In Eukaryotes:
1. The structural genes are split. They have coding sequences (exons) interspersed with non-coding sequences (introns).
2. The primary transcript of RNA undergoes a process called splicing, by which the introns are removed and the exons are joined together.
3. The hnRNA (precursor of mRNA) undergoes capping and tailing to become mRNA.
4. In capping, methyl guanosine triphosphate is added to the 5' end of hnRNA.
5. In tailing, adenylate residues (about 200-300) are added at the 3' end.
6. The fully processed mRNA is released from the nucleus into the cytoplasm.

(i) ATCGTACTA.
(ii) Base pairs are held together by weak hydroyen bodsin a DNA molecule. Adenine pairs with thymine by two H-bonds and guanine pairs with cytosine by three H-bonds.
(iii) According to basc complementarity rule proposed by Erwin Chargalf for a double-stranded DNA, the ratios between adenine-thymine and guanine-cytosine are constant and equal to one.

(a) Francis Crick.
(b)
(c) It looks like inverted L.

(i) Differences

(ii) Differences

(iii) Differences

(a) A-5', B-3'
(b) The figure represents the continuous and discontinuous synthesis of DNA strands at the replication fork, during replication of DNA.
(c) Replication fork is the y-shaped structure formed with small opening of DNA double helix.
(d) DNA polymerase catalyses polymerisation of nucleotides only in \({ 5 }^{ ' }\longrightarrow { 3 }^{ ' }\) direction.
(e) Both the strands of (parental)DNA act as templates for the synthesis of new strands.
(f) On the template strand with \({ 3 }^{ ' }\longrightarrow { 5 }^{ ' }\) polarity, the new strand is synthesised as a continuous stretch; it is called continuous synthesis.
(g) On the other strand with \({ 5 }^{ ' }\longrightarrow { 3 }^{ ' }\) polarity, DNA is synthesised as short stretches; it is called discontinuous synthesis.
Later the short stretches of DNA are joined by DNA-ligases into a continuous strand.

(a) It is a nucleosome.
(b) a - Histone octamer;
 b - DNA;
 c - \({ H }_{ 1 }\) Histone.
(c) In prokaryotes, the DNA is held with some positively-charged proteins to form a nucleoid.

(a) a to a' is \({ 5 }^{ ' }\longrightarrow { 3 }^{ ' }\)
 No more amino acid will be added.
(b) TCA; anticodon is UCA.
(c) The untranslated regions are required for efficient translation process.
They are present before the initiation codon at the 5'-end and after the stop/termination codon, at the 3'-end.

(i) a - AUG
 b - UAA/UAG/UGA. 
(ii) AUG codes for methionine.
UAA/UAG/UGA does not code for any amino acid, but brings about termination of polypeptide synthesis.
(iii)There are two sites in the large subunit of ribosome, where the subsequent amino acids bind to and come close enough for formation of peptide bond; it is catalysed by peptidyl transferase.
The ribosome also acts as a catalyst (in bacteria) for the formation of peptide bond.

(a) Avery, MacCleod and McCarty gave the proof that "Transforming agent" is DNA
Avery, MacCleod and McCarty experiment:
1) Oswald Avery, colin MacCleod and McCarty in 1933-34 revealed the chemical nature of the transforming substance to be DNA
2) They purified DNA, RNA, Protein from heat-killed S-strain to see which of them could transform R-cells \(\rightarrow \)S-cells.
3) They also observed that protein digesting enzyme (protease) and RNA digesting enzyme (RNAase) have no effect on transformation whereas digestion of DNA with DNAase would not cause transformation
4) This finding established that transforming genetic material is DNA
Result of experiment

(b) Griffith's in vitro experiments demonstrated the occurrence of transformation in Pneumococcus. They provide no indication as to the molecular basis of the transformation phenomenon. Avery and MacCleod carried their experiments in vitro employing biochemical analysis to demonstrate that transformation was mediated by DNA
(c) Griffith showed that a transforming substance existed. Avery et.al. defined it as DNA

(i) Oncogenes are cancer causing genes. They are formed from proto-oncogenes which are present in a  normal cell. oncogenes responsible for inducing uncontrolled cell divisions in a cell as a result of which cancer is caused
(ii) Reverse transcription The synthesis of a DNA molecule from the single-stranded RNA in the presence of an enzyme reverse transcriptase is called reverse transcription
A group of viruses referred to as Retroviruses has RNA as the genetic material
The single-stranded RNA of the virus gives rise to double-stranded DNA through the reverse transcription mechanism involving the enzyme reverse transcriptase. The original viral RNA is degraded and the double-stranded DNA is integrated into the host chromosome giving rise to the provirus. Transcription of the provirus may lead to the expression of viral oncogenes causing cancer. It is also possible that the provirus gives rise to the RNA and proteins leading to the information and release of more retroviral particles.
Thus, these viruses carry the genes for reverse transcription and the enzyme reverse transcriptase catalyses the conversion of RNA to DNA. Retroviruses are connected with one or the other type of cancer

(b) Inducer, It is a chemical which may be a substrate hormone or some other metabolic which after coming in contact with the repressor, changes the latter into non-DNA binding state so as to free the operator gene. Thus the "switch on" occurs
The expression of the genes is usually controlled to achieve maximum cellular economy. This mean that gene will be turned on or off as per requirement. A set of gene will be switched on when there is necessity to handle and metabolise a new subtrate. when these genes are turned on enzymes are produced, which metabolise the new subtrate. The phenomenon is known as induction

It constitutes 15% of total RNA and is smallest out of three with only 70-85 nucleotides having sedimentation coefficient 45. It is of 100 types. Nitrogen bases of some nucleotides are modified to provide coiling to the otherwise single stranded RNA. The tRNA has two models clover leaf and L-form model. It has different specific loops as shown:

mRna caries a message from DNA to ribosome sin the form of sequence of triplet codes.It acts as a plateform where protein synthesis takes place.tRNA transfer aminoacids to protein synthesizing apparatus.mRNA possess codons and tRNA possess anticodons.The anticodons are---(i)UUA,(ii)GUC,(iii)AUA,(iv)CGU

(a)
\(\\ \overline { ^{ 3' }TAC\quad CAT\quad TAG\quad GAT\\ _{ 5' }\underline { AUG\quad GUA\quad AUC\quad CUA } _{ mRNA } } ^{ 5' }\)

DNA fingerprinting is used for identification of kinship.
Procedure:
1. Variable number of tanden repeats (VNTR's) are satellite DNA's that show high degree of polymorphism. They are used as probes in DNA fingerprinting.
2. Fragments of DNA from an individual are isolated and cut with restriction endonucleases.
3. Fragments are separated according to their size and molecular weight through gel electrophoresis.
4. Fragments separated through electrophoresis gel are blotted (immobilised) on a synthetic membrane such as nylon or nitrocellulose.
5. Immobilised fragments are hybridised with a VNTR probe.
6. Hybridised DNA fragments can be detected by autoradiography.
7. VNTRs are different in size, ranging from .1 to 20 kb. Hence, in the autoradiogram, a band of different sizes will be obtained.
8. These bands are the characteristic feature of an individual. They are different in each and ever} individual except identical twins.

(1) RNA polymerase binds to the promotor and initiates transcription. It uses nucleotide triphosphates as substrates and polymerises in a template dependent fusion following the rule of complementary. It somehow also facilitates opening
of the helix structure and continues elongation. Only a short stretch of RNA remains bound to the enzyme. Once the polymerase reaches the terminator region, the nascent RNA falls off, so also the RNA polymerase. This results into termination
of the transcription.
(2) RNA polymerase associates transiently with termination factor (rho) to terminate the transcription. Association of this factor alters the specificity of the RNA polymerase to terminate.

(i) Normal haemoglobin
(ii) Sickle cell anemia carrier haemoglobin (Heterozygous)
(iii) Sickle cell anaemia (Homozygous condition)
(iv) Carrier woman for Haemophilia
(v) Haemophilic man

The DNAstrand with 3'-5' polarity only is trancribed and not the other because the RNA-polymerase can polymerize RNA only in 5'-3' direction.