DNA contains the sugar D -2- generated when a phosphate group is connected to the 5'-OH deoxyribose. Cytosine and thymine are pyrimidine bases in of a nucleoside via phosphodiester linkage. To make a DNA, while guanine and adenine are purine bases. The structure of DNA is a double strand -helix. Because DNA Two chains have antiparallel polarity. One 5’ to 3’ and 3’to molecules are so big, their molecular mass can vary greatly. 5’. DNA has a unique replicating characteristic. The transmission The bases in two strands are linked together by H-bonds. of hereditary effects is controlled by RNA. Guanine and Cytosine form triple hydrogen bonds, whereas Adenine and Thymine form double hydrogen bonds. Two chains are coiled in the right hand. The pitch of the DNA helix is 3.4 nm, with each turn containing around 10 Q1. A polynucleotide is made up of. bp. (a) Pentose sugar To provide stability, the plane of one base pair stacks (b) Nitrogenase base over the plane of the other in a double helix. Other (c) Phosphate group than this hydrogen bonding and the presence of (d) All of the above thymine in place of uracil confers additional stability S1. (d) to the DNA. Q2. Which of the following is a pyrimidine? (a) Adenine (b) Guanine (c) Uracil (d) All of the above S2. (d) Double Helical Structure of DNA by Watson and Crick James Watson and Francis Crick suggested the double helix concept for the structure of DNA based on X-ray diffraction evidence collected by Maurice Wilkin and Rosalind Franklin. According to this model: DNA is made of two polynucleotide chains in which backbone is made up of sugar-phosphate and bases Double Standard Polynucleotide chain projected inside it. The Central dogma of molecular biology, developed by Francis Crick, holds that genetic information flows from DNA — –> RNA —–> Protein. In RNA, nucleotide residues have an extra –OH group at the 2'-position in ribose, and uracil replaces Thymine. Packing of DNA Helix and stains dark. Euchromatin is active transcriptionally, In prokaryotes, the nucleus is not clearly defined, and whereas heterochromatin is inactive. negatively charged DNA is mixed with positively charged proteins known as nucleoids. In eukaryotes, histones are positively charged proteins that are arranged into 8 molecules termed histone octamers. To construct a nucleosome, negatively charged DNA wraps around a histone octamer. Histones contain a high concentration of the basic amino acid residues lysines and arginines. The side chains of both amino acid residues are positively charged. A single nucleosome includes around 200 base pairs. Chromatin is the nucleosome's repeating unit. Some regions of chromatin in the nucleus are loosely packed (and stain light) and are referred to as euchromatin. Heterochromatin is chromatin that is more densely packed Structure of nucleosome  polysaccharide coat and become virulent. This must be the result of genetic material transfer. Biochemical Characterisation of Transforming Principle Q1. Histones are rich in. (a) Arginine (b) Valine Oswald Avery, Colin MacLeod, and Maclyn McCarty worked (c) Lysine (d) Both (a) and (c) together to determine the biochemical basis of Griffith's transformative principle. S1. (d) They extracted biochemicals (proteins, DNA, RNA, and so on) Q2. The pitch of the DNA helix is. from heat-killed S cells to determine which ones may turn (d).34 nm (b) 3.4 nm living R cells into S cells. They determined that DNA from S (c).034 nm (d).0034 nm bacteria alone enabled R bacteria to convert. As a result, they S1. (b) came to the conclusion that DNA is the genetic material. Search for Genetic Material: Experimental Proof that DNA is the genetic material The Transforming Principle: Frederick Griffith conducted In one formulation, the protein component was rendered an experiment on the microorganisms Streptococcus radioactive, whereas the nucleic acid (DNA) component was pneumoniae in 1928. (bacterium responsible for not. pneumonia). This bacterium has two strains: These two phage preparations were allowed to infect an E.coli those that generate smooth shining colonies (S) and culture. Before cell lysis, the E.coli cells were gently agitated those that form rough colonies (R) (R). in a blender to release the clinging phage particles, and the Mice infected with the S strain (virulent) develop pneumonia, culture was centrifuged. but mice infected with the R strain do not. The heavier infected bacterial cells settled to the bottom, In brief his experiment was as follows: while the lighter virus particles remained in the supernatant. Inject S strain into mice, it dies (i) R strain injected into mice, it survives (ii) When a bacteriophage with radioactive DNA was utilized to Inject S strain (heat-killed) into mice, it survives (iii) infect E.coli, the pellet contained radioactivity. Inject S strain (heat-killed) plus R strain (living) into mice, it When a bacteriophage with a radioactive protein coat dies (iv) infected E.coli, the supernatant held the majority of the Griffith came to the conclusion that R strain bacteria had been radioactivity. transformed by heat-killing S strain bacteria. Some His work demonstrates that protein does not penetrate the transforming factors were transmitted from the S strain to bacterial cell and that the only genetic substance is DNA. the R strain, allowing the R strain to produce a smooth An experiment conducted by Hershey and Chase  RNA is employed as a genetic material as well as a catalyst, and because it is more reactive, it is less stable. As a result, DNA has evolved from RNA. Q1. Proof that DNA is the genetic material was given by. (a) Martha Chase (b) Alfred Hershey Replication: Watson and Crick proposed that two strands of (c) Both (a) and (b) (d) None of the above DNA split and serve as a template for the creation of new complementary strands. After replication, each DNA S1. (c) molecule would contain one parental and one freshly Q2. RNA is the genetic material in. synthesised strand; this is known as semiconservative (a) Tobacco Mosaic Virus (b) QB bacteriophage replication. (c) Both (a) and (b) (d) None of the above Messelson and Stahl demonstrate semiconservative replication experimentally by growing E.coli on S2. (c) nutritional media containing nitrogen salts (15NH4Cl) Properties of A Genetic Material tagged with radioactive 15N. It should be able to replicate itself (replication) Alfred Hershey and Martha Chases (1952) studied It needs to be chemically and structurally stable. bacteriophages, which are viruses that infect bacteria. It should allow for the gradual changes (mutation) essential for evolution. 15N was integrated into both strands of DNA, resulting in It should be able to express itself using 'Mendelian DNA that was heavier than DNA obtained from E.coli Characters.' cultured on 14N-containing media. The E.coli cells were then moved to a 14N-containing media. When compared to RNA, DNA is chemically less reactive but structurally more stable. As a result, DNA is superior genetic They extracted the DNA and measured its density after material. one generation when one bacterial cell multiplied into two. Its density was halfway between that of heavier 15N- DNA and lighter 14N-DNA. Because a new DNA molecule with one 15N-old strand and a corresponding 14N-new strand was generated during replication (semi-conservative replication), its density is intermediate between the two. Meselson and Stahl’s Experiment Replication of DNA Enzyme DNA polymerase is required for DNA replication, which catalyses polymerisation on one strand 5' to 3' after unwinding with the help of Helicase enzyme. As a result, replication in one strand is continuous while replication in the other strand is discontinuous in order to synthesise Okazaki fragments that are linked together by the enzyme DNA ligase. The replicating fork  (d) None of the above S1. (b) Q1. What is the function of DNA ligase during replication? Q2. The replication of DNA takes place during which of the (a) Joins the continuously synthesizing strands of DNA following phase? (b) Joins the discontinuously synthesizing strands of (a) Interphase (b) S-phase DNA (c) G1 phase (d) G2 phase (c) Both (a) and (b) S2. (b) Transcription: It is the process of copying genetic information from one strand of DNA into RNA. In transcription only one segment of DNA is copied in RNA. The Adenosine forms base pair with Uracil instead of Thymine. A promoter, a structural gene, and a terminator are all involved in DNA transcription. The strands with polarity 3' to 5’ operate as templates and are referred to as template strands, whereas the other strand is referred to as coding strands. Process of transcription in bacteria Structure of a transcription unit The promoter is positioned at the 5' end and binds the process, in which introns are deleted and exons are RNA polymerase enzyme to initiate transcription. connected in a certain order. The sigma factor also aids in the initiation of Capping and tailing are processes that hnRNA transcription. (heterogeneous nuclear RNA) goes through. Capping the 5' end of hnRNA with an uncommon nucleotide The terminator is normally positioned at the 3'end of the (methylguanosine triphosphate). Tailing polyadenylate coding strand and defines the end of transcription where is the addition of a tail at the 3'end of a template in an the rho factor will attach to halt transcription. autonomous way. Exons are sequences found in mature and processed RNA. Exons are broken up by introns. In mature and processed RNA, introns do not exist. In eukaryotes, three RNA polymerase enzymes, I, II, and Q1. A cistron is a. III, catalyse the production of all kinds of RNA. (a) Segment of RNA coding for a polypeptide (b) Segment of DNA coding for a polypeptide RNA polymerase I : rRNAs (c) Segment of protein coding for a polypeptide RNA polymerase II : messenger RNA (d) None of the above RNA Polymerase III: tRNA The mRNA serves as a template, the t-RNA transports S1. (b) amino acids and reads the genetic information, and the Q2. An exon. rRNA performs structural and catalytic functions during (a) Appear in a immature RNA translation. (b) Appear in a mature DNA The primary transcript is non-functional and contains (c) Appear in an immature DNA both exons and introns. It goes through the splicing (d) Appear in mature RNA S2. (d) Genetic Code: The link between amino acid sequences in Mutations and Genetic Code polypeptides and nucleotide/base sequences in mRNA is The shift of amino acid residue glutamate to valine leads in a known as the genetic code. It governs the sequencing of single base pair alteration (point mutation) in the 6th amino acids during protein synthesis. position of the Beta globin chain of Haemoglobin. This George Gamow proposed that the genetic code be a develops in a disorder known as sickle cell anaemia. combination of three nucleotides that code for 20 amino Insertion and removal of three or more bases, Insert or acids. delete one or more codons, resulting in one or more amino H.G. Khorana developed chemical method for acids and the reading frame remaining unchanged. Frame- synthesising RNA molecules with defined combination of shift insertion or deletion mutations are examples of such bases. mutations. Marshall Nirenberg’s cell free system for protein synthesis finally helped the code to be deciphered. Features of the Genetic Code Q1. The function of AUG IS. The code is triplet. There are 61 codons that code for (a) It codes for methionine amino acids and three stop codons that do not code for (b) It acts as an initiator codon any amino acids (UAG, UGA and UAA). (c) It acts as a terminator codon Codon is clear and specific; it codes for a single amino (d) Both (a) and (b) acid. S1. (d) The code is degenerate. Some amino acids are coded by Q2. Sickle cell anaemia is an example of. multiple codons. (a) Frame shift mutation (b) Point mutation The codon is read in mRNA in a continuous, punctuated (c) Both (a) and (b) (d) None of the above form. S2. (b) The codon is almost ubiquitous. AUG has two purposes. It encodes methionine and serves as an initiator codon. The Adapter molecule-tRNA The t-RNA molecules are known as adaptor molecules. It has an anticodon loop with bases corresponding to the coding found on mRNA, as well as an amino acid acceptor to which amino acid attaches. Each amino acid has its own t-RNA. The clover-leaf secondary structure of t-RNA is illustrated. The t-RNA molecule is a compact molecule that looks like an inverted L. tRNA-the adapter molecule The clover leaf structure (inverted L-shaped) Translation: The process of polymerisation amino acids to (a) Mediator RNA (b) Initiator RNA generate a polypeptide is known as translation. The sequence (c) Both (a) and (b) (d) None of the above of nucleotides in the mRNA determines the order and S2. (b) sequence of amino acids. Peptide bonds joins the amino acids. The following steps are involved: Regulation of Gene Expression Charging of tRNA All of the genes are not always required. The genes that are only needed sometimes are known as regulatory genes, and Peptide bond formation between two charged tRNA. they are designed to function only when needed while AUG is the start codon. Untranslated regions are extra remaining inactive at other times. Such controlled genes must sequences in an mRNA that are not translated (UTR). thus be turned 'on' or 'off' when a certain function begins or ends. Here are some examples: The ribosome attaches to mRNA at the start codon to initiate translation. Ribosomes migrate from codon to The lac operon: One regulatory gene (i) and three structural codon along mRNA in order to extend the protein chain. genes comprise the Lac operon (y,z and a). Gene i encodes the lac operon repressor. The z gene encodes beta-galactosidase, At the end of the process, release factors bind to the stop which hydrolyzes disaccharide, lactose into monomeric units, codon, halting translation and releasing polypeptides galactose, and glucose. Gene y codes for permease, which from the ribosome. enhances cell permeability. Transacetylase is encoded by gene a. Lactose is the substrate for the enzyme beta-galactosidase, and it governs the operon's switching on and off, thus the name inducer. Negative regulation refers to the control of the lac operon by a repressor. Positive regulation also governs the operation of the lac operon. Q1. Which of the following gene, synthesises the repressor Diagram showing Translation of the Lac operon all the time-continuously? (a) Gene y (b) Gene a (c) Gene i (d) Gene z S1. (c) Q1. Aminoacylation of t-RNA takes place during which of Q2. The gene in the lac operon that codes for beta- the following process? galactosidase is. (a) Replication (b) Transcription (a) Gene i (b) Gene a (c) Translation (d) All of the above (c) Gene z (d) Gene y S1. (c) S2. (c) Q2. tRNA is also called as. The lac operon The Human Genome Project: The Human Genome Project (i) the first involves identifying all of the genes that express was launched in 1990 with the goal of discovering the whole as RNA, known as Express sequence tags (EST). DNA sequence of the human genome through the use of (ii) The second step is to sequence all of the genome's genetic engineering techniques and bioinformatics to extract coding and non-coding sequences, which is known as and clone the DNA segment for determining DNA sequence. sequence annotation. Goals of Human Genome Project: Features of Human Genome Project: There are 3164.7 million nucleotide bases in the human Identify all the genes (20,000 to 25,000) in human DNA. genome. Determine the sequence of the 3 billion chemical base A typical gene has 3000 bases, although sizes vary widely, pairs that make up human DNA. with dystrophin being the biggest known human gene of 2.4 million bases. Store this information in database. Proteins are coded in less than 2% of the genome. Improve tools for data analysis. Repeated sequences account for a sizable component of the human genome. Transfer related information to other sectors. Repetitive sequences are DNA sequence lengths that are To address the legal, ethical and social issues that may repeated numerous times, often hundreds to thousands of arise due to project. times. Chromosome 1 has the most genes (2,968), whereas The US Department of Energy and the National Institute chromosome Y has the fewest (231). of Health oversaw the experiment. Researchers have found around 1.4 million places in The strategy included two key approaches: humans where single base DNA variations (SNPs - single nucleotide polymorphism) occur. DNA fingerprinting is a simple approach to compare the DNA sequences of two people. It entails finding changes in a specific section of a DNA sequence known as repetitive DNA because a tiny length of DNA is repeated multiple times in this region. Satellite DNA is divided into numerous groups based on its base makeup, segment length, and quantity of repeating units. Polymorphism in DNA sequence provides the foundation for both genetic mapping of the human genome and fingerprinting. Alec Jeffrey was the first to create fingerprinting technology. He employed a satellite DNA probe to detect such high polymorphism as Variable Number of Tendon Repeats (VNTR). DNA Fingerprinting  Nucleic acids are unique in their ability to direct their own replication. The resemblance of offspring to their parents depends on the precise replication of DNA and its transmission from one generation to the next. It is this DNA program that directs the development of your biochemical, anatomical, physiological, and (to some extent) behavioral traits. Once T. H. Morgan’s group showed that genes are located on chromosomes, the two constituents of chromosomes—proteins and DNA—were the candidates for the genetic material. Watson and Crick discovered the double helix by building models to conform to X-ray data. Maurice Wilkins and Rosalind Franklin used X-ray crystallography to study the structure of DNA. James Watson learned from their research that DNA was helical in shape, and he deduced the width of the helix and the spacing of nitrogenous bases. Watson and his colleague Francis Crick began to work on a model of DNA with two strands, the double helix. Watson and Crick’s model, semiconservative replication, predicts that when a double helix replicates, each of the daughter molecules will have one old strand and one newly made strand. Positively charged basic proteins that surround the DNA is known as histones. The DNA wraps around the positively charged histone octamer and forms a structure called nucleosome that contains 200 base pairs of DNA helix. The discovery of the genetic role of DNA began with research by Frederick Griffith in 1928. In 1952, Alfred Hershey and Martha Chase showed that DNA was the genetic material of the phage T2. DNA replication is a process of producing two identical copies of DNA from a single DNA molecule. It is a process of biological inheritance. Transcription is the process of formation of RNA such as messenger RNA from DNA before gene expression or protein synthesis occurs and translation is the process of gene expression or protein synthesis that occurs in cytosol. Ribosomes are the cell organelles that are involved in protein synthesis. The set of rules by which information encoded in genetic material is translated into proteins in the living cells is called genetic code. All the genes in the living cells is not active all the time. They become active when needed. Expression is controlled by genes are known as regulatory genes. Regulation in eukaryotes can occur at the transcriptional level, processing level, transport of mRNA from nucleus to the cytoplasm and translational level. Lac operon consists of structural genes, operator genes, promoter genes, regulator genes, and repressor. Lac operon consist of lac Z, lac Y and lac A genes. A mega project of sequencing human genome was launched in the year 1990 called the Human Genome Project. HGP was closely associated with the rapid development of a new area in biology called Bioinformatics. The Human Genome Project was a 13-year project coordinated by the U.S. Department of Energy and the National Institute of Health. The project was completed in the year 2003. DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called as repetitive DNA, because in these sequences, a small stretch of DNA is repeated many times. A bacteriophage known as φ ×174 has 5386 nucleotides. A cistron as a segment of DNA coding for a polypeptide, The pitch of the DNA helix is 3.4 nm. Stacking of base pairs one over monocistronic genes are found in eukaryotes and polycistronic in the other and hydrogen bonding provides stability to the DNA. prokaryotes and most bacteria. Francis Crick proposed the central Dogma of molecular biology. In bacteria, the mRNA provides the template, tRNA brings Histones are positively charged basic proteins, their positive charge aminoacids and reads the genetic code, and rRNAs play structural is due to amino acids lysine and arginine. and catalytic role during translation. In eukaryotes, RNA polymerase I transcribes rRNAs, 28S, 18S, and A typical nucleosome contains 200 bp of DNA helix. 5.8S), whereas the RNA polymerase III is responsible for Euchromatin is said to be transcriptionally active chromatin, transcription of tRNA, 5srRNA, and snRNAs (small nuclear RNAs). whereas heterochromatin is inactive. The RNA polymerase II transcribes precursor of mRNA, the heterogeneous nuclear RNA (hnRNA). DNA as the genetic material was unequivocally resolved from Hershey-Chase experiment. Regulation of lac operon by repressor is referred to as negative regulation. RNA is unstable and mutates at a faster rate. Polymorphism in DNA sequence is the basis of genetic mapping of The main enzyme of DNA replication is DNA polymerase, the human genome as well as of DNA fingerprinting. discontinuously synthesised fragments during replication are later The technique of DNA Fingerprinting was initially developed by Alec joined by the enzyme DNA ligase. Jeffreys.  MULTIPLE CHOICE QUESTIONS Q1. Which of the following are nucleic acids found in Q10. According to Chargaff’s law. living systems? (a) The ratio between AT and GC is constant and (a) DNA (b) RNA unequal (c) Protein (d) Both (a) and (b) (b) The ratio between AT and GC is not constant but equal Q2. What is genomics? (c) The ratio between AT and GC is not constant and (a) it is the study of all of a person's genes and their is also unequal interactions with each other and with the (d) The ratio between AT and GC is constant and equal environment (b) it is the study of all of a person's protein and Q11. Which of the following is correct about DNA double their interactions with each other and with the helix? environment (a) It is made up of two polynucleotide chains (c) it is the study of all of a person's blood count and (b) The two chains have anti-parallel polarity their interactions with each other and with the (c) The bases in the two strands are paired through environment H-bonds (d) it is the study of all of a person's behaviour and (d) All of the above their interactions with each other and with the Q12. The number of hydrogen bonds between Adenine and environment Thymine and Guanine and Cytosine in the bases of the Q3. How can we define the length of a DNA? two strands of DNA are. (a) by defining the number of nucleosides present in (a) 2, 6 (b) 6, 2 it (c) 2, 3 (d) 3, 2 (b) by defining the number of nucleotides present in Q13. The Central Dogma in molecular biology is. it (a) DNA RNA Protein (b) RNA DNA Protein (c) by defining the number of amino acids present in (c) Protein RNA Protein (d) None of the above it (d) by defining the number of acid groups present in Q14. What is the charge on DNA? it (a) Neutral (b) Negative (c) Positive (d) None of the above Q4. What is the haploid content of human DNA? (a) 3.3 x 108 bp (b) 3.3 x 109 bp Q15. Histones are. (c) 3.3 x 10 bp 10 (d) 3.3 x 1011 bp (a) Acidic proteins (b) Basic proteins (c) Neutral (d) None of the above Q5. Which of the following are the components of a nucleotide? Q16. Which of the following amino acids make histones (a) A nitrogenous base (b) A pentose sugar basic in nature? (c) A phosphate group (d) All of the above (a) Aspartic acid (b) Lysine (c) Arginine (d) Both (b) and (c) Q6. Which of the following base is common for both DNA and RNA? Q17. A typical nucleosome contains. (a) Adenine (b) Guanine (a) 100 bp of DNA helix (c) Cytosine (d) Thymine (b) 200 bp of DNA helix (c) 300 bp of DNA helix Q7. Which of the following linkage is present between two (d) 400 bp of DNA helix nucleotides? (a) N-glyosidic linkage Q18. Which of the following constitutes the repeating unit (b) 3’-5’ phosphodiester linkage of chromatin? (c) 5’-3’ phosphodiester linkage (a) Histone (b) Histone octamer (d) None of the above (c) Nucleosome (d) All of the above Q8. Which of the following forms the backbone of a Q19. Which of the following is transcriptionally active polynucleotide chain? chromatin? (a) Sugar and protein (b) Protein and fat (a) NHC (b) Heterochromatin (c) Fat and protein (d) Sugar and phosphate (c) Euchromatin (d) None of the above Q9. Who of the following first identified DNA? Q20. Who of the following performed experiments on (a) Francis Crick (b) Friedrich Meischer Streptococcus pneumonia? (c) James Watson (d) All of the above (a) Mendel (b) T.H. Morgan (c) Frederick Griffith (d) All of the above Q21. What was the observation of Frederick Griffith after Q31. Which of the following provides the ‘origin of he perform experiments on Streptococcus regarding replication’ for DNA replication to start? the ‘R’ strain of bacteria. The bacteria howed. (a) DNA polymerase (b) Template strand (a) Binary fission (b) Budding (c) A vector (d) All of the above (c) Transformation (d) Fragmentation Q32. In which phase of the cell cycle the replication of DNA Q22. Who of the following proved that DNA is the genetic takes place? material? (a) M-phase (b) G1-phase (a) Griffith (c) Interphase (d) S-phase (b) Oswald Avery Q33. What is transcription? (c) Alfred Hershey and Martha Chase (a) copying of genetic information from one strand of (d) All of the above the DNA into DNA Q23. In which of the following RNA acts as a genetic (b) copying of genetic information from one strand of material? the DNA into RNA (a) Tobacco Mosaic Virus (c) copying of genetic information from one strand of (b) QB bacteriophage the DNA into protein (c) Both (a) and (b) (d) copying of genetic information from one strand of (d) All of the above the DNA into amino acids Q24. Why is DNA better genetic material than RNA? Q34. Which of the following is correct about transcription? (a) It is less reactive (a) The DNA of an organism gets duplicated (b) It is structurally stable (b) Only a segment of DNA and one strand is copied (c) It does not degrade easily into RNA (d) All of the above (c) Both (a) and (b) (d) None of the above Q25. The protein synthesising machinery revolves around. (a) DNA (b) RNA Q35. Why both the strands of DNA are not copied during (c) Amino acids (d) All of the above transcription? (a) Both stands may code for RNA molecule with Q26. DNA replicated. different sequences. (a) Conservatively (b) If two RNA molecules are formed, then they can (b) Separately form dsRNA (c) Semi-conservatively (c) If dsRNA would be formed, how would translation (d) Uniformly occur Q27. What was the composition of hybrid DNA and light (d) All of the above DNA in the culture that was extracted by Meselson Q36. Which of the following flank the structural gene in a and Stahl from E.coli culture after 40 minutes of transcription unit? growth? (a) A promoter (b) A terminator (a) Intermediate density (c) Both (a) and (b) (d) None of the above (b) Equal density of hybrid DNA and light DNA (c) More hybrid DNA and less light DNA Q37. Look at the picture and name a, b and c. (d) Less hybrid DNA and more light DNA Q28. Which of the following is the main enzyme of DNA replication? (a) DNA dependent RNA polymerase (b) DNA dependent DNA polymerase (c) DNA ligase (d) All of the above Q29. DNA replication occurs in which of the following direction? (a) 5’ 3’ (b) 3’ 5’ (c) Both (a) and (b) (d) None of the above Q30. Which of the following enzymes joins the (a) H1 histone, DNA, Histone octamer discontinuously synthesized DNA fragments? (b) Histone octamer, H1 histone, DNA (a) DNA polymerase (b) Taq polymerase (c) DNA, Histone octamer, H1 histone (c) DNA ligase (d) RNA polymerase (d) DNA, H1 histone, histone octamer  Q48. RNA polymerase II transcribes which of the following Q38. Look at the picture and main a, b and c type of RNA? (a) Precursor mRNA (b) hnRNA (c) Both (a) and (b) (d) None of the above Q49. What is splicing? (a) Removal of exons and joining of introns (b) Removal of introns and joining of RNA (c) Removal of introns and joining of amino acids (a) (a) Transcription, (b) replication, (c) translation (d) Removal of introns and joining of exons (b) (a) Translation, (b) replication, (c) transcription Q50. In which of the following process methyl guanosine (c) (a) Replication, (b) transcription, (c) translation triphosphate is added to 5’ end of hnRNA? (d) (a) Translation, (b) transcription, (c) replication (a) Tailing (b) Capping Q39. Which of the following is a DNA sequence that (c) Extension (d) Termination provides binding site for RNA polymerase during Q51. How many adenylate residues are added at the 3’end transcription? in a template independent manner in the tailing (a) Structural gene (b) Promoter process of hnRNA? (c) Terminator (d) All of the above (a) 300-400 (b) 200-300 (c) 100-200 (d) 50-100 Q40. Which of the following is the functional unit of inheritance? Q52. Which among the following are the salient features of (a) Chromosome (b) Gene a genetic code? (c) Protein (d) None of the above (a) The code is degenerate (b) The code is universal Q41. Which of the following is a segment of DNA that (c) The codon is triplet quotes for a polypeptide? (d) All of the above (a) Intron (b) Exon (c) Cistron (d) None of the above Q53. What is the speciality of AUG codon? (a) It codes for methionine (met) Q42. Which of the following is correct about exons? (b) It acts as a stop codon (a) They appear in a processed RNA (c) It acts as initiator codon (b) They are the expressed sequences (d) Both (a) and (c) (c) They are interrupted by introns (d) All of the above Q54. Which of the following mutation causes sickle cell anaemia? Q43. Which of the following types of RNA are present in (a) Frame shift mutation (b) Point mutation bacteria? (c) Both (a) and (b) (d) All of the above (a) mRNA (b) tRNA (c) rRNA (d) All of the above Q55. Which of the following RNA are specific for each amino acid? Q44. Which of the following RNA play structural and (a) mRNA (b) rRNA catalytic role during translation? (c) tRNA (d) All of the above (a) mRNA (b) tRNA (c) rRNA (d) All of the above Q56. Which of the following part of the tRNA binds to the amino acids? Q45. Which of the following acts as substrate in (a) Anticodon loop (b) Acceptor end transcription? (c) Both (a) and (b) (d) None of the above (a) ATP Q57. The secondary structure of tRNA is. (b) ADP (a) Inverted-S (b) Inverted-V (c) Nucleoside triphosphate (c) Clover leaf shaped (d) Inverted-L (d) All of the above Q58. What is translation? Q46. Which of the following factor acts as initiation factor (a) it is the process of polymerisation of protein to in transcription? form a polypeptide (a) Rho factor (b) Sigma factor (b) it is the process of polymerisation of NTP to form (c) Both (a) and (b) (d) None of the above a polypeptide (c) it is the process of polymerisation of RNA to form Q47. Which of the following RNA transcribes rRNA? a polypeptide (a) RNA polymerase III (b) RNA Polymerase II (d) it is the process of polymerisation of amino acid to (c) RNA polymerase I (d) All of the above form a polypeptide Q59. Which of the following is correct about aninoacylation Q69. Who of the following developed the technique of DNA of tRNA? fingerprinting? (a) Amino acids are activated in the presence of ATP (a) Alec Jefferys (b) Har Gobind Khorana (b) Amino acids get’s linked to their cognate tRNA (c) Maruice Wilkins (d) All of the above (c) The process is also called as charging of tRNA Q70. SNPs stand for. (d) All of the above (a) Stand nucleotide polymorphism Q60. Which of the following is the cellular factory for the (b) Single nucleoside polymorphism synthesis of proteins inside a cell? (c) Single nucleotide polymorphism (a) Mitochondria (d) None of the above (b) Endoplasmic reticulum (c) Ribosome ASSERTION AND REASON (d) Nucleus Direction: in the following questions, a statement of Q61. The process of translation begins when. assertion (A) is followed by a statement of reason (R). Choose (a) The small subunit encounters an mRNA the correct option among a, b, c and d. (b) The small subunit encounters an tRNA (c) The small subunit encounters an rRNA Q1. Assertion (A): the replication occur within a small (d) All of the above opening of the DNA helix, referred to as replication fork. Q62. Which of the following RNA in bacteria acts as a Reason (R): The discontinuously synthesised catalyst? fragments during DNA replication are later joined by (a) 18sRNA (b) 5.8sRNA the enzyme helicase. (c) 28S rna (d) 23s rRNA (a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion Q63. In eukaryotes, regulation of gene expression can be (A) exerted at the. (b) Both assertion (A) and reason (R) are true but (a) Transcriptional level reason (R) is not the correct explanation of (b) Processing level (splicing level) assertion (A) (c) Transport of mRNA from nucleus (c) Assertion (A) is true but reason(R) is false (d) All of the above (d) Assertion (A) is false but reason(R) is true Q64. Which of the following gene in lac operon codes for Q2. Assertion (A): DNA is the predominant genetic repressor? material in most of the organisms. (a) Gene z (b) Gene y Reason (R): A molecule that can act as a genetic (c) Gene i (d) Gene a material should be stable chemically and structurally. Q65. Which of the following gene codes for permease in the (a) Both assertion (A) and reason (R) are true and lac operon that increases the permeability of the cell reason (R) is the correct explanation of assertion to beta galactosidase? (A) (a) Gene i (b) Gene y (b) Both assertion (A) and reason (R) are true but (c) Gene a (d) All of the above reason (R) is not the correct explanation of assertion (A) Q66. Which of the following is the substrate for enzyme (c) Assertion (A) is true but reason(R) is false beta galactosidase and regulates the switching on and (d) Assertion (A) is false but reason(R) is true off of the lac operon? Q3. Assertion (A): The unequivocal proof that DNA is the (a) Glucose (b) Galactose genetic material came from the experiments of Alfred (c) Lactose (d) All of the above Hershey and Martha Chase. Q67. Regulation of lac operon is referred to as. Reason (R): They worked on Streptococcus (a) Positive regulation pneumonia. (b) Negative regulation (a) Both assertion (A) and reason (R) are true and (c) Neutral reason (R) is the correct explanation of assertion (d) None of the above (A) (b) Both assertion (A) and reason (R) are true but Q68. BAC stands for. reason (R) is not the correct explanation of (a) Bacterial artificial case assertion (A) (b) Bacterial artificial chromosome (c) Assertion (A) is true but reason(R) is false (c) Bonus artificial chromosome (d) Assertion (A) is false but reason(R) is true (d) Bright artificial case Q4. Assertion (A): a set of positively charged, basic TRUE AND FALSE proteins is called histones. Reason (R): Histones are rich in the basic amino acid Q1. The unequivocal proof that DNA is the genetic material came from the experiments of Alfred residues lysine and arginine Hershey and Martha Chase. They grew some viruses (a) Both assertion (A) and reason (R) are true and on a medium that contained radioactive magnesium reason (R) is the correct explanation of assertion and some others on medium that contained radioactive nitrogen. (A) (b) Both assertion (A) and reason (R) are true but Q2. Nucleoid is a region in DNA where it is held with some proteins. reason (R) is not the correct explanation of Q3. Mono-cistronic genes are mostly found in assertion (A) prokaryotes and bacteria. (c) Assertion (A) is true but reason(R) is false Q4. The mRNAs play structural and catalytic role during (d) Assertion (A) is false but reason(R) is true translation. PRACTICE QUESTIONS Q1. Assuming that 50 heavy (i.e. containing N15) DNA (d) 28S, 18S and 5S rRNA molecules replicated twice in a medium containing Q7. The core enzyme requires a factor for termination of N14, we expect. RNA synthesis at some sites. This is known as. (a) 100 half heavy and half light and 150 light DNA (a) Sigma factor (b) Rho factor molecules (c) Gamma factor (d) Alpha particle (b) 100 half heavy and half light and 100 light DNA molecules Q8. If one strand of DNA has the base sequence (c) 50 heavy and 150 light DNA molecules ATCCACGACTAG and the second strand undergoes (d) 50 heavy and 100 light DNA molecules transcription what would be the base sequence on mRNA? Q2. The enzyme which shows polymerising activity in (a) TACGTGCTGATC (b) ATCCACGACTAG 5'→ 3' direction is. (c) AUCCACGACUAG (d) AUGCACGACTAG (a) DNA polymerase III (b) DNA polymerase II Q9. During protein synthesis, amino acid gets attached to (c) DNA polymerase I tRNA with the help of. (d) All of these (a) mRNA (b) Aminoacyl synthetase (c) Ribosome (d) rRNA Q3. DNA polymerase I is involved in. (a) Removal of RNA primer Q10. The first amino acid in any polypeptide chain of (b) Filling of gap prokaryote is always. (c) Joining of okazaki fragments (a) Formylated methionine (d) Both (a) and (b) (b) Formylated arginine (c) Lysine Q4. DNA replication in lagging strand of most of the (d) Methionine eukaryotic organisms is. (a) continous (b) discontinous Q11. Which site of a tRNA molecule forms hydrogen bonds (c) Both (a) and (b) (d) None of the above with mRNA molecule? (a) Codon Q5. Unidirectional flow of information called central (b) Anticodon dogma was given by (c) 5' end of the t-RNA molecule (a) F.H.C. Crick (b) Temin (d) 3' end of the t-RNA molecule (c) Baltimore (d) Dulbecco Q12. To code the 50 amino acids in a polypeptide chain, Q6. In eukaryotes, RNA III catalyses the synthesis of. what will be the minimum number of nucleotides in (a) All rRNA and tRNA its cistron? (b) mRNA, HnRNA and SnRNA (a) 50 (b) 153 (c) 5S rRNA, tRNA and SnRNA (c) 306 (d) 309 Q13. The genetic code is called a degenerate code because. (a) Antiparallel polarity of two polynucleotide strands (a) One codon has many meanings (b) Hydrogen bonding (b) More than one codon has the same meaning (c) Pairing between one purine and one pyrimidine (c) One codon has one meaning (d) All the above (d) There are 64 codons present Q22. Positive charge and basic nature of histone is due to Q14. In nucleoside which of the following bond exists abundance of. between sugar and nitrogenous base? (a) Lysines and tryptophan (a) Phosphodiester bond (b) Arginine & threonines (b) Hydrogen bond (c) Lysines and arginines (c) Phosphoester bond (d) Tryptophan and threonines (d) N-glycosidic bond Q23. Negative charge of DNA is due to which of the Q15. By which of the following bond phosphoric acid following constituent. remain linked with 5' carbon of sugar in one (a) Sugar nucleotide? (b) Nitrogenous base (a) Phosphodiester bond (c) Phosphoric acid (b) N-Glycosidic bond (d) Hydroxyl group (–OH) present on sugar (c) Hydrogen bond (d) None of the above Q24. Which of the following is actual sequence of packaging of DNA in eukaryotic cells from left to right below? Q16. In RNA, every nucleotide residue has an additional – (a) DNA , Chromatin, Nucleosome, Chromosome OH group at which of the following position. (b) DNA, Nucleosome, Chromosome, Chromatin (a) 2' position of deoxyribose (b) 1' position of ribose sugar (c) DNA, Nucleosome, Chromatin, Chromosome (c) 3' position of ribose sugar (d) DNA, Chromosome, Chromatin, Nucleosome (d) 2' position of ribose sugar Q25. The packaging of chromatin at higher level requires Q17. DNA as an acidic substance present in nucleus was additional set of proteins that is known as. first identified by. (a) Histone proteins (a) Wilkins and Franklin (b) NHC proteins (b) Watson and Crick (c) Homeotic proteins (c) Friedich meischer (d) Domain proteins (d) Altmann Q26. Regarding to Meselson and Stahl experiment for semi Q18. Double helix model of DNA proposed by Watson and conservative nature of DNA replication select the Crick was based on. wrong statement? (a) X-ray diffraction data of Meischer (a) 15N of 15NH4Cl was incorporated in DNA and (b) X-ray crystallography data of Wilkins and Franklin other compounds (c) X-ray diffraction data of Watson and Crick (b) 15N & 14N can be differentiate on the basis of (d) X-ray diffraction data of Chargaff radioactive activity (c) Heavy and normal DNA molecules could be Q19. Regarding the features of double helix structure of DNA which of the following is wrong? distinguished by CsCl density gradient (a) Two polynucleotide chains have antiparallel centrifugation polarity (d) 15N used in 15NH4Cl was not a radioactive (b) The bases in two strands are paired through isotope phosphodiester bonds Q27. If normal E.Coli is allow to grow for 80 minutes in (c) Adenine form two hydrogen bonds with thymine 15NH4Cl medium then what would be the proportion (d) The pitch of the helix is 3.4 nm of hybrid and heavy density DNA molecules? Q20. In addition to hydrogen bonding which of the (a) 1 : 7 (b) 7 : 1 following feature confers stability to helical structure? (c) 14 : 2 (d) 1 : 4 (a) Phosphodiester bond (b) Pairing between one purine and one pyrimidine Q28. Which of the following is not a criterion for (c) Glycosidic linkage between sugar and nitrogenous determination of genetic material? base (a) Ability of replication (d) The plane of one base pair stacks over the other (b) Chemically and structurally stable (c) It should be non mutable Q21. Which of the following is responsible for constant (d) Ability to express itself in from of Mendelian distance between two polynucleotide chains in DNA? characters Q29. At which of the following levels, regulation of gene Reason (R): The two chains have parallel polarity. expression in eukaryotes does not occur? (a) Both assertion (A) and reason (R) are true and (a) Transcription level reason (R) is the correct explanation of assertion (b) Processing level (A) (c) Transport of ribosomal subunits from nucleus to (b) Both assertion (A) and reason (R) are true but cytoplasm level reason (R) is not the correct explanation of (d) Translation level assertion (A) (c) Assertion (A) is true but reason(R) is false Q30. Regarding to role of RNA in protein synthesis find out (d) Assertion (A) is false but reason(R) is true the odd one out. (a) m-RNA - provides the template Q3. Assertion (A): The DNA-dependent DNA (b) t-RNA - brings amino acids polymerases catalyse polymerisation only in one (c) r-RNA - read genetic code direction, that is 5' → 3’ direction. (d) sn-RNA splicing Reason (R): The discontinuously synthesised fragments during replication are later joined by the ASSERTION AND REASONING enzyme DNA helicase. (a) Both assertion (A) and reason (R) are true and Direction: in the following questions, a statement of reason (R) is the correct explanation of assertion assertion (A) is followed by a statement of reason (R). Choose (A) the correct option among a, b, c and d. (b) Both assertion (A) and reason (R) are true but Q1. Assertion (A): Central dogma is the flow of reason (R) is not the correct explanation of information from DNA to mRNA and then decoding assertion (A) the information present in mRNA in the form of (c) Assertion (A) is true but reason(R) is false protein. (d) Assertion (A) is false but reason(R) is true Reason (R): In retroviruses, reverse of central dogma Q4. Assertion (A): There are three RNA polymerases in occurs. the nucleus of eukaryotes. (a) Both assertion (A) and reason (R) are true and Reason (R): Amon the three RNA polymerases, RNA reason (R) is the correct explanation of assertion polymerase III is responsible for transcription of (A) tRNA, 5srRNA, and snRNAs. (b) Both assertion (A) and reason (R) are true but (a) Both assertion (A) and reason (R) are true and reason (R) is not the correct explanation of reason (R) is the correct explanation of assertion assertion (A) (A) (c) Assertion (A) is true but reason(R) is false (b) Both assertion (A) and reason (R) are true but (d) Assertion (A) is false but reason(R) is true reason (R) is not the correct explanation of Q2. Assertion (A): DNA is made of two polynucleotide assertion (A) chains, where the backbone is constituted by sugar- (c) Assertion (A) is true but reason(R) is false phosphate. (d) Assertion (A) is false but reason(R) is true SOLUTIONS MULTIPLE CHOICE S1. (d) DNA and RNA are two types of nucleic acids S6. (c) cytosine is common for both DNA and RN. found in living systems, DNA acts as the genetic material in most of the organisms while RNA S7. (b) two nucleotides are linked by 3’- acts as genetic material in some of the virus. 5’phosphodiester linkage to form a dinucleotides. S2. (a) the determination of the complete nucleotide sequence of the Human Genome during the last S8. (d) the backbone of a polynucleotide chain is formed decade has set in a new era of genomics. due to sugar and phosphate, the nitrogenous bases linked to sugar moiety project from the S3. (b) the length of the DNA can be defined as a number backbone of a DNA. of nucleotide (base pairs) present in it. S9. (b) DNA was first identified by Fredrich Meischer in S4. (b) Each organism has different content of DNA base the year 1869. pair content. S10. (d) Chargaff summarised that for a double-stranded S5. (d) the structure of a polynucleotide is complex. The DNA the ratios between adenine and thymine chain is composed of various nucleotides that and guanine and cytosine are constant and are further made of a nitrogenous base, pentose equals one. sugar and a phosphate group. S11 (d) it was in 1953 that James Watson and Francis radioactive sulphur, with subsequent Crick based on the X-ray diffraction data experiments they found that DNA is the genetic produced by Maurice Wilkins and Rosalind material. Franklin proposed a very simple but famous S23. (c) In most, DNA is the predominant material, RNA double helix model for the structure of DNA. acts as the genetic material only in some of them. S12. (c) the bases in two strands are paired through S24. (d) the genetic material should be stable enough not hydrogen bonds forming base pairs. Adenine to change with stages of life cycle, age or with forms two hydrogen bonds with thymine from change in physiology of the organism, all these the opposite stand and vice versa while guanine properties are there in DNA therefore it makes it is paired with cytosine with three hydrogen a better genetic material than RNA. bonds. S13. (a) The central dogma is same in all organisms S25. (b) both DNA and RNA are able to mutate, RNA can leaving some virus in which the flow of directly code for synthesis of protein and can information is in the reverse direction. easily express characteristics therefore the protein synthesizing machinery has evolved S14. (b) The charge on DNA is negative so it runs towards around RNA. the positive pole when run on agarose gel electrophoresis. S26. (c) the two strands of DNA act as a template for the synthesis of new complementary strands, after S15. (c) the DNA in the nucleoid is organised in last loops the completition of replication each DNA has one that are held together by a basic protein called parental and one newly synthesized strand, this histones. is semiconservative DNA replication. S16. (d) protein acquire charge depending upon the S27. (b) the experiments were performed by Matthew abundance of amino acids structure with Meselson and Franklin Stah by growing E.coli in charged side chains, histones are rich in the a medium containing a heavy isotope of basic amino acid residue, lysine and arginine. Nitrogen. S17. (b) the negatively charged DNA is wrapped around S28. (b) DNA polymerase is the main enzyme of DNA the positively charged histone octamer to form a replication and uses a DNA template to catalyse structure called nucleosome that contains 200 the polymerisation of the deoxynucleotides. base pairs of DNA helix. S29. (a) the DNA dependent DNA polymerases catalyse S18. (c) nucleosomes constitutes the repeating unit of polymerisation only in one direction that is 5’ → chromatin thread like stained bodies seen in 3’ nucleus. S30. (c) on the template strand the replication is S19. (c) in a nucleus, some region of chromatin is loosely continuous while on the other strand with the packed and stains light and is referred to as polarity of 5’ → 3’prime the replication is euchromatin, the chromatin that is more densely discontinuous, the discontinuously synthesised packed and stains dark is called strands are later joined by enzyme DNA ligase. heterochromatin. Euchromatin is said to be transcriptionally more active. S31. (c) there is a definite region in DNA where replication originate, such regions are termed as S20. (c) in 1928, Friedrich Griggith in a series of ‘origin of replication’ and the vectors provide the experiments with Streptococcus witness the origin of replication. miraculous transformation the bacteria. S32. (d) in eukaryotes the replication of DNA takes place S21. (c) after his experiments Frederick Grifitth at the S-phase of the cell cycle. concluded that the ‘R’ strain of bacteria that somehow been transformed by the heat killed ‘S’ S33. (b) in transcription, the DNA acts as a template so bacteria. Some transforming principle that it can be copied into the RNA. transferred from the heat killed ‘S’ strain had S34. (b) In replication the total DNA gets copied while in enabled the ‘R’ strain to synthesise a smooth transcription, it is not so, only a segment of DNA polysaccharide coat and become virulent. gets transcribed. S22. (c) Alfred Hershey and Martha Chase in 1952 S35. (d) Both strands of DNA are not copied because it worked with viruses that infect bacteria called may produce two RNA strands that may form a bacteriophages , they grew some virus on a dsRNA, a stable molecule, and would not be able medium that contained radioactive phosphorus to provide a template for translation to occur. and some others on medium that contained S36. (c) in a transcriptional unit, a structural gene is S52. (d) George Gamow proposed that there are four flanked by the promoter and a terminator. bases that code for 20 amino acids. Har Gobind S37. (d) the negatively charged DNA is wrapped around Khorana developed a chemical method to the positively charged histone octamer to form a synthesise RNA molecules with defined structure that is called a nucleosome. combinations of bases. Marshall Nirenberg’s cell S38. (c) Francis Crick proposed the central dogma in free system for protein synthesis finally helped molecular biology which states that the genetic the code to be deciphered. information flows from DNA to RNA and RNA to protein. S53. (d) AUG has dual functions, it codes for amino acid methionine and serves the function of an S39. (b) promoter and terminator flank the structural initiator codon, while the stop codons are UAA, gene in a transcription unit, promoter is located UAG, UGA. upstream of the structural and is a sequence that provides binding site for RNA polymerase. S54. (b) in sickle cell anaemia, point mutation causes a change of single base pair in the gene for beta S40. (b) functional unit of inheritance is gene, that were globin chain that results in the change of amino called as ‘factor; by Mendel. acid residue, glutamate to valine. S41. (c) Cistron is a segment of DNA that quotes for a S55. (c) tRNA is also called as soluble RNA and acts as an polypeptide adaptor molecule and is specific for each amino S42. (d) Exon is a portion of a gene that codes for amino acid. acids, it is interrupted by introns, when a RNA S56. (b) tRNA has an anticodon loop that has bases gets processed, the intertwining sequences are complementary to the code and it also has an removed and they do not appear in a mature amino acid acceptor and to which it binds to RNA. amino acids. S43. (d) all the three types of RNA present in bacteria and S57. (c) the secondary structure of tRNA is a clover leaf, all of them are needed to synthesise a protein in in actual structure tRNA is a compact molecule a cell. which looks like inverted L. S44. (c) mRNA provide the template, tRNA brings amino S58. (d) translation is the process of formation of a acids and reads the genetic code and rRNA plays polypeptide by the coming together of amino structural and catalytic role during translation. acids whose order and sequence are defined by S45. (c) RNA polymerase uses nucleoside triphosphates the sequence of bases in the mRNA. as substrates and polymerises in a template S59. (d) amino acylation of tRNA is the first phase of dependent fashion. translation and energy consuming process. S46. (b) the Sigma factor acts as an initiation factor and S60. (c) protein synthesis takes place on the ribosome. associates transiently to start transcription. S61. (a) the ribosome consists of structural RNA and S47. (c) RNA polymerase I transcribes rRNA (28S, 18S, different proteins in its inactive state, when the 5.8S) RNA. small subunit encounters an mRNA the process S48. (c) hnRNA is the heterogeneous RNA and precursor of translation of the mRNA into protein begins. RNA are synthesised by RNA polymerase II. S62. (d) the ribosome (23S rRNA in bacteria is the S49. (d) The primary transcripts consists of both exons enzyme-ribozyme) acts as a catalyst for the and introns so it is subjected to splicing where formation of peptide bond. introns are removed and exons are joined in a S63. (d) regulation of gene expression is a very broad defined order. term and in eukaryotes it can be exerted at any S50. (b) in capping, an unusual nucleotide, methyl of the above mentioned levels. guanosine triphosphate is added to the 5’ end of heterogeneous RNA. S64. (c) the i gene codes for the repressor of the lac operon, gene z, y, and a are the structural genes. S51. (b) in the tailing process adenylate residues (200 to 300) are added at the 3’ and in a template S65. (b) the gene y codes for permease which increases independent manner, it is the fully processed the permeability of the cell to beta galactosidase hnRNA that is now called as mRNA and is all the 3 gene products in Lac Operon are transported out of the nucleus for translation. required for metabolism of lactose. S66. (c) lactose is the substrate for enzyme beta S2. (a) For a molecule to act as a genetic material it galactosidase hence is it is also called as inducer should be able to generate its replica, it should for the operon. be stable chemically and structurally and it should be able to express itself in the form of S67. (b) The repressor of the operon is synthesised from 'Mendelian Characters’. DNA possess all these the i-gene all the time. In the presence of inducer features so it is the genetic material in most of (lactose) the repressor is inactivated by the organisms. interaction with the inducer, that allows the RNA polymerase to access the promoter and S3. (c) Alfred Hershey and Martha Chase worked with transcription proceeds. viruses that infect bacteria called bacteriophages. S68. (b) BAC is bacterial artificial chromosome that is used as a vector in cloning a segment of DNA. S4. (a) Histones are rich in the basic amino acid residues lysine and arginine. Both the amino S69. (a) in DNA fingerprinting a satellite DNA is used as a acid residues carry positive charges in their side probe that shows very high degree of chains. Histones are organised to form a unit of polymorphism. eight molecules called histone octamer. S70. (c) single nucleotide polymorphism in humans is an information that promises to revolutionise the process of finding chromosomal locations for TRUE AND FALSE disease associated sequences and tracing human history. S1. (False) Alfred Hershey and Martha Chase grew some viruses on a medium that contained ASSERTION AND REASON radioactive phosphorous and some others on medium that contained radioactive sulphur. S2. (True) S1. (c) The discontinuously synthesised fragments S3. (False) Mono-cistronic genes are mostly found in during DNA replication are later joined by the eukaryotes. enzyme DNA ligase. S4. (True)  PRACTICE SOLUTIONS S1. (b) Semi conservative type of DNA replication, Fresh amino acids, the minimum length of cistron will DNA molecule has one parent strand i.e. (N15) which be 51 x 3 = 153 bp. is heavy and other strand (N14) N14 lighter. S13. (b) many codons have same meanings so genetic Therefore, 50 heavy DNA molecule in first replication code is degenerate. makes 100 hybrid DNA molecule and other replication 100 DNA will be also hybrid (1/2 heavy S14. (d) In DNA and RNA the nitrogen base is attached to the and 1/2light) and 100 light DNA molecules. sugar molecule to form the nucleoside. The sugars S2. (c) DNA polymerase I catalyze the polymerization deoxyribose and ribose are linked to the nitrogenous directed by the template of nucleotides into base by glycosidic linkage. It is also known as N- double-stranded DNA in a 5'-3' direction. DNA glycosidic bond. Polymerase I exhibits a 3’ – 5’ exonuclease S15. (a) The diester bond between phosphoric acid and two function or a "proofreading", that lessens the sugar molecules in the DNA and RNA backbone links failure rate during replication of DNA. two nucleotides together to form oligonucleotide S3. (d) DNA polymerase I is involved in the removal of polymers. The phosphodiester bond links a 3' carbon RNA primer and filling of gaps. to a 5' carbon in DNA and RNA. During the reaction of two of the hydroxyl groups in phosphoric acid with a S4. (b) DNA replication in lagging strand of most of the hydroxyl group in two other molecules, two ester eukaryotic organism is discontinuous. bonds in a phosphodiester group are formed. the 3’ S5. (a) the uni-directional flow of information was end has a free hydroxyl group at the 3’ carbon of a given by Crick. sugar, and the 5' end has a free hydroxyl group or phosphate group at the 5’-carbon of a sugar. The S6. (c) In eukaryote cells, RNA polymerase III transcribes synthesis proceeds from the 5’ to the 3’ end. DNA to synthesize ribosomal 5S rRNA, tRNA and other small RNAs. S16. (d) the additional –OH group is present at the 2’ position of the ribose sugar. S7. (b) ρ is a transcription terminator that binds a CA-rich sequence called as a rut (rho utilization) element on S17. (c) Friedrich Meischer was a Swiss physician and was mRNA and migrates in the 5' --> 3' direction until it the first to isolate nucleic acid or DNA as a distinct reaches the transcription complex that is paused at a molecule. He named it 'nuclein' that is DNA associated termination site. with proteins and isolated it from the cell nuclei. S18. (b) Watson and Crick's proposed model of DNA was S8. (c) it would be AUCCACGACUAG. based on the data given from various experiments S9. (b) During protein synthesis, amino acid gets attached to and important X-ray crystallography work by tRNA with the help of aminoacyl-tRNA synthetase Rosalind Franklin and Maurice Wilkins S10. (a) The first amino acid in any polypeptide chain of a S19. (b) The bases in DNA in two strands are paired prokaryote is always formylated methionine. The through hydrogen bond (H-bonds). first amino acid is methionine in eukaryotes. This is because AUG is a start codon that codes for S20. (d) The factors conferring stability to ds DNA are the formylated methionine in prokaryotes and base pair stacking i.e., the individual bases form a methionine in eukaryotes. strong stacking interaction thereby providing S11. (b) The complementary bases on the codon and stability to the double helix and hydrogen bonds anticodon are held together by hydrogen bonds. between the nitrogenous bases. Codon is present on the mRNA and anticodon is S21. (d) The distance between two complementary strands present on the tRNA. Codon on mRNA forms always remains the same because there are hydrogen hydrogen bonds with anticodon site of a tRNA. T