NAGE 1 - Nucelic Acids & Chromosomes Flashcards
What is a nucleotide?
A nitrogenous base, sugar and one or more phosphate groups.
How do deoxyribose and ribose differ?
Deoxyribose lacks an oxygen at carbon 2.
What are the nitrogenous bases?
Pyramidines - thymine, cytosine, uracil
Purines - adenine and guanine
What is a nucleoside?
A base and a sugar.
What is the bond joining the sugar and the base in nucleosides?
B-glycosidic linkage
List the nuceoside versions of each base.
Adenosine, guanosine, cytidine, uridine and thymidine
Describe the structure of the DNA helix.
2nm wide, 10bp per helical turn. Chains are antiparrallel and run in opposite directions. There is a major groove and a minor groove.
Describe the process of melting and reannealing.
The double strand is broken by heat or low salt (melting/denaturing) and then reformed by cool or high salt (re-annealing or hybridising).
What is the karyotype?
An organised profile of someones chromosomes.
What is the lowest level of packing?
Nucelosome is lowest level of packing (DNA wrapped around histone proteins in a left handed superhelix. Histones are positively charged, 150 base pairs of DNA wrap wound each histone in 7 fold condensation).
How are nucleosomes packaged?
Packaged into a 30nm fiber, which gives a 40 fold condensation. These are then packaged as chromatin in the nucleus. In interphase the DNA is condensed even more.
What is meant by Watson-Crick base-pairing.
Adenine forms two hydrogen bonds with thymine, while cytosine forms three hydrogen bonds with guanine. A purine must always pair with a pyramidine.
