Tag: biology

Questions Related to biology

Choose the correct answer from the alternatives given :
Control of gene expression takes place at the level of

expression of gene inherited changes biology

  1. DNA-replication

  2. Transcription

  3. Translation

  4. None of the above.

Show answer
Correct Option: B,C
Explanation:

Regulation of gene expression refers to a very broad term that may occur at various levels. In eukaryotes the gene expression can be regulated at transcriptional level, processing level, transport of mRNA from nucleus to the cytoplasm, and translational level whereas in prokaryotes, control of the rate of transcriptional initiation is the predominant site for control of gene expression.

So, the correct answer is 'Transcription and Translation'.

In an operon model, regulator gene function as

expression of gene inherited changes biology

  1. Repressor

  2. Regulator

  3. Inhibitor

  4. All of the above

Show answer
Correct Option: D
Explanation:

Operon model contains a cluster of genes which are under the control of single promoter. It consists of an operator, promoter, regulator and structural genes. The regulator gene function as a repressor as it produces repressor protein that binds to the operator and thus inhibits the transcription of the structural genes. It functions as regulator as it regulates the transcription of structural gene. The product of regulator gene is inhibitor that keeps the operon model turned off.

Thus, the correct answer is option D.

Match the columns and find out correct combination.

Gene Product Function of the product
I. Z-gene $\beta$-galactosidase Hydrolysis of lactose
II. y-gene Transacetylase Uptake of lactose
III. a-gene Permease protien Function not-known
IV. Inhibitor gene Repressor protien Switch off operator gene
expression of gene inherited changes biology

  1. II and III

  2. I and III

  3. I, III, IV

  4. I and IV

Show answer
Correct Option: D
Explanation:

I. The z gene that codes for the enzyme beta-galactosidase that hydrolyzes lactose to glucose and galactose.

IV. Inhibitor is a represser protein which switch off the process in lac operon process. 

Morphogensis is controlled by______________ 

expression of gene inherited changes biology

  1. Gibberellins and Cytokinin

  2. Auxin and Cytokinin

  3. Auxin and Gibberellins

  4. Gibberellins and Zeatin

Show answer
Correct Option: A
Explanation:

Morphogenesis is a process that controls the organized spatial distribution of cells during embryonic development. It can also take place in a matured organism in cell culture or in tumor cell masses. It is concerned with the shape of tissues. Plant growth regulators such as gibberellins, cytokinins, abscisic acid and ethylene control growth and development in plants. Gibberellins and cytokinins are the two instrumental hormones that play a key role in morphogenesis. Whereas auxins stimulate the plant cell to grow long.

So the correct answer is 'gibberellin and cytokinin'.

When Tryptophan is present

expression of gene inherited changes biology

  1. repressor is unable to bind to the operator

  2. transcription of structural genes occurs

  3. repressor is able to bind to the operator

  4. both (a) and (b)

Show answer
Correct Option: C
Explanation:

The Trp operon is an example of a repressible operon; it is on unless turned off by a repressor protein. The repressor protein is synthesized by trpR. While the repressor protein is always present in the cell, it is synthesized in an inactive form. When a corepressor is present, in this case, tryptophan, it binds to the repressor protein in an allosteric site. This changes the conformation of the protein such that it can bind to the operator and block transcription by preventing the binding of RNA polymerase to the promoter. In this way, the cell saves energy by not producing tryptophan when it is already present.

So, the correct option is 'repressor is able to bind to the operator'.

A mutation that renders the regulatory gene of a repressible operon nonfunctional would result in

expression of gene inherited changes biology

  1. excessive synthesis of a catabolic activator protein

  2. irreversible binding of the repressor to the promoter

  3. inhibition of transcription of the structural genes

  4. continuous transcription of the structural genes

Show answer
Correct Option: D
Explanation:

In a repressible operon, the operon is normally on and transcription occurs for the synthesis of enzymes. This synthesis of enzymes takes place with the help of the structural genes.

In presence of corepressor (for e.g. tryptophan in trp operon) inactive repressor (aporepressor) gets converted to the active repressor. This active repressor binds to operator region and stops transcription. If any mutation takes place in regulatory genes i.e. those involved in the formation of operator and repressor, operon will never get turned off. This will result in continuous transcription of the structural genes. 
So, the correct option is 'continuous transcription of the structural genes'.

Inducible operons differ from repressible operons in that

expression of gene inherited changes biology

  1. operator of inducible operons is switched off by a repressor protein

  2. inducible operons have an operator that controls binding of RNA polymerase to the promoter region

  3. inducible operons use activators and positive control to regulate their transcription

  4. inducible operons usually include structural genes that function in catabolic pathways

Show answer
Correct Option: D
Explanation:

The inducible operon is usually off and it can be induced in the presence of inducer like lactose. After getting induced, the operon is turned on and transcription takes place to catabolize these inducers. Hence, the inducible operon is usually involved in catabolism. 

While repressible operon is on normally and results in transcription of structural genes to produce the desired product for e.g. tryptophan. Hence, it works at times when the bacterial cell does not require these products like tryptophan and the presence of tryptophan from external source turns off this operon. 
So, the correct option is 'inducible operons usually include structural genes that function in catabolic pathways'.

Choose the correct answer from the alternatives given :
Repressible operon system is usually found in (i) pathways. The pathways end product serves as a (ii) to activate the repressor, turn off enzyme synthesis and prevent overproduction of the end product of the pathway. Genes for this operon are usually switched (iii) and the repressor is synthesised in an (iv) form.

expression of gene inherited changes biology

  1. (i) anabolic, (ii) corepressor, (iii) on, (iv) - inactive

  2. (i) anabolic, (ii) inducer, (iii) off, (iv) - active

  3. (i) catabolic, (ii) inducer, (iii) off, (iv) - active

  4. (i) catabolic, (ii) corepressor, (iii) on, (iv) - inactive

Show answer
Correct Option: A
Explanation:

Repressible operons are generally involved in anabolic pathways, or the synthesis of an essential component, while inducible operons are generally involved in catabolic pathways or the breakdown of a nutrient. Positive control of an operon is when gene expression is stimulated by the presence of a regulatory protein. The repressible operon work on the feedback inhibition mechanism which is the phenomenon where the output of a process is used as an input to control the behavior of the process itself and the co-repressor serves as to activate the repressor. Genes of a repressible operon are switched off as they are required to synthesize the structural/functional genes in the absence of the repressor. The presence of the repressor can stop this process and hence the repressor is present in the inactive form. 

So, the correct option is '(i) anabolic, (ii) corepressor, (iii) on, (iv) - inactive'.

Kupffer's cells are.

biology immunity phagocytosis cells in immune system immune system, its cells, mediators and antigens

  1. Hormone secreting

  2. Fat cells

  3. Mast cells

  4. Phagocytic

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Correct Option: D

Which of the following cells does not exhibit phagocytic activity?

biology immunity phagocytosis cells in immune system immune system, its cells, mediators and antigens

  1. Monocytes

  2. Neutrophil

  3. Basophil

  4. Macrophage

Show answer
Correct Option: C
Explanation:

Phagocytes have the ability to phagocytose or kill foreign cells and particles like pathogens by ingesting them. Many blood cells have this function, including monocytes, neutrophils and macrophages. Basophils do not have phagocytic activity.

Thus, the correct answer is 'Basophil.'