1. ___________ is responsible for maintaining biologically native structure of an enzyme and even nucleic acid.
a) pH
b) Proton
c) ATP
d) Electrons
Explanation: Proton is responsible for maintaining biologically native structure of an enzyme and even nucleic acid. ATP required for performing metabolic activities is also a result of proton coupled to electron transport chain. Protons can be added or removed when change in pH occurs. Electrons have no role to play in maintaining structure of enzyme and nucleic acid.
2. Increase or decrease in _________ leads to protonation or deprotonation of bases which leads to melting of DNA in turn isolating the enzyme after centrifugation.
a) temperature
b) ionic strength
c) pH
d) detergent use
Explanation: Protons are responsible for maintain the biologically native structure of enzymes and nucleic acids. Hence increase or decrease in pH results in protonation or deprotonation of bases which leads to denaturation if DNA. The resultant extract in then centrifuged to isolate enzymes. The main limitation of this technique is the loss of enzymes due to denaturation.
3. The increase in pH affects the inter H2 bonds and intramolecular hydrophobic bonds are majorly affected leading to denaturation of DNA.
a) True
b) False
Explanation: Increase or decrease in pH leads to protonation and deprotonation of bases which leads to denaturation of DNA. In this case, the inter H2 bonds and intramolecular hydrophobic bonds are majorly affected to due to increase in temperature and not pH. This leads to denaturation of DNA and isolating the required enzyme. The main limitation in this case is denaturation of enzymes also, which can be prevented by optimizing the temperature and time parameters.
4. Cetyl trimethyl ammonium bromide is a cationic detergent.
a) true
b) false
Explanation: Cetyl trimethyl ammonium bromide is a cationic detergent because this positively charged detergent interacts electrostatically with negatively charged phosphodiester backbone of DNA. Followed by centrifugation, the precipitated DNA can be removed and enzymes can be isolated.
5. Which of the following chemical is not used to isolate enzymes from cell free extract?
a) Polyethyleneimine
b) Polyvinylpyrrolidone
c) EDTA
d) Magnesium chloride
Explanation: EDTA is a chelating agent which is used to chelate ions which are important for cell wall stability. Hence EDTA is a chemical method to extract enzymes from the cells. Whereas polyethyleneimine, polyvinylpyrrolidone, magnesium chloride etc., are used to isolate enzyme from cell free extract which contains nucleic acids as the major contaminant.
6. __________ is a compound which is frequently used for DNA removal.
a) 1.4% buffered sucrose
b) Protamine sulphate
c) Sodium hydroxide
d) Lysozyme
Explanation: Protamine sulphate is a compound which is frequently used for DNA removal, inturn isolating the enzyme of interest. 1.4% buffered sucrose is used for osmotic shock which is a chemical method for extracting the enzyme from cells. Sodium hydroxide is used in the alkali treatment which brings about nucleophilic attack and releasing the cell contents. Lysozyme is used to extract enzymes from gram positive bacteria as they have high content of peptidoglycan. As lysozyme catalyzes β(1 → 4) glycosidic linkage between NAG and NAM present in bacterial peptidoglycan.
7. Which of the following is the best method for isolating enzymes from cell free extract?
a) pH treatment
b) Temperature treatment
c) Chemical treatment
d) Osmotic shock
Explanation: Temperature and pH treatment have a major drawback of denaturing the enzyme itself. Hence the best treatment is chemical treatment as it has no major drawback. Osmotic shock is not a method for isolating enzyme, but extracting it. Hence it cannot be considered.
8. Which of the following is not a step involved in purification?
a) Precipitation
b) Dialysis or ultrafiltration
c) Chromatographic techniques
d) Freezing technique
Explanation: Freezing technique is a method wherein the cells are subjected to cold temperatures of about -15°C to -20°C. This is nothing but a cold or psychrophilic shock. It is a physical method for extraction of enzymes. Purification involves the following steps: precipitation, dialysis or ultrafiltration, chromatographic techniques and purity checking by chromatography or spectrophotometry.
9. Insulin is purified under ___________ purifications.
a) analytical
b) chromatography
c) preparative
d) ultrafiltration
Explanation: Purification is classified into preparative or analytical. Preparative purification is targeted towards producing large quantities of purified proteins which are of commercial important. Examples which are purified by the preparative technique are laccase, insulin, HbS Ag, etc. Analytical purification is used to produce small scale lab production of purified proteins. Ultrafiltration and chromatography are the steps involved in purification.
10. Purifications of purified proteins involved in small scale lab productions meant mainly for research purposes are referred to as _____________
a) preparative purifications
b) chromatographic techniques
c) analytical purifications
d) dialysis techniques
Explanation: The two main classification of purifications are preparative and analytical. Analytical purification are involved in small scale lab preparations and mainly used for research purposes. Examples purified by analytical purifications are as follows: pronase, dispase, caspase etc. Preparative purifications involve large scale productions of commercial important proteins. Chromatography and dialysis techniques are the steps involved in purification.