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Structure of dna - class-XI

Description: structure of dna
Number of Questions: 67
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Tags: biology structure of chromosome, cell cycle and cell division heredity and variation molecular genetics zoology heredity
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The two polynucleotide strands of DNA are held together by 

  1. Hydrogen bonds

  2. Covalent bonds

  3. Metallic bonds

  4. Ionic bonds

  5. Polar covalent bonds


Correct Option: A
Explanation:

Two polynucleotide chains of DNA are wound around the same axis and are held together by complementary base pairing between nitrogenous bases of two strands in the same plane. Adenine of one strand forms two hydrogen bonds with thymine of other strand and guanine forms three hydrogen bonds with cytosine.  The two bases forming hydrogen bonds to joins the polynucleotide strands together are present in the same plane. Thus, the correct answer is A.

Which of the following bonds link the base of one chain and the base of other chain of DNA?

  1. Hydrogen bonds

  2. Covalent bonds

  3. Ionic bonds

  4. None of the above


Correct Option: A
Explanation:

As per Watson and Crick standard base pairing rules, adenine forms double hydrogen bond with thymine and guanine forms triple hydrogen bond with cytosine. Hence, content of adenine is equal to content of thymine and content of guanine is equal to content of cytosine.

The distance between two nucleotide pairs of DNA is

  1. 0.34 nm

  2. 34$\mathring A$

  3. $3.4 :\mu $m

  4. 34 nm


Correct Option: A
Explanation:

Nucleotides are organic molecules that serve as the monomers, or subunits, of nucleic acids like DNA and RNA. The building blocks of nucleic acids, nucleotides are composed of a nitrogenous base, a five-carbon sugar-ribose or deoxyribose, and at least one phosphate group. Thus, a nucleoside plus a phosphate group yields a nucleotide. The distance between two nucleotide pairs in DNA is 0.34nm.

Histone proteins are associated with

  1. DNA

  2. mRNA

  3. rRNA

  4. snRNA

  5. tRNA


Correct Option: A
Explanation:

Nucleosomes are fundamental organizational units of chromatin which appear as “beads-on-a-string” arrangement. Here beads represent complexes of histones and DNA. Each bead contains a core of histone octamer: two copies each of H2A, H2B, H3, and H4; out of 200 bp DNA, 146 bp DNA is bound tightly around the histone core and the remainder serve as linker DNA between nucleosomal beads. The H1 histone associates with the linker DNA to pack adjacent nucleosomes together and forms a compact 30-nm chromatin fiber. Thus, the correct answer is A.

Which of the following is not present in genetic material?

  1. Cytosine

  2. Thymine

  3. Arginine

  4. Guanine

  5. Uracil


Correct Option: C
Explanation:

RNA and DNA are genetic materials. Cytosine, Thymine, Guanine, and Uracil are all nitrogenous bases. They are present in RNA. Uracil is replaced by adenine in DNA. Arginine is an amino acid which is basic in nature. It is the building block of protein. 

Hence, 'Arginine' is the right answer.

The purine bases of DNA are

  1. U and G

  2. A and G

  3. A and C

  4. None of the above


Correct Option: B
Explanation:

Purines and pyrimidines, make up the two groups of nitrogenous base which plays on important role in structural backbone of DNA. Adenine and guanine are purines, while cytosine and thymine are pyrimidines. Purines pairs with pyrimidines, by formation of H-bonds. Adenine attaches to thymine, by two hydrogen bonds, while cytosine and guanine forms three hydrogen between them.

The two strands of DNA in the double helix is connected by ___________.

  1. Covalent bonding

  2. Ionic bonding

  3. Hydrogen bonding

  4. Hydrophobic interactions

  5. Teritary structure


Correct Option: C
Explanation:

Genetic information is carried in the linear sequence of nucleotides in DNA. Each molecule of DNA is a double helix formed from two complementary strands of nucleotides held together by hydrogen bonds between G-C and A-T base pairs.

Hence, C is the correct option. 

The distance between two DNA strands is 

  1. 20$\mathring{A}$

  2. 34$\mathring{A}$

  3. 3.4$\mathring{A}$

  4. 2$\mathring{A}$


Correct Option: A
Explanation:

According to the Watson Crick double helical model of DNA, the diameter of DNA molecule is 20 angstrom. Hence, the distance between two DNA strand is 20 angstroms.
So, the correct answer is option A.

The histone occupies the major groove of a DNA at an angle of

  1. $60^{\circ}$

  2. $90^{\circ}$

  3. $45^{\circ}$ to helix axis

  4. $30^{\circ}$ to helix axis


Correct Option: D
Explanation:

DNA is acidic. For its compaction, it requires basic (histone) proteins. The histone proteins, are positively charged and occupy the major grooves of DNA at an angle of 30° to helix axis. 

Therefore, the correct answer is option D.

DNA strands are joined by

  1. Oxygen bonds

  2. Hydrogen bonds

  3. Carbon bonds

  4. Nitrogen bonds


Correct Option: B
Explanation:
Double helical structure of DNA was proposed by Watson and Crick. DNA is made up of a nitrogenous base, phosphate, and sugar. It has deoxyribose sugar which has hydrogen at second carbon. The nitrogenous bases present in the DNA are purines and pyrimidines. Purines are double ring while pyrimidines are single ring structure. Adenine and guanine are purines while thymine and cytosine are pyrimidines. A purine is attached to pyrimidine by hydrogen bond. Adenine is attached to thymine by two hydrogen bonds while three hydrogen bond is present between guanine and cytosine.
So, the correct answer is option B.

Sugar found in DNA is

  1. Dextrose

  2. Levulose

  3. Glucose

  4. Deoxyribose


Correct Option: D
Explanation:
DNA has deoxyribose sugar while RNA has ribose sugar. The deoxyribose sugar has hydrogen at second carbon while the ribose sugar has the hydroxyl group at the second carbon of the hexose ring. Ribose sugar is a monosaccharide which has five carbon atom. C$ _5$H$ _{10}$O$ _5$ is the chemical formula of ribose and it is a pentose sugar. 
So, the correct answer is option D.

The distance between two complementary strands of DNA almost remains the same because 

  1. Hydrogen bonds between the complementary nitrogen bases of the two chains

  2. Hydrophobic interactions between nitrogen bases

  3. Base pairing between purines and pyramidines

  4. All the above


Correct Option: D
Explanation:

The distance between two complementary strands always remains the same because there are hydrogen bonds between the nitrogen bases of two strands restricting movement. The bonds are formed correctly on the opposite ie the bonds are between purines and pyrimidines.

Also, these interactions between nitrogen bases are hydrophobic.
So, the correct option is D.

The strands of DNA are associated with the help of

  1. Hydrogen

  2. Carbon

  3. Oxygen

  4. Nitrogen


Correct Option: A
Explanation:

DNA has a double stranded structure where, the purines are linked to pyrimidines with the help of hydrogen bonds. Adenine is linked to thymine by two hydrogen bonds while, cytosine is linked to guanine by three hydrogen bonds.

In DNA, guanine pairs with

  1. Cytosine

  2. Thymine

  3. Uracil

  4. Adenine


Correct Option: A
Explanation:

According to the base pair rule, purine pairs with pyrimidine. Hence, guanine pairs with cytosine by formation of three hydrogen bonds.

In the structure of DNA, one-nucleotide purine base joins with pyramid type by which bond?

  1. Aster

  2. Weak hydrogen

  3. Glycosidic

  4. Peptide


Correct Option: B
Explanation:

Answer is option B i.e. "Weak hydrogen"
DNA is made up of nucleotide. Nucleotides join up with one another based on chemical compatibility of their nitrogen bases that are held together by weak hydrogen bond. In DNA, this hydrogen bond helps in stabilizing the nucleic acid structure.

For two closely related species, the DNA would be

  1. Completely different

  2. Somewhat different

  3. Very different

  4. Very similar

  5. Identical


Correct Option: D
Explanation:

Species that are very closely related have very similar DNA with only minor differences. They are related through a common ancestor. 

The base pairs of DNA are correctly shown as

  1. A $\equiv $ T and C = G

  2. A = T and C = G

  3. A = T and C $\equiv $ G

  4. A $\equiv $ T and C $\equiv $ G


Correct Option: C
Explanation:

In DNA, purines pairs with pyrimidines. Adenine pairs with Thymine with double hydrogen bond and Guanine pairs with Cytosine with the help of triple hydrogen bond.

Diameter of DNA is/Wilkin's X-ray diffraction showed DNA diameter to be

  1. $200 \mathring{A}$

  2. $100 \mathring{A}$

  3. $20 \mathring{A}$

  4. $50 \mathring{A}$


Correct Option: C
Explanation:
DNA has the double helical structure where the two strands are tightly coiled over each other. B- DNA has right-handed helix with the major and minor groove. The diameter of the DNA is 20 A$^o$. The number of base pairs in one turn is 10 and the distance between base pairs is 3.4 A$^o$. The total length of one turn of DNA is 34 A$^o$.
So, the correct answer is option C.

Which of the following is TRUE regarding sense and antisense strands?

  1. Both the strands are present on RNA

  2. Both the strands are present on DNA

  3. Sense strand is on DNA and antisense on RNA

  4. Sense strand is on RNA and antisense on DNA


Correct Option: B
Explanation:

Both sense and antisense strands are present in DNA as these act as antisense strand acts as a template during transcription and sense strand has the same sequence as mRNA in the nucleus.

So, the correct option is B.

In which of the following DNA sequences the sequence of nucleotides is the same when one strand is read left to right and the other strand is read right to left?

  1. RFLP

  2. RAPD

  3. VNTR

  4. Palindromic sequence


Correct Option: D
Explanation:
A palindromic sequence is a sequence made up of nucleic acids within double helix of DNA or RNA that is the same when reading from 5' to 3' on one strand and 5' to 3' on the other, complementary strand. 
So, the correct answer is 'Palindromic sequence'.

The double-helix structure of DNA was described by

  1. Watson

  2. J.D. Watson and F. H. C. Crick

  3. Maurice Wilkins

  4. All of the above


Correct Option: D
Explanation:

The structure of DNA was deciphered by Watson and Crick in 1953 on the basis of X-ray diffraction data generated by Wilkins, Astbury and Franklin. Wilkins, Watson and Crick were awarded Nobel prize for their model in 1962.
So, the correct answer is option D.

The characteristic feature of Z-DNA is

  1. Left handed

  2. Right handed

  3. 12 base pairs in each turn

  4. Both A and C


Correct Option: D
Explanation:

DNA duplex of Watson and Crick is right handed and is called as B-DNA. Z-DNA is left handed double helix, which contains zigzag backbone of phosphodiester bonds and 12 base pairs per turn. The diameter of Z-DNA is 18 $\mathring A$ as against B-DNA diameter of 20 $\mathring A$.
So, the correct answer is option D.

Which of the following has higher surface area (SA) to volume (V) ratio?

  1. Red blood cell

  2. Nails

  3. DNA

  4. Human Hair


Correct Option: C

A five carbon sugar with molecular formula $C _5H _{10}O _4$

  1. Deoxyribose

  2. Ribose

  3. Glucose

  4. Lactose


Correct Option: A
Explanation:

Glucose (C$ _6$H$ _1$$ _2$O$ _6$), Deoxyribose (C$ _5$H$ _1$$ _0$O$ _4$), Lactose (C$ _1$$ _2$H$ _2$$ _2$O$ _1$$ _1$), Ribose (C$ _5$H$ _1$$ _0$O$ _5$)

So, the correct answer is option A.

The number of base pairs in each turn of Z-DNA and B-DNA helices respectively is

  1. 9 and 11

  2. 12 and 10

  3. 10 and 13

  4. 12 and 11


Correct Option: B
Explanation:

B-DNA is physiologically the most important form of DNA. The double helical secondary structure model of DNA described by Watson and Crick was the B-DNA. As per the original model, it contains 10 bp per turn but later measurements showed that it contains 10.5 base pairs per turn. Z DNA is the zigzag DNA. It is left handed helix. There are 12 base pair per turn, with a rise of 0.38 nm per base pair.
So, the correct answer is option B.

Which one is correct

  1. Catalytic converter can precipitate particular matter of less than 2-5

  2. Histones are acidic and form core of packing

  3. Template with ${ 5 }'\longrightarrow 3'$ polarity shows continuous DNA replication

  4. Lactobacillus is not present in dough for idli preparation


Correct Option: A
Explanation:
  • DNA replication goes in the 5' to 3' direction because DNA polymerase acts on the 3'-oh of the existing strand for adding free nucleotides.
  • Histones are rich in the basic amino acid residues lysines and arginines and forms histone octamer.
  • Catalytic converters, having expensive metals namely platinum-palladium and rhodium as the catalysts, are fitted into automobiles for reducing the emission of poisonous gases.
  • As the exhaust passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water, and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively.
  • Fermentation of idli or dosa batter is carried out largely by lactic acid bacteria, the same class of microorganisms that are found in ‘curd.’
  • So the correct answer is " Template with 5′⟶3′ polarity shows continuous DNA replication ".

What is the nature of the 2 strands of a DNA duplex?

  1. Identical & Complimentary

  2. Antiparallel & complimentary

  3. Dissimilar & non complimentary

  4. Antiparallel & non complimentary


Correct Option: B
Explanation:

DNA is a macromolecule of high molecular weight made up of repeating units called nucleotides. Each nucleotide is made up of

 1) a 5 carbon sugar 
2) a phosphate group 
3) a nitrogenous base.
DNA molecule is a helix with bases stacked perpendicularly to the main axis of the molecule. The two strands of a DNA, double helix are called complimentary due to specific base pairing, i.e, each chain has a sequence of nucleotides attached together by phosphodiester bonds joining the adjacent deoxyribose molecules. The base pairing,is specific as adenine is always paired with thymine and guanine with cytosine and vice-versa, i.e, one purine with another pyrimidine and one pyrimidine with another purine. This property of complimentarity makes DNA unique to store and transmit genetic information. The sugar-phosphate backbones of two complimentary strands are antiparallel as they have opposite chemical polarity. Therefore, one strand of the double helix has 5'-3' polarity while the other has 3'-5' polarity. 

The method of DNA replication, in which two strands of DNA separates and synthesize new strands is called as

  1. Dispersive

  2. Conservative

  3. Semi conservative

  4. Non conservative


Correct Option: C
Explanation:

DNA replication, is the process of producing two identical replicas from one original DNA molecule. This biological process, occurs in all living organisms and forms the basis for biological inheritance. DNA is made up of two strands and each strand of the original DNA molecule serves as a template for the production of the complementary strand, a process referred to as semiconservative replication.

The purine & pyrimidine pairs of complementry strands of DNA are held together by

  1. H bonds

  2. O bonds

  3. C bonds

  4. N bonds


Correct Option: A
Explanation:

The purine & pyrimidine pairs of complementry strands of DNA are held together by hydrogen bonds. A set of five nitrogenous bases is used in the construction of nucleotides, which in turn build up the nucleic acids like DNA and RNA.

These nitrogenous bases are adenine (A), guanine (G), thymine (T), and cytosine (C) and uracil (U - in RNA replacing thymine). These nitrogenous bases have hydrogen bond between opposing DNA strands to form the rungs of the "twisted ladder" or double helix of DNA or a biological catalyst that is found in the nucleotides. Adenine is always paired with thymine, and guanine is always paired with cytosine. These are known as base pairs. 

Which purine & pyrimidine bases are paired together by H bonds in DNA?

  1. AC and GT

  2. GC and AT

  3. GA and TC

  4. None of the above


Correct Option: B
Explanation:

Purines and pyrimidines, make up the two groups of nitrogenous base which plays on important role in structural backbone of DNA. Adenine and guanine are purines, while cytosine and thymine are pyrimidines. Purines pairs with pyrimidines, by formation of H-bonds. Adenine attaches to thymine, by two hydrogen bonds, while cytosine and guanine forms three hydrogen between them.

If DNA is subjected to high temperature of about 90 - 100$^o$C, the following changes occur

  1. Hydrogen bonds of the bases break down.

  2. Phosphate changes to phosphoric acid.

  3. Bonds between only thymine and adenine break down.

  4. Bonds between only cytosine and guanine break down.


Correct Option: A
Explanation:

If DNA is subjected to high temperature, the hydrogen bonds between the nitrogenous bases break down and the two strands separate. This process is called as melting of DNA. More the content of guanine (G) and cytosine (C) in the DNA, higher will be the melting temperature because G forms three hydrogen bonds with C as against adenine (A) and thymine (T) which form two hydrogen bonds.
So, the correct answer is option A.

Which bond in B-DNA will have to be rotated to convert it from syn to anti conformation?

  1. Hydrogen bond

  2. Glycosidic bond

  3. Phosphodiester

  4. Hydropbobic


Correct Option: B
Explanation:

The C$ _1$ of pentose sugar in nucleotides is linked to the N1 or N9 position of pyrimidine or purine bases through a glycosidic bond. The syn and anti conformations, are the two conformational forms of nucleotides around this bond. The two forms are interconvertible by rotating the glycosidic bond without a need to break the bond.
So, the correct answer is option B.

Z-DNA is

  1. Left handed

  2. Right handed

  3. Single stranded

  4. Double stranded


Correct Option: A
Explanation:

The DNA duplex of Watson and Crick is right handed helix and is called the B-DNA. There are five more models (A-DNA, C-DNA, D-DNA, E-DNA and Z-DNA) have been proposed. The Z-DNA is left handed double helix which contains zigzag back and 12 base pairs per turn.
So, the correct answer is option A.

If base order in one chain of DNA is "ATCGA" then how many no. of H-bond found in DNA duplex?

  1. 20

  2. 12

  3. 10

  4. 11


Correct Option: B
Explanation:

The base pairing confers a unique property to the polynucleotide chains. The chains are complimentary to each other, such that if the sequence of one strand is known then the sequence of other strand can be predicted. Also if each strand of DNA acts as a template, for the synthesis of a new strand, the two double stranded DNA molecule thus produced would be identical to the parent molecule. The bases in the two strands of a double stranded DNA molecule are paired through hydrogen bonds forming base pairs (bp). Adenine forms two hydrogen bonds with thymine from opposite strand and vice versa. Similarly cytosine is bonded with guanine from three H bonds. As a result, always a purine comes opposite to a pyrimidine. This generated approximately, equal distance between the two strands. If base order in one chain of DNA is "ATCGA" then the number of H bonds will be 2, 2, 3, 3 and 2 respectively for the given nucleotides to base pair. Thus, the total number of hydrogen bonds will be 12.

Wilkins X-ray diffraction showed the diameter of the DNA helix is

  1. 10 $\mathring { A }$

  2. 20 $\mathring { A }$

  3. 30 $ \mathring { A }$

  4. 40 $ \mathring { A }$


Correct Option: B
Explanation:

Wilkins X -ray diffraction showed the diameter of the DNA helix is around 20 $\mathring A$.  According to Maurice Wilkins, the structure of DNA of all species comprises two helical chains each coiled round the same axis, and each with a pitch of 34 angstroms and a radius of 10 angstroms. According to another study, when measured in a particular solution, the DNA chain measured 20 to 26 angstroms wide, and one nucleotide unit measured 3.3 long. Although each individual repeating unit is very small, DNA polymers can be very large molecules containing millions of nucleotides.
So, the correct answer is option B.

The back bone in the structure of DNA molecule is made up of

  1. Pentose sugar and phosphate

  2. Hexose sugar and phosphate

  3. Purine and pyrimidine

  4. Sugar and phosphate


Correct Option: A
Explanation:

DNA is a polymer of deoxyribonucleotides. The deoxyribonucleotides are made up of phosphoric acid and deoxyribonucleosides. The deoxyribonucleosides are made up of deoxyribose sugars and nitrogenous bases. The deoxyribonucleotides are joined to each other with the help of 3', 5' phosphodiester bonds forming the backbone of single DNA chain. In a molecule of DNA, two such chains are present attached with each other with the help of hydrogen bonds between the nitrogenous bases of deoxyribonucleotides.

The DNA molecule has uniform diameter due to

  1. Double strandedness.

  2. Presence of phosphate.

  3. Specific base pairing between purine and pyrimidine.

  4. None of the above.


Correct Option: C
Explanation:

DNA molecule has uniform diameter due to specific base pairing between purine and pyrimidine. In DNA, the bases adenine and guanine form hydrogen bonds with their complementary pyrimidines; thymine and cytosine, respectively, this is called as complementary base pairing.

Most DNA molecules consist of two biopolymer strands coiled around each other to form a double helix. The two DNA strands are known as polynucleotides since they are composed of simpler units called nucleotides. Each nucleotide is composed of a nitrogen-containing nucleobase either guanine (G), adenine (A), thymine (T), or cytosine (C) as well as a monosaccharide sugar called as deoxyribose and a phosphate group.
So, the correct answer is option C.

The two long polynucleotide chains of DNA are held together by

  1. Hydrogen bonds

  2. Covalent bonds

  3. Metallic bonds

  4. Ionic bonds

  5. Polar covalent bonds


Correct Option: A
Explanation:

DNA is a double helical molecule made of two antiparallel strands of nucleotides which is linked by hydrogen bonds between complementary base pairs. DNA carries the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms. Adenine (A) pairs with Thymine (T) via two hydrogen bonds. Guanine (G) pairs with Cytosine (C) via three hydrogen bonds. Hence option A is correct.

The DNA strands are anti-parallel because of

  1. H bonds

  2. Phospho-diester bonds

  3. Disulphide bonds

  4. Phosphate bonds


Correct Option: B
Explanation:

The DNA strands runs anti-parallel, due to phosphodiester bonds. A phosphodiester bond occurs when exactly two of the hydroxyl groups in phosphoric acid react with hydroxyl groups on other molecules to form two ester bonds. Phosphodiester bonds are central to most life on Earth, as they make up the backbone of the strands of DNA. In DNA and RNA, the phosphodiester bond is the linkage between the 3' carbon atom of one sugar molecule and the 5' carbon atom of another, deoxyribose in DNA and ribose in RNA. Strong covalent bonds form between the phosphate group and two 5-carbon ring  two ester bonds. Due to this bond the DNA strands run anti-parallel.

In the DNA molecule,

  1. The proportion of adenine in relation to thymine varies with the organism.

  2. There are two strands which run antiparallel one in $5'\rightarrow 3'$ direction and other in $3'\rightarrow 5'$.

  3. The total amount of purine nucleotides and pyrimidine nucleotides is not always equal.

  4. There are two strands which run parallel in the $5'\rightarrow 3'$ direction.


Correct Option: B
Explanation:

DNA (Deoxyribonucleic Acid) is composed of two polynucleotide strands (the polymers of nucleotides), which form what looks like a ladder. The nitrogenous bases in DNA store the instructions for making polypeptide chains, essentially coding for every feature of the entire organism. The two polynucleotide strands run 'antiparallel' to each other, with nitrogenous bases projecting inwards. The term 'antiparallel' means that the strands run in opposite directions, parallel to one another. The antiparallel strands twist in a complete DNA structure, forming a double helix.

In the speculation concering the origins of life, one theory states that the combination of purines, pyrimidines, sugars, and phosphates is called as______________.

  1. Nucleotides

  2. Nucleosides

  3. Carbohydrates

  4. Fats

  5. Proteins


Correct Option: A

If one strand of DNA sequence is - 5'-GAATTG-3' - then the sequence of the opposite strand is

  1. 5'-CAATTC-3'

  2. 5'-CTTAAC-3'

  3. 5'-GAATTG-3'

  4. 5'-GTTAAG-3'

  5. 5'-TAATTC-3'


Correct Option: A
Explanation:

A DNA strand is complementary. This means adenine pairs with thymine and cytosine pairs with guanine in the opposite strand. The given strand has a sequence 5'-GAATTG-3'. Hence the complementary strand will have a sequence 5'-CAATTC-3'. Thus the correct answer is option A.

DNA is directly involved in the synthesis except that of

  1. DNA

  2. Protein

  3. tRNA

  4. mRNA


Correct Option: B
Explanation:
DNA is genetic material found in the living cell. It helps to carry characters from one generation to the other. The process by which the DNA replicated and forms another DNA molecule is known as replication. Parent strand of the DNA strand act as a template for synthesis of another DNA molecule.
Transcription is the process by which DNA is converted into RNA. The enzyme RNA polymerase plays an important role in transcription. The sequence of the nitrogenous base on the DNA acts as a template and determines the sequence of the nitrogenous base on the RNA. The RNA formed by the DNA are messenger RNA, t- RNA and ribosomal RNA.
Protein is formed by the m-RNA by process of translation.
So, the correct answer is option B.

A $340\overset{o}{A}$ long segment of DNA molecule has $20$ thymine nitrogenous bases, what will be the number of guanine nitrogen bases in the same segment?

  1. $10$

  2. $40$

  3. $30$

  4. $160$


Correct Option: C
Explanation:
Option (C) 30

$ 34A = 10 $ nucleotides
$ 340A = 100 $ nuclotides
$ A = T = 20 $
$ 100-40 = 60 $ nucleotides
$ G = C = 60 $
Hence $ G = 60/2 = 30 $ nuclotides

The DNA strands are antiparallel because of the presence of

  1. H-bonds

  2. Peptide bonds

  3. Disulphide bonds

  4. Phosphate-diester bonds

  5. None of the above


Correct Option: A
Explanation:

When DNA strands run in opposite direction one strand from 5 prime to 3 prime and another strand from 3 prime to 5 prime is called as antiparallel. The 5 prime end have phosphate in 5$^{th}$position of sugar and 3 prime end have a hydroxyl group on 3$^{rd}$ position of sugar. DNA strands are antiparallel because of the presence of hydrogen bond. Hydrogen bond binds the complementary bases (purine and pyrimidine)

In DNA, adenine pairs with

  1. Guanine

  2. Thymine

  3. Cytosine

  4. Uracil


Correct Option: B
Explanation:

The nitrogenous bases present in the DNA are purines and pyrimidines. The purines are adenine and guanine. The pyrimidines are thymine and cytosine. The purines are double ring structure while the pyrimidines are the single ring made up of carbon and nitrogen. Purines pair with the pyrimidines by hydrogen bonds. Adenine pairs with thymine by two hydrogen bond while the cytosine pairs with the guanosine by three hydrogen bonds.

So, the correct answer is option B.

DNA is composed of repeating units of

  1. Ribonucleosides

  2. Deoxyribonucleosides

  3. Ribonucleotides

  4. Deoxyribonucleotides


Correct Option: A
Explanation:
DNA is a chain of polynucleotide which are joined by the phosphodiester bonds. The nucleotide consists of a deoxyribose sugar, nitrogenous bases, and phosphate.The two nucleotide is linked by the phosphodiester bond. It is formed by the linkage between the 3' carbon atom of one sugar molecule and the 5' carbon atom of another. Two hydroxyls (OH) groups on the phosphate molecule bind to the 3’ and 5’ carbons on two independent pentose sugars to form a bond.
So, the correct answer is option D.

Major and minor grooves can be seen in

  1. Polypeptide

  2. RNA

  3. DNA

  4. Chromatin


Correct Option: C
Explanation:
DNA has the double helical structure where the two strands are tightly coiled over each other. B- DNA has right-handed helix with the major and minor groove. The diameter of the DNA is 20 A$^o$. The number of base pairs in one turn is 10 and the distance between base pairs is 3.4 A$^o$. At major grooves, the base pairs are far apart while at minor groove the base pairs are closer. Major grooves have base pairs at a distance the DNA binding protein can easily interact with the bases.
So, the correct answer is option A.

Base pairs present in one turn of DNA are

  1. $12$

  2. $11$

  3. $10$

  4. $9$


Correct Option: C
Explanation:
DNA has the double helical structure where the two strands are tightly coiled over each other. B- DNA has right-handed helix with the major and minor groove. The diameter of the DNA is 20 A$^o$. The distance between base pairs is 3.4 A$^o$. The total length of one turn of DNA is 34 A$^o$. The total number of the base pair in each turn is 34/3.4 = 10.
So, the correct answer is option C.

The similarity between bacterial and eukaryotic DNA is that both are

  1. Circular

  2. Single stranded

  3. Double stranded

  4. All the above


Correct Option: C
Explanation:
Nucleic acids are DNA and RNA. DNA is a genetic material which is mainly present in the nucleus of the cell in eukaryotes like mammals. The genetic material is covered by a nuclear membrane. In prokaryotes like bacteria the genetic material lie freely in the cytoplasm. The region where the nucleic acid are present is known as nucleoid. The similarity between bacterial and eukaryotic DNA is that both are double stranded DNA.
So, the correct answer is option C.

Length of one turn of DNA is

  1. $34 \mathring{A}$

  2. $3.4 \mathring{A}$

  3. $0.34 \mathring{A}$

  4. $20 \mathring{A}$


Correct Option: A
Explanation:
DNA has the double helical structure where the two strands are tightly coiled over each other. B- DNA has right-handed helix with the major and minor groove. The diameter of the DNA is 20 A$^o$. The number of base pairs in one turn is 10 and the distance between base pairs is 3.4 A$^o$. So the total length of one turn of DNA is 10 x 3.4 =  34 A$^o$.
So, the correct answer is option A.

The two strands of DNA are held together by bonds of

  1. Nitrogen

  2. Oxygen

  3. Hydrogen

  4. Carbon


Correct Option: C
Explanation:
The nitrogenous bases present in the DNA are purines and pyrimidines. Purines are double ring while pyrimidines are single ring structure. Adenine and guanine are purines while thymine, uracil, and cytosine are pyrimidines. A purine is attached to pyrimidine by hydrogen bond. Adenine is attached to thymine by two hydrogen bonds while three hydrogen bond is present between guanine and cytosine.
So, the correct answer is option C.

DNA is very long. It is accommodated in small sized nucleus by

  1. DNA-ase digestion

  2. Super coiling

  3. Elimination of repetitive DNA

  4. Deletion of non-essential genes


Correct Option: B
Explanation:

DNA is very long. It is accommodated in the small-sized nucleus by super coiling. The enzyme topoisomerase helps in the supercoiling of the DNA which helps in packaging and some biological process. The super coiled DNA is uncoiled during the process of transcription and translation. During transcription the enzyme helicase cuts the phosphate backbone and separates the two super coiled DNA strands while the topoisomerase balances the strain and prevents the recoiling of the DNA.

So, the correct answer is option B.

A $68nm$ length double stranded DNA has 24 adenine nucleotices. What must be the number of guanine nucleotides?

  1. $48$

  2. $72$

  3. $76$

  4. $176$


Correct Option: D
Explanation:

Length of $3.4 nm $ includes $10$ base pairs.So, $68 nm $ will include $200$ base pairs that is $400$ bases.

A=T AND G=C,
A+T+G+C=$400$,
$24$+$24$+$2G$=$400$.,
$2G$ = $352$.
So, Guanine nucleotides would be $176$.
Hence, the correct answer is option D.

The genetic information in the body is encoded in the

  1. Structural proteins

  2. Enzymes

  3. DNA

  4. DNA and enzymes


Correct Option: C
Explanation:

Deoxyribose Nucleic Acid or DNA carries the genetic information in the form of small segments known as genes and is also the genetic material in various organisms including humans.

Structural proteins and enzymes are the gene products that are synthesised from DNA through the process of translation.
Hence, the correct answer is 'DNA'.

Information from X-ray crystallographic data collected by was used by Watson and Crick in their development of the model of DNA.

  1. Chargaff

  2. Griffith

  3. Franklin

  4. Hershey and Chase


Correct Option: C
Explanation:

Although the discovery of the structure of DNA was attributed to Watson and Crick, a keynote player in helping them discover this structure was a scientist by the name of Rosalind Franklin. Rosalind Franklin, along with Francis Wilkins, worked on DNA applying X-ray crystallography to find out its structural properties. X-ray crystallography required the process of exposing a crystal specimen (DNA) to X-rays to determine the locations of the atoms in the “molecules that comprises basic unit of crystal called unit cell”. 

So, the correct option is 'Franklin'.

The purines of DNA are represented by guanine and thymine.

  1. True

  2. False


Correct Option: B
Explanation:

Adenine and Guanine are the two purines found in DNA and RNA. The pyrimidines of DNA are represented by thymine and cytosine. 

Hence, the correct answer is false. 

Which of the following general statement about the structure of DNA is true?

  1. The hydrogen bonds connecting base pairs exist in a polar environment.

  2. Both major and minor grooves are formed between the phosphate-sugar backbone.

  3. The same C and N atoms are present in each groove.

  4. The amount of energy required to break down the AT and GC pairs is the same.


Correct Option: A
Explanation:

The DNA double helical structure has two different environments. The nitrogenous bases have an aromatic ring structure and are hydrophobic and interact with each other through base pair stacking interactions. At the same time, the back bone of DNA formed by phosphodiester bonds is hydrophilic and interacts with water. The nitrogenous bases of one nucleotide chain form hydrogen bonds with the nitrogenous bases present directly opposite them on the other chain. The hydrogen bonds are formed in polar aqueous environment. The adenine base pairs with thymine with two hydrogen bonds and guanine base pairs with cytosine with three hydrogen bonds.
So, the correct answer is option A.

If there are 10,000 base pairs in DNA, then its length

  1. 340 nm

  2. 3400 nm

  3. 34000 nm

  4. 340000 nm


Correct Option: B
Explanation:

According to the most widely accepted model of DNA structure, the distance between any two base pairs in DNA is approximately 3.4 angstroms. Thus for a DNA molecule having 10,000 base pairs; the length will be 10,000 x 3.4 or 34000 angstroms or 3400 nanometers.
So, the correct answer is option B.

In a DNA sample the proportion of A is 17%, the amount of G + T and C will be respectively.

  1. 50% and 33%

  2. 66% and 17%

  3. 66% and 33%

  4. 33% and 50%


Correct Option: A
Explanation:

In any double stranded DNA, adenine (A) pairs with a thymine (T) and Guanine (G) pairs with a cytosine (C).
Now, since each A always pairs with a T, the percentage of A and T will always be the same. Therefore, percentage of T will also be 17%.
So we can conclude that A+T=17+17=34%
The rest would account for G+C which would be 100-34=66%, thus G+C=66%.

Now, since each G always pairs with a C, thus the individual proportions of G and C will be 33%. 
So we get the base composition of DNA as A=T=17% and G=C=33%
Therefore, G+T=33+17=50% and C=33%.
Hence the correct answer is '50% and 33%'.

The eukaryotic chromosome contains nucleosome spools.

  1. True

  2. False


Correct Option: A
Explanation:
A nucleosome is a basic unit of DNA packaging in eukaryotes, consisting of a segment of a DNA wound in sequence around eight histone protein octamer cores. This structure is often compared to thread wrapped around a spool. Nucleosome constitutes the repeating unit of a structure in nucleus called chromatin, thread-like stained (colored) seen in the nucleus. The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called DNA helix.
So, the statement is 'True'.

How many amino acids will be coded by the given sequence of ribonucleotides, if the 15$^{th}$ base is substituted by G?
'5AUGGUGUAGAGGUACCAU3'

  1. Four

  2. Five

  3. Six

  4. Two


Correct Option: D
Explanation:

Amino acid synthesis stops when any STOP codon is encountered by ribosome. There are total 3 stop codons, UAG, UGA, UAA. Codons are always read in triplets. So the given ribonucleotide sequence will be read as: AUG,GUG, UAG, and so on. Notice that the third codon (UAG) is a stop codon, so the protein synthesis will stop at the third codon itself. It doesn't matter if the 15th base is substituted by G or not, the given sequence will code for only two amino acids, AUG (methionine) and GUG (Methionine)

So, the correct answer is 'Two'.

DNA cannot pass through a cell membrane as

  1. It is too big to cross the membrane

  2. It is a hydrophilic molecule

  3. Membrane does not have specific proteins to facilitate the transport

  4. None of these


Correct Option: B
Explanation:

DNA cannot pass through a cell membrane as it is hydrophilic in nature whereas cell membrane is made up of lipid bilayer. 

So, the correct option is 'Option B' .

Feulgen test, is unique for DNA, is a

  1. Gentian violet

  2. Neutral red

  3. Basic fuchsin

  4. Cotton blue


Correct Option: C
Explanation:
  • The feulgen test is a staining technique discovered by Robert Feulgen and used in histology to identify chromosomal material or DNA in cell specimens.
  • The Feulgen test, is unique for DNA, is a Basic Fuchsin.
  • It is used for demonstration of DNA (deoxyribonucleic acid) in tissue sections. 
  • So, the correct answer is 'Basic fuchsin',   

Bonding between deoxyribose and base in pyrimidine nucleoside molecule is :-

  1. $1'-1'$ glycosidic linkage

  2. $1'-6'$ glycosidic linkage

  3. $1'-9'$ glycosidic linkage

  4. $1'-4'$ glycosidic linkage


Correct Option: A
Explanation:

Bonding between deoxyribose and base in pyrimidine nucleoside molecule is $1'-1'$ glycosidic linkage because 


when the base is pyrimidine, then $N-1$ is bonded to $C-1$ of the sugar.

Which of the following is not related to Watson and Crick model of DNA?

  1. X-ray crystallography

  2. The Meselson-Stahl experiment

  3. Chargaff's rules

  4. The different sizes of purines and pyrimidines

  5. The transforming principle of Avery et al


Correct Option: E
Explanation:

Meselson-Stahl experiment -  DNA Replication is Semiconservative.

Meselson and Stahl proved that the semiconservative model of DNA replication was correct.
Watson-Crick Structure of DNA. Deoxyribonucleic Acid (DNA) is a double-stranded, helical molecule. It consists of two sugar-phosphate backbones on the outside, held together by hydrogen bonds between pairs of nitrogenous bases on the inside.
X-ray crystallography - the study of crystals and their structure by means of the diffraction of X-rays by the regularly spaced atoms of crystalline materials. X-ray crystallography is a tool used for identifying the atomic and molecular structure of a crystal, in which the crystalline atoms cause a beam of incident X-rays to diffract into many specific directions.

Chargaff's rules states that DNA from any cell of all organisms should have a 1:1 ratio (base Pair Rule) of pyrimidine and purine bases and, more specifically, that the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine.
Avery's experiments showed that DNA is the transforming principle. It stated that bacterial transformation was caused by DNA. It is not correlated with Watson and crick model of DNA.
So, the correct answer is option E.

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