Enzymes Flashcards
What is the Vmax?
Maximum initial velocity or rate of an enzyme-catalysed reaction
What kind of proteins are enzymes?
Globular
What is an enzyme?
A protein that acts as a catalyst in biological reactions
What is the relationship between the shape of the active site and the shape of the substrate?
They have complementary shapes
Give an example of an intracellular enzyme
Catalase
Give an example of an extracellular enzyme
Amylase
Define metabolic reactions
The reactions occurring inside the bodu at any given time
Where are enzymes produced?
On the ribosomes of a cell
How do enzymes speed up the rate of reaction?
They reduce the activation energy of a reaction
What are the two models for enzyme action?
The lock and key
and
The induced fit
Describe the lock and key model of enzyme action
The enzyme is the lock and the substrate is the key
The correct key must be used to fit in the correct lock
Only a key that fits exactly into the lock will work
What does the lock and key model of enzyme action suggest about the active site?
The active site is ridgid
Describe the induced fit model of enzyme action
- The substrate and active site are complementary in shape but not an exact fit
- the active site is able to change shape slightly to create a perfect fit
What does the induced fit model suggest about the active site?
The active site has a degree of flexibility
Outline how an enzyme causes a reaction to occur
- the substrate and active site collide, forming an enzyme-substrate complex
- the active site puts pressure on the bonds of the substrate
- this causes them to break, forming an enzyme-product complex
- the products are released and the enzyme reused
How do enzymes reduce the activation energy of a reaction?
- They put pressure on the bonds in a substrate
- They bring atom groups close enough to react
Define metabolic pathway
A series of enzyme reactions whereby the product becomes the substrate of the next
What are anabolic reactions?
Reactions that build molecules
What are catabolic reactions?
Reactions that break bonds/break up molecules
How do R-groups of the enzyme help to break apart substrates?
The R-groups interact with the substrate, forming temporary bonds with the substrate which puts pressure on the bonds in the substrate bonds
Outline how starch is broken down in the body
- starch polymers are partially broken down into maltose by amylase
- amylase is released into the mouth via the salivary glands
- amylase is released into the small intestine via the pancreas
- maltose is then broken down into glucose by maltase in the small intestine
Outline how protein is broken down in the body
- trypsin is produced by the pancreas
- trypsin breaks proteins into smaller peptides in the small intestine
-other proteases then break the small peptides into amino acids
What is the active site?
the area of an enzyme with a shape complementary to a specific substrate allowing the enzyme to bind to a substrate with specicifity
Why are enzymes important to life?
- life processes require chemical reactions
- the reactions need to happen quickly
- enzymes allow these reactions to occur quickly without high pressure/temperature
- allow organisms to get the nutrients needed to function i.e through digestion
What is activation energy?
The energy required for a reaction to start
What is the substrate of catalase?
Hydrogen peroxide
What are the products of the reaction of catalase?
2H2O and O2
What is the substrate of amylase?
Starch
What are the products of the reaction of amylase?
Maltose
What is the substrate of trypsin?
Protein
What are the products of the reaction of trypsin?
polypeptides
How are metabolic pathways controlled?
- By allosteric enzymes whereby the end product of the pathway binds to the allosteric site
- once the end product levels fall, the inhibition is lifted
Give an example of control of a metabolic pathway
In respiration the enzyme PFK is inhibited by ATP and activated by ADP
What is the approximate optimum temperature for most enzymes in the human body?
40 degrees
What happens to the rate of reaction during the exponential phase?
-rate of reaction doubles every time temperature increases by 10 degrees
Why does the rate of reaction increase up to 60 degrees, as temperature increases?
- as temperature increases, kinetic energy of particles increases
- this means particles move faster and collide more frequently
- increasing rate of reaction
Why does the rate of reaction decrease beyond 60 degrees?
- hydrogen bonds and ionic bonds break
- loss of tertiary structure
- change in shape of the active site
- substrate no longer fits
- decreasing rate of reaction
Across how many pH units do enzymes work across?
4
Describe the rate of reaction graph for pH
- symmetrical curve
- optimum pH
- range of pH, 2 pH units either side of optimum
- rate of reaction falls to 0 beyond pH range
What is lost in denaturation?
tertiary structure/ shape of active site
What occurs in denaturation?
- active site changes shapes
- shape no longer complementary to the substrate
- substrate can no longer fit into the active site
- enzyme no longer acts as a catalyst
How does an increase in substrate concentration increase rate of reaction?
- higher chance of collisions
- limited by enzyme concentration
- higher chance of successful collisions
- more substrate-enzyme complexes can be formed
Is the change in shape of active site due to pH reversible?
Yes
Which 5 factors affect rate of enzyme controlled reaction?
- temperature
- pH
- substrate concentration
- enzyme concentration
- enzyme inhibitors
What are the two main types of inhibitors?
- competitive
- non-competitive
What is the effect of an increase in enzyme concentration on the rate of reaction?
- it increases the rate of reaction
- up to a point where rate of reaction is limited by substrate concentration
Why does an increase in enzyme concentration increase rate of reaction?
- there are more active sites
- higher chance of a successful collision
- to form an enzyme-substrate complex
How do competitive inhibitors reduce rate of reaction?
- compete with the substrate for the active site
- sit in the active site and block the substrate from entering the active site
What is the relationship between the shape of the inhibitor for a particular reaction and it’s substrate?
They have SIMILAR shapes
Are competitive inhibitors reversible?
Yes
Why are competitive inhibitors reversible?
They do not cause the enzyme to lose its shape
What is the degree of inhibition caused by competitive inhibitors dependent on?
The relative concentrations of substrate and inhibitor
What is the effect of a greater concentration of a competitive inhibitor on the rate of reaction?
It decreases the rate of reaction
Why does a greater concentration of a competitive inhibitor decrease the rate of reaction?
- a greater concentration of inhibitor relative to substrate means:
- the probability of a collision between an enzyme and an inhibitor is greater than the probability of a collision between an enzyme and a substrate
Give a difference between competitive and non-competitive inhibitors
-non-competitive do not compete with the substrate for the active site whilst competitive do
or
-non-competitive inhibitors bind to allosteric site whilst competitive do not
What are the two types of non-competitive inhibitor?
- reversible
- irreversible
Give an example of a reversible non-competitive inhibitor
Metabolic poisons, such as cynanide
How does cyanide act as a poison?
- acts on cytochromeoxidase (an enzyme involved in respiration)
- inhibits respiration
- no ATP therefore is produced so death occurs
What reaction is cytochromeoxidase involved in?
Aerobic respiration
How does the antidote to cyanide work?
It has a higher affinity for cyanide than cytochromeoxidase
How do non-competitive inhibitors inhibit the action of enzymes?
-they bind to the allosteric site
causing the active site to change shape so the substrate no longer fits
Give an example of an irreversible non-competitive inhibitor
Heavy metals, such as mercury
How does mercury act as an irreversible non-competitive inhibitor?
- breaks covalent bonds in the enzyme
- loss of tertiary and quaternary structures
- loss of shape of active site
- substrate can no longer fit so the enzyme loses its function
Which enzyme does cyanide act on?
Cytochromeoxidase
Define cofactors
non-protein components required for the effective functioning of an enzyme
What are the 3 types of cofactors?
- inorganic ion cofactors
- coenzymes
- prosthetic groups
What are coenzymes?
Organic molecules, mostly derived from B vitamins, which bind temporarily to an enzyme
Give an example of a coenzyme
NAD
What is NAD synthesised from?
Vitamin B3
What process is NAD used in?
Aerobic respiration
Which reaction of aerobic respiration does NAD take part in?
The reaction of pyruvate to Acetyl Coenzyme A
link reaction
What is the function of NAD?
Used to transfer hydrogen atoms between molecules
What happens to NAD during the reaction of pyruvate to acetyl coenzyme A?
It is reduced
What is coenzyme A used for?
Breakdown of fatty acids and carbohydrates (in respiration)
What process is conezyme A used in?
Aerobic respiration
Do cofactors bind temporarily or permanently to an enzyme?
Temporarily
Define inorganic ion cofactor
Inorganic ions obtained from the diet which bind temporarily to the enzyme
Give an example of an inorganic cofactor
Cl- ion for amylase
How does Cl- act as a cofactor for amylase?
Temporarily binds with amylase active site
Modifies the active site shape
Allowing the starch (substrate) to fit into the active site and the enzyme to work
Which enzyme requires a zinc ion as a prosthetic group?
Carbonic anhydrase
Define prosthetic group
Organic or metal ions which bind permanently to the enzyme
What is the function of carbonic anhydrase?
Enables CO2 to be quickly dissolved in the blood for transporation
What is a precursor/apo enzyme?
An inactive form of a particular enzyme
Which enzyme is a chloride ion an essential cofactor for?
Amylase
What is a zymogen/protoenzyme?
Enzymes which require part of their polypeptide to be removed to bring about a change in the shape of the active site/ to reveal the active site to activate the enzyme
Give two factors which can activate a protoenzyme?
- Protease
- Change in pH
How does protease activate a protoenzyme?
removes part of the protoenzyme by cleaving certain bonds to reveal the active site
How does a change in pH activate a protoenzyme?
Results in changes in the tertiary structure to reveal the active site
What is the difference between a coenzyme and an ion cofactor?
A coenzyme is an organic molecule whereas ion cofactors are inorganic ions
How can the effect of concentration of an enzyme be investigated experimentally?
- serial dilutions of trypsin are made
- milk powder is added to each
- the time taken for text behind the test tube to become visible is recorded
Give 2 examples of competitive inhibitors
Aspirin and statins
Why might enzymes be produced in inactive forms?
- the enzymes could otherwise damage cells/tissues
- the action of the enzymes needs to be controlled/only used under certain conditions
Give 3 ways a precursor enzyme can be activated
- change in pH
- protease
- cofactor added
