Lectures 25-27 BCM 475 - M001
Popular in Biochemistry I
Popular in Biochemistry
BCM 475 - M001
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This 13 page Class Notes was uploaded by Annie Notetaker on Sunday November 15, 2015. The Class Notes belongs to BCM 475 - M001 at Syracuse University taught by M. Braiman, R. Welch in Fall 2015. Since its upload, it has received 95 views. For similar materials see Biochemistry I in Biochemistry at Syracuse University.
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Date Created: 11/15/15
Lecture 11/02: DNA Structure/ Replication/ Repair I (p. 819-835) DNA Replication and Repair • DNA replication occurs with high fidelity -The error rate must be less than 1 bp per 3 x10 bp -Error rate of DNA synthesis: 1 error per 10 -10 bp 6 7 -Error rate of DNA synthesis with proofreading: 1 error per 10 -10 bp 9 10 -Error rate of DNA synthesis with postreplication mismatch repair: 1 error per 10 -10 bp • DNA must still be protected after DNA replication from the following hazards: -UV light, ionizing radiation -Certain chemicals -DNA cross-links -Single-strand breaks -Double-strand breaks -Error-free and error-prone repair mechanism • DNA damage must be repaired The Complexity of DNA replication • The following features of the DNA double helix make DNA replication a complex process: 1. The two strands in a double helix run in opposing directions 2. The bases lie in the interior of the double helical structure -Therefore, for DNA replication to occur, the two strands must be separated 3. The two strands in a double helix are intertwined -Therefore, for DNA replication to proceed, the strands must be unwound—a process that can result in supercoils DNA Polymerase • DNA polymerases catalyze the step-by-step addition of nucleotides (first addition to the 3’ end) to a template DNA chain -DNA polymerase à template-directed enzymes • “DNA polymerase catalyzes the nucleophilic attack by the 3’-hydroxyl group terminus of the polynucleotide chain on the alpha phosphoryl group of the nucleoside triphosphate to be added” • DNA polymerases require a primer—an initial segment of a polymer from which DNA synthesis will take place DNA Polymerase Structure • Different DNA polymerases are, as a whole, structurally similar -DNA polymerases resemble a right hand, with domains of fingers and a thumb that appear to surround the DNA and hold it within its active site—the region resembling the palm of the hand • Klenow fragment -Fragment of E.coli DNA polymerase I -Possesses the structure resembling the right hand mentioned above 1 -Contains a domain with exonuclease activity -The domain with exonuclease activity within the Klenow fragment of DNA polymerase I enables DNA polymerase I to act as a proofreading enzyme, “removing and repairing mismatched bases on the daughter strand” -“DNA polymerase I is a repair enzyme filling in gaps during DNA replication” DNA Polymerase Mechanism • Metal ions play a crucial role in the catalytic activity of DNA polymerases • All DNA polymerases possess two metal ion sites in the enzyme’s active site 2+ • Two metal ions (usually Mg ) are involved in DNA replication via DNA polymerases: -Metal #1 à “Coordinates the 3’-hydroxyl group of the primer” and binds the deoxynucleoside triphosphate (dNTP) -Metal #2 à Interacts only with the dNTP -Carboxylate groups of two aspartate residues located within the enzyme’s active site are responsible for holding metal #1 and metal #2 close to each other (Asp has a delocalized charge) -“The metal ion bound to the primer activates the 3’-hydroxyl group of the primer, facilitating its attack on the alpha phosphoryl group of the dNTP substrate in the active site” (alpha-phosphate bridges form between the two metals) -Following the attack by the primer mentioned above, a negatively charged pentacoordinate transition state is generated on the pyrophosphate product and metal #2 that interacts solely with dNTP is responsible for stabilizing this negative charge Shape Complementarity • While the formation of hydrogen bonds between base pairs is relevant in DNA replication, it is not as significant as the shape complementarity that must exist between the newly added base and its complement on the template strand • For example, a study showed that when an adenosine analog that possessed the same shape as adenosine but lacked key nitrogen atoms responsible for forming hydrogen bonds between base pairs was placed into a DNA template strand, the adenosine analog was still capable of directing the insertion of thymidine • Reason for shape complementarity significance 1. Minor-groove interactions -“Residues of the enzyme form hydrogen bonds with the minor-groove side of the base pair in the active site” -“All Watson-Crick base pairs have hydrogen bond acceptors at equivalent positions in the minor groove” 2. Shape selectivity -Following the binding of dNTP to the active site of DNA polymerase, the finger domain of DNA polymerase clamps down to form a “tight pocket into which only a properly shaped base pair will readily fit” Remember, the base pair contains 1. dNTP and 2. Complementary base in template strand 2 Priming • DNA replication requires the presence of an RNA primer—a segment of RNA with a free 3’-end -DNA replication occurs in the 5’ à 3’ direction • RNA primers are synthesized by an RNA polymerase called primase -“Primase synthesizes a short stretch of RNA (about 5 nt) that is complementary to one of the template DNA strands” -Because primase is an RNA polymerase, it is capable of synthesizing RNA without the presence of a primer • The short stretch of RNA synthesized by primase to initiate DNA replication is hydrolytically removed and replaced with DNA once DNA replication begins Leading and Lagging Strand Synthesis • Replication fork: “site of DNA synthesis” • There must be leading and lagging strand synthesis because DNA polymerases only synthesize DNA in the 5’ à 3’ direction and there are two antiparallel DNA strands that serve as templates for DNA replication • Leading strand synthesis: -Continuous synthesis of DNA in the 5’ à 3’ direction • Lagging strand synthesis: -Discontinuous synthesis of short pieces known as Okazaki fragments (~1000 nt) -The synthesis of Okazaki fragments is primed with RNA primers synthesized by RNA polymerases -The RNA primers are eventually replaced with DNA and DNA ligase links the Okazaki fragments DNA Ligase • “Catalyzes the joining of one DNA strand with a free 3’-hydroxyl group to another with a free 5’-phosphoryl group” to form a phosphodiester bond • Requires ATP as an energy source Helicase • Helicases use the energy of ATP hydrolysis to separate the two strands of DNA for DNA replication -Each separated strand functions as a template stand for DNA synthesis -Separation occurs ahead of the replication fork • Hexameric protein (6 subunits) Helicase Asymmetry • Active helicase does not have 6-fold symmetry • Experiments revealed that only four of helicase’s six subunits bind an ATP analog called AMP-PNP -In addition, each subunit has a different degree of rotation (“subunits are rotated out of the plane of the hexamer”) 3 Helicase Mechanism 1. “One of the strands of the double helix passes through the hole in the center of the helicase” 2. ATP binds to two subunits without any nucleotides 3. ATP hydrolysis occurs and ADP and P areireleased from two other subunits 4. Helicase undergoes a structural change 5. DNA is dragged through the central hole of helicase and subsequently separated DNA Supercoiling • The formation of tertiary structures • Both linear DNA and circular DNA molecules can form supercoils • Tw = number of double helical twists; number of turns • Wr = writhe number; number of supercoils; “the number of times a superhelix crosses over itself” • Lk = linking number; topological invariant; “the number of times that a strand of DNA winds in the right-handed direction around the helix axis when the axis lies in a plane” -Topological isomers (topoisomers) à “molecules differing only in linking number” • Lk = Tw + Wr • “A lowering of Lk causes both right-handed (negative) supercoiling of the DNA axis and unwinding of the duplex” • There are more negatively supercoiled DNA molecules than positively supercoiled ones because negative supercoils are easier to unwind Topoisomerase I • Topoisomerase I possesses a central cavity in which a DNA molecule is located • Topoisomerase I relaxes supercoiled DNA in steps (eliminates supercoils) -Supercoils are removed to prevent the tangling of DNA strands during DNA replication Topoisomerase I Mechanism (The Relaxation of Negatively Supercoiled DNA) 1. DNA binds to topoisomerase I at the enzyme’s central cavity 2. Tyrosine 723 of topoisomerase I performs a nucleophilic attack on the phosphoryl group of the DNA molecule 3. A phosphodiester bond is formed between topoisomerase I and the DNA molecule One strand of the DNA is cleaved 4. “One end of the helix can now rotate around the unbroken strand” This rotation is responsible for unwinding the supercoils 5. Topoisomerase reseals the DNA backbone to prevent the rapid unwinding of DNA • Formation of a partially or completely relaxed supercoiled plasmid • An easily reversible reaction that does not require an input of energy Topoisomerase II • Aka DNA gyrase • Topoisomerase II uses energy released from ATP hydrolysis to introduce negative supercoils into DNA molecules • Structure: -Dimer 4 -ATP-binding sites and DNA-segment-binding sites • “Topoisomerase II inhibitors of the prokaryotic enzymes are antibiotics” -E.g. nalidixic acid and ciprofloxacin Topoisomerase II Mechanism 1. Gate (G) segment (a DNA duplex) binds to topoisomerase II 2. T segment (another DNA duplex) loosely binds to topoisomerase II 3. Two ATP molecules each bind to separate ATP-binding sites located in domains in both monomers of the topoisomerase II dimer 4. Domains containing ATP-binding sites come closer together 5. T segment is trapped Both strands of the G segment are cleaved and the strands remain bound to the enzyme 6. T segment enters the large central cavity of topoisomerase II 7. G segment is ligated 8. T segment is released from topoisomerase II 9. “ATP hydrolysis resets the enzyme to perform another cycle with the G-strand still bound” Highly Processive Polymerases • Replicative polymerases à “high catalytic potency, fidelity, and processivity” -Processivity: “the ability of an enzyme to catalyze many consecutive reactions without releasing its substrate” -????2 functions as a sliding DNA clamp and enables polymerases to maintain a high catalytic rate DNA Replication Machinery • Helicase separates the double helix into two strands • “Two DNA core polymerase enzymes operate at each replication fork” -E. coli DNA polymerase à 2000 nt/ sec (40 min for replication of 4.6 M base pairs) • Single-stranded-binding proteins (SSB) ensure strands separated by helicase remain separated Leading Strand Synthesis • Continuous synthesis of DNA in the 5’ to 3’ direction (beginning at RNA primer) by DNA polymerase III • “Topoisomerase II concurrently introduces right-handed (negative) supercoils to avert a topological crisis” DNA Polymerase III Holoenzyme • Components: 1. Two polymerase core enzymes each containing the following: -???? subunit à DNA polymerase -???? subunit à proofreading exonuclease -???? subunit -???? 2ubunit à sliding clamp 2. Central structure to which both core enzymes are linked 5 -Clamp loader -Subunits that interact with single-stranded-DNA-binding proteins -Hexameric helicase (e.g. DnaB) Trombone Model • Lagging-strand synthesis occurs in the same direction, 5’à 3’, as the leading-strand synthesis in the trombone model 1. An RNA primer is added to the lagging-strand template 2. The lagging strand is looped out of the ????2subunit (sliding clamp) with the addition of nucleotides in the 5’ to 3’ direction -Formation of an Okazaki fragment 3. DNA polymerase III releases the sliding clamp after the addition of about 1000 nucleotides 4. Loop collapses 5. New loop forms 6. Sliding clamp is added 7. RNA primer is added 8. Formation of another Okazaki fragment 9. Cycle repeat • This process is called the trombone model because “the loop lengthens and shortens like the slide on a trombone • The DNA polymerase holoenzyme and the trombone model depict the coordinated synthesis of both the lagging strand and the leading strand - As the lagging strand is looped out of one of the 2 subunits with the addition of nucleotides, the leading strand is synthesized through the other 2 subunit of the same DNA polymerase Lecture 11/04: DNA Structure/ Replication/ Repair II (p. 835-846) Origin of Replication in E.coli • DNA replication originates at one unique site in E. coli—the oriC locus • oriC locus -245 bp -Tandem array of 13-mer sequences (AT rich) -Five binding sites for DnaA protein Preparation for DNA Replication in E.coli 1. “The binding of DnaA proteins to DNA is the first step in the preparation for replication” -DnaA monomer à ATPase domain + DNA-binding domain -DnaA monomers bind to DnaA binding sites on oriC locus -Bound DnaA “come together with DnaA molecules bound to lower-affinity sites to form a cyclic hexamer” and “DNA is wrapped around the outside of the DnaA hexamer” 2. “Single DNA strands are exposed in the prepriming complex” -DNA helicase DnaB binds to DNA and unwinds the AT-rich regions 6 -Single-stranded-binding proteins trap the AT rich region -Prepriming complex is generated 3. “The polymerase holoenzyme assembles” -ATP hydrolysis triggered -DNA replication initiated 4. “The DnA hexamer breaks up” -To prevent new replications DNA Polymerases • Prokaryotic Polymerases -DNA polymerase III à “primary enzyme of DNA synthesis” • Eukaryotic Polymerases -DNA polymerase ???? à “primary enzyme of DNA synthesis” Eukaryotic Replication Initiation • Eukaryotes have multiple origins of replication, whereas prokaryotes have one distinct origin of replication -About 30,000 origins in humans • Human chromosome à linear E. coli chromosome à circular • Eukaryotic replication initiation: 1. Assembly of the ORC -ORC à Origin of Replication Complexes -ORC is assembled around AT-rich sequences -ORC recruits many proteins 2. Recruitment of different proteins -Helicase that separates the parent DNA -Single-stranded-DNA-binding proteins that ensure the separated strands remain separated 3. Polymerases -DNA replication is initiated by polymerase ???? - Polymerase switching: polymerase ???? à DNA polymerase ???? -Proliferating cell nuclear antigen (PCNA), the eukaryotic equivalent of the 2 subunit (sliding clamp) of E.coli polymerase III, binds to DNA polymerase ???? -“The binding of PCNA to DNA polymerase ???? renders the enzyme highly processive and suitable for long stretches of replication” Eukaryotic Cell Cycle • S phase: DNA synthesis • G 2hase: gap; short growth period in which the cell prepares for mitosis • M phase: mitosis; cell division • G 1hase: gap; longest phase; rapid growth and metabolic activity • Licensing of replication à late M phase or early G 1hase • Checkpoints -Regulate cell cycle 7 -“If a checkpoint is not passed properly, programmed cell death (apoptosis) usually occurs” -Regulated by small proteins called cyclins and cyclin-dependent protein kinases Telomeres • Problem: “The lagging strand would have an incomplete 5’ end after the removal of the RNA primer and each round of replication would further shorten the chromosome” • Solution: telomeres • Telomeres -Tandem repeats of a 6 nt sequence that functions to protect the ends of chromosomes from deterioration and adjacent chromosomes (repeating sequence in humans à AGGGTT) -Structure: large duplex loops Telomerase • Function: replicates telomeres • Polymerase with its own RNA template • Telomere formation: -“Primer ending in GGTT is added to human telomerase” -Elongation: telomerase adds AGGGTT to form the sequence GGTTAGGGTT -Translocation: RNA template reset for next elongation -Cycle repeated: elongation, translocation, elongation, and translocation… • High expression of telomerase à cancer -Telomeraseà target for anticancer drugs Sources of DNA Damage • Insertion of incorrect base -Leads to errors and possibly mutations • Hydroxyl radical -Mutagen -Guanine + hydroxyl radical à 8-oxoguanine (oxidation reaction) -8-Oxoguanine base pairs with adenine rather than cytosine • Deamination -Adenine can be deaminated and generate a hypoxanthine that base pairs with cytosine instead of thymine -Mutagenic -Guanine and cytosine can also be deaminated • Alkylation -Aflatoxin B1 is converted into a reactive epoxide (active carcinogen) by a liver enzyme -As a result, guanosine experiences G—C to T—A transversion • UV radiation à Intrastrand cross-links -Cross-linked dimer of two thymine bases -“Ultraviolet light induces cross-links between adjacent pyrimidines along one strand of DNA” and prevents strand separation during DNA replication because “the pyrimidine dimer cannot fit into the double helix” 8 - Can lead to the formation of cyclobutane photodimers • Chemicals à Interstrand cross-links -“Psoralens can form photodimers between bases on different strands” and prevent DNA replication by inhibiting the parent strands to separate DNA Damage Repair • Guideline for DNA repair: -“Recognize the offending base(s)” -“Remove the offending base(s)” -“Repair the resulting gap with a DNA polymerase and DNA ligase” • Proofreading 1. An insertion of an incorrect base will result in a decreased rate of DNA synthesis and fluctuations caused by the loosely bound mismatched base -These enable the enzyme to sense a problem 2. Newly synthesized strand is migrated to the exonuclease site in the ???? subunit of DNA polymerase III in E.coli during the delay 3. “DNA is degraded, one nucleotide at a time” 4. DNA returns to the polymerase active site 5. DNA polymerase continues synthesis • Mismatch repair in E. coli (procedure similar across different cells) 1. Protein MutS detects abnormal shape of G-T mismatch 2. Protein MutL binds to MutS 3. MutL recruits endonuclease MutH 4. “MutH cleaves the backbone in the vicinity of the mismatch” 5. Exonuclease I removes the segment of DNA containing the mismatched T 6. DNA polymerase III re-synthesizes the segment of DNA removed by exonuclease I • Base-excision repair 1. Glycosylase enzyme (e.g. E. coli enzyme AlkA) binds to damaged DNA and “flips the affected base out of the DNA double helix” and into its own active site 2. Glycosylase enzyme cleaves glycosyl linkage to sugar 3. Damaged base is released 4. AP site, hole with a missing base, is formed on DNA -Apurinic (no A or G) -Apyrimidinic (no C or T) 5. “AP endonuclease nicks the backbone” 6. “Deoxyribose phosphodiesterase excises the residual deoxyribose phosphate unit” 7. DNA polymerase I inserts the correct base 8. DNA ligase seals the repaired strand • Nucleotide-excision repair (NER) 1. “Excision of a 12-nt fragment by uvrABC excinuclease” in E. coli -In eukaryotes, 25-30 nucleotides are removed 2. DNA synthesis by DNA polymerase I 3. DNA ligase joins the newly synthesized strand with the original strand 9 Repair of dU • Problem: spontaneous deamination of cytosine à uracil; daughter strands will form U-A base pairs rather than C-G base pairs • Solution: base-excision repair 1. “Uracil DNA glycosylase hydrolyzes the glycosidic bond between the uracil and deoxyribose moieties but does not attack thymine-containing nucleotides” -Repair enzyme: uracil DNA glycosylase -Reason why thymine, not uracil, is present in DNA 2. AP endonuclease 3. DNA polymerase I and DNA ligase Ames Test • Test used to detect chemical that could cause cancer • Protocol: 1. Construct a plate (plate #1) with Salmonella bacteria mutagens incapable of growing without histidine - The addition of a chemical mutagen to plate #1 generates many new mutations and a small number of revertants (mutations that reverse the original mutation and enable histidine to be synthesized) - “The mutagen is activated by a liver extract” - “A potent mutagen produces many revertants” 2. Construct a control plate (plate #2) with mutagens that are capable of synthesizing histidine -Few spontaneous revertants are formed on the control plate Lecture 11/06: RNA Synthesis I (p. 851-859) RNA Polymerase • Catalyzes RNA synthesis • “All RNA polymerases have similar folds” -Metal ion binding site in active site near large cleft RNA Synthesis • (RNA) + nibonucleoside triphosphate ⇌ (RNA) n+1+ PP i -Catalyzed by RNA polymerase -“The 3’-hydroxyl group of the last nucleotide in the chain nucleophilically attacks the alpha phosphoryl group of the incoming nucleoside triphosphate with the concomitant release of a pyrophosphate (PP)”i -Degradation of the pyrophosphate to orthophosphate leads to an irreversible reaction -“Most newly synthesized RNA chains carry a highly distinctive tag on the 5’ end: the first base at that end is either pppG or pppA” - When PP ài2P, thi reaction is driven in the forward direction • RNA synthesis à 1. Initiation 2. Elongation 3. Termination 10 RNA Polymerase Active Site • Contains two metal ions (normally Mg )2+ 1. Metal #1 à Remains tightly bound to RNA polymerase; stabilized by two Asp residues 2. Metal #2 à “Comes in with the nucleoside triphosphate and leaves with the pyrophosphate”; stabilized by an Asp residue Subunits of RNA Polymerase from E. coli • At the initiation of RNA synthesis: -RNA polymerase has six subunits à ???? ???????? 2???? à the holoenzyme -The ???? subunit has a mass of 70 kd • For the second stage of RNA synthesis, elongation: -???? dissociates -RNA polymerase has five subunits (core polymerase) à ???? ????????′2 à the core enzyme RNA Transcript • +1 à first nucleotide of a DNA template strand that will be transcribed into RNA +2 à second nucleotide to be transcribed • DNA template strand à complement of RNA transcript DNA template strand à antisense (-) strand DNA template strand is written 3’ – 5’ • DNA coding strand à identical to RNA transcript DNA coding strand à sense (+) strand DNA coding strand is written 5’ – 3’ RNA transcript is written 5’ – 3’ Elongation Mechanism 1. Binding of ribonucleoside triphosphate at the active site of RNA polymerase adjacent to the growing RNA chain (pppN enters) 2. Formation of a Watson-Crick base pair between the incoming ribonucleoside triphosphate and the DNA template strand 3. “The 3’-hydroxyl group of the growing RNA chain, oriented and activated by the tightly bound metal ion, attacks the alpha-phosphoryl group to form a new phosphodiester bond, displacing pyrophosphate” (pN addition and leaving of PP) i Translocation Mechanism • “After nucleotide addition, the RNA-DNA hybrid can translocate through the RNA polymerase, brining a new DNA base into position to base-pair with an incoming nucleoside triphosphate” Backtracking • The movement of the RNA-DNA hybrid in the reverse direction of elongation -The movement of the hybrid in the direction opposite that of a mismatched base • Energetically less favorable because bonds between base pairs are broken as a result • Crucial for proofreading 11 • Process: 1. Backtracking of the active site (metal) of RNA polymerase 2. Hydrolysis of the phosphodiester bond linked to the mismatched nucleotide 4 5 • Net result: 1 mistake per 10 or 10 nucleotides incorporated Transcription Bubble • Site of RNA synthesis • A region of DNA separated by RNA polymerase • Unwound dsDNA of about 17 bp exposes the DNA template strand from which RNA will be synthesized RNA-DNA Hybrid Separation • The RNA-DNA hybrid is forcibly separated by a structure within RNA polymerase • The DNA coding strand exits the enzyme in one direction while the RNA product exits in a different direction • “Polymerase keeps the RNA and DNA from each other so the DNA-DNA duplex reforms as the replication bubble moves onward” Promoter Sequences • Elongation processes à conserved among all organisms • Initiation and termination à varies between bacteria and eukaryotes • Holoenzyme ▯ -Bacterial RNA polymerase with the composition ???? ????????2???????? -???? à aids in locating the promoter site—site on DNA where RNA transcription is initiated Bacterial Promoter Sequences • Sequences upstream of the promoter site also play a role in determining the location for the initiation of transcription 1. -10 sequence à Consensus sequence: TATAAT à 10 nt upstream of start site 2. -35 sequence à Consensus sequence: TTGACA à 35 nt upstream of start site • Consensus sequence: TATAAT -Consensus for a strong promoter—a promoter for RNA transcribed at high rates • Weak promoters -“Stray from the consensus at -10 and/or -35 and/or there are more or fewer bases between the two sites” RNA Polymerase Holoenzyme Complex 12 • Holoenzyme -Bacterial RNA polymerase with the composition ???? ???????? ???????? ▯ 2 • ???? -Aids RNA polymerase in locating the promoter site—site on DNA where RNA transcription is initiated -“Recognizes the -35 and -10 elements of the promoter DNA” -“Also recognizes upstream elements at -40 and -60 in proteins that are very highly expressed” -RNA polymerase moves along a DNA strand until the sigma factor finds a promoter site to initiate transcription -Once the newly synthesized RNA strand has grown by 9 or 10 nucleotides, the sigma factor is released Alternative Promoter Sequences • “E. coli has 7 distinct ???? factors for recognizing several types of promoter sequences in E. coli DNA” • ???? à recognizes the standard promoters -35 and -10 32 • ???? à “recognizes heat shock promoters to produce proteins that help E. coli survive elevated temperatures” DNA Unwinding • For RNA synthesis to take place, a segment of DNA must be unwound • Closed promoter complex (dsDNA) à open promoter complex (DNA with unwound segment) • Closed complex -Zero bonds between base pairs in the double helix is broken -Promoter complex to which RNA polymerase initially binds • Open complex -The bonds between about 17 base pairs in the double helix is broken -Transcription bubble formed Elongation at the Transcription Bubble • Transcription bubble contains RNA polymerase, DNA, and RNA strand being synthesized • “Helicases and topoisomerases unwind DNA before the bubble and rewind it after the bubble” • Newly synthesized RNA + template DNA à hybrid helix -The RNA-DNA hybrid helix is about 8 bp long • Rate of RNA synthesis: 50 nt/ second (slower in GC-rich regions) • Rate of DNA replication: 1,000-2,000 nt/ second Note: Quotations indicate text obtained directly from textbook or lecture notes References: Berg, Jeremy, John Tymoczko, and Lubert Stryer. Biochemistry. 7th ed. W.H. Freeman, 2012. 1- 246. Print 13
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