Question

30 ) 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.

40 Which of the following statements about the cytoskeleton is false?

	A.	The cytoskeleton is important for cell division and DNA segregation.
	B.	The cytoskeleton is made up of three types of protein filament.
	C.	The polymerization of protein monomers leads to the formation of cytoskeletal filaments.
	D.	The intermediate filaments of the nuclear lamina are present in both plant and animal cells

Help please both of them thanks

Answer 1

30) the answer is (A) The lac operon produces RNA when lactose is present and glucose is absent.

A low level of LAC operon transcription does occur even when both lactose and glcose are present in the media of the bacteria.

It ain't the case that the mRNA is produced onlt when lactose is present and glucose is absent. Low level of transcription does happen, even when both the sugars are present. However, very high transcription (high mRNA amounts) occurs when only lactose is presnt and glucose is absent from the media.

Looking at the other options:

-- The CAP activator can only bind DNA when it is bound to cAMP.

This is true, the CAP protein Upon binding cAMP (adenosine 3', 5' monophosphate, or cyclic AMP), CAP binds to a conserved DNA sequence from which it can either activate or repress transcription initiation from various promoters. In some cases clusters of several promoters are all controlled by a single cAMP-CAP complex bound to the DNA.

--The Lac repressor binds to the operator DNA when lactose is not present in the cell.

The LAC repressor is a protein that represses (inhibits) transcription of the lac operon. It does this by binding to the operator, which partially overlaps with the promoter. When bound, the lac repressor gets in RNA polymerase's way and keeps it from transcribing the operon.

When lactose is not available, the lac repressor binds tightly to the operator, preventing transcription by RNA polymerase. However, when lactose is present, the lac repressor loses its ability to bind DNA. It floats off the operator, clearing the way for RNA polymerase to transcribe the operon.

-- As soon as the CAP activator is bound to DNA, the Lac operon will be transcribed.

This is also true.

As it turns out, RNA polymerase alone does not bind very well to the lac operon promoter. It might make a few transcripts, but it won't do much more unless it gets extra help from catabolite activator protein (CAP). CAP binds to a region of DNA just before the lac operon promoter and helps RNA polymerase attach to the promoter, driving high levels of transcription.

Once CAP has bound cAMP, the protein exhibits a higher affinity for a specific conserved DNA sequence. When the intracellular level of cAMP increases, the second messenger is bound by CAP and the cAMP-CAP complex binds to the DNA. Once bound, it is able to stimulate the transcription of the aforementioned genes. DNA bound by the CAP-cAMP complex is bent by ~90 degrees. This DNA bend, coupled with a protein-protein interaction between CAP and RNA polymerase is thought to be the mechanism by which CAP regluates transcription initiation on the chromosome.

For more information please refer to the following:

https://www.khanacademy.org/science/biology/gene-regulation/gene-regulation-in-bacteria/a/the-lac-operon

http://biology.kenyon.edu/BMB/jmodel/index.htm

https://en.wikipedia.org/wiki/Lac_operon

40) The answer is d)

The intermediate filaments of the nuclear lamina are present in both plant and animal cells.

  It provides mechanical support to the nucleus and nuclear envelope, and as well as facilitating the connection of the nucleoskeleton to the cytoskeleton, it is also involved in chromatin organization, gene regulation, and signaling. In metazoans, the nuclear lamina consists of a polymeric layer of lamins and other interacting proteins responsible for its association with the INM and chromatin. In plants, field emission scanning electron microscopy of nuclei, and thin section transmission electron microscopy of isolated nucleoskeletons, reveals the lamina to have a similar structure to that of metazoans. Moreover, although plants lack lamin genes and the genes encoding most lamin-binding proteins, the main functions of the lamina are fulfilled in plants. Hence, it would appear that the plant lamina is not based on lamins and that other proteins substitute for lamins in plant cells. The nuclear matrix constituent proteins are the best characterized structural proteins in the plant lamina. Although these proteins do not display strong sequence similarity to lamins, their predicted secondary structure and sub-nuclear distribution, as well as their influence on nuclear size and shape, and on heterochromatin organization, suggest they could be functional lamin analogs.

ALL the other options are true:

The cytosekelton does play an important role in spindlr formation, chromosome segregation and mitosis.

polymerization of actin, tubulin subunits forms higher order cytoskeleton filaments.

the cytoskeleton is made up of 3 protein filaments viz. microfilaments, microtubules and intermediate filaments

please refer to the following for more information:

https://www.nature.com/scitable/topicpage/microtubules-and-filaments-14052932/

https://www.khanacademy.org/science/biology/structure-of-a-cell/tour-of-organelles/a/the-cytoskeleton

https://microbenotes.com/cytoskeleton/