▪️1.4 -enzymes And Biological Reactions Flashcards
Define catalyst
An atom or molecule that alters the rate of a chemical reaction without taking part in the reaction or being changed by it
Define metabolic pathway
A sequence of enzyme controlled reactions in which a product of one reaction is a product in the next
Define metabolism
All of the chemical reactions in the body
Name an example of a metabolic pathway
- Anabolic reaction, building up molecules e.g protein synthesis
- catabolic reactions, breaking down molecules e.g digestion.
What are metabolic pathways controlled by?
Enzymes, the product of one enzyme controlled reaction becomes the reactant in the next
What are enzymes?
Enzymes are globular proteins with a tertiary structure and the protein chain folded into a spherical molecules with the R groups on the outside of the molecule
They are catalysts
Why are enzymes called biological catalysts?
Because they are made by living cells
Name the properties that chemical catalysts and enzymes share in reactions
- speed up reactions
- not used up
- not changed
- have a high turnover rate (they catalyse many reactions per second)
What makes enzymes soluble?
The enzymes have a hydrophilic R variable group on the outside of the molecule
What determines the bonds the amino acids in the polypeptide chain make with each other?
The elements in the R group
Name the bonds present in enzymes
What do they do?
Hydrogen bonds Disulphide bridges Ionic bonds Hydrophilic interactions They hold the enzyme molecule in its tertiary form e.g maintaining the active site of the enzyme
Name the 3 sites where enzymes act
Extracellular
Intracellular (in solution)
Intracellular (membrane bound)
Give an example of an enzyme that catalyse extracellular reactions
Amylase, made in the salivary glands, moves down the salivary ducts to the mouth.
Amylase is an enzyme secreted from cells by exocytosis and then catalyses extracellular reactions
Give an example of an enzyme which catalyse intracellular reactions in solution
Enzymes in the solution in the storms of the chloroplasts catalyse the synthesis of glucose
Give an example of an enzymes that catalyses membrane bound intracellular reactions
Enzymes on the cristae of mitochondria transfer electrons and hydrogen ions in ATP formation
Define active site
The specific 3D site on an enzyme molecule to which the substrate binds by weak chemical bonds
Define enzyme substrate conplex
Intermediate structure found during an enzyme catalysed reaction in which the substrate and enzyme bind temporarily such that the substrates are close enough to react
What is enzyme specificity mean,
An enzyme is specific for its substrate, an enzyme with a specific active site can only catalyse one type of reaction.
What does lock and key theory state
The substrate can fit into the active site of an enzyme like a key fits into a lock, they are specific to each other
What does the lysozyme and the induced fit model state?
The enzyme shape is not fixed as previously thought and alters slightly to accommodate the substrate to form an enzyme substrate complex
Define the term activation energy
The minimum energy that must be put into s chemical system for a reaction to occur
How do catalysts speed up reactions in living organisms
They lower the activation energy required for the reaction to occur. When a substrate enters the active sit if an enzyme, the shape of the molecule alters, allowing the reaction to occur at lower temperatures
How can the progress of an enzyme catalysed reaction be measured?
By measuring the formation of product or disappearance of substrate
Describe what happens after an enzyme and substrate are mixed together (can be used to explain graph)
- the enzyme and substrate molecules are in motion and collide
- substrate molecules bing to the active site of enzymes, in “successful” collisions the substrate is broken down and products released
When does the enzyme concentration become a limiting factor?
When all of the conditions are optimal and all active sites are full of substrates
When does the substrate concentration become a limiting factor?
As the reaction continues there are less substrate and more product. The enzyme concentration is constant. The substrate is used up eventually and no more product can be formed so ROR plateaus
Why does a line on an enzyme time graph go through the origin
Because at 0 time no reaction had occurred and therefore 0 product is produced
On a graph what gives you the rate of reaction at a specific time
The gradient
Name the percentage increase in mass equation
(Actual increase in mass/initial mass) x100
Name the 4 factors that can effect the rate of enzyme action
Temperature
pH
Enzyme concentration
Substrate concentration
Describe how temperature can increase the rate of enzyme controlled reactions
As temperature increase (until around 40 degrees) the KE of enzymes increase meaning there’s more successful collisions increasing ROR
Name the general rule about the effect of temperature on enzyme controlled reactions
The rate of reaction doubles for every 10 degrees increase up to about 40 degrees
Describe how temperature can decrease the rate of enzyme controlled reactions above 40 degrees
Molecules have more KE but their increasing vibration breaks hydrogen bonds, changing the shape of the enzymes tertiary structure and hence active site so the substrate can no longer fit. The enzyme is denatured.
Why is there a very low rate of reaction at low temperatures?
At low temperatures the enzyme is inactivated as the molecules have very low KE.
Shape is unchanged ::enzyme will work again if temperature is raised
Define denaturation
The permanent damage to the structure and shape of a protein molecule cause by High temperature/extreme pH
Define inactivation
Reversible reduction of enzyme activity at low temperatures as molecule have insufficient KR to form enzyme substrate complex’s
What can affect the charges of the amino acids side chain of the enzymes active site?
Hydrogen or hydroxyl ions
How can a extremely low pH denature an enzyme?
At low pH, exzess H+ ions are attracted to negative charges and neutralise them distrusting the ionic and hydrogen bonds maintaining the shape of the active site, changing their shape.
How can extremely high pH denature enzymes
At high pH, excess OH- ions neutralise was the positive charges disrupting the ionic and hydrogen bonds maintaining the shape of the active site, changing their shape.
Define limiting factor
Factor is limiting when an increase in its value caused an increase in the rate of reaction
If the enzyme concentration is constant what happens to the ROR when substrate concentration increases
ROR increases
What happens to the ROR when there is low substrate concentration
The enzyme molecules have only a few substrates to collide with so the active sites aren’t working to full capacity, this means the substrates become a limiting factor as they control the ROR
When is an enzyme saturated?
When all of the active sites are full with substrates, meaning the ROR is at its maximum
Why does the line on a substrate concentration graph plateau?
Because if even more substrate is added, the reaction can’t be catalysed any faster as all active sites are occupied
When the line on a substrate concentration graph plateaus, why is substrate concentration no longer a limiting factor?
Because it is no longer controlling the rate of reaction, it is now controlled by other factors such as temperatures and pH
Why is the enzyme concentration directly proportion to the rate of reaction
- The value of substrates normally outweighs the value of enzymes
- this means as the enzyme convey increase, there are more active sites available and therefore the rate of reaction increase
What is a turn over number?
The number of substrate molecules that one enzyme can turn into products in a given time.
Why is only a low enzyme concentration needed to catalyse a large number of reactions?
Because once a product leaves the active site, the enzyme molecule can be reused
Define inhibitor
A molecule or ion that binds to an enzyme and reduces the rate of the reaction it catalysed
Define competitive inhibition
Reduction of the rate of an enzyme controlled reaction by a molecule or ion that had a complementary shape to the active site, similar to the substrate which binds to the active site preventing the substrate from binding and forming an enzyme substrate complex
Basic purpose of the inhibitor
Combines with an enzyme and prevents it from forming an enzyme substrate complex
Give an example of a competitive inhibitor
The Krebs cycle is catalysed by the enzyme succinic dehydrogenase
Succinic acid —> catalysed by succinic dehydrogenase —-> fumaric acid + hydrogen
Malonic acid has a similar shape to succinic acid and do they compete for the active site of succinic dehydrogenase.
How can you reduced the effect of a competitive inhibitor?
By increasing the concentration of the substrate, because the more substrate the greater the chance of them binding to the enzyme reducing the chance of the inhibitor
What happens to the ROR if the inhibitor concentration increases
The ROR slows as the inhibitor would bind to more active sites
Define non-competitive inhibitor:
An atom, molecule or ion that reduced the rate of an enzyme by binding at a position other than the active site, altering the shape of the active site and preventing the substance from successfully binding to it
What is an ‘allosteric site’ ?
A site that a non competitive inhibitor binds to other than the active site
How to non-competitive inhibitors affect the rate of reaction
They bond to the allosteric site, affecting the bonds within the enzyme molecule (ionic and hydrogen), altering its overall shape including the active site so no enzyme substrate complex’s form
What happens to the ROR as the concentrations of non-competitive inhibitor increases
As it increases more enzyme molecules are denatured and do the rate of reaction (and final mass of product) decrease
Give an example of a non competitive inhibitor
Heavy metal ions such as Lead (Pb2+) and arsenic (As3+)
Is the effect of non-competitive inhibitors reversible?
Some bind reversely some bind irreversibly
Define immobilised enzyme
Enzyme molecules bound to an inert material, over which the substrate molecules move
When are enzymes immobilised?
Enzymes are immobilised if they are fixed, bound or trapped on an inert matrix such as sodium alginate beads or cellulose microfibrils
How can you use immobilised enzymes
Substrate is added to the top of a column full of alginate beads, and flows down
2) the molecules bind to the enzymes active site both in the bead surface and inside the bead (substrate molecules can diffuse in)
3) the product can be collected at the bottom of the container and the column can be used again
Give an example of where immobilised enzymes are used
Used in industrial processes such as fermentation as they can be recovered for reuse
Why are the products of immobilised enzymes and a substrate easy to purify?
Because the enzyme is fixed and does not contaminate the products
Will the same volume of material split into less larger alginate beads or more smaller alginate beads produce a faster rate of reaction?
Smaller beads because the substrate molecules will have easier access to enzyme molecules and so they will produce a higher rate of reaction
Name one factor preventing wider use of enzymes that are free in solution.
Enzyme instability
Why does immobilising enzymes make them more stable?
Immobilising enzymes with a polymer matrix makes them more stable because it creates a micro environment allowing reactions to occur at higher temperatures than normal
Why do immobilised enzymes not denature at higher temperatures/ more extreme pH
Because it is trapped in the alginate bubble it prevents the shape change that would denature the active site
-this means enzyme can be used in a wider range of physical conditions than if it were in a free solution.
Why do immobilised enzymes in beads have a lower rate of reaction than immobilised enzymes on a membrane
This is because some of the active sites are inside the alginate beads and therefore the substrates take time to diffuse through them. Enzymes on a membrane are readily available for binding so give a higher reaction rate.
Name some advantages of using immobilised enzymes
- increased stability and function over wider range of pH / temp than enzymes free in solution
- products are not contaminated by enzyme
- enzymes are easily recovered for reuse
- sequence of columns can be used so serveral enzymes with different pH or temp optimum can be used in one process
- enzymes can be easily added/removed giving greater control over reaction
Define biosensor
A device that combines a biomolecule, such as an enzyme, with a transducer, to produce an electrical signal which measures the concentration of a chemical
Name 2 uses for immobilised enzymes
1- biosensor
2-lactose free milk (milk passed down column containing immobilised lactose)
3- immobilised on rest strips, e.g glucose oxidase is bound to pregnancy test to detect glucose in urine
Describe how a biosensor works using the example of glucose oxidase
The enzyme glucose oxidase, immobilised on a selectively permeable membrane is placed in a blood sample and binds to glucose. This produces a small electric current, detected by the electrode
