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USMLE-1 ENZYMES
| Question | Answer |
|---|---|
| Which enzyme is responsible for unwinding the DNA template at the replication fork? | Helicase |
| Which enzyme is responsible for relaxing the DNA strand by creating single- or double-stranded breaks in the DNA helix to add/remove supercoils? | Topoisomerase |
| What is another name for prokaryotic topoisomerase II? | DNA gyrase |
| What class of drugs inhibits prokaryotic topoisomerase II and topoisomerase IV? | fluoroquinolones |
| What chemotherapeutic drugs (2) inhibit eukaryotic topoisomerase II? | etoposide/teniposide |
| Which enzyme is responsible for making an RNA primer on which DNA polymerase III can initiate replication (prokaryotes)? | Primase |
| Which enzyme is responsible for elongating the DNA strand? | DNA polymerase (specifically, DNA polymerase III in prokaryotes) |
| ————— must see a RNA primer to bind, which is complementary and antiparallel to the polymerase | DNA polymerase |
| DNA/RNA polymerase always read in the ————- direction | 3' to 5' |
| DNA/RNA polymerase always build in the —————-direction | 5' to 3' |
| DNA polymerase pauses and checks ("proof-reads") via | 3' -> 5' exonuclease activity |
| Which enzymes are responsible for removing the RNA primer in eukaryotes? | RNase H and FEN-1 |
| Which enzyme catalyzes the formation of a phosphodiester bond between Okazaki fragments? | DNA ligase |
| The enzyme which adds TTAGGG::sequence to 3' ends of chromosomes to avoid loss of genetic material with every duplication is known as | Telomerase |
| Which replication enzyme is a RNA-dependent DNA polymerase, and thus a major example of reverse transcriptase activity, in humans? | Telomerase |
| Telomerase is a rare example where ——————activity occurs endogenously in humans | reverse transcriptase enzyme activity |
| What pathology is associated with increased telomerase activity? | Cancer |
| What pathology is associated with decreased telomerase activity? | progeria (premature aging) |
| ———— doesn't have to see a RNA primer to bind | RNA polymerase |
| Does RNA polymerase have 3' exonuclease activity (proof-reading)? | No |
| Lac Operon: In the presence of low glucose, there is increased ——— activity, leading to an increase in ——— | adenylyl cyclase, cAMP |
| The enzyme that recognizes and excises pyrimidine dimer mutations is | excision endonuclease |
| The enzymes that repair pyrimidine dimer mutations are: | DNA polymerase and DNA ligase |
| Recognition and facilitation of excision of mismatched nucleotides occur via enzymes found on two genes: | MSH2 (MutS) or MLH1 (MutL) |
| The enzymes that repair mismatched base mutations are | DNA polymerase and DNA ligase |
| What pathology is characterized by a deficiency of the enzymes used in mismatch base repair? | Lynch syndrome (hereditary nonpolyposis colorectal cancer [HNPCC]) |
| In base excision repair, base-specific ——— remove the altered base and create an ————— | glycosylases, AP (apurinic/apyrimidinic) site |
| Which base excision repair enzyme is responsible for removing nucleotides at the 5' end? | AP-endonuclease |
| Which base excision repair enzyme is responsible for removing nucleotides at the 3' end? | Lyase |
| Which base excision repair enzymes are responsible for filling and sealing the gap from the excised bases? | DNA polymerase-β::specific (filling) and DNA ligase III::specific (sealing) |
| Does reverse transcriptase require a primer? | Yes! Because it is a DNA polymerase (RNA dependent DNA polymerase) |
| While DNA polymerase binds to a primer, RNA polymerase binds to a ——— | promoter |
| In eukaryotes, each gene has it's own promoter, to which ——— may bind | RNA polymerase II |
| Enhancers increase transcription via enhanced activity of the enzyme ——— | RNA polymerase II |
| RNA polymerase I makes ———, RNA polymerase II makes ——— and RNA polymerase III makes ——— | tRNA and 5S rRNA |
| In eukaryotes, RNA polymerase II may be inhibited by ————— | α-amanitin |
| What drug is an inhibitor of prokaryotic RNA polymerase? | Rifampin |
| What drug is an inhibitor of both prokaryotic AND eukaryotic RNA polymerase? | Actinomycin D |
| How many different RNA polymerases do prokaryotes have? | One (makes all 3 kinds of RNA) |
| Does Poly-A polymerase require a template (post-transcriptional processing)? | No |
| tRNA is joined with its specific amino acid via the enzyme ———- | aminoacyl-tRNA synthetase |
| Aminoacyl-tRNA synthetase requires ——- and releases inorganic PPi | ATP |
| Aminoacyl-tRNA synthetase and binding of charged tRNA to the codon are responsible for ———of amino acid selection | accuracy |
| Peptide bond formation is facilitated by the ribozyme | peptidyl transferase |
| After aminoacyl-tRNA binds to the A site of the ribosome, —————-, a ribozyme, catalyzes peptide bond formation (translation) | peptidyl transferase |
| Which enzyme phosphorylates mannose in the Golgi apparatus, facilitating protein trafficking? | Phosphotransferase |
| What pathology is associated with a defect in the enzyme N-acetylglucosaminyl-1-phosphotransferase? | I-cell disease (inclusion cell disease/mucolipidosis type II) |
| I-cell disease is characterized by high plasma levels of | lysosomal enzymes |
| Formation of lysine-hydroxylysine cross-linkages (collagen synthesis) requires both: | copper and the enzyme lysyl oxidase |
| The defective Menkes protein (Menkes disease) leads to decreased activity of the enzyme —— | lysyl oxidase |
| Elastin is broken down by the enzyme ————, which is normally inhibited by ————- | elastase, α1-antitrypsin |
| Emphysema may be caused by an α1-antitrypsin deficiency, resulting in excess ————- activity in alveoli | elastase |
| What class of enzymes cleaves nucleotides at the ends of a DNA strand? | Exonucleases |
| What class of enzymes cleaves nucleotides in the middle of a DNA strand? | Endonucleases |
| Cloning: Isolated mRNA is exposed to —————— to produce cDNA (lacks introns) | reverse transcriptase |
| In the final step of PCR, heat-stable —————- elongates the DNA sequence following each primer | Taq DNA polymerase |
| How many primers are needed for polymerase chain reaction (PCR)? | Two (one for the 3' end of each DNA strand) |
| In eukaryotes, RNA polymerase II may be inhibited by ————— | α-amanitin |
| Recognition and facilitation of excision of mismatched nucleotides occur via enzymes found on two genes: | MSH2 (MutS) or MLH1 (MutL) |
Created by:
AminNehreer
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