NEET Practice Questions (MCQs) with Answers & Solutions

In the process of protein synthesis, the messenger RNA (m-RNA) is responsible for carrying the genetic code transcribed from DNA to specialized sites within the cell (called ribosomes) where the information is translated into protein composition. The sequence of amino acids in a particular protein is determined by the sequence of nucleotides in m-RNA.

Sequence of t-RNA, c-DNA or r-RNA do not decide the amino acid sequence in protein synthesis.

(d) 'One gene-one enzyme' hypothesis was given by Beadle and Tatum (1948) which states that particular gene controls the synthesis of specific enzyme. Later, it was modified to 'one gene-one polypeptide hypothesis by Yanofsky et.al. (1965).

J.D. Watson and F.H.C. Crick (1953) showed that DNA has a double helical structure with two polynucleotide chains connected by hydrogen bonds and running in opposite directions (antiparallel). The antiparallel strands of a DNA molecule means that the phosphate groups at the start of two DNA strands are in opposite position (pole).

Scientists finished the first genetic sequence of a plant, that of the weed Arabidopsis thaliana, in December 2000. It is called Drosophila of plant kingdom.

Okazaki fragments are short DNA fragments created on the lagging strand during DNA replication that ar subsequently joined to form a single continuous strand of DNA.

With the synthesis of complimentary DNA strands the  leading strand always reads 3’ to 5’. Its antiparallel compliment strand, the lagging strand reads from 5’ to 3’. Because the original strands of DNA are antiparallel and only one new strand can begin at the 3’ end (the preferred end), the other strand must grow in the opposite direction. Regarding the lagging strand, the result of this strand’s discontigous replication is the production of a series of short sections of DNA called Okazaki fragments. It was originally discovered by Reiji and his wife Tsuneko Okazaki and their colleagues while studying replication of bacteriophage DNA in Escherichia coli.

Transcription is the process through which a DNA sequence is enzymatically copied by an RNA polymerase to produce a complementary RNA. Transcription is divided into 3 stages: initiation, elongation and termination. In eukaryotes, it takes place in the nucleus and the RNA is transferred out to the cytoplasm for translation.

Group banding is used in staining both plant and animal chromosomes. Chromosomes are stained with special fluorescent dyes that have differential affinity for difficult parts of chromosomes. There are many types of staining techniques which show different banding patterns. C-banding is common to both plants and animals. It stains region having constitutive heterochromatin.

Nonsense codons (or terminating codons) are those codons which do not code for any of the 20 essential amino acids. UAA (ochre), UAG (amber) and UGA (opal) are three codons which when present in mRNA, would bring termination of polypeptide chain, which would then be released from the ribosome.

Frameshift mutation occurs when one or more nucleotides are either added or deleted from DNA.

Example of frameshift mutation due to deletion is as follows:

Original (wild type) message or reading frame

The triplet code is a degenerate one with many codons than the number of amino acid types coded. An explanation for this degeneracy is provided by the Wobble hypothesis proposed by F.H.C. Crick in 1966.