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Correct Answer is : (a) ³²P

(c) Hershey-Chase experiment

1. Self Replication: It should be able to replicate. According to the rule of base pairing and complementarity, both nucleic acids (DNA and RNA) have the ability to direct duplications. Proteins fail to fulfill this criteria.

2. Stability: It should he stable structurally and chemically. The genetic material should be stable enough not to change with different stages of life cycle, age or with change in physiology of the organism. Stability as one of property of genetic material was clearly evident in Griffith’s transforming principle. Heat which killed the bacteria did not destroy some of the properties of genetic material. In DNA the two strands being complementary.

if separated (denatured) by heating can come together (renaturation) when appropriate condition is provided. Further 2’ OH group present at every nucleotide in RNA is a reactive group that makes RNA liable and easily degradable. RNA is also known to be catalytic and reactive. Hence, DNA is chemically more stable and chemically less reactive when compared to RNA. Presence of thymine instead of uracil in DNA confers additional stability to DNA.

3. Information storage: It should be able to express itself in the form of ‘Mendelian characters’. RNA can directly code for protein synthesis and can easily express the characters. DNA, however depends on RNA for synthesis of proteins. Both DNA and RNA can act as a genetic material, but DNA being more stable stores the genetic information and RNA transfers the genetic information.

4. Variation through mutation: It should be able to mutate. Both DNA and RNA are able to mutate. RNA being unstable, mutates at a faster rate. Thus viruses having RNA genome with shorter life span can mutate and evolve faster. The above discussion indicates that both RNA and DNA can function as a genetic material. DNA is more stable, and is preferred for storage of genetic information.

1. Self replication 

2. Information storage 

3. Stability 

4. Variation through mutation

(c) R explains A

Correct Answer is : RNA

In capping an unusual nucleotide, methyl guanosine triphosphate is added at the 5’ end of hnRNA, whereas adenylate residues (200- 300) (Poly A) are added at the 3’ end in tailing.

(b) 4 × 10⁶m

In the absence of lactose, the repressor protein binds to the operator and prevents the transcription of structural gene by RNA polymerase, hence the enzymes are not produced. However, there will always be a minimal level of lac operon expression even in absence of lactose.

(c) Meselson and Stahl

(d) Semi-conservative nature of DNA replication

In eukaryotes, the promoter has AT rich regions called TATA box or Goldberg-Hogness box. It acts as a binding site for RNA polymerase.

(b) Replication occurs as each base is paired with another exactly like it

(c) UUU, Phenylalanine

In eukaryotes, the structural gene is monocistronic coding for only one protein whereas in prokaryotes the structural gene is polycistronic coding for many proteins.

(d) There are numerous different bacterial chromosomes, with replication occurring in each at the same time.

d)There are numerous different bacterial chromosomes, with replication ocurring in each at the same time.

UGA, UAA and UAG are the non-sense codons, which terminates translation.

1. DNA polymerase I Involved DNA repair mechanism 

2. DNA polymerase II Involved DNA repair mechanism 

3. DNA polymerase III Involved in DNA replicaton

The genetic code is universal. It means that all known living systems use nucleic acids and the same three base codons (triplet codon) direct the synthesis of protein from amino acids. 

For example, the mRNA (UUU) codon codes for phenylalanine in all cells of all organisms. Some exceptions are reported in prokaryotic, mitochondrial and chloroplast genomes. However similarities are more common than differences.

Two number of codons, codes for cystine.

Exceptions to universal nature of genetic code is noticed in prokaryotic mitochondrial and chloroplast genomes.

(d) Ambiguous

Correct Answer is : (b) ii and iv

A degenerate code means that more than one triplet codon could code for a specific amino acid. For example, codons GUU, GUC, GUA and GUG code for valine.

Correct Answer is : (b) UAU, UAU

Correct Answer is: (c) Sixth

1. AUG is the initiator codon and also codes for methionine. 

2. UAA is a terminator codon.

A translation unit in mRNA is the sequence of RNA that is flanked by the start codon on 5’ end and stop codon on 3’ end and codes of polypeptide.

Tetracycline inhibits binding between aminoacyl tRNA and mRNA.Streptomycin inhibits initiation of translation and causes misreading.

AUG has dual functions. It acts as a initiator codon and also codes for the amino acid methionine.

1. Exons: Expressed sequences (Coding sequences) of an eukaryotic gene 

2. Introns: Interveining sequences (noncoding sequences) of an eukaryotic gene

Bacterial (prokaryotic) RNA polymerase consists of two major components, the core enzyme and the sigma subunit. The core enzyme (β1, β, and α) is responsible for RNA synthesis ” whereas a sigma subunit is responsible for recognition of the promoter.

1. DNA Polymerase I Involver in DNA repair mechanism 

2. DNA Polymerase II Involver in DNA repair mechanism 

3. DNA Polymerase III Involver in DNA replication

The 5’ end of the mRNA of prokaryotes has a special sequence which precedes the initial AUG start codon of mRNA. This ribosome binding site is called the Shine – Dalgamo sequence or S-D sequence. This sequences base-pairs with a region of the 16Sr RNA of the small ribosomal subunit facilitating initiation.

The negatively charged DNA is wrapped around the positively charged histone octamere to form a structure called nucleosome. A typical nucleosome contains 200 bp of DNA helix.

mRNA also have some additional sequences that are not translated and are referred to as Untranslated Regions (UTR). UTRs are present at both 5’ end (before start codon) and at 3’ end (after stop codon).

According to Erwin Chargaff, 

1. Adenine pairs with Thymine with two hydrogen bonds. 

2. Guanine pairs with Cytosine with three hydrogen bonds.

(c) Addition of aminoacid leads to hydrolysis of tRNA

Komberg proposed a model for the nucleosome, in which 2 molecules of the four histone proteins H2A, H2B, H3 and H4 are organized to form a unit of eight molecules called histone octamere.

The negatively charged DNA is wrapped around the positively charged histone octamere to form a structure called nucleosome. A typical nucleosome contains 200 bp of DNA helix. The histone octameres are in close contact and DNA is coiled on the outside of nucleosome.

The process of addition of amino acid to tRNA is known as aminoacylation or charging and the resultant product is called aminoacyl- tRNA (charged tRNA). Aminoacylation is catalyzed by an enzyme aminoacyl – tRNA synthetase.

Three molecular biologists in the early 1980’s (Leslie Orgel, Francis Brick and Carl Woese) independently proposed the ‘RNA world’ as the first stage in the evolution of life, a stage when RNA catalysed all molecules necessary for survival and replication. The term ‘RNA world’ first used by Walter Gilbert in 1986, hypothesizes RNA as the first genetic on Earth. There is now enough evidence to suggest that essential life processes (such as metabolism, translation and splicing etc.,) evolved around RNA. RNA has the ability to act as both genetic material and catalyst. There are several biochemical reactions in living systems that are catalysed by RNA. This catalytic RNA is known as ribozyme. But, RNA being a catalyst was reactive and hence unstable.

This led to evolution of a more stable form of DNA, with certain chemical modifications. Since DNA is a double stranded molecule having complementary strand, it has resisted changes by evolving a process of repair. Some RNA molecules function as gene regulators by binding to DNA and affect gene expression.

Some viruses use RNA as the genetic material. Andrew Fire and Craig Mellow (recipients of Nobel Prize in 2006) were of the opinion that RNA is an active ingredient in the chemistry of life.

The transfer RNA, (tRNA) molecule of a cell acts as a vehicle that picks up the amino acids scattered through the cytoplasm and also reads specific codes of mRNA molecules. Hence it is called an adapter molecule. This term was postulated by Francis Crick.

In DNA, the two strands being complementary, if separated (denatured) by heating can come together (renaturation) when appropriate condition is provided. Further 2 OH group present at every nucleotide in RNA is a reactive group that makes RNA liable and easily degradable. RNA is also known to be catalytic and reactive. Hence, DNA is chemically more stable and chemically less reactive when compared to RNA. Presence of thymine instead of uracil in DNA confers additional stability to DNA.

(c) Nucleotide containing sugars, nitrogen bases and phosphates

DNA: 

1. Sugar is deoxyribose sugar. 

2. Double stranded structure. 

3. Nitrogen bases are Adenine, Guanine, Cytosine and Thymine.

RNA: 

1. Sugar is ribose sugar. 

2. Single stranded molecule. 

3. Nitrogen bases are Adenine, Guanine, Cytosine and Uracil

(d) Gene that switched other genes on or off

mRNA,  tRNA.

Heterochromatin: 

1. Region of nucleus where the chromatin are loosely packed and stains light are called Heterochromatin. 

2. Transcriptionally inactive.

Euchromatin: 

1. Region of nucleus where the chromatin are tightly packed and stains dark are called Euchromatin. 

2. Transcriptionally active.

Leading strand: 

1. Leading strand has the polarity 3’ → 5’. 

2. Replication is continuous. 

Lagging strand: 

1. Lagging strand has the polarity 5’ → 3’.

2. Replication is discontinuous.

The ribosomes of eukaryotes (80 S) are larger, consisting of 60 S and 40 S sub units. ‘S’ denotes the sedimentation efficient which is expressed as Svedberg unit (S). The larger subunit in eukaryotes consist of a 23 S RNA and 5Sr RNA molecule and 31 ribosomal proteins. The smaller eukaryotic subunit consist of 18Sr RNA component and about 33 proteins.