Tag: structure of dna

Questions Related to structure of dna

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

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

  1. 50% and 33%

  2. 66% and 17%

  3. 66% and 33%

  4. 33% and 50%

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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.

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

  1. True

  2. False

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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'

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

  1. Four

  2. Five

  3. Six

  4. Two

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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

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

  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

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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

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

  1. Gentian violet

  2. Neutral red

  3. Basic fuchsin

  4. Cotton blue

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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 :-

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

  1. $1'-1'$ glycosidic linkage

  2. $1'-6'$ glycosidic linkage

  3. $1'-9'$ glycosidic linkage

  4. $1'-4'$ glycosidic linkage

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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?

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

  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

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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.