Chemistry 9701 A-Level Questions and Answers

Chemistry 9701 A-Level Questions and Answers Natures of amino acids polar, non-polar, electrically-charged Properties of amino acids white crystalline solids, high melting point, soluble in H2O Effect of pH on enzyme activity increases then decreases above the optimum pH Why does the enzyme activity decrease above optimum pH? the active site is changed due to the ionic bonds Describe the effect of substrate concentration on enzyme activity increases then constant Enzyme inhibitors non-reversible inhibitor and reversible inhibitor Types of cofactors prosthetic groups and coenzymes What is the difference between deoxyribose and ribose? ribose has 3 -OH groups while deoxyribose has 2 -OH groups on their rings Types of RNA messenger RNA, transfer RNA, ribosomal RNA Briefly describe DNA replication bonds between bases are broken, free nucleotides are attracted, forms a new DNA Briefly describe DNA transcription DNA unravelsstrand used as a templatefree nucleotides are attractedforms an mRNA Briefly describe translation tRNA carries amino acids by bonding temporarily, brings to mRNA corresponding to its amino acid, amino acid form a peptide bond with another amino acid of another tRNA, leaves and continue until stop codon reached Types of DNA mutations deletion, substitution, duplication, addition What type of mutation is deletion? cystic fibrosis What are the effects of sickle-cell anaemia? causes red blood cells to become rigid and sickle-shaped and causes blood vessels blockage What are the effects of cystic fibrosis? What causes it? causes thick mucus making lungs blocked due to malfunctioning CFTR (cystic fibrosis transmembrane regulatory) protein Define proteins condensation polymers formed from amino acids which are bonded by peptide bond and they are polypeptides Define amino acids organic molecules containing -NH2 and -COOH groups Side chain of alanine CH3 Side chain of valine CH(CH3)2 Side chain of serine CH2OH Side chain of lysine (CH2)4NH2 Example of non-polar amino acid alanine Example polar amino acid serine Example of electrically-charged amino acid lysine How is zwitterion formed? Internal acid-base reaction at pH 7 Physical properties of amino acids white crystalline solids, soluble in water, high melting point Define peptide bond covalent bond formed when amine group of an amino acid combined with carboxylic acid group of another amino acid with the removal of water Describe the primary structure of proteins long chains of amino acids bonded by peptide bonds with covalent bonds between atoms Describe the secondary structure of proteins they are the α-helix and β-pleated structures where there are interactions between adjacent function al groups Describe the tertiary structure the interaction between R-groups of the polypeptide backbone which gives the protein its three-dimensional shape Describe the quarternary structure of proteins the union of polypeptide units to form the structure of protein Describe the characteristics of enzyme catalysis specific to a substrate, only small quantity needed and needs specific pH or temperature for maximum efficiency Describe the effect of temperature/pH on enzyme activity activity increases with increasing temperature/pH reaching a maximum at the optimum then decreases with higher temperatures/pH What happens to the tertiary structure of proteins when the temperature or pH is too high or too low? breaks ionic interactions in tertiary structure which disrupts the structure of the active site Describe the effect of substrate concentration on rate of reaction concentration of substrate is directly proportional to rate of reaction. At higher substrate concentration, all active sites are occupied so adding more substrate would have no effect Define inhibitor chemical substance which reduce the rate of an enzyme-catalysed reaction Two types of inhibitors non-reversible inhibitor and reversible inhibitor Two types of reversible inhibitor competitive inhibitor and non-competitive inhibitor Describe competitive inhibitor has the similar shape as the substrate so it competes with substrate and no catalysis takes place Describe non-competitive inhibitor binds to the enzyme away from the active site changing the tertiary structure and thus changing the shape of the active site so no catalysis takes place Factors affecting competitive and non-competitive inhibition [substrate], [inhibitor], relative affinity of the active site for the inhibitor and substrate, relative affinity for the enzyme Factors that causes enzyme denaturation high temperature, extremes of pH, presence of non-reversible inhibitors What are cofactors? non-protein groups necessary for enzymes to function Types of cofactors prosthetic group and coenzymes What is nanotechnology? the science of the very small with big potential Describe the structure of buckyballs 60 carbon atoms arranged to form a sphere with five-carbon and six-carbon atoms rings Properties of buckyballs harder than diamond, more slippery than Teflon, insulator or conductor, soluble in water Uses of buckyballs removes dangerous chemicals, improves electrical conductivity, lubricant, superconductors, traps atoms What is a carbon nanotube? a nano-sized cylinder of carbon atoms Describe the structure of carbon nanotube the sides are rolled up sheets of graphite and the ends are like half-spheres of buckyballs Properties of carbon nanotubes stronger than steel, lighter than steel, better conductor than copper Applications of carbon nanotubes cars and airplanes, batteries and solar cells Advantages of using nanotubes in cars and airplanes better fuel efficiency, increases safety Advantages of using nanotubes in batteries and solar cells improves efficiency Advantages of using nanotubes over normal test tubes faster reaction and higher yield What is meant by 'peas in a pod'? buckyballs containing trapped atoms, themselves inside a carbon nanotube What is the application of peas in a pod ? information storage display What is meant by supramolecular? beyond the molecule Function of the crown ether recognise and binds metal ions What is a molecular motor? a large molecule powered by light How does a molecular motor work? uv light causes cis-trans isomers to rotate about the carbon-carbon double bond and chiral centres rotates polarised light What are quantum dots? devices that contain trapped electrons What is the size of quantum dots? few nanometres to few microns What are the applications of quantum dots? emits light or single photon of specific wavelength, use of optical computer capable of vast calculations What are the promises of nanotechnology? Sunscreen, Clothing, Medical, Environment, Industrial Describe the promise of nanotechnology on clothing nano particles can absorb uv light and repel water so that it is stain resistant Describe the promise of nanotechnology on environment nanorobots can rebuild ozone layer and removes contaminants in water Describe the promise of nanotechnology on medicine stops aging process, immortality, end of sickness Describe the promise of nanotechnology on industrial computer becomes smaller and faster Problems of nanotechnology weapons and health Describe the problem of nanotechnology on weapons they are destructive and accessible Describe the problem of nanotechnology on health very dangerous as they are unnoticeable if inhaled and can cause death Define asymmetric synthesis process of creating useful isomer Modifications of designing drugs minimize number of reactions and find similar molecules with fewer side effects What are liposomes? artificial microscopic vesicles whose walls are made of layers of phospholipids that make up the cell membrane What is a phospholipid? a molecule that is hydrophilic at one end and hydrophobic at the other end What are the properties of liposomes? biodegradeable and non-toxic What are the advantages of liposomes? shield healthy cells from drug toxicity and prevent drug concentration in vulnerable tissues Structure of PEG HO-(CH2-CH2-O)n-OH What is PEGlylation? attachment of PEG to drug molecules What are the advantages of PEG? biocompatibility, ease of modification What are the disadvantages of PEG? Only carry two drug molecules at a time How to increase the number of drug molecules that PEG can carry? use side-chains in monomers that are polar What is condensation reaction? a reaction in which molecules join together by splitting off a small molecule such as water