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.