Q25 of 26 Page 1

Observe the representation of genes involved in the lac operon given below –


(a) Identify the region where the repressor protein will attach normally.


(b) Under certain conditions repressor is unable to attach at this site. Explain.


(c) If repressor fails to attach to the said site what products will be formed by z, y and a?


(d) Analyze why this kind of regulation is called negative regulation.


OR


Transcription in eukaryotes is more complex process than in prokaryotes. Justify and compare the initiation, elongation and termination in bacterial cells with eukaryotes.


(a)The region where the repressor protein will attach normally is the ‘operator region’ or O. It is a short region of DNA which interacts with the regulatory protein that controls the transcription of the operon.


(b) Repressor is unable to attach at this site in presence of an inducer which is Lactose.


(c) If repressor fails to attach to the said site following products would be formed at the following sites.


z: -β galactosidase


y: permease


a: Transacetylase


(d)This kind of regulation is called negative regulation because it has repressor attached to it all the time. It is also known as constitutive repressor because of which the operon is always in off position. It gets switched on only when an inducer such as Lactose or Allolactose gets attached to the site.


OR


Transcription in eukaryotes is more complex process than in prokaryotes because:


1. In prokaryotes only one RNA polymerase enzyme is involved. Whereas in eukaryotes three RNA polymerase enzymes are involved.


2. In prokaryotes translation and transcription occurs at the same time inside the cytoplasm. Whereas in eukaryotes translation and transcription occurs at different sites.


Eukaryotes:


Initiation:


It takes place with the help of three different RNA polymerase enzymes and several initiation factors.


Elongation:


Elongation in eukaryotes requires different elongation factors which stimulate the elongation of RNA.Here the addition of nucleotides takes place in the DNA strand. This makes the DNA strand longer.


Termination:


Termination marks the end of transcription and release of RNA polymerase also takes place.


In eukaryotes post transcription changes also takes place which includes:


1. Cleavage: In this process large RNA strand is cleaved into smaller DNA strands.


2. Splicing: In this process extra segments from the DNA strands are removed (introns) by the enzyme nucleases.


3. Terminal additions: In this process extra nucleotides may be added for particular fuctions.


More from this chapter

All 26 →
22

Rajesh was doing gel electrophoresis to purify DNA fragments. Given below is the sketch of the observations of the experiment performed by him.


(a) At which end he would have loaded the samples and where?


(b) Analyse the reason for different positions taken up by the DNA bands.


(c) Elaborate the step he would have followed to visualize DNA bands.


 23

Mohit and Sumit want to buy a new car for their company. Mohit insisted on buying a CNG car with a better mileage but Sumit insisted on buying a diesel version of a high end car with better music system and A.C but relatively low mileage.

(a) Being a responsible citizen of Delhi, how will Mohit convince Sumit about his decision in the wake of rising pollution levels?


(b) What qualities of personality are being exhibited by Mohit in doing so?


(c) Suggest two more measures which can help in reducing vehicular pollution.


 24

Human female is not fertile after menopause whereas males can produce gametes at any age after puberty. Analyse the statement and schematically represent a comparison between gametogenesis in males and females.

OR


A village health worker was taking a session with women. She tells the women that one has to be very careful while using oral pills as method of birth control. Wrong usage can actually promote conception.


(a) Analyze the statement and compare the merits and demerits of using oral pills and surgical methods of birth control.


(b) Village women were confused as to how a thin metallic Copper loop can provide protection against pregnancy. Justify the use explaining the mode of action of IUDs.


 26

The graph below shows species –area relationship.


(A) If b denotes the relationship on log scale


i) Describe a and b.


ii) How is slope represented? Give the normal range of slope. iii) What kind of slope will be observed for frugivorous birds and mammals in a tropical forest?


(B) Species diversity of plants (22%) is much less than that of animals (72%). Analyze the reasons for greater diversity of animals as compared to plants.


OR


(a) Which of the above represents the increase or decrease of population?


(b) If N is the population density at time t, then what would be its density at time? Give the formula.


(c) In a barn there were 30 rats. 5 more rats enter the barn and 6 out of the total rats were eaten by the cats. If 8 rats were born during the time period under consideration and 7 rats left the barn, find out the resultant population at time.


(d) If a new habitat is just being colonized, out of the four factors affecting the population growth which factor contributes the most?