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All DNA replication takes place in a ___________ manner
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explain the process of semiconservative replication
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Genetics Chapter 9
DNA replication and recombination
| Term | Definition |
|---|---|
| All DNA replication takes place in a ___________ manner | semiconservative |
| explain the process of semiconservative replication | DNA's two nucleotide strands separate, and each serves as a template on which a new strand is synthesized |
| initially, three models were proposed for DNA replication: | conservative replication, dispersive replication, and semiconservative replication |
| conservative replication | the entire double-stranded DNA molecule serves as a template for a whole new molecule of DNA, and the original DNA molecule is fully conserved during replication (some new some old) |
| dispersive replication | both nucleotide strands break down into fragments, which serve as templates for the synthesis of new DNA fragments, and then somehow reassemble into two complete DNA molecules. (each resultant is both new and old) |
| semiconservative replication | two nucleotide strands unwind and each serves as a template for a new DNA molecule (hybrid and new) |
| which two people demonstrated that replication in E. coli is semiconservative? | Meselson and Stahl |
| investigators confirmed that other organisms also use semiconservative replication. Was evidence found for conservative and/or dispersive replication as well? | no |
| there are several different ways semiconservatice replication can take place, differing in the nature of the TEMPLATE DNA- whether is is ______ or circular _______ | linear or circular |
| individual units of replication are called ________ | replicons |
| replicons contain a replication origin. What happens here? | replication starts at the origin and continues until the entire replicon has been replicated |
| compare bacterial chromosomes and eukaryotic chromosomes with respects to replication origins | bacterial chromosomes have a SINGLE replication origin while eukaryotic chromosomes have many |
| a common type of replication that takes place in circular DNA is called ______ replication | theta (because it generates a structure that resembles the Greek letter theta |
| theta replication: replication of _______ DNA | circular |
| theta replication: how is it initiated? | by the unwinding of the two nucleotide strands, producing a REPLICATION BUBBLE |
| theta replication: unwinding may at one or both ends of the bubble, making it progressively _______ | larger |
| theta replication: DNA replication on both of the template strands is s__________ with unwinding | simultaneous |
| theta replication: the point of unwinding, where the two single nucleotide strands separate from the double-stranded DNA, is called a ________ ______ | replication fork |
| theta replication: if there are two replication forks, one at each end of the replication bubble, what happens? | the forks proceed outward in both directions in a process called BIDIRECTIONAL REPLICATION |
| theta replication: what happens simultaneously during the bidirectional replication? | simultaneous unwinding and replicating the DNA until they eventually meet. |
| theta replication: What happens if there is a SINGLE replication fork present? | it proceeds around the entire circle to produce two complete circular DNA molecules |
| theta replication: the two complete circular DNA molecules each consist of what? | one old and one new nucleotide |
| circular DNA molecules that undergo theta replication have a ______ origin of replication. | single |
| ________ cells contain far too much DNA to be replicated speedily from a single origing | eukaryotic |
| linear eukaryotic replication: each chromosome contains numerous ______ | origins |
| linear eukaryotic replication: at each replication origin, what happens? | The DNA unwinds and produces a REPLICATION BUBBLE |
| linear eukaryotic replication: DNA synthesis takes place on both strands at each end of the bubble as the replication forks proceed ________ | outward |
| linear eukaryotic replication: Once the replication forks begin moving outward towards eachother, what then happens to the replicons? | the forks of adjacent replicons run into each other, and the replicons fuse to form a long stretches of new DNA |
| linear eukaryotic replication: the replication and fusion of all the replicons lead to what? | two identical linear DNA molecules |
| What are the three requirements of replication? | (1)single-stranded DNA template (2)substrates growing a nucleotide strand (3)enzymes and other proteins |
| What do the enzymes and proteins do? | they "read" the template and assemble the substrates into a DNA molecule |
| direction of replication: in DNA sunthesis, new nucleotides are joined one at a time to the _' end of the newly synthesized strand | 3' |
| direction of replication: DNA __________, the enzymes that synthesize DNA, cadd add nucleotides ONLY to the 3' end of the growing strand | polymerases |
| direction of replication: Since DNA polymerases can only add to the 3' end and not the 5' end, in which direction will the DNA strands elongate? | always in the same 5'-->3' direction |
| all DNA synthesis is 5'-->3' meaning what? | that new nucleotides are always added to the 3' end of the growing nucleotide strand |
| at each replication fork, synthesis of the leading strand proceeds _________ and that of the lagging strand proceeds ___________ | continuously, discontinuously |
| continuous replication: replication of the leading strand in the _____ direction as that of unwinding, allowing new nucleotides to be added continuously to the 3' end | same |
| discontinuous replication: replication of the lagging strand in the direction ________ that of unwinding, which means that DNA must be synthesized in SHORT stretches | opposite |
| What are these short stretches produced by discontinuous replication called? | Okazaki fragments |
| Replication takes place in four stages: | initiation, unwinding, elongation, and termination |
| initiation: replication is initiated at a replication origin, where an _______ _______ binds and causes a short stretch of DNA to unwind | initiator protein (this unwinding allows helicase and other single-strand-binding proteins to attach to the polynucleotide strand) |
| unwinding:DNA _________ breaks hydrogen bonds at a replication fork | helicase |
| unwinding: single-strand-binding proteins do what to the strands? | stabilize and separate |
| unwinding: DNA ______ reduces the torsional strain that develops as the two strands of double-helical DNA unwind | gyrase |
| elongation: DNA is synthesized using ______-stranded DNA as a template | single |
| elongation: this process requires a series of ______ | enzymes |
| elongation: all DNA polymerases require a nucleotide with a _'-__ group to which a new nucleotide can be added | 3'-OH group |
| elongation: DNA polymerases cannot initiate DNA sunthesis one a bare template, they require a ______ to get started | primer |
| elongation: the enzyme primase does what? | synthesizes a short stretch of RNA nucleotides (primers) to get DNA replication started |
| elongation: the primers provide what? | a 3'-OH group for the attachment of DNA nucleotides to start DNA synthesis |
| elongation: all DNA molecules initially have short RNA primers embedded within them these primers are later removed and replaced by what? | DNA nucleotides |
| elongation: on the leading strand,primers are required where? | only at the 5' end of the newly synthesized strand |
| elongation: on the lagging strand, primers are synthesized where? | at the beginning of each Okazaki fragment |
| elongation: after DNA has unwound and a primer has been added, DNA polymerases elongate the strand by catalyzing DNA ____________ | polymerization |
| elongation: DNA plolymerase adds new nucletides to the _' end of a growing polynucleotide strand | 3' end |
| elongation: bacteria have two DNA polymerases that have primary roles in replication. What are they? | DNA polymerase III and DNA polymerase I |
| elongation: what does DNA polymerase III do? | synthesizes new DNA on the leading and lagging strands (elongates DNA) |
| elongation: what does DNA polymerase I do? | removes and replaces primers |
| elongation: DNA polymerases II, IV, and V function in what? | DNA repair |
| elongation: DNA ligase does what? | seals the breaks that remain in the sugar-phosphate backbones when the RNA primers are replaced by DNA nucleotides |
| elongation: the major enzymatic components of elongation- DNA polymerases, helicase, primase, and ligase interact at the ___________ ______ | replication fork |
| elongation: in summary, each active replication fork requires five basic components which are? | helicase, single-strand-binding proteins, topoisomerase gyrse, primase, and DNA polymerase |
| elongation summary: replication fork requires helicase to do what? | unwind the DNA |
| elongation summary: replication fork requires single-strand-binding proteins to do what? | protect the single nucleotide strands and prevent secondary structures |
| elongation summary: replication fork requires topoisomerase gyrase to do what? | remove strain ahead of the replication fork |
| elongation summary: replication fork requires primase to do what? | synthesize primers with a 3'-OH group at the beginning of each DNA fragment |
| elongation summary: replication fork requires DNA plymerases to do what? | synthesize the leading and lagging nucleotide strands |
| termination: what are a few ways replication is terminated? | whenever two replication forks meet or specific termination sequences block further replication |
| replication is extremely accurate. The high level of accuracy in DNA replication is produced by what three things? each process catching errors missed by the preceding ones | nucleotide selection, proofreading, and mismatch repair |
| in comparison with prokaryotes (bacteria), where are some differences in the genome structure of eukaryotic cells that affect how replication takes place? | the size of eukaryotic genomes, the linear structure of eukaryotic chromosomes, and the association of DNA with histone proteins |
| the much greater size of eukaryotic genomes requires that replication be initiated at multiple _______ | origins (therefore many origins of replication) |
| at each origin, a multiprotein complex, the origin-recognition complex (ORC) does what? | binds to initiate the unwinding of the DNA |
| precise replication at multiple origins in eukaryotes is ensured by what? | a replication LICENSING FACTOR that must attach to an origin before replication can begin |
| some significant differences in the processes of bacterial and eukaryotic replication are in the number and functions of DNA ________ | polymerases |
| eukaryotic cells contain a number of different DNA polymerases that function in _________, _________, and DNA _____ | replication, recombination, DNA repair |
| DNA polymerases alpha, delta, and epsilon do what? | carry out replication on the leading and lagging strands |
| other DNA polymerases do what? | replicate organelle DNA, DNA repair, and help bring about recombination |
| the ends of chromosomes, the telomeres, possess several unique features, one of which is the presence of many copies of a short repeated sequence. The single-stranded protruding end of the telomere is known as the __ _______, since it is a G-rich strand | G overhang |
| the ends of linear eukaryotic chromosomes (the G overhang) are replicated by what? | RNA-protein enzyme called telomerase |
| the RNA part of telomerase is __________ to the G-rich strand and pairs with it, providing a template for synthesis | complementary |
| nucleotides are then added to the __ end of the G-rich strand | 3' |
| after several nucleotides have been added, the RNA template moves along the DNA and more nucleotides are added. Then the telomerase is _________ | removed |
| synthesis takes place on the complementary strand, what does this do? | fills in the gap due to the removal of the RNA primer at the end |
| recombination takes place through the ________, _________, and ______ of DNA | breakage, alignment, and repair |
| homologous recombination takes place during what? | crossing over |
| homologous recombination requires the formation of ___________ DNA | heteroduplex DNA |
| what does heteroduplex DNA consist of? | one nucleotide strand from each of two homologous chromosomes paired together |
| homologous recombination can take place through several different pathways one is the Holliday model: | homologous recombination is accomplished though a single-strand break in the DNA, strand displacement, and branch migration |
| the holliday model pathway is initiated by what? | single-strand break in each of two DNA molecules in the same position |
| then what happens to the free end of each broken strand? | they migrate to the other DNA molecule, creating the HOLLIDAY JUNCTION |
| branch migration takes place as the two nucleotide strands exchange position, creating two duplex molecules. This is called __________ DNA | heteroduplex |
| the exchange of nucleotide strands produce the holliday intermediate, which can be cleaved in one of two ways. What can this predict? | the holliday model predicts noncrossover or crossover recombinant DNA, depending on whether cleavage is in the horizontal or the vertical plane |
| cleavage in the horizontal plane produces _________ recombinants consisting of two heteroduplex molecules | noncrossover |
| cleavage in the vertical plane produces _________ recombinants consisting of two heteroduplex molecules | crossover |
Created by:
cmccartney2
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