DNA Replication and Repair Flashcards
What is chromatin?
DNA
Histones
Non-histone proteins
What are the types of histones and their functions?
H1 - links
Cores: H2A, H2B, H3, H4
What is a nucleosome?
Basic unit of DNA organization around histone octomer
What is a histone octomer?
Two of each of the 4 core histones
What is the interphase chromosome?
Nucleosomes arranged for transcription, replication and repair
What is the mitotic chromosome?
Chromatin is condensed for cell division
What is a telomere?
Caps at ends to prevent deterioration
TTAGGG repeated
What is a centromere?
Noncoding DNA that binds to mitotic spindle with satellite DNA sequences
What are the two types of chromatin?
Heterochromatin - condensed
Euchromatin - dispersed
What are the two types of heterochromatin?
Constitutive - always condensed
Facultative - can be condensed or as euchromatin
When does DNA replication occur?
In the S phase of the cell cycle
What are the requirements for DNA replication?
Template DNA
Free deoxyribonucleotides
Unwinding by helicase
RNA primer
What initiates replication?
RNA primer by DNA primase
-Used multiple times on lagging strand
What are the functions of DNA polymerase?
DNA elongation
Proofreading and correction
What removes RNA primers?
DNA polymerase I in prokaryotes
RNase H in eukaryotes
How are DNA strands resealed?
DNA ligase
What is the function of topoisomerases?
Unwind supercoiling and any tangles ahead of replication fork
What are the DNA polymerases in prokaryotes and its functions?
DNA pol I - RNase activity and fills in gap left
DNA pol II - repair
DNA pol III - elongation
What are the types and functions of DNA pol in eukaryotes?
DNA pol alpha - synthesis of short fragments from primer - Okazaki
DNA pol gamma - mitochondrial DNA replication
DNA pol delta and epsilon - elongation from pol alpha
What are the properties topoisomerase type I?
Cleaves one strand of DNA
ATP not required
What are the properties of topoisomerase type II?
Cleaves both strands of DNA
Requires ATP
What is the role of telomerase?
Adds telomeres using RNA template
Not expressed in most cells
What are 5 causes of DNA damage?
Replication errors
Spontaneous
Chemical
Reactive oxygen species
Radiation (UV and ionizing)
What are three types of DNA damage?
Single base
Two base
Strand breaks
What are 5 repair pathways?
Base excision
Nucleotide excision
Nonhomologous end joining
Homologous recombination
Mismatch repair
What is the general mechanism for DNA repair?
Recognition
Excision
Replacement
Ligation
What are the types of single base damages?
Incorrect base pairing
Alteration of bases (chemical changes or deamination)
Deletion of bases
Insertion of extra nucleotides
What is base excision repair?
2 step removal of damaged base
-base removed
-sugar removed
DNA pol adds new nucleotide
Nick sealed by DNA ligase
What are the types of two base alteration?
UV light causing thymine-thymine or C-C or C-T
Two base alteration - crosslinking
-interstrand or intrastrand
What type of DNA damage occurs with bulky adducts?
Cause kinks in DNA structure
What is nucleotide excision repair?
Remove section of one strand and replace
What is non-homologous end joining?
Double-stranded staggered break with loss of some nucleotides before ends are rejoined
Error prone
What is homologous recombination?
Occurs after replication
Double-stranded break with nucleotide loss, but repaired using information for sister chromatid
