Part 4. DNA Replication An important characteristic of DNA is its replicability.
ID: 209468 • Letter: P
Question
Part 4. DNA Replication An important characteristic of DNA is its replicability. DNA replication precedes every cell division-to produce new cells in an embryo, to maintain cells during adulthood, or to produce sperm and eg DNA replication is a complex process that involves many enzymes (proteins that act as cellular tools that perform specific functions). Here are a few of the main enzymes: DNA Helicase: Unzips the complementary DNA strands from one another RNA Primase: Creates RNA primers which act as binding sites for DNA Polymerase. DNA Polymerase: Reads an old strand of DNA in the 3 to 5' direction and makes a new complementary DNA strand. Also replaces RNA primers with DNA. DNA Ligase: Connects the sugar-phosphate backbones of adjacent DNA fragments. The combined action of these old strand that it is paired with. In the diagram below, the strand marked A is the old strand and enzymes produces a new DNA strand that is complementary to the trand. In the same way, the strand marked D is the old strand and the strand marked C is the new strand. This produces double-stranded DNA molecules that are half old and half new. This pattern of DNA replication is called semi-conservative. strand DNA 8 3 DNA Helicase 5 5' 3 strand Okazaki fragment Lagging Newly made DNA strand RNA DNA strands polymerase Refer to the diagram above. a. What type of biological molecule is DNA Helicase? What is its role in DNA replication? b. What is the role of RNA primers? What is the fate of primers after they finish this role? c. What enzyme reads the old DNA strand and creates a new complementary DNA strand? d. What is the name of the enzyme that connects sugar-phosphate backbones of adjacent . DNA fragments along the same DNA strand?Explanation / Answer
1. DNA helicase is an enzyme that catalyzes the breaking of H-bonds within DNA thereby separating the complementary DNA and provide a single stranded DNA template for the replication.
2. DNA polymerase is not alone capable for initiating replication, they can add nucleotide in the newly synthesized strand but not able to initiate therefore, a small stretch of RNA strand used as a starting point for DNA synthesis. Later on RNA primers are removed by RNase-H enzyme.
3. DNA polymerase read the old DNA strand and make new DNA strand.
4. DNA ligase connects dsugar phosphate backbone to the adjacent DNA fragment along the same DNA strand.
5. DNA replication is semiconservative because during replication parental strand separated and each parental strand act as a template for the synthesis of the complementary daughter strand, producing two identical progeny. This process is called as semiconservative.
6. 5’ AGTTAG 3’ A DOUBLE HELIX DNA
3’TCAATC 5’ D
5’ AGTTAG3’ EACH STRAND IS WITH PRIMER FOR DNA REPLICATION.
3’AATC5’
5’ AGTT3’
3’ TCAATC5’
5’AGTTAG 3’ A REPLIACTION PRODUCES TWO IDENTICAL DAUGHTER.
3’TCAATC 5’ B
5’AGTTAG 3’ C
3’TTAATC 5’ D
7. As DNA replication is semiconservative process, so half strand belongs to parental strand and half is newly synthesized daughter strand from the free nucleotides, which align on the basis of complementarity (complementary base pair rule) moreover, DNA pol l has proof reading activity so any incorrect nucleotide is corrected by DNA pol l.