USABO Latest Update with Verified Solutions

USABO Latest Update with Verified Solutions Eukaryote An organism whose cells contain complex structures enclosed within membranes. The defining membrane bound structure thats sets them apart from prokaryotic cells is the nucleas or nuclear envelope within which the genetic material is carried. All species of large complex species are eukaryotes, including animals, plants and funghi. Euchromatin This shows as pale areas in the nucleas under electro magnification. It is a less densly packed form of chromatin; 10% is even less condensed and in this form it can be actively transcribed to produce RNA. Heterochromatin This shows as dark areas on the eukaryotic nucleas; it is densly packed chormatin (DNA and protein complex) which cannot be transcribed. Histones Special proteins around which DNA is wrapped. Lamins Intermediate filament proteins which protect the structure of the nucleas, 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 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 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 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 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 considered protists. Signal Sequence Affectionately known as the 'address label' of a polypeptide. A short (3-60 amino acids long) peptide chain that directs the transport of a protein. These may also be called targeting signals, signal peptides, transit peptides, or localization signals. The amino acid sequences of these direct proteins (which are synthesized in the cytosol) to certain organelles such as the nucleus, mitochondrial matrix, endoplasmic reticulum, chloroplast, apoplast and peroxisome. Some signal peptides are cleaved from the protein by signal peptidase after the proteins are transported. Endoplasmic Reticulum The endoplasmic reticulum (ER) is a eukaryotic organelle that forms an interconnected network of tubules, vesicles, and cisternae within cells. Rough endoplasmic reticula synthesize proteins, while smooth endoplasmic reticula synthesize lipids and steroids, metabolize carbohydrates and steroids (but not lipids), and regulate calcium concentration, drug metabolism, and attachment of receptors on cell membrane proteins. Sarcoplasmic reticula solely regulate calcium levels. Smooth endoplasmic reticulum Cell organelle responsible for attachment of receptors on cell membrane proteins, synthesizing lipids and steroids, metabolizing carbohydrates and steroids (but not lipids) and regulating calcium concentration and drug metabolism. Rough endoplasmic reticulum Cell organelle responsible for synthesizing proteins. Catalytic site In molecular biology this site is part of an enzyme where substrates bind and undergo a chemical reaction.The majority of enzymes are proteins but RNA enzymes called ribozymes also exist. The active site of an enzyme is usually found in a cleft or pocket that is lined by amino acid residues (or nucleotides in ribozymes) that participate in recognition of the substrate. Residues that directly participate in the catalytic reaction mechanism are called active site residues. Vesicles Small lipid-bounded spheres which transport proteins, glyco proteins and newly synthesized lipids (which are imbedded in the sphere