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91 Cards in this Set
- Front
- Back
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What are the charges of DNA and histones?
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DNA is negative
Histones are positive |
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What is a nucleasome?
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2 loops of DNA around a histone octamer
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What is unique about H1?
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only histone not part of nucleosome
links nucleosome beads in a string |
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What is heterochoromatin?
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HeteroChromatin = Highly Condensed
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What are the methylated nucleotides (2)?
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cytosine, adenine
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What is the function of methylation in DNA replication?
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distinguishes template (methylated) strand from new strand
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What is the purpose of hypermethylation?
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inactivates DNA from transcription
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What is accomplished with histone acetylation?
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Acetylation --> Active DNA
relaxes coiling for transcription |
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purines
# of rings? |
adenine, guanine
PUR As Gold 2 rings |
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pyrimidines
# of rings? |
CUT the PY
cytosine, uracil, thymine 1 ring |
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which nucleotide bond is stronger?
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G-C bond is stronger than A-T
3 H-bonds vs. 2 H-bonds |
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What are the components of a nucleoside?
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base + ribose
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What are the components of a nucleotide?
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base + ribose + phosphate
3'-5' phosphodiester bond |
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What are key features of purine synthesis?
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start w/ sugar + phosphate (PRPP)
add base |
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What are key features of pyrimidine synthesis?
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temporary base: orotic acid
add sugar + phosphate (PRPP) modify base |
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pryimidine production requirement (1)
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aspartate
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purine production or reuse requirements (4)
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aspartate
glycine glutamine THF |
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What is done by ribonucleotide reductase?
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converts ribonucleotides --> deoxyribonucleotides
(UDP to dUDP) |
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Which pathways have carbamoyl phosphate? (2)
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1. de novo pyrimidine synthesis
2. urea cycle |
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What occurs with ornitine transcarbamoylase deficiency?
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OTC is in urea cycle
deficiency --> accumulated carbamoyl phosphate converted to orotic acid in pyrimidine synthesis pathway |
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How does hydroxyurea work?
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antineoplastic drug
inhibits ribonucleotide reductase |
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What is the function and mechanism of 6-mercaptopurine?
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immunosupressive drug
blocks de novo purine synthesis |
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What are the function and mechanism of 5-fluorouracil?
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antineoplastic
inhibits thymidylate synthase (decreases dTMP) |
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What does thymidylate synthase do?
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converts dUMP to dTMP in pyrimidine synthesis
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What is the function and mechanism of methotrexate?
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antineoplastic drug
inhibits dihydrofolate reductase (lowers dTMP) |
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What does dihydrofolate reductase do?
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converts DHF to THF for use in conversion of dUMP to dTMP
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What is the function and mechanism of trimethoprim?
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antibiotic drug
inhibits bacterial dihydrofolate reductase (lowers dTMP) |
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What is orotic aciduria?
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inability to convert orotic acid to UMP
autosomal recessive |
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What are the causes of orotic aciduria? (2 possible enzyme defects)
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orotic acid phosphoribosyltransferase
orotidine 5'-phosphate decarboxylase |
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What are the features of orotic aciduria?
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orotic acid in urine
megaloblastic anemia (unresponsive to B12 or folic acid) failure to thrive |
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What is the treatment for orotic aciduria?
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oral uridine
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What are features of ornitine transcarbamylase (OTC) deficiency?
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increased orotic acid AND hyperammonemia
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What occurs in adenosine deaminase deficiency?
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--> SCID
excess ATP and dATP imbalances nucleotide pool --> inhibition of ribonucleotide reductase low lymphocyte count |
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What does adenosine deaminase do?
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in purine salvage pathway
converts adenosine to inosine |
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What causes Lesch-Nyhan syndrome?
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absense of HGPRT in purine salvage pathway
X-linked recessive excess uric acid and de novo purine synthesis |
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What are the features of Lesch-Nyhan syndrome?
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retardation
self-mutilation agression hyperuricemia gout choreoathetosis |
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What is choreoathetosis?
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involuntary movements with chorea (migrating contractions) and athetosis (twisting and writhing)
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What are the 2 non-redundant codons?
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AUG: methionine (START)
UGG: tryptophan |
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What organisms can have genetic code that is NOT commaless/nonoverlapping?
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some viruses
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What are the origin points for eukaryotic DNA replication?
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consensus sequences
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What do single-stranded binding proteins do?
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prevent strands from reannealing during replication
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What do DNA topoisomerases do?
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create nicks in DNA helix to relieve torsion/supercoils during replication
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What is DNA gyrase?
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prokaryotic topoisomerase II
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What is the function and mechanism of fluoroquinolones?
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antibiotics
inhibit DNA gyrase |
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What is the function of primase?
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makes RNA primer for DNA polymerase III to initiate replication on the lagging strand
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What does DNA pol III do?
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prokaryotic
elongates leading and lagging strands (latter up to RNA primer) |
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Which DNA pol has 3'-->5' exonuclease activity for proofreading?
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DNA pol III
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What does DNA pol I do?
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prokaryotic
degrades RNA primer and fills gap with DNA |
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What does DNA ligase do?
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seals link between Okazaki fragments
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Where does telomerase add DNA?
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the 3' end of chromosomes
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What is the end replication problem?
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The last RNA primer on the end of the lagging strand can't be converted to DNA, so it is degraded and the new chromosome is shorter
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How does nucleotide excision repair work?
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endonucleases release oligonucleotide with damaged bases
DNA pol and ligase fill and reseal the gap |
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What causes xeroderma pigmentosum?
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mutation hampers nucleotide excision repair
thymidine dimers cannot be repaired after UV light exposure |
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How does base excision repair work?
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glycosylases recognize and remove damaged bases
AP endonuclease cuts at apyrimidinic site empty sugar is removed and gap is filled and resealed |
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What is base excision repair important for?
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spontaneous/toxic deamination
|
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How does mismatch repair work?
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unmethylated daughter strand is recognized
mismatched nucleotides are removed gap is filled and resealed |
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What causes HNPCC?
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a mutation hampering mismatch repair
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How does nonhomogynous end joining work?
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joins 2 ends of dsDNA framents
homology is not required |
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What causes ataxia telangiectasia?
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a mutation preventing nonhomologous end joining
|
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What are the features of ataxia telangiectasia?
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ataxia
telangectasias X-ray hypersensitivity lymphomas |
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Why is DNA synthesized 5' to 3'?
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Incoming 5' bears the triphosphate bond (energy source for the reaction) that is attacked by the 3' OH group
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What is the direction of protein synthesis?
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N to C
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What are the mRNA start codons?
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AUG (and rarely GUG)
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How is the starting methionine different in prokaryotes?
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It's formyl-methionine (f-Met)
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What are the 3 stop codons?
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UGA (U Go Away)
UAA (U Are Away) UAG (U Are Gone...betch) |
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Where are CAAT and TATA boxes located?
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In the promotoer
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What occurs at the promoter?
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RNA pol and transcription factors bind
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What does RNA pol I do?
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Makes rRNA
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What does RNA pol II do?
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Makes mRNA; opens DNA at the promoter site
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What does RNA pol III do?
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Makes tRNA
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What does alpha-amanitin (from death-cap mushrooms) do?
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Inhibits RNA pol II --> liver failure
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How is RNA processed before leaving the nucleus? ( 3 steps)
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Capping of 5'end
Polyadenylation of 3' end Splicing |
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What is added to the 5' end of mRNA in the cytosol?
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7-methylguanosine
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What is the polyadenylation signal?
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AAUAA
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What is unique about poly-A polymerase?
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It doesn't require a template
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How is pre-mRNA spliced?
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The transcript combines with snRNPs --> spliceosome
Lariat intermediate generated and released |
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What RNA processing proteins do patients with lupus make antibodies to?
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snRNPs
|
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How does the Lac operon repressor work?
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The repressor is bound to the operator by default
Lactose binds and inhibits it, allowing expression of lactase |
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How is the Lac operon promoted?
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Catabolite activator protein (CAP) upregulated by cAMP binds its site and helps RNA pol bind the promoter
Glucose inhibits cAMP and the CAP |
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What nucleotide sequence is present at the 3' end of all tRNAs?
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CCA - Can Carry Amino acids
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How do tetracyclines work?
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Bind 30S rRNA subunit and inhibit the attachment of aminoacyl-tRNA
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What are the eukaryotic ribosomal subunits?
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40S + 60S --> 80S
Eukaryotic = EVEN |
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What are the prokaryotic ribisomal subunits?
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30S + 50S --> 70S
ODD |
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What does ATP do to tRNA?
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ATP is Activation
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What does GTP do to tRNA?
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GTP Grips and Goes (translocates)
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What occurs at each ribosomal site during protein synthesis?
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A: receives all AA-tRNAs (except for initiatory methionine)
P: hold the growing Peptide E: the Exit site for tRNA |
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How do aminoglycosides work?
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Bind 30S and inhibit initiation complex formation
Cause mRNA misreads |
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How does chloramphenicol work?
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Inhibits 50S peptidyltransferase and peptide bond formation
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How do macrolides work?
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They block translocation of peptidyl RNA to the P site
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How does clindamycin work?
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Inhibits peptide bond formation
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What does ubiquitin do?
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Binds defective proteins, tagging them for proteosomal degradation
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