Dna helicase diagram. They use ATP hydrolysis for energy.

Dna helicase diagram. Examine Model 2. Helicase is involved in the different DNA modification processes like DNA replication, repair, recombination, transcription A labeled diagram of DNA replication, showing the steps and key components involved in the process. Some Hel contain a Helicase and RNase D C terminal Domain (HRDC). DNA helicase binds to the double-stranded DNA and unwinds it to form a replication fork, creating two single-stranded DNA templates. For example, single‐stranded DNA can be exposed at the end of DNA duplex by an exonuclease. However, when DNA helicase separates the DNA into two strands, it creates strain in the DNA molecule. In one model, semiconservative Study with Quizlet and memorize flashcards containing terms like topoisomerase, helicase, single stranded binding proteins (2) and more. Replication in prokaryotes starts from a sequence found on the chromosome called the origin of replication—the point at which the DNA opens up. Parental DNA is colored black and Poxviruses are large DNA viruses with a linear double-stranded DNA genome circularized at the extremities. Each origin generates two replication forks that move in opposite DnaB helicase is defined as the primary replicative helicase in Escherichia coli, capable of driving branch migration of a Holliday junction and potentially involved in DNA recombination in vivo. Much of our understanding of DNA replication was first determined with bacterial proteins, which are typically easier to study. 'Helicases' published in 'Encyclopedia of Biophysics'Cartoon of some the biological roles of DNA helicases and variety of DNA structures. Notice how the anti-parallel nature of DNA means that the helicase on the right opens up 3’ to 5’ information on the top DNA strand (the leading strand) while simultaneously opening up 5’ to 3’ information on the bottom DNA strand. DNA replication requires other enzymes in addition to DNA polymerase, including DNA primase, DNA helicase, DNA ligase, and topoisomerase. They are of two types, i. ______ Strands of DNA separate. Asterisks denote the 32 P-labeled end of the DNA. (a) Helicase and polymerases, involved in bacterial DNA replication. Learn how & why DNA is replicated. We now know that several human diseases (Xeroderma pigmentosum, Cockayne's syndrome Get a labeled diagram of a DNA replication fork and learn about the process of DNA replication in an easy-to-understand way. Base-Pairing Underlies DNA Replication and DNA Repair As discussed briefly in Chapter 1, DNA templating is the process in which the nucleotide sequence of a DNA strand (or selected portions of a DNA strand) is copied by complementary base -pairing (A with T, and G with C) into a complementary DNA sequence (Figure 5-2). Open boxes represent the conserved helicase motifs, and the consensus amino-acid sequence of each motif is shown by the single-letter code inside the boxes (c = D, E, H, K, R; o = S, T; x = any amino acid). This video explains the structure of a viral helicases. After labeling, students answer questions about the model. [1 Schematic drawing of selected cellular DNA helicase substrates. Know the DNA double helix definition. Once the DNA is unwound, the new complementary strands can be synthesized. Feb 14, 2025 · Explore the structure, function, and role of DNA helicase in replication, repair, and transcription. The arrows refer to the helicase movement. Single-strand binding proteins bind to the single-stranded DNA near the replication fork to keep the fork open. Multiple enzymes are used to complete this process quickly and efficiently. They use ATP hydrolysis for energy. We describe a structure of an unusual helicase domain of DNA polymerase theta (Polθ). Helicases require the energy which ATP provides. It consists of a helicase that must unwind the double helix during DNA replication. Primase synthesizes an RNA primer to initiate The frequency of lesion abundance can vary depending on the lesion type. Oct 11, 1996 · We have solved the crystal structure of a monomeric form of a DNA helicase from Bacillus stearothermophilus, alone and in a complex with ADP, at 2. DNA replication begins when an enzyme called helicase unwinds, and unzips the DNA molecule. It acts as a motor with the RecA tier and a collar with the N-terminal tier, facilitating the unwinding of DNA strands by binding to nucleotides and hydrolyzing ATP in a sequential manner. Also, learn the replication steps in order with a labeled diagram. Single-stranded DNA-binding protein (SSB) is in green. This Review discusses helicase-dependent DNA repair pathways and how Below are two Jmol buttons that explore the actual structure of DNA helicase from E. DNA helicases generally bind to ssDNA or ssDNA/dsDNA junctions and translocate mainly unidirectionally along the bound strand and disrupt the hydrogen bonds between the duplexes. Labels above the open boxes (Q, I, Ia, etc Start studying DNA Replication Model. Learn vocabulary, terms, and more with flashcards, games, and other study tools. e. Students label DNA replication showing how enzymes like helicase, ligase, and polymerase create a new copy of DNA. ” Figure 4: A diagram depicting the unwinding activity of DNA helicase, represented in green, as it separates the two strands of DNA in the double helix by breaking the hydrogen bonds between base pairs. Since then RNA and DNA helicases with diverse functions have been found in all organisms. As DNA replication begins, Helicase separates the two strands of DNA to act as templates for replication. Feb 20, 2013 · The Structure and Function of DNA Helicase DNA helicases are generally highly sophisticated ring-shaped multimeric ATP-fuelled nanomachines, with molecular weights of more than 300kDa. Topoisomerase works at the region ahead of the replication fork to prevent supercoiling by introducing breaks in the DNA and then resealing them. In reality, the strands of DNA form a double helix. Discover DNA unwinding enzymes, with diagrams. Synthesis goes on inside these bubbles. The ladder model of DNA is a simplified representation of the actual structure and shape of a DNA molecule. ______ Hydrogen bonds between nucleotides break. May 2, 2025 · Helicase’s role during DNA replication Helicases are pivotal in DNA replication, ensuring precise genome duplication before cell division. Each has a slightly different structure and method of operation. The enzyme comprises two domains with a deep cleft running between them. 6. WRN is a member of the RecQ Helicase family. These include helicase, DNA gyrase, DNA primase, DNA polymerase (I and III) and DNA ligase Helicase Helicase unwinds and separates the double-stranded DNA by breaking the hydrogen bonds between base pairs This occurs at specific regions (origins of replication), creating a replication fork of two strands running in antiparallel directions DNA Jul 26, 1996 · DNA helicases play essential roles in key biological processes such as the replication, repair, recombination, and transcription of DNA. It uses ATP (shown in red) to power this motion. Separating the strands of the double helix would provide two templates for the synthesis of new complementary strands, but exactly how new DNA molecules were constructed was still unclear. Helicase encounters with specific DNA lesions and more novel forms of DNA damage will be discussed. The helicase-like domain of Polθ forms tetramers and this tetrameric structure might bring together broken DNA ends for microhomology-mediated end joining. Aug 9, 2019 · “DNA helicase is a class of enzymes that helps to unwind the double-stranded DNA and allow replication. During DNA replication, one new strand (the leading strand) is made as a continuous piece. So how does the structure of DNA allow it to copy itself so accurately? Model 1 — The Structure of DNA Oct 29, 2012 · This motor core consists of two RecA-like folds termed helicase domain 1 (HD1) and helicase domain 2 (HD2); HD1 and HD2 correspond to RecA-like folds 1A and 2A in SF1 motors [1, 10]. Only the helicase and the polymerases are shown with arrows indicating directions of motion. DNA helicase unwinds the DNA double helix ahead of the replication fork, while single-stranded binding proteins prevent the reannealing of the DNA strands. DNA Structure and Replication How is genetic information stored and copied? why? Deoxyribonucleic acid or DNA is the molecule of heredity. The process involves synthesizing new DNA strands using the original strands as templates. ______ Free nucleotides are attracted to exposed bases C A G 10. Structure of DNA helicase Helicases separates two strands of nucleic acid into their corresponding single chain. 5 and 2. Apr 27, 2004 · Schematic diagram representing organization and involvement in the catalytic functions of the best conserved motifs of the DEAD-box helicases. Autoradiogram of the gel: lane 1, reaction without enzyme; lane 2, heat-denatured substrate and The replisome structure cartooned at the replication fork consists of clamp proteins, primase, helicase, DNA polymerase, and single-stranded binding proteins, among others. In this article, we shall discuss the structure of DNA, the steps involved in DNA replication (initiation, elongation and termination) and the clinical consequences that can occur when this process goes wrong. DNA can replicate itself because its two strands are complementary. An enzyme called DNA helicase breaks Since the discovery of the first DNA helicase in Escherichia coli in 1976, several have been isolated from both prokaryotic and eukaryotic systems. AI generated definition based on: Trends in Biochemical Sciences, 2003 DNA helicase is a type of enzyme that plays a crucial role in various processes involved in maintaining the integrity of the genome, such as DNA replication, recombination, and repair. Helicase protein was first discovered in Escherichia coli in 1976 (1, 2). The solid lines are the parent DNA strands with 3', 5 Is a Dna replication diagram worksheet dna replication labeling (with word bank) dna polymerase single strand binding proteins dna ligase helicase ligase DnaB Helicase is a protein structure based on the RecA fold, consisting of hexameric rings with N- and C-terminal globular regions. Mutations in genes encoding DNA helicases are often associated with diseases related to genomic instability. As a result, the replication factors Nov 21, 2023 · Learn what a replication bubble is. The unwinding process facilitates the separation of the two complementary DNA strands Jun 9, 2025 · Recruitment of repair enzymes: The unwound DNA region allows repair enzymes to access and bind to the damaged DNA. Steps to DNA Replication The helicase enzymes unwind the parent DNA and then unzip it by breaking the hydrogen bonds between the complementary base pairs. Scheme of biochemical assay for measuring unwinding activity of ATP/Mg 2+ -dependent DNA helicase. These helicases share a common mechanism of action but exhibit some variations in structure and function. It contains the genetic blueprint for life. DNA helicases not only play essential roles in replication, DNA repair, and recombination, but they also influence gene expression and chromosome structure and act to resolve dynamic DNA structures that pose a source of genomic Jun 8, 2025 · DNA replication, also known as semi-conservative replication, is the process by which DNA is doubled. Replication begins at specific points in the DNA sequence called origin, where initiator proteins bind to DNA, triggering the process. Model 2 – DNA Replication Direction of DNA helicase DNA helicase Start studying DNA Replication Labeling. The partial duplex DNA helicase substrate was prepared by annealing the radiolabeled DNA oligo (small DNA) to longer ssDNA as described [2], [3]. Its primary function is to unwind the double-stranded DNA molecule, enabling the separation of two complementary strands. Although Jan 29, 2018 · DNA replication requires separation of genomic duplex DNA strands, an operation that is performed by a hexameric ring-shaped helicase in all domains of life. Repair of DNA damage: Repair enzymes repair the damaged DNA, and DNA helicase continues to unwind the DNA, allowing the repair process to proceed. Dec 1, 2024 · The unwinding of the DNA helix at the replication fork is primarily catalyzed by two DNA helicases working together: one helicase operates on the leading strand, and the other on the lagging strand. Nov 21, 2023 · Helicase can bind to DNA like a ring structure, or as a multi-subunit structure, to unwind DNA. B. Chromosome size and structure varies between organisms, but since DNA molecules are the reservoir of genetic information for all forms of life, many replication challenges and solutions are the same for different organisms. Learn about the structure, function and mechanism for DNA helicase. This unit will also focus on the individuals responsible for the discovery of the DNA helix and Each helicase unwinds and separates the DNA helix into single-stranded DNA. Hel falls into 5 superfamilies (SF1-SF5). Because two helicases bind, two replication forks are formed at the origin of replication; these are extended in both directions as replication proceeds creating a replication bubble. coli (PDB ID: 4esv). Cyclopyrimidine dimers generated by UV irradiation are recognized by XPC protein or RNA polymerase. Before replication can start, the double strands of DNA need to separate from each other. The DNA tends to become more highly coiled ahead of the replication fork. The subunits in gp4 and E1 are marked as A-F following the order from the 3′-to-5 Jan 23, 2025 · Types of Helicases and Variability Across Organisms The DNA helicase family is diverse, and different helicases are found in both prokaryotic and eukaryotic organisms. 309,846,392 stock photos online. [5] Helicase enzymes generally unwind and separate double-stranded DNA. A. Download scientific diagram | Architecture of the bacterial replication fork. Feb 1, 2002 · Structural information on helicase proteins has expanded recently beyond the DNA helicases Rep and PcrA, and the hepatitis C virus RNA helicase to include UvrB, members of the DEA (D/H)-box RNA helicase family, examples of DnaB-related helicases and RuvB. For organisms to grow and repair damaged cells, each cell must be capable of accurately copying itself. New nucleotides are added through complementary base pairing: A pairs with T, and C with G. Helicase and translocase proteins constitute a broad family of nucleic acid-dependent molecular motors that consume nucleoside triphosphates (typically ATP) as fuel for directed movement. AI generated definition based on: Methods in Enzymology, 2022 The elucidation of the structure of the double helix by James Watson and Francis Crick in 1953 provided a hint as to how DNA is copied during the process of DNA replication. Their presence and importance in DNA metabolism was first recognized 20 years ago, when Escherichia coli DNA helicase I was shown to unwind duplex DNA into two single strands. DNA helicases often require some single‐stranded DNA to begin unwinding. Number the steps below in order to describe the replication of DNA in a cell. This means that one strand can be used as a template to make the other strand. An RNA primer is synthesized, and is elongated by the DNA polymerase. Helicases are shown in blue and other proteins in red. 11 hours ago · This problem requires analyzing the provided diagram of DNA replication and applying knowledge of the enzymes and mechanisms involved. Figure 14 4 1: A replication fork is formed when helicase separates the DNA strands at the origin of replication. This process uses energy derived from hydrolysis of ATP. On the leading strand, DNA is synthesized continuously, whereas on the lagging strand, DNA is synthesized in short stretches. The N-terminal domains (NTD, or primase (Pri) domain in gp4) are shown as semi-transparent molecular surfaces, and the C-terminal helicase (Hel) domains are shown in cartoons. Examine a DNA replication bubble diagram, identify how replication bubbles form, and discover the role of DNA replication is semiconservative, meaning that each strand in the DNA double helix acts as a template for the synthesis of a new, complementary strand. May 16, 2020 · The function of helicase is to remodel the structure of DNA by breaking the hydrogen bonds between the paired nucleotides. coli in 1976. Helicase, another key player, unwinds the double helix structure of the DNA molecule, exposing the individual strands for replication. Ligase repairs gaps in the sugar-phosphate Jul 11, 2013 · Several cancers and genetic disorders are linked to defects in helicases that have roles in genome maintenance and stability. DNA helicase is also important during the repair of DNA damage and the process of transcription. The helicase is a homohexamer that encircles the lagging strand and binds directly to the primase synthesizing the Schematic diagram of the replication process. Model 2 – DNA Replication Direction of DNA helicase DNA helicase. Understand how DNA is unwound, duplicated, and reassembled during this essential process in biology. Table. The diagram of DNA replication class 12 shows how DNA unwinds, separates, and serves as a template for the synthesis of new DNA strands during cell division. The sliding clamp helps to Structural information on helicase proteins has expanded recently beyond the DNA helicases Rep and PcrA, and the hepatitis C virus RNA helicase to include UvrB, members of the DEA(D/H)-box RNA helicase family, examples of DnaB-related helicases and RuvB. Helicase opens up the DNA double helix, resulting in the formation of the replication fork. Function Helicase (Hel) is a motor protein which separates nucleic acid strands like DNA double helix or self-annealed RNA. Helicase polarity, which is also deemed "directionality", is defined as the direction (characterized as 5'→3' or 3'→5') of helicase movement on the DNA/RNA single-strand along which it is moving. This process entails the recognition of each nucleotide in the DNA template The replisome is a system in which various factors work together to solve the structural and chemical challenges of DNA replication. DNA helicase was discovered first in E. DNA polymerase creates a new complementary strand of DNA on each of the originals halves that were separated by helicase. The other (the lagging strand) is made in small pieces. The helicase-primase D5, composed of six identical 90 kDa subunits, is required for DNA replication. A helicase is defined as an enzyme that catalyzes the separation of double-stranded nucleic acids into single strands in an ATP-dependent reaction, playing a crucial role in various DNA-related processes such as replication, repair, and transcription. If you recall the structure of DNA, you may remember that it consists of two long strands of nucleotides held together by hydrogen bonds between complementary nitrogenous bases. The DNA fragments are joined by DNA ligase (not shown DNA replication requires the action of three main enzymes each with their own specific role: Helicase unzips and unwinds the DNA molecule. For example: Prokaryotic Helicase: In bacteria like Escherichia coli, the DnaB helicase is the primary enzyme responsible Download 139 Replication Dna Helicase Stock Illustrations, Vectors & Clipart for FREE or amazingly low rates! New users enjoy 60% OFF. Helicase is the class of enzyme that separates the double strands of nucleic acids into single strands. Replication always starts at specific locations on the DNA, which are called origins of replication and are recognized by their sequence. DNA helicase is defined as an unwinding enzyme that catalyzes the breakage of hydrogen bonds between complementary strands of double-stranded DNA, utilizing nucleotide triphosphate hydrolysis, and providing single-stranded DNA templates necessary for nucleic acid metabolic pathways such as DNA replication, repair, recombination, and transcription. Mar 19, 2025 · Cryo-electron microscopy structures of DNA helicases in various conformations provide insight into an ATP-hydrolysis-dependent ‘entropy switch’ that drives unwinding of DNA for replication Sep 5, 2024 · DNA Structure and Replication 3 Model 2 - DNA Replication Direction of DNA helicase DNA helicase Free Nucleotides 11. Here is the step-by-step solution: Analysis of FIGURE 3 FIGURE 3 shows a replication fork where the parental DNA double helix is being unwound by Helicase. These activities are necessary before DNA can be copied in preparation for cell division (DNA replication). The α-thalassemia and mental retardation X-linked syndrome helicase (ATRX ), contains an ATRX-Dnmt3-Dnmt3L (ADD) domain in Jan 10, 2025 · The enzyme helicase is responsible for unzipping the DNA double helix, exposing the nucleotide bases for replication and transcription. Explore its functions, structure, and disorders, then test yourself with a short quiz. DNA replication requires separation of genomic duplex DNA strands that is performed by hexameric ring shaped helicase machines in all domains of life. Single-strand binding proteins bind to the single DNA helicase continues to unwind the DNA forming a structure called the replication fork, which is named for the forked appearance of the two strands of DNA as they are unzipped apart. Helicase opens up the DNA at the replication fork by breaking hydrogen bonds between the nucleotide base pairs. Helicase enzymes are also Study with Quizlet and memorize flashcards containing terms like What are the three parts of the nucleotide?, What kind of sugar is found in a nucleotide?, Which nucleotide component contains nitrogen? and more. Helicase works in conjunction with other enzymes such as DNA polymerase, which synthesizes new DNA strands, and primase, which creates RNA primers for DNA polymerase. As the DNA opens up, Y-shaped structures called replication forks are formed. (a-f) Orthogonal views of hexameric helicase-DNA complexes of gp4 (a-b), E1 (c-d), and CMG (e-f). It happens right before cell division via mitosis or meiosis so that each new daughter cell can have a complete genome. Know the definition of DNA helicase in our informative video lesson. Although the mechanism by which DnaB both couples ATP hydrolysis to translocation along DNA and denatures the duplex is unknown, a change in the quaternary structure of the protein involving dimerisation of the N-terminal domain has been observed and may occur during the enzymatic cycle. , DNA helicase and RNA helicase. The structure of the helicase on DNA was derived at Rockefeller University’s cryo-electron microscopy (cryo-EM) core facility, leveraging a groundbreaking imaging technology that has revolutionized scientists’ ability to visualize and understand the role of fundamental biological processes. The enzyme DNA helicase, which is not shown in the diagram, accomplishes this step by breaking the hydrogen bonds between the complementary strands. Oct 24, 2024 · DNA helicases are ubiquitous enzymes found in all domains of life and associated with nucleic acid metabolisms such as DNA replication, transcription, translation, DNA repair, recombination, ribosome biogenesis, and decay. Helicases couple the chemical energy of NTP2 binding and hydrolysis to separate the complementary strands of double-stranded nucleic acids, remove nucleic acid-associated proteins, or catalyze homologous DNA recombination. Refer to the double helix diagram in Model 1 and describe its shape using a complete sentence. This exposes the two halves of the DNA molecule and creates a replication fork, which moves down the duplicated DNA as helicase continues to unwind it. Werner syndrome ATP-dependent helicase, also known as DNA helicase, RecQ-like type 3, is an enzyme that in humans is encoded by the WRN gene. This is an important process taking place within the dividing cell. Jun 2, 2024 · DNA Replication has three steps - Initiation, Elongation, and Termination. Introduction DNA polymerase theta (Polθ, encoded by the POLQ gene) is one of ∼15 DNA polymerases in the human genome, first identified by homology to Nov 21, 2023 · Learn about the function of helices in DNA replication. Single-strand binding proteins bind to each strand to stabilize and prevent them from reforming the double helix. The expanding database of structures has clarified the structural ‘theme and variations’ that relate the different helicase families May 21, 2024 · Helicase enzymes are important for the cellular processes of DNA replication and repair, transcription of DNA to RNA, protein translation, and the creation of ribosomes. It is also known as the helix destabilizing enzyme. The helicase surrounds a single-stranded portion of the DNA (shown here in orange) and inches its way along the strand, separating the double helix as it goes. Like a zipper that has unzipped in the middle, the separated DNA strands form a little open pucker. The crystal structures of the Bacillus stearothermophilus DNA helicase PcrA bound to ADP [5 DnaB helicase is an enzyme in bacteria which opens the replication fork during DNA replication. Changing affinities of the two motor domains for DNA during the ATPase cycle bias the energy landscape and enables directional translocation. ______ Hydrogen bonds between nucleotides form. Feb 17, 2023 · What is DNA replication. Topoisomerase breaks and reforms DNA’s phosphate backbone ahead of the replication fork, thereby relieving the pressure that results from this supercoiling. A replication bubble is an unwound and open region of a DNA helix where DNA replication occurs. The ladder model of DNA is a simplifi ed representation of the actual structure and shape of a DNA molecule. Learn its impact on genetics, disease, and biotech Superfamily I is a large and diverse group of monomeric and dimeric helicases defined by a set of conserved sequence motifs. The structures and chemomechanical C A G 10. The expanding database of structures has clar … Jan 17, 2025 · DNA polymerase, the central enzyme, facilitates the assembly of new DNA strands by sequentially adding nucleotides that match the base sequence of the template strand. In the DNA Structure and Replication we will extend our knowledge on the DNA Structure from Topic 2. Translocases track along a DNA or RNA substrate; helicases further separate paired nucleic acid strands. The structures and chemo-mechanical actions of these fascinating machines are coming into focus. Learn about the steps of DNA replication through a detailed diagram. Certain adducts such as oxidative base modifications can be quite numerous, and their effects can be helix-distorting or subtle perturbations to DNA structure. Nov 14, 2019 · This worksheet was designed for students to help them learn or study the steps in involved in DNA replication and the enzymes used in the process, such as helicase and polymerase. Jul 23, 2025 · The diagram of DNA replication shows a replication fork at the replication origins. Directionality In addition to the DNA polymerases, other proteins such as DNA helicase, single-stranded binding proteins, and DNA ligase are also shown in the diagram. Ligase repairs gaps in the sugar-phosphate DNA replication requires the action of three main enzymes each with their own specific role: Helicase unzips and unwinds the DNA molecule. DNA helicases have emerged as a prominent class of nucleic acid-metabolizing enzymes that play important roles in genome maintenance and cellular homeostasis. Members of this class are involved in essential processes in both DNA and RNA metabolism in all organisms. This occurs in a particular directional and consecutive manner, without released DNA. 9 A resolution, respectively. AI generated definition based on: Helicases from All Domains of Life, 2019 Sep 15, 1997 · DNA helicases were first identified over twenty years ago [3], [4] and although we now know quite a lot about how these enzymes bind DNA and hydrolyze NTPs, and can determine the direction in which they move along DNA, we know little about the molecular mechanisms of translocation and DNA unwinding. When & where does the process occur. There are many different types of helicase enzymes, including 24 different helicases in the human body. The following diagram illustrates the mechanism of DNA helicase in DNA repair: Dec 23, 2007 · Structure-guided mutational studies indicate an important role for the N-terminal tier in binding primase and regulating primase-mediated stimulation of helicase activity. This is the replication bubble. Single-strand binding proteins (SSBs) coat the DNA around the replication fork to prevent rewinding of the DNA. Oct 24, 2024 · DNA helicase is a crucial enzyme that plays an essential role in various cellular processes involving DNA. D5 consists of a primase fragment An enzyme called helicase is used to separate these two strands. Nov 2, 2023 · DNA helicase continues to unwind the double helix of DNA and thus forms a structure called replication fork, named after the forked appearance of two strands of DNA when unzipped apart. An enzyme called helicase unzips the DNA by breaking the hydrogen bonds between the nitrogenous base Structure of hexameric helicases. These enzymes expose single‐stranded DNA and recruit the ART CONNECTION Figure 9 2 3: A replication fork is formed by the opening of the origin of replication, and helicase separates the DNA strands. 729fq 6665n zs kpj 98mw iuq4h2 vcx vo1p atqqs jfjd