Enzymes Flashcards
All 24 cards in this deck
What is an enzyme?
A biological catalyst — a protein that speeds up reactions without being used up.
What are proteins broken down into by enzymes, and which enzymes do this?
Amino acids, by proteases.
What are lipids (fats) broken down into by enzymes, and which enzyme does this?
Fatty acids and glycerol, by lipase.
What is starch broken down into by enzymes, and which enzyme does this?
Sugars, e.g. maltose and glucose, by amylase (a carbohydrase).
Besides breaking molecules down, what other role do enzymes have in the body?
They catalyse synthesis reactions — joining small molecules into large ones.
e.g. glucose molecules joined to make starchWhat is the active site of an enzyme?
The part of the enzyme where the substrate binds.
What is the name of the model used to describe how an enzyme binds its substrate?
The lock-and-key model.
What is formed when a substrate binds to the active site of an enzyme?
An enzyme-substrate complex.
Why is an enzyme specific to only one substrate?
Its active site is complementary in shape to only that substrate; other substrates do not fit.
What does it mean to say an enzyme is denatured?
The shape of its active site has changed, so the substrate no longer fits and no enzyme-substrate complexes form.
Which two conditions can denature an enzyme?
High temperature and a pH far from the optimum.
True or false? Enzymes are killed by high temperatures.
False. Enzymes are not alive, so they cannot be killed — high temperatures denature them.
What happens to the rate of enzyme activity as temperature increases up to the optimum?
The rate increases.
What is the optimum pH of pepsin, and where in the body does it work?
pH 2, in the stomach (which secretes hydrochloric acid).
What happens to the rate of an enzyme reaction as substrate concentration increases?
The rate increases, then levels off when all the active sites are full.
What equation gives the rate of an enzyme reaction from the amount of product formed?
rate = amount of product formed ÷ time taken, e.g. in cm³/s
What equation gives the rate of a reaction from the time it takes to finish (e.g. until the starch has gone)?
rate = , with units of (per second)
True or false? A shorter time taken to collect a fixed volume of product means a faster rate of reaction.
True. Rate is inversely proportional to time, so less time means a faster rate.
In the enzymes and pH core practical, what colour change shows that starch is still present?
Iodine solution turns blue-black.
Name two variables that must be controlled in an investigation into the effect of pH on enzyme activity.
Temperature and the concentration/volume of the solutions used.
How can the temperature be kept constant in an enzyme practical?
Use a water bath (or incubator) set to the required temperature.
What is a substrate?
The molecule an enzyme acts on: it binds to the enzyme's active site and is changed in the reaction.
What is the optimum temperature of an enzyme?
The temperature at which the enzyme works fastest, so the rate of reaction is highest.
In the enzymes and pH core practical, how do you know when all the starch has been broken down?
A drop of the mixture no longer turns the iodine blue-black – the iodine stays orange-brown. The time taken to reach this point is recorded.