Step 1 First Aid - Biochemistry Questions and Correct Detailed Answers (Verified Answers) ||Already Graded A+||Newest Version

Step 1 First Aid - Biochemistry Questions and
Correct Detailed Answers (Verified Answers)
||Already Graded A+||Newest Version
Quiz: Chromatin structure

Ans: Negatively charged DNA loops twice around histone octamer (2 each of the positively
charged H2A, H2B, H3, and H4) to form nucleosome bead. H1 ties nucleosomes together in
a string. (Think of "beads on a string"; H1 is the only histone that is not in the nucleosome
core.) In mitosis, DNA condenses to form mitotic chromosomes. <img src="66a -
Euchramatin strxr.JPG" />



Quiz:Heterochromatin

Ans: Condensed, transcriptionally inactive ("H eteroC hromatin = H ighly C ondensed.")



Quiz:Euchromatin

Ans: Less condensed, transcriptionally active (Eu = true, "truly transcribed")



Quiz:Purines

Ans: A, G 2 Rings ("PUR e A s G old = PUR ines") <img src="67b - Purine strxr.JPG" />



Quiz:Pyrimidines

Ans: C, T, U 1 ring ("CUT the PY (pie): PY rimidines") <img src="67c - Pyrimidine strxr.JPG"
/>



Quiz:Functional groups of the nucleosides


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in the number given.

, Ans: Guanine has a ketone. Thy mine has a methy l. Deamination of cytosine makes uracil.



Quiz:Base differences btw RNA and DNA

Ans: Uracil is found in RNA; Thymine in DNA



Quiz:Base pair bonds

Ans: G-C bond (3 H-bonds) is stronger than A-T bond (2 H-bonds). Incr G-C content --<
higher melting temperature.



Quiz:AA's necessary for purine synthesis

Ans: G lycine A spartate G lutamine



Quiz:Nucleoside

Ans: Base + ribose



Quiz:Nucleotide

Ans: Base + ribose + phosphate; linked by 3'-5' phosphodiester bond.



Quiz:Purines are made from...?

Ans: IMP precursor (see bottom/right) <img src="68a - Nucleotide synthesis.JPG" />



Quiz:Pyrimidines are made from...?




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in the number given.

, Ans: Orotate precursor, with PRPP added later. <img src="68a - Nucleotide synthesis.JPG"
/>



Quiz:Deoxyribonucleotide synthesis

Ans: Ribonucleotides are synthesized first and are converted to deoxyribonucleotides by
ribonucleotide reductase. <img src="68a - Nucleotide synthesis.JPG" />



Quiz:ABX and anti-neoplastic drugs that function by interfering w/ nucleotide synthesis (list)

Ans: Hydroxyurea 6-mercaptopurine 5-fluorouracil Methotrexate Trimethoprim



Quiz:Hydroxyurea

Ans: Inhibits ribonucleotide reductase. <img src="68a - Nucleotide synthesis.JPG" />



Quiz:6-mercaptopurine (6-MP)

Ans: Blocks de novo purine synthesis. <img src="68a - Nucleotide synthesis.JPG" />



Quiz:5-Fluorouracil (5-FU)

Ans: Inhibits thymidilate synthase (decr dTMP). <img src="68a - Nucleotide synthesis.JPG"
/>



Quiz:Methotrexate

Ans: Inhibits dihydrofolate reductase (decr dTMP) <img src="68a - Nucleotide
synthesis.JPG" />



Quiz:Trimethoprim
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in the number given.

, Ans: Inhibits bacterial dihydrofolate reductase (decr dTMP) <img src="68a - Nucleotide
synthesis.JPG" />



Quiz:Transition vs. transversion

Ans: Transition: Substituting purine for purine or pyrimidine for pyrimidine ("TransI tion =
I dentical type") Transversion: Substituting purine for pyrimidine or vice versa ("TransV
ersion = conV ersion btw types")



Quiz:Genetic code: unambiguous

Ans: Each codon specifies only 1 AA.



Quiz:Genetic code: degenerate/redundant

Ans: < 1 codon may code for the same AA. (Methionine is encoded by 1 codon: AUG)



Quiz:Genetic code: Commaless, nonoverlapping

Ans: Read from a fixed starting point as a continuous sequence of bases. *some viruses
are an exception.



Quiz:Genetic code: universal

Ans: Genetic code is conserved throughout evolution. *exceptions include mitochondria,
archaebacteria, Mycoplasma , and some yeasts



Quiz:Silent mutation

Ans: Same AA, often base change in 3rd position of codon (tRNA wobble)


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in the number given.