Biology

Molecular Biology and Genetics

717 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

DNA strands are joined by

  1. Oxygen bonds

  2. Hydrogen bonds

  3. Carbon bonds

  4. Nitrogen bonds
Reveal answer Fill a bubble to check yourself
B Correct answer
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.
Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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

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

The strands of DNA are associated with the help of

  1. Hydrogen

  2. Carbon

  3. Oxygen

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

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

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

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

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

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

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. $50 \mathring{A}$
Reveal answer Fill a bubble to check yourself
C Correct answer
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.
Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance


Two nucleotides in a strand are linked through H-bond form a dinucleotide.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

  • The two strands of the double helix DNA have base pairing between complementary purines and pyrimidines. Adenine pairs with Thymine or vice versa by two hydrogen bonds and Guanine pairs with Cytosine or vice versa by three hydrogen bonds. 
  • The two nucleotides on the same strand are linked through phosphodiester bond between 5' phosphate group of one mononucleotide and 3' OH group of other mononucleotide, to form a dinucleotide.
Hence, the statement given in the question is incorrect.
So, the correct answer is 'False'.

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

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

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

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