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DNA and chromatin
DNA and chromatin structure
| Question | Answer |
|---|---|
| Purines | Adenine and Guanine |
| Pyrimidine | Cytosine, Thymine (DNA) and Uracil (RNA) |
| Nucleosides | Purines or pyrimidines covalently linked to ribose or deoxyribose via N-beta-glycosidic bonds. |
| Linked to D-ribofuranose | Ribonucleosides |
| Linked to 2-deoxy-D-ribofuranose | Deoxynucleosides |
| Syn and anti comformation | Purines can exist in anti and syn conformation with anti being preferred. Pyrimidines occur in the anti conformation. |
| Nucleotides | Phosphate esters of nucleosides which can form at the hydroxyl groups at 2', 3' or 5' carbons of a ribonucleoside |
| Nucleic acids | Polymers of nucleotides joined by diester bonds linking the 3'-OH in the sugar of one nucleotide with the 5'-PO4 in the sugar of the adjoining nucleotide |
| DNA structure | DNA is a double helix, intertwined anti-parallel. Each chain linked by phosphodiester bonds between 3'-OH and 5' phosphate group deoxyribose. |
| Chargaff's Rules | Percentage of A=T and G=C |
| Structural forms of DNA | B-most common, right handed. A-right handed. Z-left handed. Dehydration induces transition from B to A DNA. Z can be formed in regions in which purines alternate with pyrimidines. |
| RNA stability vs. DNA stability | The 2'hydroxyl group makes RNA susceptible to base-catalyzed hydrolysis, which results in cleavage of the phosphodiester backbone. The removal decreases the rate of hydrolysis by 100 fold. |
| DNA disruption | Heating the solution of DNA which disrupts the hydrogen bonds (reversible). They re-associate when temp is below melting(annealing). |
| Melting Temperature | Temperature at which half the helical structure is lost. |
| Other forms of separating strands | Adding acid or alkali to ionize the nucleotide bases and disrupt base pairing. |
| Hypochromism | Stacked bases in nucleic acids absorb less ultraviolet light than do unstacked bases |
| 260nm significance | Melting of nucleic acids is easily followed by monitoring their absorption of light, which peaks at wavelenght of 260nm |
| E. Coli genome vs. human genome | E. Coli consist of single circular DNA of ca 4 million base pairs. Human consist of ca. 3.2 billion base pairs organized into 23 pairs of chromosomes in the nucleus. |
| Genome in human dna | Each 10^14 cells approximately have their own copy of genome except RBCs which lack a nucleus. |
| Metaphase in Mitosis | Human genome can be visualized during metaphase when they are in highly condensed form. |
| Eukaryotic DNA | Packed in compact form, by being wrapped around histones to form nucleosomes. |
| Non-dividing cells (G0 and interphase) | DNA is packaged in the nuclei in complexes with various proteins and is referred to as chromatin |
| Nucleosomes make up | 50% DNA and 50% protein roughly |
| Four histones | Small basic proteins, a 1/4 of the residues are arginine or lysine. H2A, H2B, H3 and H4. Associate with one another to form an octamer. DNA wraps around to form 2 turns about 145bp in the 2 turns |
| H1 | A fifth histone binds the two DNA strands where they enter and leave the core histone which seals the assembly |
| SMC (structural maintenance of chromosomes) | SMC proteins are responsible for keeping the sister chromatids organized together during the cell cycle |
| How are the nucleosomes arranged? | In helical array to form a series of stacked layers with a diameter of about 30nm-30nm fibers. Further compacted during mitosis to form a metaphase chromosome. Folding involves attachment to a nuclear scaffold with H1, topoisomerase 2 and SMC. |
Created by:
Kahiranoel@gmail.com
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