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

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

  1. 340 nm

  2. 3400 nm

  3. 34000 nm

  4. 340000 nm
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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

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

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

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

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

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

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

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

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

Multiple choice structure of dna and rna nucleic acids and polynucleotides nucleic acids and protein synthesis molecular biology biology

Genome is the complete complement of  __________ including all ___________ and the inter genetic regions.

  1. DNA and RNA

  2. DNA and genes

  3. RNA and genes

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
A genome is an organism's complete set of DNA, including all of its genes in the genetic regions.
So, the correct option is 'DNA and genes'
Multiple choice structure of dna and rna nucleic acids and polynucleotides nucleic acids and protein synthesis molecular biology biology

DNA is a polymer of a

  1. Glucose

  2. Amino acid

  3. Nucleotide

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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 as 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. The nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. According to base pairing rules (A with T and C with G), hydrogen bonds bind the nitrogenous bases of the two separate polynucleotide strands to make double-stranded DNA. So, nuclotides are building blocks of DNA and not glucose or aminoacid. Thus, the correct answer is option C.

Multiple choice structure of dna and rna nucleic acids and polynucleotides nucleic acids and protein synthesis molecular biology biology

The diameter of DNA molecule is

  1. $10 \mathring{A}$
  2. $100 \mathring{A}$
  3. $200 \mathring{A}$
  4. $20 \mathring{A}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
DNA is made of two ("duplex DNA") dextrogyre (like a screw, right- handed) helical chains or strands ("the double helix"), coiled around an axis to form a double helix of $20 \mathring{A}$ of diameter. The two strands are antiparallel. The general appearance of the polymer shows a periodicity of $3.4 \mathring{A}$, corresponding to the distance between 2 bases, and another one of $34 \mathring{A}$, corresponding to one helix turn.
So, the correct answer is "$20 \mathring{A}$".
Multiple choice structure of dna and rna nucleic acids and polynucleotides nucleic acids and protein synthesis molecular biology biology

As the base sequence present on one strand of DNA decides the base sequence of other strand, this is considered as _____.

  1. Descending strand

  2. Leading strand

  3. Lagging strand

  4. Complimentary strand
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Because the two strands of DNA are complementary, the sequence of one strand dictates the sequence of the other. This property is known as complementarity.

Multiple choice structure of dna and rna nucleic acids and polynucleotides nucleic acids and protein synthesis molecular biology biology

The basis of life (secret of life) is

  1. Lipid

  2. Protein

  3. Nucleic acid

  4. Nucleoprotein
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

All the bio-molecules are important for life but as per the question the nucleic acids stand out, because they only have genetic information coded in them and can pass on this information to next generation of cells. So, nucleic acid plays a significant role  in the basis of life. 

Multiple choice structure of dna and rna nucleic acids and polynucleotides nucleic acids and protein synthesis molecular biology biology

UAG is triplet nitrogen base on m RNA. What will be the corresponding triplet on the coding strand?       

  1. TAG

  2. UAG

  3. ATC

  4. TUA
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
  • In DNA transcription, the coding strand is the DNA strand whose base sequence corresponds to the base sequence of the RNA transcript produced (although with thymine replaced by uracil).
  •  It is this strand which contains codons, while the non-coding strand contains anticodons.
  •  Hence, UAG is triplet nitrogen base on m RNA, TAG will be the corresponding triplet on the coding strand. 
  •  So, the correct answer is 'TAG'.