Why in nucleic acid replication one strand is ahead while the other strand is behind?

Because the leading strand is synthesized continuously while the lagging strand is discontinuously synthesized.

Explanation:

Two DNA strands have opposite polarity, that is, the 5' end of one strand lies opposite to the 3' end of the other strand. However, DNA replication can occur in 5' to 3' direction only since the formation of phosphodiester bonds require the presence of nucleophile 3' OH to attack the 5' phosphate of an incoming deoxyribonucleotide.  

The problem is solved by the synthesis of the leading strand continuously and the synthesis of the lagging strand in a discontinuous manner. Lagging strand synthesis requires the formation of primers and their elongation to form Okazaki fragments that may have few hundreds to few thousands of nucleotides. Removal of primers from Okazaki fragments is followed by joining them together to make the long lagging strand. The discontinuous replication of the lagging strand makes the replication at the leading strand ahead of it.  

answer: c.

explanation:

transcription is a process in which information is rewritten. it is something our cells must do, in a more specialized and narrowly defined way. in biology, transcription is the process of copying out the dna sequence of a gene in the similar alphabet of rna. it needs to happen in the nucleus because that's where the dna is. dna is always inside the nucleus unless the cell is dividing.

transcription is the first step in gene expression, which involves copying a gene's dna sequence to make an rna molecule. transcription is performed by rna polymerases. it has three stages: initiation, elongation, and termination. rna molecules must be processed after transcription in eukaryotes.

explanation:

long version:

the protein synthesis consists two processes which are, transcription and translation. transcription takes place in the nucleus. it uses dna as a template to make an rna molecule. rna then leaves the nucleus and goes to a ribosome in the cytoplasm, where translation occurs. transcription is the first part of the central dogma of molecular biology: dna → rna. it is the transfer of genetic instructions in dna to messenger rna (mrna). during transcription, a strand of mrna is made that is complementary to a strand of dna.  

these three stages are:

  initiation: in which   is the beginning of transcription.occuring when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

    elongation: in which is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

    termination: in which is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.