BIOCHEM 501: Clicker questions part 4
31 Cards in this Set
| Front | Back |
|---|---|
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Phosphoryl transfer reactions are initiated by a ______, which is a _______.
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Hydroxyl
Nucleophilic
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What makes a sequence more likely to melt at a lower temperature?
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More A-Ts and shorter
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What amino acid is necessary for recombinases?
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Serine or tyrosine (Something with a hydroxyl)
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Topoisomerases use what amino acidx to break wwhat bonds in a double helix?
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Tyrosine,
Covalent bonds
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Why is AMP necessary with DNA ligase?
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Because o- is a bad leaving group and cannot seal itself
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How does tautomerization affect hydrogen bonds that thyine can form
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It switchs the n group from a donor to acceptor
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What coponent(s of DNA polymerase are critical for replication fidelity?
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Aspartates that coordinate Mg++ because activates C3'OH to catylize nucleotide addition
AND 3'5' exonulcease b/c it is critical for replicaton fidelity
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Methyltion of cytosine at c'5 position wiill result in a mutation- true or faulse?
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Faulse
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DNA glycosylase cleaves the bond between what parts? What type of bond does it cleave
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Base and ribose
glycosidic bond
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If cells lack glycosylase what mutations cannot be repaired/ What repair system cant continue?
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Deaminated nucleotides
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What exonuclease generates the 3' overhang?
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5'-3' exonuclease
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Do serine recombinases generate holliday junctions?
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no they do not b/c they cut both bonds at once
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Does DNA melting change topology?
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No
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AZT which kinda looks like a base is used to combat HIV, how does it block replication?
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Lacks 3'oh necessary for nucleotide addition
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Hoe do b-galactosidase levels change when cells are switched from glucose to lactose?
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Little B-glac is in glucose media, but levels increase when they are switched to lactose
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When you add glucose to cells, a gene expression decreases. How does glucose regulate expression of this gene?
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Glucose activates a repressor protein
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What amino acid can make sequence specific contact with DNA?
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Lysine due to the positive charge on the NH3+
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Do histone proteins make sequence specific contact with DNA?
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No, they don't contact nucleotide bases
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What amino acids are enriched in hsitone proteins?
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Basic AAs- lys, arg, his
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Could single strand DNA be spliced by a spliceosome?
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No because the first step involves using an OH which is only found in RNA not DNA
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X rays creat a double standed break in DNA how are double stranded breaks repaired?
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Homologous recombination
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Four nucleotides can generate 64 codons how many tRNA would cells need if tRNA did not form a wobble base pair?
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61 b/c woble means the cell needs fewer than 61 tRNAs
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How is deamination o a DNA base repaired?
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Base excision repair
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Where is the start of translation?
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between the 5' UTR and the coding region
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an mRNA transcript has many AUGs how is the start one found?
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base pair interactions between mRNA and rRNA
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Does changing cytosine to 5 methyl cytosine affect h bonding
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doesnt affect it
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What does the 3' to 5' exonuclease recognize?
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3' misincorporated nucleotides that fail to base pair with the template during DNA synthesis
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What does mRNA 3' end processing involve?
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A protein recognition of an RNA sequence
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Which hydroxyl groups do mRNA intron removal associated phosphoryl transfer chemistry?
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2' and 3'
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DNA litigation involves what type of chemistry?
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Phosphoryl transfer chemistry
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Do both serine and tyrosine recombinases utilize double stranded DNA?
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No
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BIOCHEM 501: Practice Exam