How are DNA and RNA replicated?

Answer 1

During interphase.

Answer 2

s phase

Answer 3

The process of DNA replication begins at specific sites in the chromosomes termed origins of replication, requires a primer bearing a free 3'-OH, proceeds specifically in the 5'->3' direction on both strands of DNA concurrently and results in the copying of the template strands in a semiconservativemanner. The semiconservative nature of DNA replication means that the newly synthesized daughter strands remain associated with their respective parental template strands.

The large size of eukaryotic chromosomes and the limits of nucleotide incorporation during DNA synthesis, make it necessary for multiple origins of replication to exist in order to complete replication in a reasonable period of time. The precise nature of origins of replication in higher eukaryotic organisms is unclear. However, it is clear that at a replication origin the strands of DNA must dissociate and unwind in order to allow access to DNA polymerase. Unwinding of the duplex at the origin as well as along the strands as the replication process proceeds is carried out by helicases. The resultant regions of single-stranded DNA are stabilized by the binding of single-strand binding proteins. The stabilized single-stranded regions are then accessible to the enzymatic activities required for replication to proceed. The site of the unwound template strands is termed the replication fork.

In order for DNA polymerases to synthesize DNA they must encounter a free 3'-OH which is the substrate for attachment of the 5'-phosphate of the incoming nucleotide. During repair of damaged DNA the 3'-OH can arise from the hydrolysis of the backbone of one of the two strands. During replication the 3'-OH is supplied through the use of an RNA primer, synthesized by the primase activity. The primase utilizes the DNA strands as templates and synthesizes a short stretch of RNA generating a primer for DNA polymerase.

Synthesis of DNA proceeds in the 5'->3' direction through the attachment of the 5'-phosphate of an incoming dNTP to the existing 3'-OH in the elongating DNA strands with the concomitant release of pyrophosphate. Initiation of synthesis, at origins of replication, occurs simultaneously on both strands of DNA. Synthesis then proceeds bidirectionally, with one strand in each direction being copied continuously and one strand in each direction being copied discontinuously. During the process of DNA polymerases incorporating dNTPs into DNA in the 5'->3' direction they are moving in the 3'->5' direction with respect to the template strand. In order for DNA synthesis to occur simultaneously on both template strands as well as bidirectionally one strand appears to be synthesized in the 3'->5' direction. In actuality one strand of newly synthesized DNA is produced discontinuously.

The strand of DNA synthesized continuously is termed the leading strand and the discontinuous strand is termed the lagging strand. The lagging strand of DNA is composed of short stretches of RNA primer plus newly synthesized DNA approximately 100-200 bases long (the approximate distance between adjacent nucleosomes). The lagging strands of DNA are also called Okazaki fragments. The concept of continuous strand synthesis is somewhat of a misnomer since DNA polymerases do not remain associated with a template strand indefinitely. The ability of a particular polymerase to remain associated with the template strand is termed its' processivity. The longer it associates the higher the processivity of the enzyme. DNA polymerase processivity is enhanced by additional protein activities of the replisome identified as processivity accessory proteins.

How is it that DNA polymerase can copy both strands of DNA in the 5'->3' direction simultaneously? A model has been proposed where DNA polymerases exist as dimers associated with the other necessary proteins at the replication fork and identified as the replisome. The template for the lagging strand is temporarily looped through the replisome such that the DNA polymerases are moving along both strands in the 3'->5' direction simultaneously for short distances, the distance of an Okazaki fragment. As the replication forks progress along the template strands the newly synthesized daughter strands and parental template strands reform a DNA double helix. The means that only a small stretch of the template duplex is single-stranded at any given time.

The progression of the replication fork requires that the DNA ahead of the fork be continuously unwound. Due to the fact that eukaryotic chromosomal DNA is attached to a protein scaffold the progressive movement of the replication fork introduces severe torsional stress into the duplex ahead of the fork. This torsional stress is relieved by DNA topoisomerases. Topoisomerases relieve torsional stresses in duplexes of DNA by introducing either double- (topoisomerases II) or single-stranded (topoisomerases I) breaks into the backbone of the DNA. These breaks allow unwinding of the duplex and removal of the replication-induced torsional strain. The nicks are then resealed by the topoisomerases.

The RNA primers of the leading strands and Okazaki fragments are removed by the repair DNA polymerases simultaneously replacing the ribonucleotides with deoxyribonucleotides. The gaps that exist between the 3'-OH of one leading strand and the 5'-phosphate of another as well as between one Okazaki fragment and another are repaired by DNA ligases thereby, completing the process of replication

Answer 4

First the two strands of DNA are unwound by the enzyme helicase. The bases of the DNA are revealed and binding proteins stabilize the sing DNA strand. DNA polymerases attach the free nucleotides with the original exposed bases. A newly formed DNA strand is constructed consisting of one of the old strands and a new strand. The DNA polymerase than correct any errors that MAY have occurred in the process such as the mismatched pairs, and pair it with the correct pair.

RNA is synthesized through a process called transcription, which is a lot like DNA replication. The process begins when part of the DNA helix is unwound, where RNA enters to use the strand of DNA as a template. RNA like DNA uses polymerases to attach matching nucleotides, but instead of using Thymine (found in DNA), RNA uses Uracil. The RNA then separates itself from the DNA strand and the DNA rewinds itself. The newly formed mRNA molecule is neither finished, nor ready for use before leaving the nucleus. The 5' end of the mRNA is capped with a special nucleotide that can serve as a start signal for translation. A poly-A tail of about 100 - 200 molecules of adenine-containing nucleotides are added to the 3' end of the mRNA. Lastly, noncoding portions (introns) are snipped out, and actual coding regions (exons) are spliced together to finish off the newly formed mature transcript.

Answer 5

The DNA first breaks into two strands .Those strands are half part of a DNA.those strands grow to become two separate DNA's

Answer 6

S Phase (APEX)

Answer 7

during interphase