DNA Replication

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DNA replication • DNA replication • Process of Replication in E. coli • Origin of replication • Role of Primase: RNA Primer • Elongation • Lagging strand synthesis: Okazaki fragments • Error rate of DNA synthesis • Eukaryotic Replication Types of replication Meselson-Stahl Experiment: Semi-conservative replication Eukaryotic chromosomes with base Analog 5-Bromodeoxyuridine with staining Process of Replication in E. coli Polymerases • DNA Polymerases • I,II, III • No initiation of replication • Primase: RNA polymerase • Lays down RNA nucleotides (primer) Origin of replication • Origin: 245 bp, containing repeats • Proteins involved, DNA A (initial denaturing), DNA B and C (further opening/destabilize helix) • unwinding of the helix: helicases (DNA B/C) • stabilization of the helix: single stranded binding proteins • role of topoisomerases, DNA gyrases Initiation Elongation • Anti-parallel strands • DNA Polymerase III • Leading strand synthesis DNA polymerase Replisome Lagging strand synthesis • Role of DNA Polymerase I • removal of primer • exonuclease activity • DNA ligase DNA Ligase Proofreading • Error rate of DNA synthesis • Proofreading • Base Pairing rules Eukayotic Replication • Multiple origins • Polymerases • Linear chromosomes Multiple origins Eukaryotic DNA Replication • DNA helicase promotes unwinding at the replication fork, • DNA pol δ with RFC and PCNA synthesizes DNA on the leading strand. • DNA pol α initiates synthesis on the lagging strand by generating an RNA primer (red segment) followed by a short segment of DNA. Then, RFC and PCNA load a second DNA polymerase (δ or ε ) to continue synthesis of the Okazaki fragment. • B, as DNA pol δ approaches the downstream Okazaki fragment, • Cleavage by RNase H1 removes the initiator RNA primer leaving a single 5 -ribonucleotide. Then, FEN1/RTH1 removes the 5 -ribonucleotide. The resulting nick is sealed by DNA ligase. Volume 272, Number 8, Issue of February 21, 1997 pp. 4647-4650 ©1997 by The American Society for Biochemistry and Molecular Biology, Inc. Linear chromosomes Telomerase= ribonucleoprotein with RNA, template for DNA synthesis.

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Glossary - Cellbiology
1 Glossary - Cellbiology Blotting: (Blot Analysis) Widely used biochemical technique for detecting the presence of specific macromolecules (proteins, mRNAs, or DNA sequences) in a mixture. A sample first is separated on an agarose or polyacrylamide gel usually under denaturing conditions; the separated components are transferred (blotting) to a nitrocellulose sheet, which is exposed to a radiolabeled molecule that specifically binds to the macromolecule of interest, and then subjected to autoradiography. Northern B.: mRNAs are detected with a complementary DNA; Southern B.: DNA restriction fragments are detected with complementary nucleotide sequences; Western B.: Proteins are detected by specific antibodies. Cell: The fundamental unit of living organisms. Cells are bounded by a lipid-containing plasma membrane, containing the central nucleus, and the cytoplasm. Cells are generally capable of independent reproduction. More complex cells like Eukaryotes have various compartments (organelles) where special tasks essential for the survival of the cell take place. Cytoplasm: Viscous contents of a cell that are contained within the plasma membrane but, in eukaryotic cells, outside the nucleus. The part of the cytoplasm not contained in any organelle is called the Cytosol. Cytoskeleton: (Gk. ) Three dimensional network of fibrous elements, allowing precisely regulated movements of cell parts, transport organelles, and help to maintain a cell’s shape. • Actin filament: (Microfilaments) Ubiquitous eukaryotic cytoskeletal proteins (one end is attached to the cell-cortex) of two “twisted“ actin monomers; are important in the structural support and movement of cells. Each actin filament (F-actin) consists of two strands of globular subunits (G-Actin) wrapped around each other to form a polarized unit (high ionic cytoplasm lead to the formation of AF, whereas low ion-concentration disassembles AF).
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Telomeres Secondary article Elizabeth H Blackburn, University of California, San Francisco, California, USA Article Contents . Introduction Telomeres are specialized DNA–protein structures that occur at the ends of eukaryotic . The Replication Paradox chromosomes. A special ribonucleoprotein enzyme called telomerase is required for the . Structure of Telomeres synthesis and maintenance of telomeric DNA. Synthesis of Telomeric DNA by Telomerase . Functions of Telomeres Introduction . Telomere Homeostasis . Alternatives to Telomerase-generated Telomeric DNA Telomeres are the specialized chromosomal DNA–protein . Evolution of Telomeres and Telomerase structures that comprise the terminal regions of eukaryotic chromosomes. As discovered through studies of maize and somes. One critical part of this protective function is to fruitﬂy chromosomes in the 1930s, they are required to provide a means by which the linear chromosomal DNA protect and stabilize the genetic material carried by can be replicated completely, without the loss of terminal eukaryotic chromosomes. Telomeres are dynamic struc- DNA nucleotides from the 5’ end of each strand of this tures, with their terminal DNA being constantly built up DNA. This is necessary to prevent progressive loss of and degraded as dividing cells replicate their chromo- terminal DNA sequences in successive cycles of chromo- somes. One strand of the telomeric DNA is synthesized by somal replication. a specialized ribonucleoprotein reverse transcriptase called telomerase. Telomerase is required for both
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