Presentation on theme: "Nucleotides and DNA Structure C483 Spring 2013. 1. Purine(s) which are found mainly in both deoxyribonucleotides and ribonucleotides are A) thymine and."— Presentation transcript:
Nucleotides and DNA Structure C483 Spring 2013
1. Purine(s) which are found mainly in both deoxyribonucleotides and ribonucleotides are A) thymine and cytosine. B) cytosine and uracil. C) cytosine. D) guanine and cytosine. E) adenine and guanine. 2. The abbreviation dGp indicates A) 5' deoxyguanylate. B) 3' deoxyguanylate. C) 3', 5' deoxyguanylate. D) 5', 3'deoxyguanylate. E) dGMP 3. Much of the stability of the double stranded helical DNA structure is the result of A) hydrogen bonding between purines. B) the phosphodiester backbone. C) Ionic nucleobase attraction. D) the stacking interactions between base pairs.
All five histones are rich in ________ amino acid residues whose positive charges allow binding to the sugar-phosphate backbone of DNA. A) lysine and alanine B) lysine and arginine C) leucine and alanine D) leucine and arginine Which does not apply to most bacterial DNA? A) Circular. B) Relaxed. C) Not packed into nucleosomes. D) Supercoiled. Which best describes the structure of a nucleosome core particle? A) A histone octamer with DNA threaded through its center. B) About 50 bp of DNA associated with one histone H1 molecule. C) One nucleosome plus one histone H1 and linker DNA. D) A histone octamer wrapped approximately two times around with DNA.
Denaturation Melting point Melting curve UV-absorption cooperative
A/T Rich and G/C Rich strands GC rich strands harder to denature due to STACKING (not H-bonds) Cooperativity due to initial unstacking, which exposes bases to water, which destabilizes H- bonds, which leads to further denaturation
Supercoiling Bacterial DNA Closed, circular DNA Topology and topoisomerases
Eukaryotic DNA Chromatin 8000x packing ratio – Nucleosomes (10x) – 30nm chromatin fiber (4x) – RNA/Protein scaffold holds loops (200x condensation of DNA length
Nucleosomes Beads on string Histones form octamer Core particle
Unpacking Histones serve as negative supercoiling Histone acyltransferases (HATS) Necessary for expression
Chromosome Scaffold of RNA and protein 30nm fibers are looped many times Picture of histone- depleted chromosome: DNA strands have fallen off of scaffold