DNA Replication - Tut Group Case 2 (DNA/RNA)

**DNA replication** - Where does replication take place in cell cycle? - late G1/ mostly S-phase of the interphase 1. *the replication* - **The adding of the complementary bases :** - **Okazaki-fragments** 2. *finishing the replication* 3. *telomerase* - **Store genetic informat...

**DNA replication** - Where does replication take place in cell cycle? - late G1/ mostly S-phase of the interphase 1. *the replication* - **The adding of the complementary bases :** - **Okazaki-fragments** 2. *finishing the replication* 3. *telomerase* - **Store genetic information** - **Replication** - **Gene expression** - **Genetic variation** - Mutations + recombination happen during DNA replication - Simple structure nucleotide DNA = phosphate-sugar (deoxyribose)-nitrogenous base (A,T,C,G) Pyrimidines= 1 carbon nitrogen bases (2N) Purines= 2 carbon nitrogen ring bases (4 N) =\> step ladder model - Sugar phosphate backbone + base pairs - Formation sugar phosphate backbone  Phosphor= connected to 2 sugars -\>3' sugar above -\>5' sugar below = phosphodiester bonds (this strand=5'-3' direction) 5'=phosphate end 3'=-OH end \-\-\-\--opposite strand runs in other direction [=anti-parallel ] =\>double helix structure 2 strands -\>hydrogen bonds (easy to break during replication) DNA = chiral molecule -\>left(-)- and right(+) handed double-helix -\>reality= b-DNA , z-DNA, a-DNA =\>major/minor groove Major groove =\>bigger gap between sugar phosphate backbone Minor groove =\>smaller gap '' =\>ratio: \~1.8 = considered pure DNA Rotation of the phosphor during binding= cause rotation 10-11 turns in helix DNA turn=clockwise **DNA packaging in prokaryotic and eukaryotic cells** 1. Eukaryotic cells =\>DNA wrapped around histones to pack in smaller spaces [Histones + DNA = chromatin ] Histones=building blocks [nucleosomes] (nucleosomes=when under microscope the beads in the necklace(chromatin strand)) Nucleosome=octamer histones + DNA wrapped around DNA=wrapped around octamer of histones = important during condensing DNA -\>cell nuclear division Building histones=\>4 types proteins (h3, h4, h2a, h2b) =\>form dimer 2x h3,h4 dimer = tetramer + 2x h2a,h2b dimer =\>result =8 proteins form octamer Histones + part Dna= - = ionic bond =\>charge -H1 histone-\> packages it together =\>makes it more condensed -after DNA wrapped around histones=\>chromatin looping + condensation 2. Prokaryotic cells =\>supercoiling (-=opp.direction double helix/+=same direction double helix) supercoiling) -\>*how to decide?* =\>2 major topoisomerases indicate supercoiling and relax supercoiling (gyrase-\>negative supercoils in relaxed DNA + relax positive coils) (topoisomerase 1 -\>relaxes neg\> coiled DNA ) Tension that comes from major/minor groove DNA =\>causes the DNA to coil **DNA and ATP -\>sugar phosphate backbone + connecting bases** ATP = nucleotide with 3 phosphate groups (adenine + sugar + triphosphate) *Synthesis of the sugar phosphate backbone* Backbone = polymer -\>monomer to polymer=phosphorylation ATP -3P= AMP (nucleotide in DNA )+ energy released ! also with the nucleosides-\>have 3 phosphate groups other bases (TTP, GTP, CTP) *Replication*=\> DNA polymerase III connects nucleoside (3 phosphate groups) to correct base-\> 2 phosphate break off = release of energy to make bond between bases **=\>extra information : give the written description of the leading strand and lagging strand (definition) then=\>review the structure of the double replication fork (where is the leading and where is the lagging if you have a double replication fork)** The leading strand is continuously extended from the primer by a DNA polymerase with high [processivity](https://en.wikipedia.org/wiki/Processivity), while the lagging strand is extended discontinuously from each primer forming [Okazaki fragments](https://en.wikipedia.org/wiki/Okazaki_fragments). **=\>functions of polymerase I, II, III** Pol I =\>DNA polymerase I functions to fill DNA gaps that arise during DNA replication, repair, and recombination Pol II =\> DNA polymerase II also functions in editing and proofreading mainly in the lagging strand  Pol III =\> DNA polymerase III is the main replicative enzyme.