First Aid – Biochemistry Test And Answers.

Chromatin structure - AnswerNegatively 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" / Heterochromatin - AnswerCondensed, transcriptionally inactive ("H eteroC hromatin = H ighly C ondensed.") Euchromatin - AnswerLess condensed, transcriptionally active (Eu = true, "truly transcribed") Purines - AnswerA, G 2 Rings ("PUR e A s G old = PUR ines") img src="67b - Purine strxr.JPG" / Pyrimidines - AnswerC, T, U 1 ring ("CUT the PY (pie): PY rimidines") img src="67c - Pyrimidine strxr.JPG" / Functional groups of the nucleosides - AnswerGuanine has a ketone. Thy mine has a methy l. Deamination of cytosine makes uracil. Base differences btw RNA and DNA - AnswerUracil is found in RNA; Thymine in DNA Base pair bonds - AnswerG-C bond (3 H-bonds) is stronger than A-T bond (2 H-bonds). Incr G-C content -- higher melting temperature. AA's necessary for purine synthesis - AnswerG lycine A spartate G lutamine Nucleoside - AnswerBase + ribose