Molecular & Cell Biology Questions With 100% Correct Answers

Molecular & Cell Biology Questions With 100% Correct Answers Eukaryote - ANSWER- 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 - ANSWER- 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 - ANSWER- This shows as dark areas on the eukaryotic nucleas; it is densly packed chormatin (DNA and protein complex) which cannot be transcribed. Histones - ANSWER- Special proteins around which DNA is wrapped. Lamins - ANSWER- 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 - ANSWER- 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 - ANSWER- 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 - ANSWER- 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 - ANSWER- 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 - ANSWER- 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 - ANSWER- 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 - ANSWER- 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 - ANSWER- Cell organelle responsible for synthesizing proteins. Catalytic site - ANSWER- 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 - ANSWER- Small lipid-bounded spheres which transport proteins, glyco proteins and newly synthesized lipids (which are imbedded in the sphere itself) from the endoplasmic reticulum to the Golgi Apparatus or from the Golgi apparatus to another destination. They move short distances by the process of difussion, moving long distances requires the assistance of proteins associated with microtubules. Golgi apparatus - ANSWER- This is an organelle found in all eukaryotic cells.It was identified in 1897 by the Italian physician Camillo Golgi, after whom it is named. It processes and packages proteins after their synthesis and before they make their way to their destination; it is particularly important in the processing of proteins for secretion. Its size varies in different types of cells depending on cell function; a hormone secreting cell will contain a far larger version of this organelle than a muscle cell for example. It also forms a part of the cellular endomembrane system. Constitutive release - ANSWER- The constant release of small amounts of a substances from the cell membrane. Regulated release - ANSWER- The release of substances from a cell membrane only when specific conditions exist. A good example is the release of gastrointestinal hormones and digestive enzymes in response to food. Exocytosis - ANSWER- The process by which substances are exported from a cell. Phagocytosis/Endocytosis - ANSWER- The process by which substances or pathogens are taken in to a cell by engulfment by a vesicular structure surrounded by cell membrane. Lysosomes - ANSWER- Small organelles which contain digestive enzymes with an internal pH of around 5. They are responsible for breaking down large molecules taken in to the cell by phagocytosis and also for the breaking down of old organelles. Peroxisomes - ANSWER- Organelles that are plentiful in liver cells and adipocytes, responsible for breaking down fatty acids and amino acids in to hydrogen peroxide (among other things) via the action of an enzyme known as catalayse. MItochondrian - ANSWER- Sausage shaped organelles with a double membrane. The inner membrane folds in to cristae. This organelle plays a fundamental role in the production of ATP in eukarayote cells and they are abundant in cells which require high amounts of energy such as muscle cells. Cristae - ANSWER- Internal compartments formed by the inner membrane of a mitochondrion. They are studded with proteins, including ATP