Question

Consider the following statements :

1. DNA is much larger than RNA with millions of nucleotides.

2. DNA is self-replicating, unlike RNA.

3. DNA is synthesized from RNA.

Which of the following statements given above is/are correct?

1. 1 and 3 only
2. 2 and 3 only
3. 1 and 2 only
4. 1, 2, and 3

Answer 1

Correct Answer - Option 3 : 1 and 2 only

The correct answer is 1 and 2 only.

• A DNA molecule in a human chromosome can be up to 250 million nucleotide pairs long; in contrast, most RNAs are no more than a few thousand nucleotides long, and many are considerably shorter. Hence, statement 1 is correct.
• DNA is a self-replicating molecule where its component parts, nucleotides, have specific chemical interactions that allow for the design of self-assembled structures. Hence, statement 2 is correct.
• RNA is synthesized from a portion of one strand of DNA, which acts as a template. Hence, statement 3 is not correct.
• This process is called transcription.
• All RNA molecules are derived from the information permanently stored in DNA except the RNA genome of certain viruses.

• Humans have 46 chromosomes that contain all of the genetic information, and there are over 25,000 genes in the human genome.
• Genes are composed of DNA and it is predicted that there are over 3 billion base pairs in the human genome. 
• DNA (deoxyribonucleic acid) is the genomic material in cells that contains the genetic information used in the development and functioning of all known living organisms.
  • DNA, along with RNA and proteins, is one of the three major macromolecules that are essential for life.
  • Most of the DNA is located in the nucleus, although a small amount can be found in mitochondria (mitochondrial DNA).
  • Within the nucleus of eukaryotic cells, DNA is organized into structures called chromosomes.
    • The complete set of chromosomes in a cell makes up its genome; the human genome has approximately 3 billion base pairs of DNA arranged into 46 chromosomes.
    • The information carried by DNA is held in the sequence of pieces of DNA called genes.
  • DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds.
    • These two strands run in opposite directions to each other and are therefore anti-parallel.
  • Attached to each sugar is one of four types of molecules called nucleobases (bases).
    • It is the sequence of these four bases along the backbone that encodes information.
    • The sequence of these bases comprises the genetic code, which subsequently specifies the sequence of the amino acids within proteins.
• Ribonucleic acid(RNA) is a molecule similar to DNA.
  • An RNA strand has a backbone made of alternating sugar (ribose) and phosphate groups.
  • Attached to each sugar is one of four bases--adenine (A), uracil (U), cytosine (C), or guanine (G).
  • Different types of RNA exist in the cell: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).
  • The chemical structure of RNA is very similar to that of DNA: each nucleotide consists of a nucleobase a ribose sugar, and a phosphate group.

• Differences between DNA and RNA:

DNA	RNA
DNA is usually double-stranded, has two separate strands that are connected	RNA molecules are single-stranded and can adopt very complex three-dimensional structures.
DNA contains the slightly different sugar deoxyribose (a type of ribose that lacks one oxygen atom)	RNA contains the sugar ribose
DNA is much larger than RNA with millions of nucleotides.	RNA is smaller with hundreds of nucleotides.
DNA is self-replicating.	RNA is synthesized from DNA.