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

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.

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

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

Nucleotides are formed by the combination of purines or pyrimidines (nitrogenous bases), sugars (pentose), and phosphates. Nucleosides lack the phosphate group, making option A the correct answer.

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

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

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

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. $160$
Reveal answer Fill a bubble to check yourself
C Correct answer
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
Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

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