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