Podcast
Questions and Answers
What is the approximate number of times the AGGGTT sequence is repeated in human telomeres?
What is the approximate number of times the AGGGTT sequence is repeated in human telomeres?
- 2500 (correct)
- 500
- 11000
- 100
Telomere length increases as we age.
Telomere length increases as we age.
False (B)
What is the name of the enzyme that is able to replace lost sequences at the end of chromosomes?
What is the name of the enzyme that is able to replace lost sequences at the end of chromosomes?
telomerase
The Hayflick limit describes the point at which cells stop dividing after approximately ______ divisions.
The Hayflick limit describes the point at which cells stop dividing after approximately ______ divisions.
Match the cell type with the expression of telomerase:
Match the cell type with the expression of telomerase:
Which of the following best describes the direction in which DNA polymerase adds nucleotides?
Which of the following best describes the direction in which DNA polymerase adds nucleotides?
RNA primers are stable and remain part of the replicated DNA strand.
RNA primers are stable and remain part of the replicated DNA strand.
What enzyme joins the DNA fragments on the lagging strand?
What enzyme joins the DNA fragments on the lagging strand?
The strand of DNA synthesized continuously is called the ______ strand.
The strand of DNA synthesized continuously is called the ______ strand.
Match the following terms with their descriptions:
Match the following terms with their descriptions:
Why are telomeres needed in eukaryotic DNA replication?
Why are telomeres needed in eukaryotic DNA replication?
Prokaryotic DNA has telomeres.
Prokaryotic DNA has telomeres.
What would occur if the lost DNA sequences were part of an important gene?
What would occur if the lost DNA sequences were part of an important gene?
Flashcards
3' end of DNA
3' end of DNA
The 3' end of a DNA strand where nucleotides are added during DNA replication.
Antiparallel DNA replication
Antiparallel DNA replication
DNA polymerase can only add nucleotides to the 3' end of a DNA strand, resulting in a continuous leading strand and a discontinuous lagging strand.
RNA primers
RNA primers
Short sequences of RNA that initiate DNA synthesis by DNA polymerase.
Primer replacement
Primer replacement
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DNA Ligase
DNA Ligase
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Telomeres
Telomeres
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Loss of DNA during replication
Loss of DNA during replication
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DNA structure in prokaryotes and eukaryotes
DNA structure in prokaryotes and eukaryotes
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What are telomeres?
What are telomeres?
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What happens to telomeres as we age?
What happens to telomeres as we age?
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What is the Hayflick Limit?
What is the Hayflick Limit?
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What is telomerase?
What is telomerase?
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Why are telomeres important for DNA replication?
Why are telomeres important for DNA replication?
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Study Notes
DNA Replication
- DNA polymerase adds nucleotides to the 3' end of a DNA strand
- This results in a continuous leading strand and a discontinuous lagging strand
- DNA polymerase needs an RNA primer to start a new strand
- RNA primers are unstable and are replaced with DNA
- DNA ligase joins DNA fragments to form a continuous strand
- At the end of the lagging strand the RNA primer isn't replaced, resulting in a loss of DNA
- This occurs at the end of every replication cycle, shortening DNA
DNA Replication Forks
- Prokaryotes have circular DNA with a single origin of replication
- Eukaryotes have linear DNA with multiple origins of replication
- Okazaki fragments are short DNA segments synthesized on the lagging strand
- Replication forks are formed during DNA replication
Telomeres
- Telomeres are repetitive nucleotide sequences at the ends of chromosomes
- They protect chromosomes from deterioration
- Sacrificial bases that don't code for anything
- They are essential for eukaryotes with linear DNA
- Not present in prokaryotes with circular chromosomes
Telomere Length and Aging
- Telomere length shortens with age
- Humans have AGGGTT sequences about 2500 times repeated
- At birth, telomeres are about 11,000 bases in length
- Telomere length decreases with age to fewer than 4000 bases
- Shortened telomere length leads to a limited number of cell divisions (Hayflick limit)
Telomerase
- Telomerase is an enzyme that replaces lost telomere sequences
- It is expressed in early embryos and embryonic stem cells
- Also expressed in adult stem cells and cancer cells
- Telomerase gives these cells the potential for immortality
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