Few problems along with their solutions from this chapter are given follows:
Q. Which of the following statements is the most appropriate for sickle-cell anaemia?
(a) It cannot be treated with iron supplements
(b) It is a molecular disease
(c) It confers resistance to acquiring malaria
(d) All of the above
Ans. (d) All of the above
Sickle cell anaemia is a genetic disorder and hence cannot be treated with iron supplements. Altered shape of RBCs confer resistance to malaria in people suffering from sickle cell anaemia.
Q. Regulatory proteins are the accessory proteins that interact with RNA polymerase and affect its role in transcription. Which of the following statements is correct about regulatory protein?
(a) They only increase expression
(b) They only decrease expression
(c) They interact with RNA polymerase but do not affect the expression
(d) They can act both as activators and as repressors
Ans. (d) They can act both as activators and as repressors
Regulatory proteins control the functions of structural genes and are at called regulatory genes. The important regulatory genes are promoters, terminators, operators and repressor.
To regulate the process of transcription, transcription factors (a sequence of specific DNA-binding factor) alone or with other proteins, promoter (as on activator) or stop as a repress or the binding site of RNA polymerase to DNA.
Q. Define a cistron. Giving examples differentiate between monocistronic and polycistronic unit.
Ans. A cistron is stretch of base sequences that codes for one polypeptide chain including adjacent control regions. It may also code for a tRNA, rRNA molecule or may perform other specific functions including regulating functions of other cistrons.
This term has replaced the definition of a gene. Monocistronic transcription unit will have all the regulatory and coding sequences for a single polypeptide, whereas polycistronic may have coding sequences for more than one polypeptide,
In eukaryotic cells almost all the messenger RNAs are monocistronic. In prokaryotes, lac operon coding sequence would be an example of polycistronic DNA region.
Q. The enzyme DNA polymerase in E.coli is a DNA dependent polymerase and also has the ability to proofread the DNA strand being synthesized. Explain. Discuss the dual polymerase.
Ans. DNA polymerase uses DNA template to catalyse the polymerization of deoxynucleotides and hence it is called DNA – dependent. They process exonuclease activity as well. DNA polymerase III can proofread the newly synthesised strand and senses the wrong base insertions.
It deletes wrong bases and helps correct the mistake by putting in the right one, DNA polymerase. Hence, it’s said to be of dual nature, i.e. of reading the template and then proof reading the new strand.
Class 12 Biology NCERT Exemplar Problems:
Class 12 Biology NCERT Exemplar problems are a very good resource for preparing the critical questions like Higher Order Thinking Skill (HOTS) questions. Every year, many questions from the NCERT Exemplar are directly asked in the board exams. Also, these are the kind of questions asked in the various competitive exams and Olympiad level tests. So, it’s very important for students to practice the NCERT exemplar problems to prepare well for the boards and the competitive exams.
Main topics discussed in Class 12 Biology, Chapter 6- Molecular Basis of Inheritance, are:
- The DNA
- The Search for Genetic Material
- RNA World
- Replication
- Transcription
- Genetic Code
- Translation
- Regulation of Gene Expression
- Human Genome Project
- DNA Fingerprinting.