Enzymes Flashcards
What are enzymes ?
Enzymes are complex globular proteins
Enzymes speed up chemical reactions
by acting as biological catalysts.
What is a catalyst ?
A catalyst is a substance
which increases the speed of a reaction
without being changed or used up in the reaction.
Why are enzymes vital to life?
Enzymes are vital to life and catalyse metabolic reactions in your body e.g. DIGESTION RESPIRATION
Where are enzymes found ?
Intracellular
Extra cellular
What does intracellular mean ?
Some enzymes act inside cells
What does extra cellular mean ?
Some enzymes act outside cells
Where is catalase found ?
Catalase is a common intracellular enzyme found on nearly all organisms exposed to oxygen.
What does catalse catalyse ?
Catalse catalysed the decomposition of hydrogen peroxide to water and oxygen
Where is the catalyst hydrolases found ?
Hydrolases is found in lysosomes
What do hydrolases do?
Hydrolases break down any substances that a cell has taken in by phagocytosis
What does extracellular mean?
Any enzyme that works outside of the cell
Give an example of a type of extracellular enzymes?
Digestive enzymes e.g. Trypsin are extracellular enzymes
What is the function of trypsin?
Trypsin hydrolases proteins –> amino acids
How is every step of a metabolic pathway catalysed?
Each metabolic pathway in a living cell is one of a series of consecutive reactions
Every step of a metabolic pathway is catalysed by a specific enzyme this produces a specific product
How do enzymes work ?
Enzymes have an ACTIVE SITE which has a SPECIFIC SHAPE
The ACTIVE SITE is the part of the enzyme where the substrate molecule binds to
The substrate has to fit into the active site
The active site and substrate are complementary in shape
What are enzymes able to do?
Enzymes can:
- build large molecules from lots of smaller ones
- break down large molecules into smaller ones
- change one molecule into another
How many possible theories are there regarding how enzymes work?
- Lock and key
2. Induced fit
Describe the lock and key theory ?
In the lock and key method:
- substrate fits into the enzyme’s ACTIVE SITE in the same way a KEY fits into a LOCK
- the active site is COMPLEMENTARY in shape to the substrate - so an enzyme substrate complex is formed
What is the induced fit theory ?
In the induced fit theory:
The enzyme and substrate fit together
The interaction between the enzyme and substrate causes the enzyme’s active site to MOULD around the substrate
The active site forms a complementary shape to the substrate therefore it fits perfectly –> enzyme substrate complex
Why are many chemical reactions temporarily given extra heat energy ?
In many chemical reactions a substrate will not be converted to a product unless the reaction is temporarily given some heat energy
This is called the activation energy - it is often provided as heat
Give an example of a chemical reaction which requires activation enegry?
In the Benedict’s test
The Benedict’s reagent and sugar solution must be heated together
Before it will react
Why do human’s maintain their body temperatures at 37oC?
Human’s maintain a quite high internal temperature in order to SPEED UP METABOLIC REACTIONS
What do enzymes do that helps increase the rate of a chemical reaction?
Enzymes reduce the activation energy
Therefore reactions can occur at lower temperatures
Therefore speeding up the rate of the chemical reaction
How do enzymes lower the activation energy?
Enzymes lower the activation energy by HOLDING THE SUBSTRATE in such a way that their MOLECULES can react easier.
WHEN A SUBSTRATE BINDS TO THE ENZYME’S ACTIVE SITE –> ENZYME SUBSTRATE COMPLEX
ENZYME SUBSTRATE COMPLEX LOWERS ACTIVATION ENERGY
What is a cofactor?
Some enzymes need help to work / be activated
A cofactor is a substance that has to be present to ensure that an enzyme catalysed reaction occurs at the appropriate rate
What are cofactors which are part of the enzyme structure called?
Cofactors (substance that has to be present to ensure that the rate of enzyme-catalysed reactions occur at the appropriate rate) that are part of the enzyme structure are known as PROSTHETIC GROUPS
What are cofactors which have temporary associations to the enzymes known as?
Cofactors (substances which must be present to ensure that an enzyme-catalysed reaction occurs at the appropriate rate) which have temporary associations to the enzymes are known as ORGANIC COENZYMES or MINERAL ION COFACTORS
How is a prosthetic group PERMANENTLY BOUND to an enzyme?
A prosthetic group is PERMANENTLY BOUND to an enzyme molecule by COVALENT BONDS.
Are prosthetic cofactors often ionorganic or organic compounds?
Prosthetic cofactors are usually ionorganic compounds
Give an example of a prosthetic Group cofactor:
CHLORIDE IONS act as a COFACTOR for SALIVARY AMYLASE
SALIVARY AMYLASE will only function properly if chloride ions are present
Why does SALIVARY amylase only function properly if chloride ions are present?
Chloride ions affect the CHARGE DISTRIBUTION in an enzyme
Thus Changing the shape of the active site
Making it easier for starch to fit
Give another example of a cofactor ?
A zinc ion is PERMANENTLY BOUND to CARBONIC ANHYDRASES active site
Zinc acts as a cofactor for carbonic anhydrase
Without zinc carbonic anhydrase could not function
What is the function of carbonic anhydrase ?
Carbonic anhydrase is vital in a reaction that enables carbon dioxide to be carried in the blood from the respiring tissue to the lungs.
Tissue –blood–lungs
What is a coenzyme ?
A coenzyme is a small NONPROTEIN molecule that binds temporarily to the ACTIVE SITE of an enzyme molecule
The coenzyme binds just before or at the same time as the substrate binds
What can a coenzyme not do?
Coenzymes cannot catalyse a reaction by themselves but with the help of enzymes they can
Where are many coenzymes derived from?
Many coenzymes are derived from WATER-SOLUBLE VITAMINS
Give an example of a water-soluble vitamin which is the source of a coenzyme?
Thiamine - vitamin B1
Thiamine Vitamine B1 is found in many foods including YEAST/CEREAL GRAINS /BEANS/ NUTS /MEAT
Without thiamine the coenzyme THIAMINE PYROPHOSPHATE cannot be made
THIAMINE PYROPHOSPHATE is involved in catalysing many different reactions
What deficiency will occur due to a lack of THIAMINE vitamine B1?
A deficiency in THIAMINE B1 results in the disease BERIBERI
What factors affect the rate of an enzyme controlled reaction?
TEMPERATURE
pH
ENZYME CONCENTRATION
SUBSTRATE CONCENTRATION
How does an increase in temperature affect an enzyme controlled reaction?
As the temperature increases
The kinetic energy increases
Therefore the molecules move faster
Therefore increased chance of collisions
Thus leading to a greater chance of ES complexes forming
More ES complexes mean reaction likely to have enough activation energy (for SUBSTRATE –> products)
Therefore rate of reaction will increase
And the amount of product will increases
Describe what is meant by the optimum temperature ?
The optimum temperature gives maximum rate of reaction but is a balance between increasing the kinetic energy which increases the number of collisions but
Also ensures the vibrations do not break some of the bonds holding the tertiary structure together (ie do not change shape of active site)
As the temperature increase will the rate of reaction always increase?
No because: The vibrations (due to molecules have increased kinetic energy) means some of the ionic and hydrogen bonds that hold the tertiary structure are broken Therefore the active site changes shape Therefore the active site and substrate no longer fit
The enzyme is DENATURED
This word ‘denatured’ means the enzyme can no longer function as a catalyst and its function cannot be restored
What is pH?
pH is a measure of the concentration of hydrogen ion (H+)
What is the relationship between H+ concentration and strength of pH?
The higher the concentration of H+ ions
The lower the pH value
Why are hydrogen ions attracted towards negatively charged ions ?
As a hydrogen ion has a positive charge it will be attracted towards negatively charged ions or molecules
What can an increased H+ concentration do?
Increased H+ concentration can DISRUPT the hydrogen and ionic bond
Therefore the TERTIARY STRUCTURE can be affected
Therefore the active site can change shape
The enzyme substrate complex no longer forms and the enzyme is denatured
What is meant by the optimum pH of a reaction?
The pH at which the rate of reaction is highest
Do all enzymes have the same optimum pH?
NO
All enzymes have their own optimum pH
What happens at the optimum pH to make the rate of the reaction its highest?
At the optimum pH the concentration of hydrogen ions in the solution gives the T E R T I A R Y structure of the enzyme the BEST overall shape
How does one limit the effect that pH will have on enzymes in an investigation?
Use a buffer
What is a buffer?
A buffer is something that can resist changes in pH
Give an example of when buffers are used in the body?
There are certain chemicals in the blood that act as buffers ( help resist changes to pH) so that the blood pH remains close to pH 7.4
What is the temperature coefficient Q10 a measure of?
The temperature coefficient is a measure of the RATE OF CHANGE of a biological system as a consequence of INCREASING THE TEMPERATURE BY 10oC
How is the temperature coefficient Q10 calculated?
Rate of reaction at T+10oC / rate of reaction at ToC
What happens to the value of the temperature coefficient Q10 above an enzyme’s optimum temperature and why?
Above an enzyme’s optimum temperature the value of the temperature coefficient Q10 DROPS
This drop in the value of the temperature coefficient happens because higher temperature alter the active site
Is the following statement true:
‘The amount of substrate can be varied for a fixed concentration of enzyme molecules’
Yes
The amount of substance can be varied for a fixed concentration of enzyme molecules
Describe what happens between substrates and enzymes in low SUBSTRATE concentration ?
There are too few substance molecules to occupy all the available active sites
The rate of the reaction is only half the maximum possible rate for the number of enzyme molecules available
Describe what happens between substrate molecules and enzymes in intermediate substrate concentration?
With twice as many substrate molecules available
All the active sites are occupied at one time
The rate of the reaction has doubled to its maximum rate
Because all of the enzyme’s active sites are occupied with substrates
Describe the relationship between high substrate concentration and enzymes?
The addition of further substrate molecules has no effect at all
As all the active sites are already occupied
No increase in reaction rate
Describe the relationship between substrate concentration and rate of reaction up to the saturation point?
Increasing the substrate concentration
Increases the successful collisions with enzyme’s active site
This means more enzyme substrate complexes form
Therefore lower activation energy
So more product in a given time
When does the positive correlation between increasing substrate concentration and rate of reaction stop?
Once all the enzyme’s active sites have become occupied (SATURATION POINT)
The enzyme is said to be working at Vmax
Therefore further increase in substrate concentration has no effect
Because the enzyme concertation is now the limiting factor
Describe the relationship between the rate of a reaction and enzyme concentration?
As enzyme concentration increases
More active sites on the enzymes are available
Therefore more successful collisions between enzymes and substrate occur
More ESC can form in a given time
Less activation energy
Therefore increase in product in given time
At what point does the positive correlation between enzyme concentration and reaction rate stop?
Eventually the substrate concentration becomes the limiting factor because no matter how much more enzymes are added if the amount of substrate has been used up then no reaction will occur
How is the initial rate of a reaction calculated?
The initial rate of a reaction is casualties as the gradient of a tangent
E.g. X/y = rate
What is an inhibitor?
Inhibitors are any substances or Molecule
that slows down the rate of an enzyme-controlled reaction
by affecting the enzyme molecule in some way
What is a competitive inhibitor ?
Competitive inhibitors have similar shapes to the substrate
Therefore they can occupy the active sites which are complementary in shape
Thus preventing the substrate from entering the active site
By forming an enzyme-inhibitor complex
Regarding competitive inhibitors what does the amount of inhibition depend on?
The amount of inhibition depends on the relative concentration of substrate molecules to inhibitor molecules
The more inhibitor molecules means more inhibitors collide with enzyme active site therefore effect of inhibition is greater
How can the effects of competitive inhibitors be reversed?
Increasing the substrate concentration effectively dilutes the effect of inhibitors
If enough substrate is added the inhibitor is unlikely to collide with the enzyme
What do non-competitive inhibitors not do?
Non competitive inhibitors do not compete with the substrate for a place in the active site.
Describe what non-competitive inhibitors do to effect the enzyme molecule?
Non competitive inhibitors bind to an ALLOSTERIC SITE (site other than the active site)
This causes the active site to change shape as the tertiary shape is disrupted
This results in the substrate no longer fitting into the active site as the substrate shape and active site shape are no longer complementary
What effect does increasing the substrate concentration have on the effect of a non competitive inhibitor ?
Increasing the substrate concentration has no effect
Why can non competitive inhibitors be irreversible or reversible?
It depends on whether the inhibitor bonds briefly or permanently with the enzyme
What do inhibitors that seriously disrupt enzyme controlled reactions act as?
Inhibitors that seriously disrupt an enzyme controlled reaction act as M E T A B O L L I C P O I S O N S
By preventing vital chemical reactions
Give an example of an inhibitor which acts as a metabolic poison:
The toxin alpha-AMANITIN found in death cap mushrooms inhibits the enzymes that catalyse the production of RNA from DNA
No protein synthesis
Give another example of a metabolic poison ?
Snake venom = a mixture of enzymes and toxins
One enzyme inhibits the enzyme ACETYL CHOLINESTERASE which is involved in nerve transmission
Paralysis
What is the consequence of the following fact;
Cells do not need to accumulate too much of the end product
therefore the product of the last enzyme in a metabolic sequence often inhibits (no competitive) the first enzyme
Why do scientists always measure the initial rate of a reaction?
The measure the rate of the reaction at the star before any other factors have had a chance to have an effect
