TLS Online TPP Program

#Question id: 785


Several types of very short RNAs repress—or silence—expression of genes with homology to those short RNAs. They are produced from a variety of sources and direct the silencing of genes in the following different ways-

#Unit 1. Molecules and their Interaction Relevant to Biology
  1. Triggering destruction of the mRNA encoded by the target gene

  2. Inhibiting translation of the mRNA

  3. Inducing chromatin modifications within the target gene and thereby silencing its transcription

  4. All of the above

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TLS Online TPP Program

#Question id: 378

#Unit 1. Molecules and their Interaction Relevant to Biology

Which of the following statements about buffers is true?

TLS Online TPP Program

#Question id: 379

#Unit 1. Molecules and their Interaction Relevant to Biology

A compound has a pKa of 7.4. To 100 mL of a 1.0 M solution of this compound at pH 8.0 is added 30 mL of 1.0 M hydrochloric acid. The resulting solution is pH:

TLS Online TPP Program

#Question id: 380

#Unit 1. Molecules and their Interaction Relevant to Biology

The Henderson-Hasselbalch equation:

TLS Online TPP Program

#Question id: 381

#Unit 1. Molecules and their Interaction Relevant to Biology

Consider an acetate buffer, initially at the same pH as its pKa (4.76). When sodium hydroxide (NaOH) is mixed with this buffer, the:

TLS Online TPP Program

#Question id: 382

#Unit 1. Molecules and their Interaction Relevant to Biology

The molar ratio of sodium acetate to acetic acid in a buffer solution with a pH OF 5.76 is 10:1. Assuming the total buffer concentration is 2.2 X 10-2 mol/L, how many grams of sodium acetate (m.w. 82) and how many grams of acetic acid (m.w. 60) should be used in preparing a litre of the solution?

TLS Online TPP Program

#Question id: 383

#Unit 1. Molecules and their Interaction Relevant to Biology

Three buffers are made by combining a 1 M solution of acetic acid with a 1 M solution of sodium acetate in the ratios shown below

1 M acetic acid              

1 M sodium acetate  

Buffer 1: 10 mL

 90 mL

Buffer 2: 50 mL

50 mL

Buffer 3: 90 mL

10 mL

 Which of these statements is true of the resulting buffers?