Biology

Molecular Biology and Genetics

985 Questions

Molecular biology and genetics explore the structure and function of DNA, RNA, genetic mutations, and heredity. Understanding these building blocks of life is essential for most biology examinations. Review these practice questions to test your molecular genetics knowledge.

DNA structure and basesGenetic mutationsNucleic acids compositionDNA sequencing and replication

Molecular Biology and Genetics Questions

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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
Reveal answer Fill a bubble to check yourself
B Correct answer
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. 

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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
Reveal answer Fill a bubble to check yourself
A Correct answer
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. 

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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.
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

Z-DNA is

  1. Left handed

  2. Right handed

  3. Single stranded

  4. Double stranded
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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 }$
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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.
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

The DNA strands are anti-parallel because of

  1. H bonds

  2. Phospho-diester bonds

  3. Disulphide bonds

  4. Phosphate bonds
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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.
Reveal answer Fill a bubble to check yourself
B Correct answer
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.