11.4 Flashcards
Eukaryotic replication
Basic components/ mechanism similar to prokaryotic situation
-complicated by larger amount of DNA and multiple chromosomes
Telomeres
-Specialized structures found at ends of eukaryotic chromosomes
-composed of short repeated DNA sequences
-protect ends from nucleases and maintains chromosome integrity
Replicating the end of linear DNA
-leading strand can be replicated to the end
- but no way to replace primer with DNA
-unable to replicate last section of lagging strand
- gradual shortening of chromosome with each round of cell division
Telomerase
Allows for replication of lagging strand ends
• Contains RNA template (matches repeating sequence)
• Synthesizes last segment of DNA connnection between senescence (cell aging)
telomere length
• Expressed in embryos and childhood
• Not expressed in adults (except in stem cells)
Cancer cells generally show activation of telomerase
Multiple dna repair mechanisms
Mistakes
Mutagens
Mistakes
May occur during replication
-DNA polymerase has “proofreading” ability
-some mistakes remain and maintain genetic variation
Mutagens (radiation and chemicals)
Increase number of mutation above background level
Specific repair
Targets a single type of DNA damage and repairs only that damage
Nonspecific repair
Use a single mechanism to repair multiple types of DNA damage
Photorepair removes thymine dimers
UV light induces thymine dimers
-covalent link of adjacent thymine bases
Photorepair by photolyase
-absorbs light in visible range
-uses energy to cleave thymine dimer
Excision repair
Nonspecific repair mechanism
• Damaged region removed and replaced
• Steps:
1. Recognition of damage
2. Removal of the damaged region
3. Re-synthesis using the information on the undamaged strand as a template
