Question

Which DNA polymerase is responsible for the bulk of DNA synthesis in E.coli cells? Which DNA polymerase was identified first? Define “processivity”.

A.

Pol III; Pol I; How long the DNA polymerase complex continues to catalyze chain extension before detachment from DNA

B.

Pol I; Pol II; The stability of a DNA polymerase molecule in an E. coli cell

C.

Pol II; Pol I; How many DNA chains the polymerase can synthesize in 60 min

D.

Pol I; Pol III; How fast the DNA polymerase can synthesize a DNA chain

2. How are the Okazaki fragments joined together to complete the lagging strand?

A.

The 3’ exonuclease activity of DNA polymerase I digests the RNA primers, the DNA fragments are extended by DNA polymerase II and the nicks at the ends are ligated by the T4 DNA ligase

B.

The Okazaki fragments are joined together during DNA repair by both DNA polymerase I and DNA polymerase III

C.

The 5’ exonuclease activity of DNA polymerase I digests the RNA primers, the DNA fragments are extended by DNA polymerase I, and the nicks at the ends are ligated by DNA ligase

D.

DNA polymerase II extends the Okazaki fragments and then T4 DNA ligase ligates the fragments

3. Genes that regulate the polarity of the drosophila embryo are transcribed and translated at specific stages. Are the protein products of these genes expressed in the drosophila embryo? What is the source of these protein products?

A.

These gene products (proteins) are already present in a gradient in the drosophila egg, but they get activated by phosphorylation after fertilization of the egg

B.

These gene products (proteins) are already present in the drosophila egg, but they are distributed in a gradient by chaperone proteins expressed after fertilization of the egg

C.

The entire process of polarity determination occurs due to a combination of all the above processes

D.

The mRNA products of the polarity genes originate from the mother and are present in a gradient in the egg even before fertilization, but they are translated only in the embryo

E.

Fertilization of the drosophila egg triggers expression of transcription factors in a gradient in the embryo. Transcription and translation of the polarity genes in a gradient are thus triggered by these transcription factors

Answer 1

Which DNA polymerase is responsible for the bulk of DNA synthesis in E.coli cells? Which DNA polymerase was identified first? Define “processivity”.

A. Pol III; Pol I; How long the DNA polymerase complex continues to catalyze chain extension before detachment from DNA

Explanation :

The major DNA processing enzyme is DNA polymerase III. DNA polymerase I plays role in the joining of gaps between Okazaki fragments. Processivity is termed as the number of nucleotides added to the growing chain of DNA by DNA polymerase until it dissociates from the DNA template.

DNA polymerase I is involved in only repair and acts as an alternative polymerase enzyme.

2. How are the Okazaki fragments joined together to complete the lagging strand?

C. The 5’ exonuclease activity of DNA polymerase I digests the RNA primers, the DNA fragments are extended by DNA polymerase I, and the nicks at the ends are ligated by DNA ligase

Explanation :

Other options are incorrect since 3 ' exonuclease activity is involved in simultaneous checking of DNA replication error and removes nucleotides added by mistake. DNA polymerase III and II do not play a role in ligation and joining of Okazaki fragments.

3. Genes that regulate the polarity of the drosophila embryo are transcribed and translated at specific stages. Are the protein products of these genes expressed in the drosophila embryo? What is the source of these protein products?

D. The mRNA products of the polarity genes originate from the mother and are present in a gradient in the egg even before fertilization, but they are translated only in the embryo

Explanation :

The maternal mRNA are presnt in the egg even before fertilisation in a gradient and they are trascribed only after fertilization occurs. The genes that code for these mRNAs are called maternal effect genes. The proteins are not present in egg.