Questions and Answers
What type of DNA replication is characterized by having a single replication origin?
Which type of DNA replication has hundreds to thousands of replication origins?
What is the end replication problem?
It is the loss of DNA at the ends of linear chromosomes during replication due to the inability to extend the lagging strand after the RNA primer is removed.
What problems can occur if the end replication problem is not solved?
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How is the end replication problem solved?
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What is the enzyme that makes DNA from an RNA template called?
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How do you determine the length of telomeres?
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Why is there a smear in the lanes of the gel when determining the length of telomeres?
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What is the role of POT1?
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How does a cell distinguish a chromosome end from a broken chromosome?
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How many times can a differentiated cell (fibroblast) divide?
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How many times can an undifferentiated cell (stem cell) divide?
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Telomere length is correlated with:
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What occurs with too little telomerase?
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What occurs with too much telomerase?
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Study Notes
Bacterial DNA Replication
- Features a single replication origin and specific sequence for initiation.
- Initiation relies on specific initiator proteins.
- Circular chromosome configuration prevents the end replication problem.
Eukaryotic DNA Replication
- Involves hundreds to thousands of replication origins.
- Lacks a specific sequence for replication origins in humans.
- End replication problem occurs due to linear chromosomes.
End Replication Problem
- Affects the lagging strand during DNA replication; the RNA primer at the 3' end cannot extend.
- Results in loss of genetic material from chromosome ends unless addressed.
Consequences of Unresolved End Replication Problem
- Potential loss of genetic material at the ends of chromosomes, risking genomic integrity.
Solution to End Replication Problem
- Telomeres, composed of repetitive sequences (e.g., GGGTTA in humans), and telomerase provide a solution.
- Telomerase recognizes and elongates telomeres using RNA templates for synthesis.
- DNA polymerase then fills in the remaining DNA.
Reverse Transcriptase
- Defined as the enzyme that synthesizes DNA from an RNA template.
Determining Telomere Length
- Terminal restriction fragmentation is used, involving:
- DNA isolation and treatment with specific restriction enzymes that do not cut telomeres.
- Gel electrophoresis followed by transfer to a membrane for detection of telomere sequences.
Gel Smear in Telomere Length Analysis
- Represents the average lengths of telomeres across different chromosomes.
Role of POT1
- POT1 is a protein that, when overexpressed, can increase telomere length.
Distinction of Chromosome Ends from Breaks
- Telomere-specific proteins, such as shelterin, and the formation of a t-loop help block DNA damage repair pathways, distinguishing functional chromosome ends from breaks.
Cell Division Limits
- Differentiated cells, such as fibroblasts, can divide approximately 60 times.
- Undifferentiated cells, like stem cells, can divide indefinitely.
Telomere Length and Cell Division
- A positive correlation exists between telomere length and the number of cell divisions—longer telomeres facilitate more divisions.
Effects of Telomerase Levels
- Insufficient telomerase activity leads to cell senescence, where cells cease division.
- Excessive telomerase activity is linked to cancer development.
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Description
Explore the complexities of DNA replication in both bacterial and eukaryotic cells with this quiz. Learn key differences, such as the unique features of replication origins and the end replication problem. Perfect for students tackling Unit 2 of Molecular & Cell Biology 351.
