Chapter 4 - Enzymes Flashcards
What is an enzyme?
A globular protein made by cells that acts like a catalyst
What is a catalyst?
A chemical that speeds up the rate of reaction and is unchanged at the end
What is the role of enzymes?
Enzymes increase rate of reaction up to Vmax
Cells that produce enzymes can adjust the production according to demand
Life is dependent upon enzymes
What are the two types of enzyme reaction?
Anabolic - Building biological molecules
e.g. collagen
Catabolic - Breaking biological molecules
e.g. in digestion
What is an intracellular enzyme?
An enzyme that works inside the cell
e.g. catalase
What is an extracellular enzyme?
An enzyme that working outside of the cell
e.g. lipase/protease/amylase
What determines the shape of an enzymes active site?
Tertiary structure of the protein
e.g. hydrogen bonding, ionic bonds, disulfate bonds or polar interactions
Describe the relationship between the active site and the substrate.
They are complimentary in shape
What is activation energy?
Energy required for the enzyme and substrate to successfully collide and form an enzyme-substrate complex
What is the lock and key model hypothesis?
Enzyme is lock
Substrate is key
Substate has the perfect complimentary shape to the active site
Active site is a fixed shape and due to a random collision the substrate can collide and attach to the enzyme to form an enzyme-substrate complex
What is the induced fit hypothesis?
The active site molds to fit the substrate
When the enzyme-substrate complex occurs it puts strain on the bonds and therefore lowers the activation energy
What factors affect enzyme activity?
Temperate
pH
Enzyme concentration
Substrate concentration
How does temperature affect enzyme activity?
Too low - insufficient kinetic energy, low frequency of successful collisions
Increased temperature (close - at optimal) - increased kinetic energy, increased frequency of successful collisions increases
Too high - enzymes denature, active site changes shape and enzyme-substrate complexes can’t form, high temperatures affect the tertiary structure of the enzyme (active site changes shape)
How is the temperature coefficient calculated?
Q10 = R2/R1
R1 = rate of reaction at a temperature of X°C
R2 = rate of reaction at a temperature of (X + 10)°C
How does pH affect the rate of enzyme activity?
Interferes with the charges in the amino acids in the active site
Causes ionic and hydrogen bonds to break
Alters tertiary structure and changes the shape of the active site and the enzyme denatures
Changes in pH decrease the frequency of successful collisions
Enzymes have different optimal pH as they work in different areas
How does substrate concentration affect the rate of enzyme activity?
Low - frequency of successful collisions decreases, less enzyme substrate complexes are formed
High - frequency of successful collisions increases, however rate of reaction will plateau because all of the enzyme active sites are in use so no more enzyme-substrate complexes can be formed
How does enzyme concentration affect the rate of enzyme activity?
Low - frequency of successful collisions is low as there isn’t many active sites to form an enzyme-substrate complex
High - frequency of successful collisions increases, so more enzyme-substrate complexes are formed, unless substrate concentration is unlimited the rate of enzyme activity will plateau as there aren’t enough substrates to bind to the large number of active sites
What is a competitive inhibitor?
Bind to active site
Same shape as substrate
Prevents enzyme-substrate complexes from forming, instead enzyme-inhibitor complexes are formed
Most are reversible
Increasing substrate concentration can outweigh the effects of the inhibitor and it can reach the same rate of enzyme activity.
What is a non-competitive inhibitor?
Binds at the allosteric site
Causes active site to change shape
Less substrates can bind to that enzyme, so enzyme-substrate complexes can be formed less frequently so rate of enzyme activity decreases
How can you tell the difference between a non-competitive and a competitive inhibitor?
Effects of the competitive inhibitor can be outweighed by adding more substrates and the rate of enzyme activity would reach the same as no inhibitors
Effects of non-competitive inhibitor stay the same even when substrate concentration increases, so the rate of enzyme activity plateaus lower than without the inhibitor
What is an end product inhibitor?
Enable the reaction to be controlled
If there is a lot of product , it will inhibit the enzyme which will slow or stop the reaction
Prevents products from being wasted
Often binds to allosteric site
What is a coenzyme?
Organic non-protein molecule
Bind to the active site to make the substrate fit correctly
Catalyse the reaction
Often used in multi-step pathway reactions
Participate in the reaction
e.g. Vitamins - NAD acts as a hydrogen carrier in respiration
What is a cofactor?
Inorganic non-protein molecule
Work by helping the enzyme and substrate to bind together
Do not directly participate in the reaction
Catalyse the reaction
Often used in multi-step pathway reactions
e.g. Chloride ions for amylase - doesn’t work without presence of chloride ions
What is a prosthetic group?
Type of cofactor but are permanently attached to the enzyme by covalent or non-covalent forces
Some enzymes require activation by a cofactor called precursor activation
Ensures enzyme is only used when they are needed
Changes shape of the active site to activate it
e.g. Iron in haemoglobin needed for gas exchange
What is an inhibitor?
Molecules that bind to an enzyme and decrease it’s ability to convert substrate to product
What is precursor activation?
Many enzymes are produced in an inactive form
Activation can occur by the addition of a cofactor
