Question

1. What is the role of lac repressor molecule in bacterial gene regulation? Explain.
2. Explain the term disruptive selection in evolution giving a suitable example.
3. What are sister chromatids? Which protein hold them together during cell division? What is the phenomenon of nondisjunction?
4. What are the functions of topoisomerases and DNA polymerases in DNA replication?
5. What are photosystems ? Where exactly the splitting of water and generation of oxygen occur during light dependent reaction of photosynthesis?

Answer 1

Ans 1:- lac repressor molecule is protein involved in inhibition of gene expression of protein that involved in metabolism of lactose. lac repressor protein inhibit gene expression when lactose is not present in cell to make sure that cell divert all his energy to absorb lactose from outside into cell. when lactose become available to cell it get converted into allolactose which inhibit lac repressor binding to DNA and gene expressor of protein involved in lactose metabolism get started.

Ans 2:- Disruptive selection is essential part of evolution in which population with extreme phenotype trait favored more than intermediate phenotype trait. for example rabbits with black fur have more survival chances than rabbit with white and gray fur from predator in habitant with black rock. as black rock favor black rabbit to hide out from predator. but white and gray fur rabbit would easily identified by predator and eaten out early because they are easily get caught in black Colour rock.

Ans 3:- sister chromatids are identical copy of chromosomes which is produced by chromosome during DNA replication. these two chromatids are joined together by complex subunit protein called cohesins. non disjunction is phenomenon in which two sister chromatids do not separates during cell division.

Ans 4:- topoisomerase is enzyme that helps to prevent over winding of DNA helix ahead of replication fork and keep DNA strand open for DNA replication. to do this topoisomerase cut phosphate backbone of DNA strand and relieve tension of over winding of DNA strand. DNA polymerase is an enzyme that synthesize DNA strand from deoxyribonucleic acid, a building block of DNA. DNA polymerase is essential for DNA replication and there two DNA polymerase work together each for one strand of DNA.

Ans 5:- Photosystem consists of complex proteins those are involved in photosynthesis in plant. photosystem absorb sun light and carbon dioxide from environment and synthesize energy and release oxygen in the environment. breakdown of H2O and formation of O2 occurs in thylakoid membrane of chloroplast.