BIOLOGY 3 Marks Question

DNA Fingerprinting is a technique to find out variations in individuals of a population at DNA level.
Its applications are as follows:

1. Used in forensic science to identify suspects.
2. Used to find out history of an organism.
3. Used to find out paternity and family relations.

mRNA and tRNA.

mRNA	tRNA
It is called messenger RNA and carries the codes for amino acid sequence.	It is called transfer RNA as it carries amino acids to the site of protein synthesis.
It is a linear molecule.	It has clover leaf shape.
It is synthesised by RNA polymerase II	It is synthesised by RNA polymerase III.

The property of DNA double helix led Watson and Crick are:

• Two strands running opposite to each other, wherein bases will always pair with their counterpart-A with T and G with C (specific pairing).
• If H bonds break and bases of one strand lie exposed, unpaired, they will easily pair up with free nucleotides as well. This type of arrangement in DNA molecule led to the hypothesis that DNA replication is semi-conservative. where the two strands separate and act as a template for the synthesis of a new complementary strand.

Alfred Hershey and Martha Chase (1952) worked with viruses that infect bacteria called bacteriophages. In 1952, they chose a bacteriophage known as T2 for their experimental material. They grew some viruses on a medium that contained radioactive phosphorus (p32) and some others on medium that contained radioactive sulphur (s35). Viruses grown in the presence of radioactive phosphorus contained radioactive DNA but not radioactive protein because DNA contains phosphorus but protem does not Similarly. viruses grown on radioactive sulphur contained radioactive protein but not radio'active DNA because DNA does not contain sulphur. Radioactive phages were allowed to attach to E.coli bacteria. Then, as the infection proceeded, the viral coats were removed from the bacteria by agitating them in a blender. The virus particles were separated from the bacteria by spinning them in a centrifuge., Bacteria which was infected with viruses that had radioactive DNA were radioactive, indicating that DNA was the material that passed from the virus to the bacteria. Bacteria that were infected with viruses that had radioactive proteins were not radioactive. This indicates that proteins did not enter the bacteria from the viruses. DNA is therefore the genetic material that is passed from virus to bacteria.

Template strand and Coding strand.

Template strand	Coding strand
It is the strand which is transcribed into RNA.	It has the same sequence as mRNA.
It is called anti sense strand.	It is called sense or non-template strand.
It has 3' → 5' polarity.	It has 5' → 3' polarity

Repetitive DNA and Satellite DNA.

Repetitive DNA	Satelite DNA
It is the non-coding DNA with multiple copies of identical sequences which may lie in tandem or interspersed.	It refers to non-coding tandem repeat sequences.
These can be few base pairs to hundreds or thousands of base pairs.	These are generally short sequence repeats (up to 60 base pair long).
It appears as light bands.	It appears as small dark bands.

1. Replication of DNA occurs in small replication forks, because DNA is such a long molecule that the separation of the two strands along its entirelength requires a very high amount of energy.
2. DNA polymerase can catalyse the polymerization of nucleotides only in 5' → 3' direction.

1. So on the template strand with 3' → 5' polarity, DNA replication is continuous.
2. On the template strand with 5' → 3' polarity, DNA synthesis occurs in short stretches as the opening of replication fork continues; later these short stretches are joined by the action of DNA ligases .

2. Replication of DNA does not initiate randomly, and DNA polymerases on their own cannot initiate replication.

1. So, there is a specific sequence on DNA, called origin of replication; DNA polymerase bindsto it and continues the process.

1.  

2. On one hand, it reads the code.

On the other hand, it binds to specific amino acid.

Function of Methylated Guanosine Cap:

1. Attachment of mRNA: it helps in the attachment of mRNA to smaller ribosomal subunit during initiation of translation.
2. Function of poly A tail: It helps in the Protection of translational region.

Since there are only four bases which code for twenty amino acids, the code should be made up of three bases, i.e., (4 × 4 × 4) = 64 codons; a number more than the required. If the codon consists of four letters, only (4 × 4), only sixteen codons are possible, which is less than the required. Hence the codon is a triplet. As the ribosome moves on mRNA, continuously without break, the codons are read in a contiguous manner.

Unambiguous -One codon codes for one amino acid, e.g. AUG (Methionine).Universal -Codon and its corresponding amino acid are the same in all organisms.
Example:- more-Bacteria to human UUU codes for phenylalanine (phe).
Degenerate - Some amino acids are by more than one codon.
Example:- UUU and UUC code for phenylalanine (phe).

Processes like metabolism, translation, splicing evolved around RNA, RNA is reactive and catalyses reaction. In some virus it is the hereditary material. It is so unstable and hence would have mutated to lead to evolution.

Three goals of human genome project:

1. To develop new and improved medicines.
2. To predict and prevent diseases.
3. To ensure that the diagnosis is accurate.

1. Centrifugation in a CsCl density gradient.
2.  

'BAC'- Bacterial Artificial Chromosome.
"YAC' - Yeast Artificial Chromosome.

1. They are the commonly used vectors for cloning the DNA fragments in the hosts like bacteria and yeast.
2. The cloning results into amplification of each fragment of DNA, so that they could be sequenced with ease.

The technique help in solving a case of paternity dispute over the custody of a child by two different families is DNA – finger printing. The technique of DNA finger printing was initially developed. He used a satellite DNA as probe that shows very high degree of polymorphism.
Step II: Amplification: Many copies of the extracted DNA are made by Polymerase Chain Reaction (PCR).

1. Separation of DNA sequence restriction fragments: The separated fragments can be visualized by Staining them with a dye that shows fluorescene under ultra violet radiation.
2. Southern Blotling: The separated DNA sequence are transferred on to a nitro cellulose or nylon membrane of Sheet placed over the gel.
3. Hybridization: The nylon membrane is immersed in a bath and radioactive proves are added: These probes target a specific nucleotide sequence that complementary to them.
4. The Probs/Result: X-ray film and dark bands develop at the probs sites which resemble the barcda.

Scheme representation of DNA fingerprinting: Few representative chromosomes have been shown to contain different copy number of VNTR. For the sake of understanding different colour schems have been used to trace the origin of each band in the gel. The two alleles (paternal and maternal) of a chromosome also contan different copy nubers of VNTR. It is clear that the banding pattern of DNA from crime scene.
matches with individual B, and not with A.

DNA fingerprinting (analysis)

• Isolation and digestion of DNA by restriction endonuclease.
• Separation of DNA fragments by electrophoresis and transferring them to synthetic membranes/nitrocellulose/nylon.
• Hybridisation using labelled VNTR probe.
• Detection of hybridised DNA fragments by autoradiography.
• Matching banding pattern of DNA/DNA fingerprints/autoradiograms of the passengers killed and that of relatives.

1. It is attached at the 3' end of RNA.
2. UUU and UUC.
3. Aminoacyl-tRNA synthetase.

The operator region is located adjacent to promoter elements/prior to structural gene. In regulation of gene expression.

• Switch off- The repressor binds to the operator region, & prevents transcription.
• Switch on- In the presence of inducer the repressor is inactivated, (by the interaction with the inducer) and operator allows RNA polymerase access to the promoter, & transcription proceeds.

S. No	RNA polymerase	DNA polymerase
(i)	It cannot carry out proofreading.	It carries out proofreading for DNA repairmechanism.
(ii)	RNA polymerase does not require RNA primer for synthesis of RNA.	DNA polymerase requires RNA primer for synthesis of DNA.
(iii)	It uses ribonucleotides for RNA synthesis.	It uses deoxyribonucleotides for DNA synthesis.

DNA finger printing:
Isolation of DNA and digestion of DNA by restriction endonucleases, separation of DNA fragments by (gel) electrophoresis and transferring (blotting) of separated DNA fragments to synthetic membrane or nitrocellulose or nylon, hybridization using VNTR probe and detection of hybridised DNA fragments by autoradiography, matching the banding pattern so obtained with that of relative.

Charging of tRNA:

1. The amino acids are activated in the presence of ATP and linked to their cognate tRNA; this process is called charging of tRNA or amino acylation of tRNA.
2. This process is necessary as the formation of peptide bond between the amino acids is favoured energetically, when they are brought together.
3. The activation of amino acids by ATP provides the energy for the formation of peptide bond.

Six features of the human genome are as follows:

• The human genome contains 3164.7 million nucleotides.
• The average gene in the human genome contains 3000 bases.
• The total number of genes is estimated to be 30,000.
• Almost all (about 99.9%) of nucleotides are same in all human beings.
• Less than 2 percent of the genome codes for protein.
• Chromosome 1 has the most genes (2968) and chromosome Y has the least (231).

Advantages of Affordable Genome Sequencing: It can help in settling disputes which may arise in case of parentage of a child. This can also help in disputes of property inheritance by finding the bonafide beneficiary. Human genome can also help in preparing a database on people with criminal record. It can help in identifying the chances of genetic disorders in a family.
Disadvantages: Genome sequencing can have serious issues of privacy. Some employers may misuse the data to blackmail their employees. Many private matters may leak into public domain; creating embarrassment for the affected person.

1. VNTR stands for “Variable Number of Tandem Repeats”.

The VNTR belongs to a class of satellite DNA referred to as mini-satellite. A small DNA sequence is arranged tandemly in many copy numbers. The copy number varies from chromosome to chromosome in an individual. The numbers of repeat show very high degree of polymorphism. As a result th size of VNTR varies in size from 0.1 to 20kb. Consequently, after hybridization with VNTR probe, the autoradiogram gives many bands of differing sizes. These bands give characteristic pattern for an individual DNA which is used to identify individuals.

2. Since DNA from every tissue (such as blood, hair-follicle, skin, bone, saliva, sperm etc.), from an individual show the same degree of polymorphism, they become very useful identification tool in forensic applications to identify criminals. Further, as the polymorphisms are inheritable from parents to children, DNA fingerprinting is the basic of paternity testing, in case of disputes.

As per the question, the RNA strand given is having Thymine which is not possible. Hence, the question is wrong. Taking U (Uracil) instead of T (Thymine) in the given strand the possible solution shall be RNA Polymerase is the enzyme which is used during transcription.

Both the strands of DNA are not copied during transcription because if both strands act as a template, they would code for RNA with different sequence the two RNA molecules, if produced simultaneously would be complementary to each other, hence would form a double stranded RNA. Transcription is when RNA is made from DNA. During transcription, RNA polymerase makes a copy of a gene from the DNA to mRNA as needed. This process is similar in eukaryotes and prokaryotes. One difference, however, is that eukaryotic RNA polymerase associates with mRNA processing enzymes during transcription so that processing can proceed quickly after the start of transcription.

1.  

a - AUG.

b - UAA/UAG/UGA.

2.  

AUG code for Methionine.

UAA/UAG/UGA - Stop codon/Nonsense codon/Does not code for any amino acid.

3.  

Charged tRNA are brought closer together on mRNA in the ribosomes, and Ribosomes acts as a catalyst (ribozyme) forming peptide bond.

The Polynucleotide Chain One end of the chain ends with a phosphate linked to the 5' carbon of the sugar and is called the 5' end. The other end of the chain ends with an hydroxyl group linked to the 3' carbon of the sugar and is called the 3' end.

1. Since 'RNA on one hand binds to a specific amino acid and on the other hand reads the codon of the amino acid bound to it through its anticodon, it is called an 'adapter'.
2.  

It actually looks like an inverted L.

Properties of genetic code:

1. AUG is the initiation codon and codes for methionine; methionine is the first amino acid in the given polypeptide.
2. Genetic code is unambiguous and specific, i.e., each codon codes only for one particular amino acid.

e.g AUG - Methionine, GUG - Valine, etc.

3. Genetic code is degenerate, i.e. some amino acids are coded by more than one codon.

​​​​​​​e.g. UUU and UUC code for phenylalanine

4. Each codon is a triplet, i.e. made of three nucleotides e.g AUG, UUU, etc.
5. UAG does not code for any amino acid; it is a termination codon.

A- Restriction endonuclease.
B- Agarose.
C- Nylon/ Nitrocellulose.
D- VNTR.
E- Hybridisation.
F- Autoradiography.

The technique that can help in the identification of victims is DNA fingerprinting which distinguishes between individuals of same species by using their DNA as sample. The chemical structure of DNA is same in everyone (99.9%) except the order of base pairs, i.e. only 0.1"of DNA makes every individual unique. DNA fingerprinting exploits the highly variable repeating sequences, i.e. VNTRs for profiling. These VNTRs are highly conserved among members of the same species.
The DNA polymorphism in simple-sequence DNA and VNTRs is revealed during DNA fingerprinting in establishing kinship since it is very remote possibility to have two individuals with same repeats of satellite DNA throughout the genome except they share a biological relationship. This is because a child gets half DNA from father and half from the mother. Restriction enzymes of genome produce the restriction fragments length polymorphisms, or RFLPs depending on the location of restriction sites which are then sorted by gel electrophoresis followed by southern blotting. The DNA sample from killed passengers and of the sample from possible relatives are compared for sequence homology using radioactive probes and kinship is established.
The presence of similarities between the victims and their relatives determines their association on the basis of which dead bodies can be identified and handed over to their families.

1. At the 3' end.
2. UUU or UUC.
3. Aminoacyl tRNA synthetase.

1.  

2. The RNA transcribed is 5' AUGCAUGCAUAG 3'.

S. No	DNA	rRNA
Structural:
(i)	It is a double-stranded structure.	It is a single-stranded structure.
(ii)	It contains nitrogen bases, A, T, G, C.	It contains nitrogen base, A, U, G, C.
(iii)	It has deoxyribose sugar.	It has ribose sugar.
Functional:
	It determines sequence of amino acid in a polypeptide by transcription and passes information from one generation to another.	It is the site of translation.

1. In eukaryotes, the hnRNA (primary transcript of mRNA) has coding sequences, called exons as well as non-coding sequences, called introns, i.e. the information is split.
2. It undergoes a process, called splicing, in which the introns are removed and the exons are joined together in a particular manner, to form the functional mRNA.

• In prokaryotes, the mRNA is polycistronic, i.e. codes for more than one polypeptide.

3. The information is continuous and no splicing is required.

1. Aminoacylation of RNA.
2. mRNA codon-AUG, RNA anticodon-UAC.
3. Enzyme-aminoacyl RNA synthetase.

Wastson and Crick had the following informations which helped them to develop a model of DNA,

1. Chargaffs’ Law suggesting A = T, and C = G.
2. Wilkins and Rosalind Franklin’s work on DNA crystal’s X-ray diffraction studies about DNA’s physical structure.
3. Watson and crick proposed:

• How complementary bases may pair.
• Semi conservative replication and.
• Mutation through tautomerism.

1. Molecule 'X' is a repressor protein. When an inducer combines with it, it is inactivated.
2. 'z' gene.
3. Transcription of gene stops.

1. Substrate (lactose) is not available.
2. Energy source (glucose) is available to the cells.

During the course of Griffith’s experiment, bacteria changed its physical form. This was termed as transformation. In this experiment, the DNA of the S strain bacteria survived heating of bacteria. When a mice was injected with mixture of killed S strain and R strain, the mice died of pneumonia. This showed that DNA had the capability of surviving adverse circumstances and manifesting itself on return of favourable conditions. Stability and survival are key considerations for a material to be classified as genetic material. Thus, transformation in Griffith’s experiment helped in identification on DNA as genetic material.

X: N-glycosidic linkage.
Y : Phosphoester linkage.
Z: 3'-5' phosphodiester linkage.
X forms nucleoside.
Y forms nucleotide.
Z forms polynucleotide.

1. RNA polymerase III transcribes tRNA, 5S rRNA and snRNAs, (small nuclear RNAs).
2.  

S. No.	Capping	Tailing
1.	It is the process of addition of methyl guanosine triphosphate to the 5' end of hnRNA after splicing.	It is the process of addition of adenylate residues to the 3' end of hnRNA after splicing.

3. Heterogenous nuclear ribonucleic acid (hnRNA).

DNA finger printing
Isolation of DNA and digestion of DNA by restriction endonucleases, separation of DNA fragments by (gel) electrophoresis and transferring (blotting) of separated DNA fragments to synthetic membrane or nitrocellulose or nylon, hybridization using VNTR probe and detection of hybridised DNA fragments by autoradiography, matching the banding pattern so obtained with that of relative.

1. Expressed Sequence Tags, Identifying all the genes that are expressed as RNA.

Sequence Annotation, sequencing the whole set of genome coding or non-coding sequences and later assigning different region with functions.

2. Yeast Artificial Chromosome used as cloning vectors. (cloning/amplification)

1. AUG GAG UAC UUC GUG UGA
2. It will code for five amino acids.

The last codon, UGA is a termination codon. that does not code for any amino acid.

S. No.	Salient features of genetic code	Reason
1.	The condin is triplet.	AUG, UUU, etc., are triplets.
2.	One codon codes for only one amino acid, so it is unambigus and specific.	UUU codes for serine, AUG, codes for methionine, etc.
3.	AUG has dual function as it codes for methionine and it also acts as initator codon.	AUG is seen at the beginning of the polypeptide chain.
4.	UAG act as a stop codon.	No amino acid is coded by UAG in the polypeptide chain given.

1.  

1. Amino acylation of tRNA or charging of tRNA.
2. mRNA codon-AUG.

tRNA anticodon-UAC.

2. The part of the chromatin that is tightly packed and stains dark, is called heterochromatin.

1. Promoter- It is a DNA sequence that provides a binding site for RNA polymerase for the initiation of transcription.
2. Structural gene- It codes for enzymes or proteins for structural functions.
3. Terminator- It usually defines the end of the transcription process.

Sequencing of human genome has opened new windows for treatment of various genetic disorders. We know that genetic disorders are caused by some alteration in genes. At present, we do not have exact information about the base pair sequence where this alteration takes place. Hence, we are unable to devise any tool to prevent genetic disorders. By proper understanding of the particular sequence responsible for a particular genetic disorder, the scientist may be able to devise some tools to prevent genetic disorders. A future may come when nobody will be suffering from genetic disorders; especially those which create serious disability.

1. TACAGATAT
2. UACAGAUAU
3.  

S. No	DNA	RNA
(i)	It is a double-stranded structure.	It is a single-stranded structure.
(ii)	It contains deoxyribose sugar.	It contains ribose sugar.
(iii)	Bases are A, T, G, C	Bases are A, G, C, U

Types of RNA:

S. No.	Types of RNA	Functions
(i)	Messenger RNA (mRNA)	1. It stores the genetic information from DNA. 2. It decides the sequence of amino acid in a polypeptide.
(ii)	Transfer RNA (tRNA)	1. It acts as an adaptor molecule that at one end reads the code on mRNA and accordingly bind to amino acid on the other end. 2. It recognises the codon on mRNA by its anticodon and leaves amino acid at the protein synthesis site.
(iii)	Ribosomal RNA (rRNA)	1. It constitutes the ribosomal structure. 2. It helps to form peptide bond.

All the genes controlling a metabolic pathway, constitute an operon.Example:
Lac operon - trp operon. Val operon - his operon.

1. The regions of a chromatin, which are stained light, are the regions where chromatin is loosely packed; they are called euchromatin.
2. The regions of a chromatin, which are stained dark, are the regions where chromatin is tightly packed; they are called heterochromatin.
3. Euchromatinis transcriptionally more active, while heterochromatin is inactive.

DNA Fingerprinting:

• Dr. Alec Jeffreys developed the technique of DNA fingerprinting in an attempt to identify DNA marker for inherited diseases.
• DNA fingerprinting uses short nucleotide repeats called Variable Number Tandem Repeats (VNTRs) as markers. VNTRs vary from person to person and are inherited from one generation to the next. Only closely related individuals have similar VNTRs.

Methodology and Technique: DNA is isolated and extracted from the cell or tissue by centrifugation. By the process of polymerase chain reaction (PCR), many copies are produced. This step is called amplification. DNA is cut into small fragments by treating with restriction endonucleases.

1. DNA fragments are separated by agarose gel electrophoresis.
2. The separated DNA fragments are visualised under ultraviolet radiation after applying suitable dye.
3. The DNA is transferred from electrophoresis plate to nitrocellulose or nylon membrane sheet. This is called Southern blotting.
4. VNTR probes are now added which bind to specific nucleotide sequences that are complementary to them. This is called hybridisation.
5. The hybridised DNA fragments are detected by autoradiography. They are observed as dark bands on X-ray film.

Schematic representation of DNA fingerprinting: Few chromosomes have been shown to contain different copy number of VNTR. The two alleles (paternal and maternal) of a chromosome also contain different copy numbers of VNTR. It is clear that the banding pattern of DNA from crime scene matches with individual B and not with A.Applications of DNA Fingerprinting:

1. It is used as a tool in forensic tests to identify criminals and criminal investigations.
2. It is used to settle paternity disputes and maternity disputes.
3. It is used to determine population and genetic diversities to study evolution.
4. It is used in the study of evolutionary biology.

1. The operator' region is adjacent to the promoter region.
2. The operator regulates the accessibility of promoter region to the RNA polymerase for transcription.
3. The operator binds to the repressor protein coded by the regulatory gene and prevents the RNA polymerase from binding to the promoter; the operon is switched "off".
4. When an inducer binds to the repressor and inactivates it, it cannot bind to the operator; this allows RNA polymerase access to the promoter and transcription continues, i.e., the operon is switched 'on'.

1. Restriction endonuclease.
2. Agarose gel.
3. Nitrocellulose/ nylon/ synthetic membrane.
4. Variable Number Tandem Repeats (VNTR).
5. Hybridisation with VNTR probe.
6. Autoradiography.

1. A-5', B-3
2.  

1. The figure represents the continuous and discontinuous synthesis of DNA strands at the replication fork, during replication of DNA.
2. Replication fork is the Y-shaped structure formed with small opening of DNA double helix.
3. DNA polymerase catalyses polymerisation of nucleotides only in 5' → 3' direction.
4. Both the strands of parental) DNA act as templates for the synthesis of new strands.
5. On the template strand with 3' → 5' polarity, the new strand is synthesised as a continuous stretch; it is called continuous synthesis.
6. On the other strand with 5' → 3' polarity, DNA is synthesised as short stretches; it is called discontinuous synthesis.
7. Later the short stretches of DNA are joined by DNA-ligases into a continuous strand.

1. a to a' is 5' → 3'. No more amino acid will be added.
2. TCA; anticodon is UCA.
3.  

1. The untranslated regions are required for efficient translation process.
2. They are present before the initiation codon at the 5'-end and after the stop/ termination codon, at the 3'-end.

In eukaryotes, there are three RNA-polymerases:

1. RNA-polymerase I catalyses transcription of rRNAs (28S, 185 and 5.85).
2. RNA-polymerase II catalyses transcription of the precursor of mRNA; it is called hnRNA.
3. RNA- polymerase III catalyses transcription of RNA, 5SrRNA and shRNAs.

This tRNA is specific for amino acid methionine and also acts as initiator tRNA.

1. Both the strands of parent DNA function as template strands.
2. On the template strand with 3' → 5' polarity, the new strand is synthesised as a continuous stretch as the DNA polymerase can carry out polymerisation of the nucleotides only in 5' → 3' direction; this is called continuous synthesis and the strand is called leading strand.
3. On the other template strand with 5 → 3' polarity, the new strand is synthesised from the point of replication fork, also in 5' → 3' direction, but in short stretches; they are later joined by DNA-ligases to form a strand, called lagging strand.

The discontinuous synthesis of DNA is as follows:

1. At the replication site, unwinding of double stranded DNA takes place by DNA gyrase and helicase.
2. ssBPs (single-stranded binding proteins) bind to the separated strands to avoid recoiling or to provide stability.
3. Since DNA polymerase can synthesise DNA only in 5′ → 3′ direction, DNA synthesis occurs discontinuously on the lagging strand.
4. These small fragments of DNA are called Okazaki fragments.
5. The enzyme primase adds primers after every fragment is formed.
6. These Okazaki fragments are then joined by DNA ligase.

In lac operon, when lactose is added, it enters the cell wall with the help of permease, a small amount of which is already present in cell. Lactose binding to activates repressor and changes its structure. The repressor now fails to bind to the operator. Then, RNA polymerase starts transcription of operon by binding to promoter site-P. All the three enzymes for lactose metabolism are synthesised.
Finally, all the lactose molecules are used up. After sometime, when whole of lactose is consumed, there is no inducer present to bind to the repressor. Then the repressor becomes active again, attaches itself to the operator and finally switches off the operon.

(DNA dependent) RNA polymerase, binds to the promoter, at 5’ end, associates transiently with initiation factor/sigma factor, using nucleoside triphosphates as substrate, and energy initiates transcription.

A- Nitrogenous base (Purine/ Pyrimidine).
B- Pentose sugar (Ribose/ Deoxyribose).
C- N-glycosidic linkage.
D- Phosphate E-Phosphoester linkage.
F- Phosphodiester linkage.

1. Since eukaryotes have split gene arrangement, the hRNA has both coding sequences (exons) and non-coding sequences (introns) and is non-functional; so it has to undergo splicing, the process, in which introns are removed and exons are joined.
2. It has to undergo two other processes, namely capping and tailing to become functional.
3. In capping, an unusual nucleotide, called methyl guanosine triposphate residues are added at the 5' end of hnRNA.
4. In-tailing, about 200-300 adenylate residues are added at the 3' end, in a template-independent manner.
5. These changes take place in the nucleus of the cell.

DNA fingerprinting
Isolation of DNA and digestion of DNA by restriction endonucleases, separation of DNA fragments by (gel) electrophoresis and transferring (blotting) of separated DNA fragments to synthetic membrane or nitrocellulose or nylon, hybridization using VNTR probe and detection of hybridised DNA fragments by autoradiography, matching the banding pattern so obtained with that of relative.

1. They do not code for any proteins,
2. They form large part of the human genome,
3. They show high degree of polymorphism/Specific to each individual.

1. Differences between unambiguous and degenerate codons are-

S. No.	Unambiguous codon	Degenerate codon
1.	No ambiguity for a particular codon.	Code is degenerate for a particular amino acid.
2.	A particular codon will always code for the same amino acid, where it is found.	One amino acid often has more than one code triplet.
3.	eg. GGA is an unambiguous codon, it codes only for glycine and no other amino acid.	e.g. Phenylalanine has two codons, i.e. UUU and UUC.

2. Functions of codon AUG is as follows-

1. Codes for methionine.
2. Serves as a signal to initiate protein synthesis (initiator codon).

1. DNA replication occurs in small replication forks. It does not occur in its entire length in one time as DNA is a very large molecule and only that part of DNA opens up which is being replicated. The opening of the whole DNA molecule would be an energetically more expensive process.
2. The main enzyme involved in DNA replication is the DNA-dependent DNA polymerase. This enzyme catalyzes the polymerization of deoxynucleotides along the 5′ → 3′ direction, and hence, replication is continuous along the 3′ → 5′ strand (leading strand) and discontinuous along the template, i.e., the 5′ → 3′ direction (lagging strand).
3. Okazaki fragments are short DNA segments on the lagging strand, formed in the 5’ – 3’ direction, starting from RNA primers. A separate RNA primer is needed for the synthesis of each Okazaki fragment. These discontinuously synthesized fragments are later joined by the enzyme DNA ligase.
4. Ori stands for Origin of replication. This site has the highly conserved sequence of DNA among various species. The replication of DNA starts here because this site attracts some proteins which help in the opening and unwinding of DNA and this leads to the initiation of replication.

The function of DNA Ligase is to join the two nucleotides. During the DNA replication process, it joins the Okazaki fragments of the daughter DNA to form the complete DNA molecule on the lagging strand.

In eukaryotes, gene regulation takes place by different mechanisms. Here proteins (histones) play major role in gene regulation. Histones are gene repressors and these mark the gene activity in non-specific manner.
If histones were mutated and made rich in acidic amino acids, they will not be able to serve the purpose of keeping the DNA coiled around them. This is because DNA is negatively charged molecule and histones are positively charged because of basic amino acids.
So, they are attracted to each other. If histones become negatively charged, instead of binding, they will rather repel DNA. The packaging of DNA in eukaryotes would not happen. Consequently, the chromatin fibre would not be formed.

A RNA nucleotide has three main components-a nitrogenous base, a ribose sugar and a phosphate group.

1. The ribose sugar and the phosphates form the backbone of a polynucleotide chain with nitrogenous base linked to sugar moiety and projecting from the backbone.
2. Nitrogenous Bases- (i) parines (Adenine & Guanine) (ii) Pyrimidines- (Cytosine and Uracil).
3. Nitrogenous base is linked to the ribose sugar through N-glycosidic linkages.
4. Phosphate group is linked to 5’ OH of a nucleoside through phosphodiester linkage to form a corresponding nucleotide.
5. Every nucleotide residue has an additional-OH group present at 2’-position in the ribose.
6. Many nucleotides are linked through 3’-5’ phosphodiester linkage to each other to form the polynucleotide chain.
7. The end of the chain which has free phosphate moiety at 5 'end of ribose sugar is referred to as 5' end the other end of the chain having a free 3'-OH group at the ribose sugar is referred to as 3' - end of the polynucleotide chain.

A.
B. DNA polymerase catalyses the polymerisation of nucleotides, Ligase joins the fragments of discontinuous synthesis.

Clover leaf shaped.
This tRNA is specific for methionine/can act as initiator tRNA.

1. Nucleosomes.
2. a - Histone octamer

b - DNA.

c- H1 histone.

3. In bacteria DNA in nucleoid, is organised in large loops held by proteins.

1. In the mammalian cells (or eukaryotes) there is a set of positively-charged basic proteins, called histones.
2. Histones are organised to form a unit of eight molecules, called histone octamer.
3. The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure, called nucleosome.
4. A typical nucleosome contains 200 bp of DNA helix.
5. The nucleosomes constitute the repeating units of chromatin, which appear as beads-on-string structure under an electron microscope.
6. These are further packaged to form the chromatin fibres, which condense to form chromosomes.
7. The packaging of chromatin at higher levels requires additional set of proteins called non-histone chromosomal (NHC) proteins.

1. In order to label protein coat of virus with radioactive sulphur, label DNA with radioactive phosphorus.
2. Bacteria which were infected with viruses having radioactive DNA were found to contain radioactive DNA later on-

Bacteria which were infected with viruses having radioactive protein coat were not found to contain radioactivity.

Conclusion- DNA is the genetic material.

Hershey and Chase selected bacteriophage for their work because of the following reasons:

1. A bacteriophage has only two components-protein and DNA.
2. They worked to find whether it was protein or DNA from the virus that entered the bacteria.
3. The bacteriophage attaches to the bacteria.
4. Its genetic material enters the bacterial cell.
5. The bacterial cell treats the viral genetic material as if it was its own and subsequently manufactures more virus particles. vi. Proving DNA to be the genetic material/by tracing the radioactivity on DNA.

1. The two strands of a DNA are said to be complementary to each other, i.e., a purine of one strand always pair with a pyrimidine.

1. Adenine (a purine) pairs with thymine (a pyrimidine) by forming two hydrogen bonds.
2. Guanine (a pyrimidine) by forming three hydrogen bonds.

2. The two chains of a DNA shows antiparallel polarity, which means that if one strand has 5' 3' polarity, the other strand has 3' → 5' polarity.

1. Chromosome 1 has the most genes and Y-chromosome has the fewest.
2. It is expected to help in:

1. Locating the disease-associated sequences of DNA on the chromosomes.
2. Tracing human history.

1.  

2. RNA polymerase III.
3. The amino acid methionine is the initiator amino acid.

DNA polymerase uses DNA template to catalyse the polymerization of deoxynucleotides and hence it is called DNA–dependent. When a new strand of DNA is being processed, this enzyme moves along to hasten the speed of polymerization. While doing so, it “proof reads” the strand being formed. By doing so, it helps in speeding up the process. Hence, its nature can be said as dual, i.e. of reading the template and then proof reading the new strand.

This change is called transformation.Transforming Principle:

• Frederick Griffith (1928) conducted experiments with Streptococcus pneumoniae (bacterium causing pneumonia).
• He observed two strains of this bacterium-one forming smooth shiny colonies (S-type) with capsule, while other forming rough colonies (R-type) without capsule.
• When live S-type cells were injected into mice, they died due to pneumonia.
• When live R-type cells were injected into mice, they survived.
• When heat-killed S-type cells were injected into mice, they survived and there were no symptoms of pnuemonia.
• When heat-killed S-type cells were mixed with live R-type cells and injected into mice, they died due to unexpected symptoms of pneumonia and live S-type cells were obtained from mice.
• He concluded that heat-killed S-type bacteria caused a transformation of the R-type bacteria into S-type bacteria but he was not able to understand the cause of this bacterial transformation.

DNA is a better genetic material for the following reasons:

1. The genetic material should be stable and should not change with age or change in physiology; this stability is given to DNA by its.

1. Double-stranded nature.
2. Presence of thymine.
3. The plane of base pair stacking over the other.

2. Because the 2-OH group of RNA nucleotides is a reactive group, it makes RNA labile and easily degradable; it is absent in DNA.
3. RNA (23S RNA) is also catalytic, i.e. it is reactive; but DNA is less reactive and more stable.

1. Once the RNA polymerase reaches the terminator sequence of the DNA, it binds transiently to the termination factor (rho/ p).
2. The RNA strand synthesised falls off, followed by the RNA polymerase, i.e., termination has occurred.

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1. Out of 64 codons 61 code for amino acids and rest 3 codons do not code for any amino acids. These function as stop codons.
2.  

1. As codon is a triplet. Out of 64 codons, 6l code for 20 amino acids and 3 codons (UAA, UGA and UAG) do not code for any amino acids. Thus, they function as terminating or stop codons.
2. Genetic code is uaambiguous and specific. Thus, one codon codes for only one amino acid, e.g. CCU codes only for proline and not for any other amino acid.
3. Since, rhe number of codons is greater, all of thc amino acids, with exceptions of methionine (AUG) and tryptophan (UGG), are coded by more than one codon, a fearure referred to as the degenerecy of genetic code, e.g. GGU, GGC, GGA and GGG all specifr the same amino acid glycine.
4. The codon is read in mRNA in a contiguous fuhion, i.e. without puncoration. Thus, the code is commaless.
5. The genetic code is nearly universal, i.e. particular codon codes for the same amino acid in all organisms except in mitochondrial codons and few Protozoans.
6. AUG is a codon with dual fi.rncdons. It codes for the amino acid methionine (met) and also acts as an intiator codon.

• Purification of biochemicals like Proteins, RNA & DNA from S cells. (heat killed)
• Presence of Protein & RNA in medium did not affect transformation.
• DNA alone from S Bacteria caused R Bacteria to transform.
• Digestion with DNAase did inhibit transformation,

Conclusion: DNA is the transforming chemical/biochemical.

1. X is N-glycosidic linkage; it forms a nucleoside.
2. Y is phosphoester linkage; it forms a nucleotide.
3. Z is a phosphodiester linkage; it forms a dinucleotide.

Lactose acts as the inducer, binds with repressor protein, frees operator gene, RNA polymerase freelymoves over the structural genes, transcribing lac mRNA, which in turn produces the enzymes responsible for the digestion of lactose A complete labelled diagram depicting the concept can be evaluated in lieu of explanation.

1. The properties that can be correlated:

1. UAA does not code for any amino acid; it is a termination codon.
2. Genetic code is specific and unambiguous, i.e. one codon codes for a particular amino acid only.
3. Each codon is a triplet.
4. Genetic code is degenerate, as one amino acid is coded by more than codon, e.g. UUU and UUC code for phenylalanine.
5. Genetic code is read in a contiguous manner without any punctuation.

2. The property that cannot be correlated:

AUG has a dual function; it is initiation codon as well as codes for methionine.

Polymorphism (variation at genetic level) arises due to mutations. Allelic sequence variation has traditionally been described as a DNA polymorphism if more than one variant (allele) at a locus occurs in human population with a frequency greater than 0.01. In simple terms, if an inheritable mutation is observed in a population at high frequency, it is referred to as DNA polymorphism. Polymorphism become very useful identification tool in forensic applications. Further, as the polymorphisms are inheritable from parents to children, DNA fingerprinting is the basis of paternity testing, in case of disputes.

Aspartic and glutamic acid are acidic amino acids, while lysine and arginine are basic amino acids. Lysine and arginine carry positive charge on their side chains which is not the case with aspartic acid and glutamic acid. DNA is negatively charged and hence is wrapped around the positively charge histone octamer. If acidic amino acids are present in histone because of mutation, DNA won’t be able to wrap around itself. Thus, long strand of DNA will not be able to fit inside the small space in the nucleus. This will mean an end to nuclear organization which is possible because of efficient packaging.

Initiation of translation:

1. When the small subunit of ribosome binds to the mRNA the process of translation starts; in bacteria the ribosome also acts as a catalyst (23S rRNA is ribozyme) for peptide bond formation.
2. The ribosome binds to mRNA at the start codon (AUG), that is recognised by the initiator RNA; it involves certain initiation factors.

Termination of translation:

1. When the ribosome falls on a termination codon, a release factor binds to it, and translation is terminated and the polypeptide is released from the ribosome.
2. Untranslated regions are present at the 5' end before the start codon and also at the 3' end after the termination codon.
3. They are required for efficient translation.

S strain bacteria when injected - mice die, R - mice live, heat killed S - mice live, heat killed S + live.
R - mice die, recovered living S from dead mice, R strain bacteria had been transformed to S strain by the genetic material of heat killed S strain.

A mutation is a stable, inheritable change in genetic material. A classical example of point mutation is a change of single base pair in the gene for B-globin chain that results in the change of amino acid residue glutamate to valine. It results into a diseased condition called Sickle-cell anaemia.
The insertion or deletion of one or two bases may change the reading frame from the point of insertion or deletion Insertion or deletion of three or its multiple bases insert or delete one or multiple codon, hence one or multiple amino acid may be formed in polypeptide. The other type of mutation is frameshift insertion or deletion mutation.

1. The regulatory gene in lac operon (also called i gene or inhibitor gene) codes for a protein, called repressor; the repressor is synthesised all the time constitutively in the cell.
2. The repressor has high affinity to the operator; it binds to the operator region and prevents the RNA polymerase from transcribing the structural genes of the operon.
3. It is called negative regulation because the operon is switched off and transcription is prevented.

DNA is genetic material.

1.  

A - Replication of DNA.

B - Transcription.

C - Translation.

2.  

1. The central dogma of molecular biology states that the genetic information flows from DNA to RNA to proteins.
2. In some viruses, the flow of information is in reverse direction, i.e. from RNA to DNA and is called reverse transcription.

Eukaryote gene structure and function differ from prokaryote gene structure and function in several important ways. Eukaryotes have many more genes and these genes are spread across multiple chromosomes. Prokaryotes have less number of genes and these genes are all located on one chromosome. The greater complexity of the eukaryote genome means that a greater variety and complexity of control mechanisms is necessary. There are also more steps in the transcription and translation process at which control of expression can occur in eukaryote.Because eukaryotes pocess a nuclear membrane thair mRNA must be completely formed and must pass across the nuclear envelope before translation. Eukaryotic mRNA s are modified before they are translated . Introns are removed and the remainng exons are spiced together . A 5'cap and a 3' poly-A tail are added . In a eukaryotic cell, transcription occurs in the nucleus, and translation occurs in the cytoplasm.

1. RNA polymerase III, Methionine.
2. This tRNA (charged with amino acid Methionine) reaches the smaller subunit of ribosome, with its anticodon UAC recognises the codon AUG on mRNA and binds by forming complementary base pairs, leaves the amino acid, initiating protein synthesis.

1. DNA-dependent DNA polymerase is the enzyme.
2. Two characteristic features of this enzyme include:

1. It catalyses the polymerisation of nucleotides in 5' → 3' direction only.
2. It polymerises approximately 2000bp per second, with high degree of accuracy.

3. Origin of replication is the region on E.coli DNA, where this enzyme can initiate replication.

This flow of information is dependent on the genetic code, which defines the relation between the sequence of bases in DNA (or its mRNA transcript) and the sequence of amino acids in a protein. The code is nearly the same in all organisms: a sequence of three bases, called a codon, specifies an amino acid. Codons in mRNA are read sequentially by tRNA molecules, which serve as adaptors in protein synthesis. Protein synthesis takes place on ribosomes, which are complex assemblies of rRNAs and more than 50 kinds of proteins.

1. RNA polymerase II.
2. Has (non functional) introns (Methyl guanosine tri-phosphate is added to 5’end) capping, tailing (Poly A tail at 3’ end added), splicing (introns are removed and exons are joined) Nucleus.

S. No	Role/ Strand	Template strand	Coding strand
(i)	Function	Codes for the protein molecule.	Does not code for anything.
(ii)	Polarity	3′ → 5′	3′ → 5′

1. a to d' is 5 → 3'.

No more amino acid will be added.

1. TCA; anticodon is UCA.
2. 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.