Molecular Basis of Inheritance Test 3

According to Chargaff's rule the DNA helix contains an equal molar ratio of A & T, G & C.... . This does not apply to RNA, as uracil is present in RNA instead of DNA. RNA contains ribose sugar in them.

Certain gene -products, such as fRNA molecules, rRNA molecules, ribosomal proteins, RNA polymerase components (polypeptides) and other enzymes catalysing metabolic processes that are frequently referred to as cellular “housekeeping” functions , are essential components of almost all living cells. Genes that specify products of this type are continually being expressed in most cells. Such genes are said to be expressed constitutively and are frequently referred to as constitutive genes.

Primary transcripts contains both introns and exon, in which introns are noncoding

parts.

Tryptophan regulates its own active synthesis by regulating the expression of its gene via feedback

mechanism and also by acting as co-repressor which attaches with repressor proteins produced by regulator gene and blocking the promoter gene site thus blocking m-RNA synthesis and further steps.

It is thus obvious that the synthesis of tryptophan is self regulatory, since it, when present in plenty, works firstly by feedback inhibition, and secondly through co-repression to stop further synthesis of tryptophan.

Assertion (A) : Termination codons or stop codons are UAA, UAG and UGA. Reason (R) : Stop codons represent termination of translation.

The function of (3-galactosidase enzyme in lactose metabolism is to form glucose by cleaving lactose. Thus if both glucose and lactose are present in the growth medium, activity of lac operon is not needed, and indeed, no (3-galactosidase is formed until virtually all of the glucose in the culture medium is consumed. The lack of synthesis of (3-galactosidase is a result of lack of synthesis of lac mRNA. No lac mRNA is made in the presence of glucose, because in addition of an inducer to inactivate the lac i repressor, another element (cAMP-CAP) is needed for initiating lac mRNA synthesis, the activity of this element is regulated by the concentration of glucose. However, the inhibitory effect of glucose on expression of lac operon is quite indirect.

Genetic codes are commaless, but they are not overlapping as no single base take

part in the formation of more than one codon, therefore they are non-overlapping.

Lactose is not a promoter gene but an inducer of lac operon as it combines with a repressor protein formed by repressor or regulatory gene and not the gene itself. The inducer joins the repressor, forming a repressor-inducer complex. This complex prevents the repressor from binding with the operator gene of the operon. This frees the operator gene so that the RNA polymerase can move from the promoter to the structural genes.

The structural genes are then transcribed, forming a piece of polycistronic mRNA. The latter is transcribed by fRNA and ribosomes into enzymes.

DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called as respective DNA, because in these sequences, a small stretch of DNA is repeated many times. These sequences normally do not code for any proteins, but they form a large portion of the human genome. These sequences show a high degree of polymorphism and form the basis of DNA fingerprinting. As the polymorphisms are inheritable from parents to children, DNA fingerprinting is the basis of paternity testing in case of disputes.

Regulator gene controls the operator gene in cooperation with a chemical compound called inducer present in the cytoplasm. The regulation gene codes for and produces a protein substance called repressor. The repressor substance combines with the operator gene to repress its function. Therefore it is called the regulator gene.

The constitutive genes keep on functioning all the time. They need not be repressed. Therefore, the regulator and operator genes are not associated with them.

Both assertion (A) and reason (R) are true. Since the half-life of the RNA molecules is shorter , uracil would suffice to achieve the function of RNA. On the other hand, DNA remains the same until the cell dies/divides. The functions of thymine and uracil are the same.

DNA polymerase enzyme is responsible for synthesizing DNA, they add nucleotides one by one to the growing DNA chain, adding those which are complementary

to the template. The template strand has polarity in 3'→5'.

It was concluded by the transforming principle', that bacteria is transferred from heat-killed S-strain to live R-strain which is non virulent.

Both assertion and reason are true and reason (R) is the correct explanation

of the assertion (A). This attachment is an essential step in the synthesis of protein. This

attachment is brought by aminoacyl-t-RNA synthetase.

The sequence of mRNA will be identical to the given sequence of coding strand except for the presence of uracil in place of thymine in mRNA.