Helicase Unwinds the DNA – Single Strand Binding Protein Hold DNA strands apart – Primase puts down RNA primer – Ligase Joins Okazaki fragments together – DNA polymerases Adding new nucleotides to 3’ end (elongation) Replacement of RNA primer with DNA Proofreading The mistakes made in replication are fixed in a number of ways: DNA polymerase will check it when it adds it and will correct it immediately. Nucleotide excision repair when mistakes evade proofreading. A cell will use a variety of – enzymes for mismatch repair. (nuclease cuts out incorrect base and correct one is filled in by DNA polymerase and fixed by ligase. Over time, we lose a little DNA Because DNA can’t attach nucleotides to the 5’ end of the daughter strand , the RNA primer on the very end of the lagging strand gets replaced by DNA. Thus the lagging strand becomes shorter each time replication occurs My telomeres are shorter than yours…and that depresses me We have DNA” at the very end of each of our chromosomes “spare This spare DNA is called a telomere and is made of DNA genes, just repeating TTAGGG…you “junk –no have between 100 and 1000 repetitions. So what’s the significance of telomeres We can make more telomeres using telomerase which is only available in some cells (such as reproductive cells) Without telomerase, the telomeres eventually run out which scientists believe is a key factor in aging and death Scientists have found telomerase in some cancerous cells.
Helicase – Unwinds the DNA Single Strand Binding Protein – Hold DNA strands apart Primase – puts down RNA primer Ligase – Joins Okazaki fragments together DNA polymerases Adding new nucleotides to 3’ end (elongation) Replacement of RNA primer with DNA Proofreading The mistakes made in replication are fixed in a number of ways: DNA polymerase will check it when it adds it and will correct it immediately. Nucleotide excision repair – when mistakes evade proofreading. A cell will use a variety of enzymes for mismatch repair. (nuclease cuts out incorrect base and correct one is filled in by DNA polymerase and fixed by ligase. Over time, we lose a little DNA Because DNA can’t attach nucleotides to the 5’ end of the daughter strand , the RNA primer on the very end of the lagging strand gets replaced by DNA. Thus the lagging strand becomes shorter each time replication occurs My telomeres are shorter than yours…and that depresses me We have “spare DNA” at the very end of each of our chromosomes This spare DNA is called a telomere and is made of “junk DNA –no genes, just repeating TTAGGG…you have between 100 and 1000 repetitions. So what’s the significance of telomeres We can make more telomeres using telomerase which is only available in some cells (such as reproductive cells) Without telomerase, the telomeres eventually run out which scientists believe is a key factor in aging and death Scientists have found telomerase in some cancerous cells.
AP%20Chapter%209%20and%2010%20Notes%202016.docx