Tag: biology

Quizzes (1160) Questions (12174)

Questions Related to biology

Multiple choice expression of gene inherited changes biology

In Negative operon : -

  1. Inducer binds with repressor

  2. Co-repressor does not binds with repressor

  3. Corepressor binds with inducer

  4. CAMP have negative effect on lac operon
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
The inducer is a molecule that regulates gene expression. An inducer can bind to protein repressors or activators. The lac operon is a negatively controlled inducible operon, where the inducer molecule is Lactose. If the inducer molecule is present, it binds to the repressor and changes its conformation so that it is unable to bind to the operator and thus gene expression is controlled.
So, the correct answer is 'Inducer binds with repressor'.
Multiple choice expression of gene inherited changes biology

The function of a repressor protein in an operon system is to prevent protein synthesis by binding to ________________.

  1. The ribosome

  2. The RNA polymerase, thus blocking transcription

  3. A specify region of the mRNA, preventing translation to protein

  4. A specific region of the operon, preventing transcription of structural genes
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In an operon system, a repressor protein binds specifically to the operator region of the operon, thereby physically preventing RNA polymerase from transcribing the structural genes.

Multiple choice expression of gene inherited changes biology

How many of the following statements are correct
(A) In prokaryotes, control of the rate of transcriptional initiation is the predominant site for control of gene expression
(B) Lac operon is under negative regulation of CAP.
(C) Presence of intron is reminiscent of antiquity.
(D) Inheritance of a character is also affected by promoter and regulatory sequence of a structural gene.

  1. $2$
  2. $3$
  3. $4$
  4. $5$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Statements A, C, and D are generally considered correct in biological contexts. Statement B is incorrect because the lac operon is under positive regulation by CAP (Catabolite Activator Protein), not negative regulation. Thus, 3 statements are correct.

Multiple choice expression of gene inherited changes biology

Regulator gene controls chemical synthesis(Operon concept) by.

  1. Inhibiting transcription

  2. Inhibiting enzymes

  3. Inhibiting passage of mRNA

  4. Inhibiting substrate enzyme reaction
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The regulator gene produces a repressor protein that binds to the operator, thereby inhibiting the transcription of the structural genes into mRNA.

Multiple choice expression of gene inherited changes biology

Read the following four statements (A-D) :
(A) In transcription, adenine pairs with uracil.
(B) Regulation of lac operon by repressor is referred to as positive regulation.
(C) The human genome has approximately 50,000 genes.
(D) Haemophilia is a sex-linked recessive disease.
How many of the above statements are correct?

  1. Three

  2. Four

  3. One

  4. Two
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
A. Transcription is the process of synthesis of RNA from a template DNA by the replicative enzyme RNA polymerase. As we know, purine bases pair with pyrimidine bases i.e. Adenine pairs with Thymine or vice versa and Guanosine pairs with Cytosine or vice versa. Since RNA has Uracil instead of Thymine, Adenine pairs with Uracil in transcription. Hence, statement A is correct.
B. The regulation of lac operon by repressor is negative regulation as in the presence of repressor (lactose in case of E. coli), the transcription of the structural gene doesn't occur because repressor binds to the operator region and due to this, RNA polymerase can't proceed transcription. Hence, statement B is incorrect.
C. Human genome has approximately 30,000-40,000 genes. Hence, statement C is incorrect. 
D. Haemophilia is a sex linked disorder. It is a X-linked recessive disease which is caused by a recessive gene located on X chromosome. Hence, statement D is correct.
So, out of all statements given in the question, statements A and D are correct.
So, the correct answer is 'Two'. 
Multiple choice expression of gene inherited changes biology

Which one of the following is wrong:

  1. $Y$ in Lac Operon is responsible for $\beta$ galactoside permease

  2. In Lac-operon the repressor becomes inactive if it binds with lactose

  3. In repressible control of gene action the repressor cannot bind to promotor if co repressor is present

  4. Tryptophan operon consists of five structural genes

  5. The mRNA produced from a bacterium is usually polycistronic
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In repressible systems, the inactive repressor (aporespressor) requires the corepressor to bind to the operator, meaning it can bind when the corepressor is present, not prevented by it. Thus, statement C is false and represents the wrong statement requested.

Multiple choice expression of gene inherited changes biology

Choose the correct answer from the alternatives given :
You have created a fusion between trp operon and lac operon which encodes the enzymes for tryptophan biosynthesis, under the regulatory control of the lac operator. Under which of the following conditions will tryptophan synthase be induced in the strain that carries the chimeric operator fused operons?

  1. Only when both lactose and glucose are absent.

  2. Only when both lactose and glucose are present.

  3. Only when lactose is absent and glucose is present.

  4. Only when lactose is present and glucose is absent.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

As the chimeric operon is under control of operator gene of lac operon, it will be functional only in the conditions required for lac operon to be functional. In lac operon lactose function as inducer hence its presence in medium is essential for proper functioning while glucose inhibits its function. So, the chimeric operon will produce tryptophan only when lactose is present and glucose is absent in the medium.

So, the correct answer is 'Only when lactose is present and glucose is absent.'.

Multiple choice expression of gene inherited changes biology

Choose the correct answer from the alternatives given.
An operon is a

  1. Protein that suppresses gene expression

  2. Protein that accelerates gene expression

  3. Cluster of structural genes with related functions

  4. Gene that switches other genes on or off
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

An operon, in genetics, is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. The promoters are the palindromic sequences that control the process of transcription. An operon can be inducible like lac operon or it can be inhibitor operon like trp operon. 

So, the correct option is 'Cluster of structural genes with related functions'.

Multiple choice expression of gene inherited changes biology

Choose the correct answers from the alternatives given.
The prokaryotic genetic system contains:       

  1. either DNA or histones

  2. neither DNA nor histones

  3. DNA and histones

  4. DNA but no histones
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The prokaryotic genetic system does not have a nucleus in their cell but the genome in a prokaryote is held within a DNA in the cytosol called nucleoid.

Eukaryotes have DNA wrapped around the histones but prokaryotes do not contain histones.
Hence, the correct answer is, 'DNA but no histones'.

Multiple choice expression of gene inherited changes biology

In Prokaryotes, the predominant site for control of gene expression is 

  1. Transcriptional intimation

  2. Processing level

  3. Transfer of mRNA from nucleus to the cytoplasm

  4. Translation initiation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Regulation of gene expression refers to a very broad term that may occur at various levels. In prokaryotes, control of the rate of transcriptional initiation is the predominant site for control of gene expression. 
Considering that gene expression results in the formation of a polypeptide, it can be regulated at several levels. In eukaryotes, the regulation could be exerted at
(i) transcriptional level (formation of primary transcript),
(ii) processing level (regulation of splicing),
(iii) transport of mRNA from the nucleus to the cytoplasm,
(iv) translational level.

So, the correct option is 'Transcriptional intimation'.