In the polymerization in vitro of actin filaments and microtubules from their su

Question

In the polymerization in vitro of actin filaments and microtubules from their subunits, what does the "lag phase" correspond to? Nucleation Reaching steady state ATP or GTP hydrolysis Tread milling Transmembrane proteins... are typically exposed only to one side of the membrane can be released from the membrane by a gentle extraction procedure such as salt treatment are sometimes covalently attached to a fatty acid chain that inserts into the membrane cannot contain beta sheets in the part of their structure that interacts with the membrane Transcription regulation has similarities and differences in bacteria and eukaryotes. Which of the following is correct in this regard? Most bacterial genes are regulated individually, whereas most eukaryotic genes are regulated in clusters The rate of transcription for a eukaryotic gene can vary in a much wider range than for a bacterial gene Transcription regulators in both bacteria and eukaryotes usually bind directly to RNA polymerase The default state of both bacterial and eukaryotic genomes is transcriptionally active This general transcription factor recognizes the TATA box in RNA polymerase II promoters. It is... the only single-subunit general transcription factor able to introduce a sharp kink in the double helix upon binding to DNA responsible for the phosphorylation of the RNA polymerase C-terminal domain during transcription initiation All of the above

Explanation / Answer

5. Answer is A

When a solution containing a sufficient concentration of tubulin dimers, GTP, and is warmed from 0°C to 37°C, the polymerization reaction begins. (MT formation in the solution can be readily measured with a spectrophotometer as an increase in light scattering.) A critical step in the formation of MTs is the aggregation of tubulin dimers into clusters called oligomers. These oligomers serve as "nuclei" from which new microtubules can grow, and hence this process is referred to as nucleation.

6. Answer is B.

Transmembrane proteins are polytopic proteins that aggregate and precipitate in water and so can be extracted using detergents or nonpolar solvents.

7. Answer is B.

Transcription initiation is much simpler in prokaryotes. Prokaryotes have different proteins which bind to promoter sequences and start transcription As specific factors bind different promoters and are responsible for a different set of genes, expression is highly regulated at this level.

In eukaryotes, the RNA polymerase itself can’t actually initiate transcription. Instead, a variety of other proteins and transcription factors are required to help recruit the RNAP to the promoter (this is partly because eukaryotic DNA is coiled around histones so needs to be opened up for a polymerase to bind it). Due to the variety of factors at play, regulation is also much more complex.

8. answer is B

TATAT Box binding protein (TBP)is one of the subunits of a general transcription factor,TFIID.

When this TBP binds to a TATA box within the DNA, it distorts the DNA by inserting amino acid side-chains between base pairs, partially unwinding the helix, and doubly kinking it.

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