B4 - Enzymes Flashcards
1
Q
What are enzymes?
A
- globular proteins that interact with substrate molecules
- they act as catalysts to metabolic reactions in living organisms
2
Q
What is a metabolic reaction?
A
- it is the sum of an anabolic (building up) and a catabolic (breaking down) reaction
- can only take place as a result of the control/order imposed by enzymes
3
Q
Example of an anabolic reaction
A
- cellulose forming the walls of plant cells
- long protein molecules forming contractile filaments of muscles in animals
4
Q
Example of a catabolic reaction
A
- growth (living processes)
- energy released from large organic molecules (glucose) in metabolic pathways
5
Q
What is ‘Vmax’?
A
- maximum initial velocity of the enzyme catalysed reaction
- enzymes can only increase the rates of reaction up to this point
6
Q
What are intracellular enzymes?
A
- a type of enzyme that aids the metabolic processes inside the cells that secreted them
7
Q
What is an example of an intracellular enzyme?
A
- catalase ensures that hydrogen peroxide is broken down into oxygen and water
- benefits = it is time efficient so it minimizes the risk of damage
8
Q
What are extracellular enzymes?
A
- a type of enzyme that works outside of the cell that secreted them
- cells require substrates (raw materials) to make products needed by the organism
- the nutrients are often in forms of large molecules and need to be broken down
- enzymes are released from the cells to break down these large nutrient molecules
9
Q
What are examples of extracellular enzymes?
A
- amylase (salivary glands/pancreas) is a digestive enzyme that breaks down starch polymers into maltose
- maltose is then broken down into glucose by maltase
- trypsin (protease) catalyses the digestion of proteins into smaller peptides
- produced in pancreas and released into small intestine
- amino acids are produced and absorbed into the bloodstream
10
Q
What are the properties of enzymes?
A
- tertiary structure (interactions between R-groups)
- active site is complementary to the shape of substrate molecule
- have the ability to reduce the activation energy required for a reaction to occur
- activity is affected by temp., pH, enzyme conc. and substrate conc.
11
Q
What is the lock and key hypothesis?
A
- idea that only a specific substrate will fit the active site of an enzyme
- forms an enzyme-substrate complex
- the substrates react and form an enzyme-product complex (products are then released)
- the right atom-groups and the R-groups (within active site) will react/interact with the substrate, forming temporary bonds
12
Q
What is the induced-fit hypothesis?
A
- recent research evidence has shown that the active site of an enzyme slightly changes its shape as substrate enters
- the initial interaction is relatively weak but they rapidly induce changes in the enzyme’s tertiary structure
- this weakens a bond/bonds in the substrate and lowers the activation energy
13
Q
What factors affect enzyme activity?
A
- temperature
- pH
- substrate/enzyme conc.
14
Q
How does temperature affect enzyme activity?
A
- increase = increases K.E. of particles which causes them to collide more frequently (increases rate of reaction)
-
Q10 is a measure of how much the rate of reaction increases with a 10 d.C. rise
- denaturation:
- at extremely high temperatures bonds holding the protein together vibrate
- this increases until they strain/break causing a change in the tertiary structure
- the change in shape means they have denatured so the active site is no longer complementary to the substrate
- optimum:
- highest rate of activity takes place
- human body = 40 d.C
- ** once enzymes have denatured past the opt. temp., the decrease in rate of reaction is rapid **
- extremes:
- cold = enzymes controlling metabolic activities of organisms
- they tend to have more flexible structures and are less stable than enzymes working at higher temps.
- thermophiles = organisms adapted to living in very hot environments
- enzymes are much more stable as they have an increased no. of bonds (H and S)
- their active sites and shapes are more resistant to temp. rises
15
Q
How does pH affect enzyme activity?
A
- change in pH = change in hydrogen ion conc.
- acidic = more
- alkaline = less
- this causes a change in the hydrogen and ionic bonds between the amino acid R-groups
-
optimum pH = active site is in the right shape
- renaturation = when pH returns to opt. and protein/active site resumes its normal shape to catalyse the reaction again
- a more significant change will irreversibly alter the structure and enzymes will become denatured
- low/high pH = less R-group interaction
- enzyme will only function within a narrow pH range
16
Q
How does substrate/enzyme conc. affect enzyme activity?
A
- substrate:
- increase = more frequent successful collisions with enzyme active sites
- so more enzyme-substrate complexes are produced
- rate of reaction increases til Vmax as all active sites are occupied by substrate particles
- enzyme:
- increase = more available active sites for the substrate
- increases rate of reaction so reaction rate rises towards higher Vmax
17
Q
How is metabolic activity controlled within cells?
A
- enzymes are activated with cofactors and inactivated with inhibitors
- inhibitors = molecules that prevent enzymes from carrying out their normal function (catalysis)
18
Q
What is competitive inhibition?
A
- a molecule that is similar to the substrate complementary to the enzyme’s active site
-
blocks substrate from entering the active site so reaction cannot take place
-
blocks substrate from entering the active site so reaction cannot take place
- substrate and inhibitors compete to bind too the active site
- this slows down the rate of reaction as less substrate molecules are bound in a given time
- e.g. statins inhibit the synthesis of cholesterol
- helps to reduce blood cholesterol concs.
19
Q
How does competitive inhibition affect rate of reaction?
A
- reduces rate of reaction but does not change the Vmax of the enzyme
- increasing substrate conc. will allow for original Vmax to be reached
20
Q
What is non-competitive inhibition?
A
- inhibitor binds to an alternative area on the enzyme (allosteric site)
- causes the tertiary structure of the protein to change, changing the active site
- so it is no longer complementary to the substrate
- this prevents the enzyme from carrying out its function
- e.g. organophosphates (insecticides, herbicides) irreversibly inhibit the enzyme for nerve impulse transmission
21
Q
How does non-competitive inhibition affect rate of reaction?
A
- increasing enzyme/substrate conc. will not overcome its effect
- increasing the conc. of the inhibitor will further decrease the rate of reaction
22
Q
What is end-product inhibition?
A
- where the product of a reaction acts as an inhibitor to the enzyme that produces it
- example of a negative feedback control mechanism
- excess products are not made/resources are not wasted
23
Q
What is the difference between a cofactor and a coenzyme?
A
- cofactor:
- transfer atoms/groups from one reaction to another (multi-step pathway)
-
inorganic = minerals like iron, chloride, calcium, zinc ions
- coenzymes:
- similar but it is an organic molecule
- derived from vitamins (B5, B3)
24
Q
What are prosthetic groups?
A
- they are cofactors which are required to carry out a catalytic function
- tightly bound to the enzyme protein to form a permanent feature
25
Q
What is precursor activation?
A
- inactive precursor enzymes = produced in an inactive form
- particularly enzymes that can cause damage within cells
- they need to change their tertiary structure in order to be activated
- precursor protein is added first (apoenzyme)
- holoenzyme = when cofactor is added and enzyme has been activated
