answers

watching

views

4 Feb 2018

Signaling cascades (4 pts)Which of the following is an example of a signaling cascade?

A. Binding of lactose to the lac repressor

B. Binding of the lac repressor to the lac operon

C. The series of proteolytic digests that occur during clotting

D. The Collins Toggle Switch

Why is it important that signaling cascades have negative feedback loops?

answers

watching

265

views

For unlimited access to Homework Help, a Homework+ subscription is required.

You have 0 free answers left.
Get unlimited access to 3.8 million step-by-step answers.

Get unlimited access

Already have an account? Log in

teacherrecoLv10

28 Jul 2023

Unlock all answers

Get 1 free homework help answer.

Already have an account? Log in

You have 0 free answers left.
Get unlimited access to 3.8 million step-by-step answers.

Get unlimited access

Already have an account? Log in

Reid WolffLv2

6 Feb 2018

Already have an account? Log in

Related questions

In the following points, I have summarized Lac operon in Ecoli. I need to check if this is on the right track? and where does 'cleavage of disaccharides' fit into this picture?

Lactose is a disaccharide and the bacteria need specific genes to manage catabolism

1) The lacl promotor gene synthesis the repressor protein which binds to the operator gene stopping the RNA polymerase from coding the lac operon genes

2)But when lactose is present, it needs the specific genes to catabolise lactose

3) So, When allolactose (a derivative of lactose)is present, it binds to the repressor protein, the repressor releases from the operator gene

4) This allows the RNA polymerase can attach to the DNA control region

5) And drive down the operon for transcription and induction of the enzyme lacZ(beta-galactosidase) lacY and lacA which breaks lactose down into glucose and galactose

6) When the lactose is all gone, the repressor returns to the operator in a feedback loop system

Are my answers correct?

1. If a bacterium with a wildtype lac operon is grown in the presence of lactose, high levels of transcription result for a while, however, eventually transcription is again down-regulated. If, on the other hand, the sugar IPTG is present (instead of lactose), transcription levels are high and remain high. What function do IPTG and lactose share? How are they differently affected by the operon product?

Lactose and IPTG are both inducers of the Lac-Operon. Lactose is a substance that the enzyme will react with (substrate), which is split or cleaved by the Beta-galactosidase. When you add lactose expressions level of lac operon will increase but as lactose is used by the beta-galactosidase expression levels of lac operon will decrease.

IPTG is a chemical cannot be split or cleaved by beta-galactosidase. The expression level of lac operon will remain the same.

Or Lactose can be easily broken down but IPTG cannot be broken down. What does expressions level mean?

2. If a lacI - bacterium is grown in the presence of the sugar X-gal, a blue dye appears; however, the concentration of X-gal decreases over time. What has happened to the X-gal?

If a lacI - bacterium is grown in the presence of the sugar X-gal, the Lacl is mutant or the gene is damaged which alters the genetic message carried by that gene. The LacI gene produces the repressor protein which switches off the operon, but since it is damaged no repressor protein is produced and the operon is switched on. The Lacl is transcribed into beta-galactosidase (lactose) The enzyme beta-galactosidase (lactose) splits or separates the X-gal which will result in decreased concentration of X-gal with time.

3. If a wildtype bacterium is grown in the presence of the sugar X-gal, transcription of the polycistronic m-RNA does not occur. What is X-gal unable to do? Without adding lactose (or genetically modifying the bacteria), how could you fix this problem

X-gal cannot form lactose, the repressor remains off and beta-galactosidase is not formed. This can be fixed by adding IPTG which can switch on the operon

QUESTION 1

In the bacterial lac repressor, which of these occurs: (select all that apply)

		(a)In the presence of glucose and the absence of lactose, the repressor is actively produced.
		(b)The lac operon can be hyper-induced in the presence of low glucose by the 'cAMP binding protein' (CAMP).
		(c)In the presence of lactose and the absence of glucose the lac operon is repressed.
		(d)Allolactose is a byproduct of Î²-galactosidase, indicating high lactose when it builds up.

1.5 points

QUESTION 2

In eukaryotes the enhancer elements can be quite a distance upstream or downstream from the promoter, and transcriptional regulation is helped by protein:protein interactions.

True

False

1.5 points

QUESTION 3

The prokaryotic promoter contains a TATA box that is at -10bp upstream from the transcriptional start site.

True

False

1.5 points

QUESTION 4

During the addition of the poly A tail which of these occurs:(select all that apply)

		(a)The transcript is synthesized beyond the poly A site (AAUAAA).
		(b)The mRNA contains a 5â cap.
		(c)The transcript is cleaved 35nt downstream from the poly A site.
		(d)An enzyme complex containing an exonuclease and polyadenylate polymerase cleaves nearby the AAUAA site.
		(e)100-300 Aâs are added to the 5â end.