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| Question | Answer |
| What is replication? | The process by which DNA molecules can direct the synthesis of identical copies of themselves. This happens prior to cell division. Replication requires a DNA template, free DNA nucleotides, primers, DNA polymerase/ligase and a source of energy (ATP). |
| Primers | Primers are short complementary sequences of nucleotides produced at the 3' end of the template strand, furthest away from the replication fork. Primers allow DNA polymerase to DNA. |
| What is a primer? | Primers are short complementary sequences of nucleotides that allow DNA polymerase to bind. |
| Stage 1- replication | The DNA molecule to be replicated uncoils and weak hydrogen bonds between bases break, using energy from ATP. The strands separate, forming a replication fork. |
| Formation of the leading strand | A primer joins the 3' end of the template strand. DNA polymerase starts to add free complementary DNA nucleotides. It also forms strong chemical bonds between the phosphates and sugars of the new strand. Weak hydrogen bonds form between the base pairs of the new strand and the template strand. The leading strand is replicated continuously towards the junction of the replication fork. |
| Formation of the lagging strand | DNA polymerase can only add nucleotides to the 3' end. This means that free DNA nucleotides attach to the 3' end of the primer in fragments. DNA polymerase forms strong chemical bonds between the phosphates and sugars of the fragments. When a fragment is complete, the primer is replaced by DNA. DNA ligase joins the fragments together to form the second new strand. The lagging strand is replicated discontinuously away from the replication fork. |
| What is the importance of DNA replication? | DNA encodes hereditary information in a chemical language. An organism's genotype is determined by its sequence of bases. DNA replication ensures that an exact copy of an organism's genetic information is passed on from cell to cell during growth, and from generation to generation during reproduction. DNA is essential for the continuation of life. |
| Many replication forks | When a long chromosome is replicated, many replication forks are formed at the same time. This ensures DNA is replicated quickly and precisely. |
| Polymerase chain reaction | PCR is a laboratory technique used to amplify sections of DNA. It involves exposing DNA to a series of temperature changes known as thermo cycling. It can be used for paternity testing or to test for genetic diseases in a growing embryo, suing embryonic cells. |
| Stages of PCR | At 95 degrees, the DNA is heated to break the hydrogen bonds, and the two strands separate. At 55 degrees, the DNA is cooled to allow complementary primers to bind to specific target sequences. At 70 degrees, heat-tolerant DNA polymerase is used to synthesise new strands from free DNA nucleotides. |
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