I. Nucleic acid structure [Covered in pre-lecture quiz] A. Monomer = nucleotide Bond by phosphodiester bondB. Polynucleotide strand: the sugar-phosphate backbone One nucleotide is formed by: Phosphate-pentose sugar (deoxyribose)-Nitrogenous baseC. RNA 1 stand Sugar is ribose Bases: AU GC #3 carbon: OH & H #2 carbon: OH & H Location in the cell: nucleusD. DNA 2 stands Sugar is deoxyribose Bases: AT GC #3 carbon: OH & H ----( can only build DNA from 3’ end- OH end)#2 carbon: H & H Location in the cell: nucleus1. Complementary base pairing Adenine (A) ---Thymine (T)Guanine (G) ---Cytosine (C)(Purines (2 rings) paired with Pyrimidines)2. Directionality: 5’ and 3’ ends 3. Anitparallel nature of polynucleotide strands Subunits run in different directionsE. Chromatin packing of the eukaryotic chromosome II.DNA replication [no slides, this will be done on blackboard]A. Overview 5’ end3’ endsee what I printed.When: before cell divide Where: nucleus Getting started: origins of replication Short stretches of DNA having specific sequence of nucleotides.B. DNA replication begins at origins of replication (ori) 1. Parental strands separate By helicase (breaks apart the 2 original DNA strands to begin replication/ unwind the double helix by breaking H bond between nucleotides)2. Replication bubble/replication forks Single-stranded binding protein: stabilize replication bubble/fork keeps single-strands apart/ protects single strand DNA from catalytic activityTopoisomerase: corrects for supercoiling/ helps relieve twisting ahead of helicaseC. The new DNA strand is made 1. DNA polymerase (need 3’-OH to work!!!)-DNA polymerase Ш can build complementary strand using template. ( adds nucleotides to the new stand)-DNA polymerase І removes RNA primers and fills in gap with DNA nucleotides. 2. Requirement for 3’-OH But it needs 3’-OH end (DNA polymerase Ш) 3. Primase and RNA primer Primase- enzyme that adds a primer, provides 3’ carbon to start replication.Primer- short stretch of RNA that is complementary to DNA template4. Leading strand (continuous synthesis) Only need one primer 5. Lagging strand (discontinuous synthesis) It needs to add primers several times!6. Okazaki fragments (DNA+Primer)Provides 3’-OH for DNA polymerase ІOkazaki fragments are short, newly synthesized DNA fragments that areformed on the lagging template strand during DNA replication.7. DNA ligase (Joins the 3’ end of the second fragment to the 5’ end of the forest fragment.)Makes phosphodiester to join sugar-phosphate backbone.Connect Okazaki fragment togetherD. Replicating the ends of DNA molecules1. Telomeres -No genes-buffer-protect chromosomes from deteriorating/ fusing togetherTelomeres will be gone after about 40 times replication and cell dies.Cells that need to pass this limit: -embryo cell-stem cell: replenish dying cells and regenerate damaged tissue.Because these cell contain telomerase.2. telomerase -enzyme that replenish telomeres-ribonucleoprotein (contain RNA+protein)-catalyzes synthesis of DNA using RNA template RNA template complementary to repeated sequence in
View Full Document
Unlocking...