Question

QUESTION 30

1. Which of the following statements regarding dynamic instability is false?

	A.	GTP hydrolysis by the tubulin dimer promotes microtubule shrinking.
	B.	The GTP cap helps protect a growing microtubule from depolymerization.
	C.	The newly freed tubulin dimers from a shrinking microtubule can be immediately captured by growing microtubules and added to their plus end.
	D.	Each microtubule filament grows and shrinks independently of its neighbors.

QUESTION 31

1. Apoptosis differs from necrosis in that necrosis _____________.

	A.	Causes cells to swell and burst.
	B.	Involves a caspase cascade.
	C.	Requires the reception of an extracellular signal.
	D.	Keep cells intact.

  

QUESTION 32

1. The extent of complementarity of a miRNA with its target mRNA determines ________________.

	A.	Whether RISC is degraded.
	B.	Whether the miRNA synthesizes a complementary strand.
	C.	Whether the mRNA will be transported to the nucleus.
	D.	Whether the mRNA will be degraded by a nuclease within the RISC or transported elsewhere in the cell for degradation.

QUESTION 33

1. Which of the following statements about the Lac operon is false?

	A.	The Lac operon only produces RNA when lactose is present and glucose is absent.
	B.	The CAP activator can only bind DNA when it is bound to cAMP.
	C.	The Lac repressor binds to the operator DNA when lactose is not present in the cell.
	D.	As soon as the CAP activator is bound to DNA, the Lac operon will be transcribed.

QUESTION 34

1. The zinc finger motif is built from ______________________ held together by a molecule of zinc.

	A.	two β sheets
	B.	an α helix and a β sheet
	C.	three α helices
	D.	two α helices

QUESTION 35

1. Which of the following statements about DNA methylation in eucaryotes is false?

	A.	Methylation of DNA attracts proteins that block gene expression.
	B.	Immediately after DNA replication, each daughter helix contains one methylated DNA strand, which corresponds to the newly synthesized strand.
	C.	Appropriate inheritance of DNA methylation patterns involves maintenance methyltransferase.
	D.	DNA methylation involves a covalent modification of cytosine bases.

QUESTION 36

1. Which of the following statements about RNAi is true?

	A.	siRNAs bind to miRNAs to induce RNAi.
	B.	RNAi is induced by foreign double-stranded RNAs, such as from a virus.
	C.	RISC uses the siRNA duplex to locate complementary foreign RNA molecules.
	D.	The RNAi mechanism is found only in plants and animals.

QUESTION 37

1. Which of the following statements is true regarding apoptosis?

	A.	Bax and Bak promote apoptosis by binding to procaspases in the apoptosome.
	B.	Cells that constitutively express Bcl2 will be more prone to undergo apoptosis.
	C.	The prodomain of procaspases contains the catalytic activity necessary for procaspase activation.
	D.	Apoptosis is promoted by the release of cytochrome c into the cytosol from mitochondria.

Answer 1

(30)

The switching between shrinking or depolymerizing and growing or polymerizing states in vivo is known as dynamic instability. Microtubules are components of various essential cellular processes like gametogenesis and reproduction.

Thus, dynamic instability is the disassembly and assembly coexistence at the ends of a microtubule. Tubulin dimers can join or bind two GTP molecules from which one can be hydrolyzed following the assembly. The cell utilizes energy to maintain the high concentration or strength of GTP-tubulin, i.e., above the significant concentration and far from equilibrium for polymerization which results in the rapid association of subunits with microtubule ends and the growth of the microtubules.

The catastrophe frequency increases and the GTP cap is eroded because of the slower elongation that allows GDP-to-GTP exchange present on terminal subunits in response to simulations that moderated these outcomes. The highly dynamic microtubules constantly shrink and grow at a constant and rapid rate.

Therefore, the options (a), (b), and (c) are incorrect.

A tubulin dimer that is newly dissociated binds to GDP which is exchanged for GTP before getting added to a microtubule that is newly grown. Therefore, the newly freed tubulin dimers from the microtubule that is shrinking do not get captured immediately by the growing microtubules.

Hence, the option (c) is correct.