Botany MCQs for NEET — Practice Questions with Answers

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.

Gene pool is the total gene present in a population. Genome is the total genetic constitution of an organism. Codon is the basic unit of genetic code, a sequence of three adjacent nucleotide in DNA or mRNA that code for an amino acid. Gene is the basic unit of heredity; a sequence of DNA nucleotide that encodes a protein.

Cistron is a segment of DNA nucleotides that codes for a polypeptide chain. Triplet is a three nucleotides sequence coding for an amino acid.

Therefore,

codon  $\approx$ triplet

cistron $\approx$ gene

DNA fingerprinting is technically called DNA profiling or DNA typing.

tRNA has four recognition sites among these one is the amino acid attachment site. It has the amino acid attachment site with the 3’ terminal – CCA sequence.

The two DNA strands are held together by weak (hydrogen) bonds between the bases on each strand, forming base pairs. Genome size is usually stated as the total number of base pairs; the human genome contains roughly 3 billion base pairs.

Southern blotting was named after Edward M. Southern who developed this procedure in Edinburgh University in the 1970’s. Southern blotting is designed to locate a particular sequence of DAN within a complex mixture. The amount of DNA needed for this technique is dependent on the size and specific activity of the probe. Before, starting the procedure, the desired DNA should be isolated from a specific nucleated cell.