Enzymes Flashcards
What are enzymes?
Biological catalysts that increase the rate
of a chemical reaction without being
permanently altered themselves
What is an advantage of enzymes in the
body?
They enable cellular reactions to take
place at lower temperatures
What is the active site of an enzyme?
The region of an enzyme to which a
substrate molecule binds and the
reaction takes place
Why are enzymes described as having a ‘high specificity’ for their substrate?
Only substrates with a specific,
complementary shape can fit into an
enzyme’s active site
Describe the ‘lock and key’ model
- Substrate collides with the active site of an enzyme
- Substrate binds, enzyme-substrate complex forms
- Substrate converted to products
- Products released from the active site which is now
free to bind to another substrate
What factors affect the rate of an enzyme-controlled
reaction?
● Temperature
● pH
● Substrate concentration
Explain how increasing temperature initially affects
the rate of an enzyme controlled reaction
● As temperature increases molecules have more KE
● Movement of molecules increases
● Probability of a successful collision increases
● More enzyme-substrate complexes form
● Rate of reaction increases
Explain how increasing temperature above the
optimum affects the rate of an enzyme controlled
reaction
● Temperature increases above the optimum
● Increased vibrations break bonds in enzyme’s structure
● Active site changes shape, enzyme is denatured
● No more enzyme-substrate complexes can form
● Rate of reaction decreases
Draw a graph to show the effect of increasing
temperature on the rate of an enzyme-catalysed
reaction.
https://pmt.physicsandmathstutor.com/download/Biology/GCSE/Notes/Edexcel/1-Key-Concepts-in-Biology/Flashcards/Flashcards%20-%20Topic%201%20Enzymes%20-%20Edexcel%20Biology%20GCSE.pdf
Page 19
Explain how pH affects the rate of an enzyme
controlled reaction
● Enzymes have an optimum pH
● pH shifts from the optimum
● Bonds in the enzyme’s structure are altered
● Active site changes shape, enzyme is denatured
● Rate of reaction decreases
Draw a graph to show the effect of
increasing pH on the rate of an
enzyme-catalysed reaction
https://pmt.physicsandmathstutor.com/download/Biology/GCSE/Notes/Edexcel/1-Key-Concepts-in-Biology/Flashcards/Flashcards%20-%20Topic%201%20Enzymes%20-%20Edexcel%20Biology%20GCSE.pdf
Page 23
Explain how the substrate concentration
affects the rate of an enzyme-controlled
reaction
● Substrate concentration increases
● Number of substrate molecules in the same volume increases
● Probability of a successful collision increases
● More enzyme-substrate complexes form
● Rate of reaction increases
● Once all active sites become full, the rate of reaction plateaus
Draw a graph to show the effect of
increasing substrate concentration on
the rate of an enzyme-catalysed reaction
https://pmt.physicsandmathstutor.com/download/Biology/GCSE/Notes/Edexcel/1-Key-Concepts-in-Biology/Flashcards/Flashcards%20-%20Topic%201%20Enzymes%20-%20Edexcel%20Biology%20GCSE.pdf
Page 27
How can the rate of an enzyme-controlled reaction
be calculated when given a value for time
rate = 1/time
What are the units for rate?
s^-1
Why must large organic molecules be broken down
into smaller, simpler molecules in the body?
● Large molecules are too big to be absorbed across
the surface of the gut wall
● ∴ large molecules are broken down into smaller
molecules for absorption into the bloodstream
Give an example of the breakdown of large
molecules into smaller molecules in plants
Starch is broken down by enzymes into
simpler sugars which are respired to
release energy
What type of molecules are proteins and
carbohydrates?
Polymers
What are the monomers of carbohydrates?
Simple sugars
Which group of enzymes catalyses the breakdown of
carbohydrates?
Carbohydrases
Which type of carbohydrase catalyses the
breakdown of starch?
Amylase
What are the monomers of proteins?
Amino Acids
Which type of enzyme catalyses the breakdown of
proteins?
Proteases
What is the function of lipases?
Enzymes which catalyse the breakdown
of lipids into fatty acids and glycerol
Why are small molecules synthesised into larger
organic molecules in the body?
- Large molecules are used for storage (e.g.
glycogen) - Used to build structures
(e. g. organelles).
Which enzyme catalyses the formation of glycogen
from glucose?
Glycogen synthase
How can the amount of energy contained in food be
measured? (biology only)
Measured using calorimetry
What is calorimetry? (biology only)
A method of measuring the heat transfer
during a chemical reaction
Describe the method used to measure
the amount of energy in a sample of food
(biology only)
- Add a set volume of water to a boiling tube, record initial temperature
- Record the mass of a small sample of food (e.g. bean)
- Stick the sample onto a mounted needle
- Using a bunsen burner light the food sample
- Hold the sample under the boiling tube until it burns up
- Record the maximum temperature reached by the water
- Record the final mass of the food sample
How can the amount of energy in the
food sample be calculated?
(biology only)
Energy in food (J) = mass of water (g) x temperature change of water (°C) x 4.2
Energy (J/g) = Energy in food (J)/ Mass of food burnt (g)
