USABO EXAM QUESTIONS AND ANSWERS

USABO EXAM QUESTIONS AND ANSWERS Eukaryote - ANS An organism whose cells contain complex structures enclosed within membranes. The defining membrane bound structure that sets them apart from prokaryotic cells is the nucleus or nuclear envelope within which the genetic material is carried. All large complex species are eukaryotes, including animals, plants and fungi. Euchromatin - ANS This shows as pale areas in the nucleus under electro magnification. It is a less densely packed form of chromatin; 10% is even less condensed and in this form it can be actively transcribed to produce RNA. Heterochromatin - ANS This shows as dark areas on the eukaryotic nucleus; it is densely packed chromatin (DNA and protein complex) which cannot be transcribed. Histones - ANS Special proteins around which DNA is wrapped. Lamins - ANS Intermediate filament proteins which protect the structure of the nucleus, they polymerize to from a network of filaments that lie just within the nuclear membrane. The network of these filament proteins is called the nuclear lamina. Nuclear Lamina - ANS The network of intermediate nuclear filament proteins (Lamins) which is located just below the nuclear membrane and is linked to the membrane and chromatin. Nuclear Pores - ANS 9nm (approx) gaps in the nuclear envelope that allow the passage of RNA and ribosomes out of the nucleas and the entry of selected small proteins and small water soluble molecules. Prokarayotes - ANS An organism of the kingdom of Monera, comprising the bacteria and cyanobacteria. Characterised by the abscence of a distinct, membrane bound nucleas or membrane bound organelles and by DNA that is not organised in to chromosomes. Also called moneran. Protoctist - ANS Any of various unicellular eukaryotic organisms and their multicellular, coenocytic or colocial descendants that belong to the kingdom of Protocista according to some taxonomic systems. The protoctists include protozoans, slime moulds, various algae and other groups. In many new classification systems, all proctists are considere