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TLS Online TPP Program

#Question id: 13161

Which of the following mechanism depends on the activation of heterotrimeric G proteins?

#Unit 4. Cell Communication and Cell Signaling
  1. During actin filament formation, the inactive formin is activated when its Rho-binding domain (RBD) binds to membrane-bound active Rho-GTP, resulting in exposure of the formin’s FH2 domain, which can then nucleate the assembly of a new actin filament.
  2. Rod cells sense light with the aid of a light-sensitive rhodopsin which is coupled to transducin. On absorption of a photon, the retinal moiety of rhodopsin is immediately converted from the cis isomeric form to the all-trans isomeric form, causing a conformational change that allows rhodopsin to bind the α subunit of transducin.
  3. Ras proteins are “switch” proteins and not directly linked to cell-surface receptors. Ras activation is accelerated by a guanine nucleotide exchange factor (GEF), which binds to the Ras∙GDP complex, causing dissociation of the bound GDP.
  4. During the regulation of microfilament organization, Cdc42 act as molecular switches, inactive in the GDP-bound state and active in the GTP-bound state.
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TLS Online TPP Program

#Question id: 3830

#Unit 3. Fundamental Processes

Why is DNA damage in skin cells from exposure to excessive UV light not completely reversed by photoreactivation?
TLS Online TPP Program

#Question id: 3831

#Unit 3. Fundamental Processes

State whether the following statements is true/false regarding DNA replication.

1. In E. coli replication begins at the origin of replication and proceeds in one direction until the entire circular DNA molecule has been copied.

2. The chromosome of the fruit fly (D. melanogaster) is about twice as large as the E. coli chromosome.

3. Prokaryotic DNA replication occurs in two steps. First, ATP provides a phosphate to the growing DNA chain. This is followed by addition of a nucleoside.

4. DNA polymerase III is the largest DNA polymerase in E. coli.

5. The β subunits of E. coli DNA polymerase form a sliding clamp that surrounds the DNA strands at the replication fork.
TLS Online TPP Program

#Question id: 3832

#Unit 3. Fundamental Processes

You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated from the bacteria, the DNA separates into two classes. One class of labeled DNA includes very large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). Which two classes of DNA do these different samples represent?
TLS Online TPP Program

#Question id: 3833

#Unit 3. Fundamental Processes

Regarding DNA replication, which, if any, of the following statements is incorrect?
TLS Online TPP Program

#Question id: 3834

#Unit 3. Fundamental Processes

In his transformation experiments, what phenomenon did Griffith observe?
TLS Online TPP Program

#Question id: 3835

#Unit 3. Fundamental Processes

State whether the following statements is true/false regarding DNA replication.

1. A short primer is added to the DNA polymerase reaction mix for Sanger DNA sequencing that has a 5ʹ free hydroxyl to which new nucleotides can be added.

2. In a sequencing gel, all fragment in one of the four lanes terminates in the same type of nucleotide base.

3. Eukaryotic cells contain at least five DNA polymerases all of which are responsible for nuclear DNA replication.

4. Since the rate of form movement in eukaryotes is much slower than that of bacteria, chromosomes require more than an hour to replicate.

5. Although histones and DNA are made in the same parts of the eukaryotic cell, the packaging of them in the nucleosome slows down replication so that it is slower than that of prokaryotes.