31 Years NEET Previous Year Questions: Molecular Basis of Inheritance - 2 - NEET MCQ

23sr RNA acts as a catalyst in a bacterial cell.

Satellite DNA is useful in forensic science. The polymorphism of minisatellite, microsatellite and minivariant repeats is analysed for DNA finger printing, DNA profiling. It helps in the resolution of crimes, legal disputes etc.

Genetic code is non ambiguous. There is no ambiguity for a particular codon. A particular codon will always code for the same amino acid, where ever it is found.

In lac operon, lactose acts as the inducer that binds with the repressor and inactivates it. This enables the operator to carry out the translation of the genes and produce enzymes. If glucose is present in the system there is no need of lac operon as it is the preferred substrate. Since galactose is not an inducer it cannot bind with the repressor.

In the absence of lactose repressor binds with the operator and does not allow translation of the genes and hence no enzymes will be formed.

The lac z gene codes for galactosidase enzyme. Permease is encoded by lac y gene.

Nirenberg and Mathaei (1961) experimen-tally proved that a single amino acid is determined by a sequence of three nitrogen bases. The sequence of three nitrogen bases determining a single amino acid is called a triplet code. Nirenberg and Mathaei experiments cracked the DNA and discovered unequivocally that a genetic code is a triplet.

Semiconservative replication of DNA was first demonstrated in Escherichia coli. E. coli is a common type of bacteria that can get into food, like beef and vegetables. The strange thing about these bacteria is that they are not always harmful to you. E. coli normally lives inside your intestines, where it helps your body breakdown and digest the food you eat.

Splicing is the removal of introns and joining the exons in a defined order in a transcription unit. In molecular biology, splicing is a modification of RNA after transcription, in which introns are removed and exons are joined.

The genetic code consists of 64 triplets of nucleotides. These triplets are called codons. With three exceptions, each codon encodes for one of the 20 amino acids used in the synthesis of proteins. That produces some redundancy in the code. Most of the amino acids being encoded by more than one codon. The genetic code can be expressed as either RNA codons or DNA codons.

Theodor O. Diener discovered the Potato Spindle Tuber Viroid (“PSTVd”), the first viroid ever identified, in 1971. PSTVd is a small, circular RNA molecule. Dr. Diener discovered that the pathogen causing potato spindle tuber disease is not a virus, as previously believed, but a much smaller, free RNA molecule.

Haploids describes a nucleus cell or organism with a single set of unpaired chromosomes. The haploid number is designated as X. Reproductive cells, formed as a result of meiosis are diploid. Fusion of two such cells restores the normal diploid number. Therefore, haploids are more suitable for mutation studies than the diploids. This is because all mutations, whether dominant or recessive are expressed in haploids.

Purine is an organic nitrogenous base sparingly soluble in water, that gives rise to a group of biologically important derivatives, notably adenine and guanine, which occur in nucleotides and nucleic acids (DNA and RNA). 

GCU indicates alanine but GUU indicates valine. Stop codons are UAG, UGA and UAA AUG is the most common start codon which does for methionine. UUA indicates leucine but UCA indicates serine. 

In the DNA molecule, there are two strands which run anti parallel one is 5' - 3' direction and other in 3' -5' direction, the two chains are held together by hydrogen bonds between their bases. Adenine (A), a purine of one chain his exactly opposite thymine (T), a pyramidine of the other chain. Similarly, cytosine (C), a pyrimidine lies opposite guanine (G), a purine. This allows a sort of lock & key arrangment between large sized purine & small sized pyrimidine. It is strengthened by the appearance of hydrogen bonds between the two. 

The process of formation of protein sequence from DNA strand is called transcription which requires RNA polymerase chain. RNA  polymerase chains are of 3-types in eukaryotes
(i)  RNA polymerase-I
(ii)  RNA polymerase II
(iii) RNA polymerase-III

It was given by Geneticists George W. Beadle and E. L. Tatum which states that each gene in an organism controls the production of a specific enzyme. It is these enzymes that catalyze the reactions that lead to the phenotype of the organism.

The DNA binding sequence for RNA polymerase is called TATA box.

A sequential expression of a set of human genes is the DNA sequence. Because gene is the functional part of DNA sequence.

The nucleosome model explains the packaging of histone proteins and DNA in the chromatin material which forms the chromosome.

Okazaki fragments in DNA are linked up by the enzyme DNA ligase. Replication always ocur in 5' - 3' direction. Okazaki fragments synthesized on 3' - 5' DNA template, join to form lagging strand which grows in 3' - 5' direction.

The genes of cytoplasmic characters occur outside the chromosome, in cytoplasm, they inherit their traits like chromosomal genes do. In a zygote formation the cytoplasm comes from the mother’s ova and hence the cytoplasmic characters must come from maternal side and this is the reason that cytoplasmic inheritance is also known as maternal inheritance.

Beadle & Tatum postulated the theory of ‘One-gene-one-enzyme’ in which they stated that in any living cell there are number of genes present on chromosomes in a linear fashion. One single gene controls the synthesis of one particular enzyme (or protein) in the cell which is responsible for its phenotypic character.

Operons are segments of genetic material which function as regulated unit or units that can be switched on and switched off. An operon consists of one to several structural genes. (Three in lac operon) These are genes which produce mRNAs for forming polypeptides / proteins / enzymes. Z (produces enzyme β galactosidase for splitting lactose into glucose and galactose). Y (produces enzyme galactoside permease required in entry of lactose) A (produces enzyme thiogalactoside trans- acetylase).
The three structural genes of the operon produce a single polycistronic mRNA.

Reverse transcriptase (RNA dependent DNA polymerase) is present in some retroviruses eg. HIV virus.

AUG—It codes for methionine only in both prokaryotes and eukaryotes, it is also an initiation codon.

Telomerase is a ribonucleoprotein which synthesize the rich strand of telomers in DNA. Telomerase is an enzyme that adds specific DNA sequence repeats ("TTAGGG" in all vertebrates) to the 3' ("three prime") end of DNA strands in the telomere regions, which are found at the ends of eukaryotic chromosomes. The telomeres contain condensed DNA material, giving stability to the chromosomes. The enzyme is a reverse transcriptase that carries its own RNA molecule, which is used as a template when it elongates telomeres, which are shortened after each replication cycle. Telomerase was discovered by Carol W. Greider in 1984.