Module 2 Termination & Repair Flashcards
In prokaryotes, replication is complete when _____ after replicating their portion of the circular DNA
In eukaryotes, many _____ fuse to become larger until it reaches the ends of the chromosomes the ____
two replication forks meet
replicons
telomeres
Chromosomal end must be repaired. The enzyme ____ prevents shortening of lagging strands during replication. It is an RNA-directed DNA polymerase, or in other words a _____
A protein component is _____, an enzyme that can make DNA copies from RNA templates
Telomerase
ribonucleoprotein
reverse transcriptase
The ends remain unpaired as there is no place for a primer to be made. They get shorter with every division.
The end of linear chromosomes are _____, which protect the genes from getting deleted.
_____ six base pair sequence repeated 100 to 1000 times
telomeres
TTAGGG
Telomerase is active in ____ and ____ but not in ____
_____ received the Nobel Prize for _____
Germ cells
Adult Stem cells
Adult Somatic cells
Elizabeth Blackburn
Nobel Prize for Medicine and Physiology in 2009
Telomerase-deficient mice had (4)
tissue atrophy
stem cell depletion
organ system failure
impaired tissue injury responses
Fidelity of DNA replication is due to three activities:
Accurate selection of ____
Immediate _____
_____ repair
Accurate selection of nucleotides
Immediate proofreading
Postreplicative mismatch repair
There are _____ genes whose products participate in DNA repair. Fialure to repair DNA leads to a _____
130 genes
mutation
Types of DNA Damage or lesion
1) _____ The loss of an amino group. Like a C converted to a U
2) ______ of the normal bases because of failure to proofread. Like U instead of T
3) ____. Which could be single ____ or _____
The frequent cause is ____ and ____
4)____ can be formed between bases.
Chemotherapeutic drugs can crosslink DNA.
Either same strand _____ or opposite strand _____
Deamination
Mismatch
Breaks in backbone
Single-stranded Break
Double-stranded Break
Crosslinks covalent linkages
Intrastrand
Interstrand
Other lesions:
_____ Removal of purines by acid and heat; removal of altered bases by DNA glycolysis
_____ ionizing radiation, alkylating agents
_____ proofreading of incorrectly incorporated bases
____ Intercalating agents cause addition or loss of nucleotide
_____ Cyclotubyl dimers resulting from UV irradiation
_____ Breakage of phosphodiester bonds by ionizing radiation ot chemicals
_____ covalent linkage of two strands by alkylating agents
______ Disruption of structure by free radicals
Missing base
Altered base
Incorrect base
Bulge due to deletion or insertion
Linked Pyrimidines
Single or doube-strand breaks
Cross-linked strands
3’ - deoxyribose fragments
Agents that damage DNA:
Certain wavelengths of ____:
- Ionizing like _____ and ___
- longer-wavelength ____ (260 nm)
Highly-reactive ____ produced during cellular respiration
Chemicals in the environment like _____ in cigarette smole
Also chemicals used in _____
radiation
gamma rays & x rays
UV-C 260 nm
oxygen radicals
hydrocarbons
chemotherapy
Types of DNA DAMAGE:
______
A) UV light induces formation of pyrimidine dimers and joined by cyclobutane ring
B) Alkylation or addition of methyl or ethly groups
C) Carcinogens add bulky chemical groups
INDUCED
Types of DNA DAMAGE:
______
A) deamination of bases
b) depurination (loss) resulting to a cleavage
SPONTANEOUS
Mechanisms of DNA repair:
General classes:
______ chemical reation responsible for DNA damage
______ removal of damaged bases and synthesis of replacement
direct reversal
Excision reversal
Three types of excision repair:
______
cause:_____
uses:_____,____
DNA repair mechanism that corrects damaged or altered bases by excising the specific damaged base, using specific glycosylases.
The gap is then filled with the correct nucleotide sequence by the action of DNA polymerase and ligase, restoring the integrity of the DNA.
Base Excision Repair (BER)
Radicals, radiation, chemo
DNA glycosylase
AP endonuclease
Three types of excision repair:
______
cause: ______
uses: ______
addresses a wider range of DNA damage, including bulky lesions and thymine dimers.
a stretch of nucleotides containing the damaged site is excised, and the gap is filled in through the action of DNA polymerase and ligase, ensuring the removal and repair of a larger segment of damaged DNA.
Nucleotide Excision Repair (NER)
UV light, hydrocarbons
Excision nuclease 30 gap
