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35 Cards in this Set

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DNA polymerase III (PolC)

functions
DNA synthesis
Multi-proteins complex
3' --> 5' proofreading exonuclease activity
primase
makes RNA primers
DNA gyrase
relieves supercoiling
DNA ligase
seals gaps in DNA strands
Cells that are defective for MMR show mutations rates of ____ times higher than normal and said to have ______ phenotype
-100-1000 times higher than normal

-mutator phenotype
what is the major post-replicaiton DNA repair system?
Mismatch repair
How does MMR work?
1. Uses DNA METHYLATION for strand discrimination between the methylated template (old) strand is distinguished from the unmethylated (new) strand.

2. Corrects the error in the unmethylated strand

3. Replaces up to several thousand baases of DNA around the error
How Bases excision repair works?
1. a damaged or inappropriate base is removed from its sugar linkage by a GLYCOSYLASE ENZYME which cut the base-sugar bond

2. the AP ENDONUCLEASE then removes the remainder of the damaged nucleotide

3. DNA polymerase and ligase repair the missing base
what is the major repair DNA repair system in mammals
Nucleotide excision repair
How Nucleotide excision repair works?
1. Recognizes DNA damage which is "bulky" and creates a block of DNA replication and transcription

2. Cleaves DNA strand containing the damage by ENDONUCLEASES on either side of damage followed by EXONUCLEASE removal of a short segment containing the damaged region (~ 30 bases in mammals)

3. DNA polymerase fills in the gaps
know the two enzymes involved in homologous recombination
RecA and RecBCD
role of RecA
-Pairing of two DNAs

-Formation of Holliday intermediates

-Branch migration

-Forms long, multiprotein helical filaments on the DNA strand
role of RecBCD enzyme complex
-helps initiate homologous recombination

-helicase (unwinding) and nuclease activities

-Recognizes Chi sites:
5' GCTGGTGG 3'
know the two enzymes involved in homologous recombination
RecA and RecBCD
role of RecA
-Pairing of two DNAs

-Formation of Holliday intermediates

-Branch migration

-Forms long, multiprotein helical filaments on the DNA strand
role of RecBCD enzyme complex
-helps initiate homologous recombination

-helicase (unwinding) and nuclease activities

-Recognizes Chi sites:
5' GCTGGTGG 3'
Used by bacteriophages (phages, bacterial viruses) to integrate their DNA into the bacterial DNA
Site-specific recombination
Recombinase aka?
Integrase
Role of Site-specific recombination
-Recombination occurs at a SPECIFIC DNA SEQUENCE that is shared by two molecules (homologous recombination can occur at any shared sequence)

-Can mediate DNA integrase and excision as well as DNA INVERSION

-Mediated by an enzyme (RECOMBINASE) that recognizes that specific sequence

-DOES NOT REQUIRE RecA
Two types of transposition?
-Simple transposition

-Replicative transposition
Simple transpostion
"cut and paste" method

leaves a double-strand break in donor strand that must be repaired
Replicative transposition
-Proceeds via formation of a cointegate intermediate

-Donor and recipient both end up with copies of the transposon
____ elements are often associated with antibotic resistance
Mobile DNA elements
Transposons
encode the protein that mediates transposion: transposase enzyme

-targets DNA sequence is duplicated when the transposon inserts itself
What are the multiple tasks in the cell homologous recombination is used for?
1. DNA Repair

2. Restarting of stalled replication forks

3. Generation of genetic diversity during meiosis

4. DNA Replication

5. Generation of antibody diversity
Flucytosine (5-fluorocytosine) target?
Antifungal agent (interfere with nucleotide synthesis)
Adensosine arabinoside target?
Antiviral (Interferance with nucleotide synthesis)
Zidovudine (AZT) target?
Anti-HIV-1 (reverse transcriptase inhibitor)

(Interference with Nucleotide Synthesis
Rifamycin target?
antibiotic

-inhibition of DNA-Directed DNA Polymerase
Ciprofloxacin target?
DNA gyrase inhibitor

-inhibition of DNA Replication
Flucytosine (5-fluorocytosine) target?
Antifungal agent (interfere with nucleotide synthesis)
Adensosine arabinoside target?
Antiviral (Interferance with nucleotide synthesis)
Zidovudine (AZT) target?
Anti-HIV-1 (reverse transcriptase inhibitor)

(Interference with Nucleotide Synthesis
Rifamycin target?
antibiotic

-inhibition of DNA-Directed DNA Polymerase
Ciprofloxacin target?
DNA gyrase inhibitor

-inhibition of DNA Replication