Nucleic acids and chromosomes Flashcards
Define genome, primary sequence and nucleic acids?
Genome: entire DNA coding for organism
Primary sequence of DNA: sequence of bases
Nucleic acids: linear polymers of nucleotides
Which direction are bases sequenced in
conventially from 5’ to 3’
What is the difference between Deoxyribose vs ribose?
Deoxyribose lacks oxygen on 2’
What is the difference between a nucleotide and nucleoside?
Nucleoside: base + (deoxy)ribose
Nucleotide: base + phosphate + sugar eg. adenosine monophosphate
What is the structure of DNA?
1’ on sugar linked to base
Sugar 5’ linked to phosphate
- For phosphodiester bond phosphate linked to base on 5’ OH and 3’ OH
5’ end has free phosphate
3’ end has free OH
Right handed double helix
10bp per helical turn, 2nm wide
Negatively charged on outside b/c phosphate groups
Grooves in backbone called major and minor groove depending on size
What bond links the phosphates?
phosphoanhydride bonds
Which bases are purines and which ones are pyrimidines?
Purines (big ones): A G, double ring structure
Pyramidine (small one): CT or CU - methyl group absent in uracil
Explain what is means by Watson Crick pairing?
Bases are planar and run perpendicular to helix
- stacked for stability
How many hydrogen bonds are in each pairing?
A-T 2 h-bonds less stable
G-C 3 h-bonds more stable
How are strands molten and reannealed?
Melting/denaturation: Heat or low salt
Re- annealing/hybridisation: cool or high salt
Define chromatin:
Chromatin: complex of DNA and proteins
What is the structure of the nucleosome?
- DNA wrapped around histone proteins (bead like particles), core DNA wraps around histones twice and moves on, joined by linker DNA
- 8 histones in centre (octamer), 2 each of 2A, 2B, 3, 4
- Histone 1 between nucleosomes
- Positively charged so interact with backbone
- Histone tails extend from nucleosome, subject to post translational modification
- nucleosomes form chains which pack into helical arrays
7 fold condensation
What is the structure of the 30nm fiber?
- Further packaging to generate more compact structure
- 6 nucleosomes stack together and condense
40 fold condensation
How do chromosomes condense further?
Chromatin fiber: folded into loops
Mitotic chromosome - 10 000 fold condensation
What is the Human karotype?
Organised Chr profile, important in diagnostic e.g can see genetic abnormalities
22 autosomes, 2 sex chr
