Questions and Answers
Cells must copy their DNA before they do what?
divide
During what part of the cell cycle is DNA copied?
S phase of interphase
In eukaryotes, where are the copies of the DNA made?
the nucleus
The process of copying DNA is known as DNA ____
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Replication of DNA begins at points called ____
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The two DNA strands ____ at origins of replication forming Y-shaped areas called ____
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New DNA strands grow at the ____
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As the two strands open at the origins of replication, replication ____ form
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Prokaryotic (bacteria) chromosomes have a ___ replication bubble
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Eukaryotic cells have ____ bubbles
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What enzyme uncoils DNA so it can be replicated or copied?
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What other job does helicase perform?
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What is the job of single-strand binding proteins?
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A RNA ___ must be present to start the addition of new nucleotides
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What enzyme makes the RNA primer?
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DNA ___ is the enzyme that adds new complementary base pairs.
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DNA polymerase can only add nucleotides to what end of the DNA molecule?
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Which DNA strand is synthesized continuously as a single strand?
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The leading strand is made from the _____ toward the ____ as it opens.
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The ___ strand is synthesized ____ the overall direction of replication.
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The lagging strand is made in ___ short segments from the ____ fork toward the ___ of replication.
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The short segments of lagging strands are called ____
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What enzyme joins Okazaki fragments together into one strand?
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DNA polymerase initially makes how many errors?
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Proof-reading enzymes correct mistakes in DNA to one in ____ base pairing errors?
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Who developed this idea about replication?
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Chemicals and ____ radiation can damage DNA in our body cells so it must be ____ repaired.
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________ occurs when any of over 50 repair enzymes remove damaged parts of DNA.
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What 2 enzymes replace damaged sections of DNA and rebind the molecule?
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Study Notes
Overview of DNA Replication
- Cells must copy DNA before cell division to ensure new cells receive identical DNA strands.
- The DNA copying process occurs during the S phase of interphase.
Location and Initiation
- In eukaryotes, DNA replication occurs in the nucleus.
- The process starts at specific sites called the Origin of Replication.
Replication Forks and Bubbles
- DNA strands separate at origins of replication, forming Y-shaped structures known as replication forks.
- New DNA strands elongate at these forks, creating replication bubbles as the strands open.
Prokaryotic vs Eukaryotic Replication
- Prokaryotic cells feature a single replication bubble.
- Eukaryotic cells have multiple replication bubbles.
Key Enzymes in DNA Replication
- Helicase uncoils DNA and separates double-stranded DNA by breaking hydrogen bonds.
- Single-strand binding proteins keep DNA strands apart and prevent them from reattaching.
- Primase synthesizes a small RNA primer, essential for starting nucleotide addition.
- DNA Polymerase adds complementary base pairs to the growing DNA strand and works primarily at the 3' end.
Leading and Lagging Strands
- The leading strand is synthesized continuously from the origin toward the opening replication fork.
- The lagging strand is synthesized discontinuously in short segments called Okazaki fragments, moving from the replication fork toward the origin.
Joining and Correcting
- DNA ligase connects Okazaki fragments into a complete strand.
- During replication, DNA Polymerase makes an error rate of 1 in 10,000 nucleotides, which is reduced to 1 in one billion due to proofreading enzymes.
Historical Context and Damage Repair
- The model of DNA replication was proposed by Watson and Crick.
- DNA can be damaged by chemicals and ultraviolet radiation, necessitating continuous repair.
- Excision repair is a mechanism where over 50 different enzymes remove and repair damaged DNA sections.
- DNA Polymerase and ligase are responsible for replacing damaged DNA and reconstructing the DNA molecule.
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Test your knowledge of DNA replication with these flashcards. The quiz covers essential concepts such as the cell cycle, the S phase, and where DNA replication occurs in eukaryotic cells. Perfect for students studying biology or preparing for exams.
