1. Biological Molecules Practicals Flashcards
aim of practical 1
-investigation into the effect of a named variable on the rate of an enzyme-controlled reaction
give examples of variables that could affect the rate of an enzyme-controlled reaction
● enzyme concentration / volume
● substrate concentration / volume
● temperature of solution
● pH of solution
● inhibitor concentration
describe how temperature can be controlled in practical 1
-use a thermostatically controlled water bath
-monitor using a thermometer at regular intervals and add hot / cold water if temperature fluctuates
describe how pH can be controlled in practical 1
-use a buffer solution
-monitor using a pH meter at regular intervals
why were enzyme & substrate solutions left in water baths for 10 mins before mixing in practical 1
-so solutions equilibrate / reach the temperature of
the water bath
describe a control experiment in practical 1
-use denatured enzymes (eg. by boiling)
-everything else same as experiment, eg. same conc.
/ volume of substrate (at start) and enzyme, same type / volume of buffer solution, same temperature
describe how the rate of an enzyme-controlled reaction can be measured
● measure time taken for reaction to reach a set point
○ rate of reaction = 1 / time;
● measure concentration / volume / mass / colour of
substrate or product at regular intervals (or using a continuous data logger) throughout reaction
○ plot on a graph with time on the x axis and whatever is being measured on the y axis
○ draw a tangent at t = 0 (or any other time for rate at a particular point)
○ initial rate of reaction = change in y / change in x
suggest a safety risk and explain how to reduce this risk for practical 1
-handling enzymes may cause an allergic reaction
-avoid contact with skin by wearing gloves and eye protection
explain why using a colorimeter to measure colour change is better than comparison to colour
standards in practical 1
-not subjective
-more accurate
explain a procedure that could be used to stop each reaction in practical 1
● boil / add strong acid / alkali → denature enzyme
● put in ice → lower kinetic energy so no enzyme-substrate
complexes form
● add high concentration of inhibitor → no enzyme-substrate complexes form
describe how processed data can be presented as a graph
- label x-axis with named independent variable and y-axis with rate of reaction
- plot a linear scale on each axis that will allow the graph to occupy over half available space
- mark data points with crosses
- join data points by straight lines if intermediate values are not known OR draw a line / curve of best fit if there is a clear trend
explain why the rate of reaction decreases over time throughout each experiment
● initial rate is highest as substrate concentration not limiting / many enzyme-substrate complexes form
● reaction slows as substrate used up and often stops as there is no substrate left
