M2, C4 Enzymes Flashcards
define enzyme
biological catalyst that interact with substrate molecules to facilitate chemical reactions
what are enzymes made of
globular proteins
define anabolic
reactions of metabolism that construct molecules from smaller units
they require energy from the hydrolysis of ATP
define active site
area of an enzyme with a shape complementary to a specific substrate, allowing the enzyme to bind a substrate with specificity
define activation energy
the energy required to initiate a reaction
define catabolic
reactions of metabolism that break molecules down into smaller units
these release energy
define substrate
a substance used, or acted on, by another process or substrate
eg. a reactant in an enzyme catalysed reaction
how does an enzyme speed up a reaction
it lowers the activation energy
this means it takes less energy to initiate a reaction hence speeding the reaction up
what is the lock and key hypothesis
- an enzyme has a specific active site which is complementary to the shape of the substrate
- when the substrate is bound to the active site and enzyme-substrate complex is formed
- the substrates then react forming an enzyme-product complex
- the products are released leaving the enzyme unchanged
- temporary bonds are also formed when the R groups of the enzymes interact with the substrate which helps the reaction along
what is the induced fit hypothesis
- modified version of the lock and key hypothesis
- the active site of the enzyme actually changes shape slightly as the substrate enters
- the initial reaction between the enzyme and substrate is relatively weak
- the enzyme’s tertiary structure changes which strengthens binding and putting strain on the substrate molecules
- this lowers the activation energy for the reaction
how would you work out metabolism
catabolic reactions + anabolic reactions
how is starch digested
starch polymers are broken down into maltose by amylase
amylase is produced by the salivary glands and pancreas and released in the saliva and pancreatic juice in the small intestine
maltose is then broken down into glucose by maltase
maltase is present in the small intestine
glucose is then absorbed into the bloodstream
how is protein digested
give an example of protease
trypsin is a protease
it catalases proteins into smaller peptides
peptides are broken into amino acids
trypsin are produced in the pancreas and released in the pancreatic juice in the small intestine
amino acids are absorbed by cells lining the digestive system and go into the bloodstream
As temperature increases how does enzyme activity change?
What’s the optimum temp in humans?
Increasing temp, increases kinetic energy in particles. The particles collide more frequently. This would mean more successful collisions between the substrate and the enzyme which increases the rate of reaction.
The rate of reaction doubles with a 10 degree Celsius temp rise.
Optimum temperature in humans is 37
Why do enzymes denature at a too high temp?
As temperature gets high the bonds between proteins vibrate more. Bonds will then strain and break. This changes the shape of the tertiary structure of the protein.
The active site changes shape so won’t fit with the substrate so the enzyme can no longer act as a catalyst.
What does the graph look like of temperature against rate of reaction
Slow increase up to the optimum temp and then a rapid decrease
What adaptions do enzymes have which are in the cold and in the hot?
More flexible structures making them less stable
Enzymes at high temp have more bonds so are more stable and are more resistant to change
What is pH and what is its relation to hydrogen ions
It’s the measure of hydrogen ion concentration
The lower the pH, the more hydrogen ions are (more acidic)
How does pH affect enzyme reactions
Hydrogen ions are attracted to negatively charged areas. Different amino acids have different charges and hydrogen ionic bonds holds amino acids in a very precise shape.
Hydrogen ions interfere with these bonds and thus change the structure of the enzyme and its active site.
What is the optimum pH for amylase? For pepsin?
Amylase - pH 7.8
Pepsin - pH 1.8
How does substrate concentration affect the rate of reaction
More concentration increases the rate of reaction because there is a higher collision rate.
However eventually all the active sites are used up and the rate of reaction can no longer increase. This is the V max.
what are intracellular enzymes
enzymes that act within the cells
eg. hydrogen peroxide which is broken down by catalase
what are extracellular enzymes
enzymes that break down substances outside of cells
for example nutrients and proteins which need to be transported from cell to cell may be too big to get into the cell so enzymes can break them down so they can fit.
they can make smaller molecules for digestion.
what are enzyme inhibitors
molecules that prevent enzymes from carrying out their normal function of catalysis
two types - competitive and non-competitive
what is competitive inhibition
A molecule that has a similar shape to the substrate of an enzyme fits into the active site of that enzyme.
It blocks the substrate from entering the active site, preventing the enzyme catalysing the reaction.
The enzyme is said to be inhibited.
The number of substrates binding with active sites reduces, hence slowing down the rate of reaction.
The inhibitor only binds temporarily for most cases.
what are some examples of competitive inhibition
Statins - inhibits the enzyme that synthesises cholesterol to stop high cholesterol levels
Aspirin - irreversibly inhibits enzymes that synthesise prostaglandins and thromboxane which produce pain and fever
what is non-competitive inhibition
The inhibitor binds to the enzyme at a location other than the active site - this is called the allosteric site.
This causes the tertiary structure of the enzyme to change which changes the shape of the active site.
The substrate therefore can no longer bind with the enzyme and is said to be inhibited.
Active sites therefore become unavailable hence decreasing the rate of reaction.
Can be reversible or irreversible
what are some examples of irreversible non-competitive inhibitors
Organophosphates - insecticides which stop the nerve impulse transmission which leads to paralysis
Proton pump inhibitors - treat long term indigestion by stopping the production of excess acid
what is end-product inhibition
When a product of a reaction then acts as an inhibitor to the enzyme that produces it.
Serves as a negative feedback control mechanism.
Stops excess products being made and stops resources being wasted.
It is non-competitive reversible inhibition.
How does respiration involve end-product inhibition
- Breaking down a glucose molecule involves the enzyme PFK (phosphofructokinase).
- This enzyme is competitively inhibited by ATP. It therefore regulates its own production.
- When ATP levels are high, more ATP binds to PFK which stops glucose being broken down.
- As ATP is used up less binds to PFK so the enzyme can catalyse more so respiration resumes leading to the production of more ATP.
define cofactor
non-protein components necessary for the effective functioning of an enzyme
define prosthetic group
non-protein component of a conjugated protein
what is a coenzyme
an organic cofactor
where are inorganic cofactors obtained from
the diet as minerals
eg. iron, calcium, chloride and zinc
what cofactor is in amylase
chloride ion
where are coenzymes derived from
vitamins in the diet
whats the difference between cofactors and prosthetic groups
cofactors are temporary and prosthetic groups are tightly bound to the enzyme and can be permanent
what are precursor enzymes
inactive enzymes which are produced like that
why is it important that some enzymes are precursor
so they don’t cause damage
so they can be controlled and activated only under certain conditions
how are precursor enzymes activated
they need to undergo a change in shape to the tertiary structure
this is done by adding a cofactor
what is an apoenzyme
a precursor enzyme before a cofactor is added
what is a holoenzyme
when a cofactor is added to a precursor enzyme so it is activated
In blood clotting describe the enzyme activation process / the coagulation cascade
when platelets touch the collagen of the skin, they become aggregated and release factor X
It is activated by the cofactor vitamin K
When it is activated it converts prothrombin to thrombin by changing the structure
Thrombin is a protease which converts soluble fibrinogen to insoluble fibrin fibres
Fibrin forms the blood clot
