A closer look at the interactions between the histones and the nucleosomal DNA reveals the structural basis for the binding and bending of the DNA within the nucleosome. Fourteen distinct sites of contact are observed, one for each time the minor groove of the DNA faces the histone octamer. State whether the following set of statements is true/false regarding this association?

I. The majority of these associations are between the proteins and the oxygen atoms in the phosphodiester backbone near the minor groove of the DNA.

II. The association of DNA with the nucleosome is mediated by a large number (about 40) of hydrogen bonds between the histones and the DNA.

III. Maximum numbers of hydrogen bonds are made between the protein side chains and the bases, and all of these are made in the minor groove of the DNA.

IV. The highly basic nature of the histones further facilitates DNA bending by masking the negative charge of the phosphates that ordinarily resists DNA bending.

V. The positively charged nature of the histones facilitates the close juxtaposition of the two adjacent DNA helices necessary to wrap the DNA more than once around the histone octamer.

#Question id: 18870

#Unit 13. Methods in Biology

#Question id: 10791

#Unit 6. System Physiology – Plant

Following are certain statements regarding furanocoumarins;

 a) furanocoumarins have an attached furan ring

 b) These compounds are toxic until they are activated by sunlight in the ultraviolet A (UV-A) region (320–400 nm)  

 c) Light activated furanocoumarins can insert themselves into the double helix of DNA and bind to the pyrimidine bases, thus blocking transcription and repair and leading eventually to cell death   

 d) Phototoxic furanocoumarins are especially abundant in members of the Umbelliferae family, including celery, parsnip, and parsley.

 Which of the following combination from the above statements is correct?

#Question id: 218

#Unit 1. Molecules and their Interaction Relevant to Biology

We use the term tetrahydrofolate to designate a family of related compounds. What is the main difference between members of this family?

#Question id: 15196

#Unit 8. Inheritance Biology

#Question id: 2983

#Unit 2. Cellular Organization

Cell cycle is regulated by master regulators (cyclin and CDKs). In vertebrates, G1 CDK activity rises during G1 and is stimulated by the presence of growth factors. When signaling from growth factors is sustained, the resulting cyclin D–CDK4/6 complexes begin phosphorylating Rb, releasing some E2F, which stimulates transcription of the genes encoding cyclin E, CDK2, and E2F itself. In a particular cell type there is a mutation in Rb such that it cannot be phosphorylated. What will be the correct expression pattern of cyclin E in these cells after mitotic stimulation?