HISTONES/NUCLEOSOMES/DNA PACKAGING ● DNA packaged with proteins ● Histones: stabilize and regulate ● Nucleosomes: group of histones ● Heterochromatin (methylated) ○ Chromatin that is not easily accessible ○ DNA was methylated (non polar) ● Euchromatin (acetylated) ○ Looser for gene accessibility PURINES/PYRIMIDINES ● Cytosine and Thymine - pyrimidines (one circle) ● Adenine and Guanine - purines (two circles?) ANTI-PARALLEL NATURE OF DNA ● 3’ to 5’ strand is happy strand ORIENTATION OF REPLICATION ● 3’ to 5’ USES OF DIFFERENT DNA POLYMERASES ● DNA polymerase 3: attaches new complementary nucleotides along sugar-phosphate backbone ○ Energy supplied in nucleotides ● DNA polymerase 1: removes the primer and adds what it can by adding to a free 3 ALL ENZYMES/PROTEINS USED IN DNA REPLICATION ● Helicases: unwind DNA and separate the DNA strands ● Topoisomerases: relieves over-twisting further up replication fork ● DNA polymerase 3: creates new strand from 5’ to 3’ and needs free OH (3rd carbon) to attach on to ○ Can only add to existing chain (needs a primer) ● RNA primase: makes RNA primer to allow DNA poly 3 to begin with free OH 3’ ● DNA polymerase 1: removes primer and adds what it can by adding to a free 3 ● Ligase: comes in to attach Okazaki fragments together ● Telomerase: comes in and adds nonsense sequences to keep ends from being continually shortened ● ssbps - creates replication fork
CAUSES OF THE LEADING/LAGGING STRAND ● Leading strand: made continuously as replication fork continues to open as this polymerase is moving 3’ to 5’ and making its new strand 5’ to 3’ (adding onto free 3’) ● Lagging strand: made in pieces on the 5’ to 3’ strand as another polymerase works “backwards” (away from fork) as replication fork continues to open ○ Creating new strand 3’ to 5’ in pieces OKAZAKI FRAGMENTS ● The pieces that make up the lagging strand SHORTENING OF TELOMERES ● Ends of chromosomes ● Huge lengths of DNA that do not contain genes ● Will absorb all cuttings so nothing good is cut ● Junk at end of telomeres, so nothing good gets cut off ● They continuously shorten USE OF TELOMERASE ● Comes in and adds nonsense sequence to keep the ends from continually being shortened THYMINE DIMERS ● Created from uV light ● Where nuclease cuts out damaged DNA, fills in gap using other strand as template ● Kink where the thymine are REPAIR MECHANISMS (EXONUCLEASES)
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