The H3.H4 tetramers and H2A.H2B dimers each interact with a particular region of the DNA within the nucleosome.

I. Histone H3.H4 tetramers occupy a key position in the nucleosome by binding the middle and both ends of the DNA.

II. The amino-terminal region of H3 most proximal to the histone-fold region forms a fourth a-helix that interacts with the final 13 bp at each end of the bound DNA.

III. The relatively short length of DNA bound by H2A.H2B dimers is sufficient to prepare the DNA for H3.H4 tetramer binding.

IV. The H3.H4 tetramer forms the bottom part of the histone octamer located across the disc from the DNA ends whereas two H2A.H2B dimer occupies the top part.

Which of the following represents the correct binding of the histones with the DNA?

TLS Online TPP Program

#Question id: 30101

#Unit 1. Molecules and their Interaction Relevant to Biology

The formation of dATP for DNA synthesis occurs primarily by:

TLS Online TPP Program

#Question id: 30102

#Unit 1. Molecules and their Interaction Relevant to Biology

Which of the following would NOT be expected to contribute to hyperuricemia (gout)?

TLS Online TPP Program

#Question id: 30103

#Unit 1. Molecules and their Interaction Relevant to Biology

Direct sources of purine ring atoms in the de novo synthesis of IMP include:

1. glutamine.

2. a component of the tetrahydrofolate one-carbon pool.

3. aspartate.

4. glycine.

TLS Online TPP Program

#Question id: 30104

#Unit 1. Molecules and their Interaction Relevant to Biology

A nucleoside phosphorylase:

1. cleaves a nucleoside with the production of ribose 1-phosphate.

2. is necessary for the major salvage pathway for pyrimidines.

3. is used in the degradation of purine nucleotides.

4. is responsible for the equilibration of nucleoside monophosphates and nucleoside diphosphate.

TLS Online TPP Program

#Question id: 30105

#Unit 1. Molecules and their Interaction Relevant to Biology

Methotrexate is an inhibitor of dihydrofolate reductase. Administration of methotrexate would inhibit:

1. de novo synthesis of UMP.

2. conversion of dUMP to dTMP.

3. conversion of IMP to GMP.

4. de novo synthesis of IMP

TLS Online TPP Program

#Question id: 30106

#Unit 1. Molecules and their Interaction Relevant to Biology

If a cell has an adequate supply of adenine nucleotides but requires more guanine nucleotides for protein synthesis:

1. Glutamine-PRPP amidotransferase will not be fully inhibited.

2. AMP will be a feedback inhibitor of the condensation of IMP with aspartate.

3. ATP will stimulate the production of GMP from IMP.

4. ATP will inhibit nucleoside diphosphate reductase.