Test: Molecular Basis Of Inheritance 4 - From Past 28 Years Questions - NEET MCQ

The inducer is an environmental agent, which triggers transcription from an operon. The inducer or effector molecule are small sized which can bind to a regular protein.

The lac operon consists of a promotor gene, an operator gene and structural genes. There are three structural genes designated as z, y and a, which code for the enzymes β-galactosidase, lac permease and transacetylase respectively. It is an example of inducible operon.

tRNA works as an adoptor molecules for carrying amino acid to the mRNA templated during protein synthesis. It bears anticodon and recognizes the specific codon on mRNA.

Replication of DNA is discontinuous over the lagging strand over which only small stretches of DNA are built due to opposite running of  DNA template. The small stretches of DNA are called okazaki fragments.

Termination codons ( triplet) are the stop signals which when encountered cause termination of polypeptide synthesis. The termination codons are UAA, UAG and UGA.

DNA finger printing is a technique to identify a person on the basis of his DNA which is specific for every individual. This technique for first time was developed by Alec Jeffreys and his colleagues at Leicester University in U.K. DNA of an individual carries specific sequences of nucleotides which are repeated many times throughout the length of DNA. This reveals polymorphism in DNA. These are inherited. Each individual inherits these repeats from his/her parents which are used as gentic markers in personal identity test.

During the activation of amino acids, in the presence of  Mg²⁺ and ATP an amino acid gets attached to a specific enzyme aminoacyl  t-RNA synthetase. Pyrophosphate is released which breaks up to release energy. During translocation, in the presence of the enzyme translocase and energy from  GTP  the ribosome moves in such a way that the peptidyl bearing t-RNA of A - site comes to lie on the P-site, exposing a new codon at A - site. In the peptidyl transferase reaction energy is provided by GTP.

Termination codons are the stop signals which when encountered cause termination of polypeptide synthesis. They are UAA (ochre), UAG (amber) and UGA (opal). Codons are determined by the sequence of  bases on the DNA. Thymine is not present on RNA.

A mutation bringing about early stoppage  of polypeptide formation is called nonsense  mutation. Frame shift  mutation is a type of gene mutation where the reading of codons is changed due to insertion or deletion of nucleotides.

DNA replication is semiconservative. i.e. at each replication one of the parental strands is retained and a new daughter strand is obtained. Thus only half of the parental DNA molecule is carried to the next generation.

Multiple alleles are multiple alternatives or alleles of the same gene which occur in the population of same species . Polygene is a gene, single dominant allele of which  express only a unit of trait . Polygenes are the genes controlling  quantitative inheritances. Oncogenes are the cancer causing  genes. 

In eukaryotes separate protein factors take part in recognition  and initiation during transcription. They are called transcription  factors. Coenzymes are non protein organic cofactors which get loosely attached to apoenzymes during the functioning of holoenzymes. 

Eukaryote RNAs contain non coding intervening segments called introns. The process of removal of introns through cutting  and joining the essential coding sequences ( exons) is called splicing.

The term "hot spots" was used by Benzer for the sites which are more mutable than other sites. Studies in 1978 revealed that 5-methylcytosine residues occur at the position of each hot spot.

DNA is complexed with histones in eukaryotes.

Transposons are sequences of DNA that can move around to different positions within the genome of a single cell, a process called transposition. In the process, they can cause mutations and change the amount of DNA in the genome. Transposons are also called “jumping genes” or “mobile genetic elements”. Discovered by Barbara McClintockearly in her career, the topic went on to be a Nobel winning work in 1983. There are a variety of mobile genetic elements, and they can be grouped based on their mechanism of transposition.

Operator gene allows the functioning of the operon. 

In  DNA adenine always pairs with thymine and guanine always pairs with cytosine,  this is called complementary base pairing.

Griffith’s experiment with Pneumococcus proves that DNA is the genetic material.

Regulator gene produces a biochemical for suppressing the activity of the operator gene.

The number of base pairs (bp) found in the haploid genome of humans is 2.9 × 10⁹.

Polygene is a gene, single dominant allele of which expresses only a unit of the trait, lethal genes on expression stop producing  vital products essential  for survival of an individual.

Ribosomes are the sites of protein synthesis. Mitochondria being a semi autonomous organelle has its own protein synthesizing machinery.

Seal the ends of chromosomes. The telomere is a "ribonucleoprotein complex" composed of a protein component and an RNA primer sequence which acts to protect the terminal ends of chromosomes. This prevents chromosomal disintegration and prevents the ends of the chromosome from being processed as a double strand DNA break, which could lead to chromosome-tochromosome telomere fusions.

In negative (re pressible) operon, the repressor co-repressor complex binds with the operator. The free repressor cannot bind to the operator.