2.4 Enzymes Flashcards
What are enzymes?
They are biological catalysts which speed up reactions.
They catalyse metabolic reactions.
(Cellular level and for an organism as a whole)
They are globular proteins
Have an active site which has a specific shape (determined by the tertiary structure), the substrate binds to it. (if complementary)
Enzyme actions can be?
Intracellular and Extracellular
Intracellular enzyme example?
Catalyse
- Catalyse works inside cell to break down hydrogen peroxide (which can kill cells) to oxygen and water
Extracellular enzyme example? 1
Amylase
- Works outside cells in the human digestive system
- Amylase is found in salvia, secreted into the mouth by salivary glands, catalyses the hydrolysis breakdown of starch into maltose
What do enzymes reduce?
Activation energy, this is often provided as heat.
Reducing the activation energy
Speeds up the rate of reaction
Extracellular enzyme example? 2
Trypsin
- Catalyses the hydrolysis of peptide bonds turning big polypeptides into small ones. It is produced in the pancreas and secreted into the small intestine
Induced fit model **
Suggests that the substrate doesn’t have to be the right shape to fit into the AS. It just needs to be able to change the shape of the AS.
Lock and key model
Suggests that they fit together in the first place, it is a tight and exact fit
Factors affecting enzyme activity?
Temperature, pH, Enzyme activity, Substrate concentration
- Details in notes
Enzyme Practicals
https://pmt.physicsandmathstutor.com/download/Biology/A-level/Notes/OCR-A/1-Practical-Skills-in-Biology/PAG%2004%20-%20Rates%20of%20Enzyme%20Controlled%20Reactions.pdf
Competitive inhibitation?
Inhibitor has a similar shape to the substrate, it competes to bind to the AS but it causes no reaction. It blocks the AS.
- Higher the concentration of the inhibitor the more AS is being taken up
- Higher the concentration of the substrate the higher the chance of the substrate binding to the AS
Cofactors and Coenzymes are
Essential for Enzymes to work
Cofactors
Some non-proteins substances bound to enzymes to allow them to work. The non proteins that bound to them are called cofactors.
Coenzymes
Organic cofactors molecules
Inorganic Molecule/Ions cofactor example
They help the enzyme and substrate to bind together. They are indirectly participating in the reaction, therefore, they will not be used up or changed.
Eg. Chloride ions for amylase
Organic Molecule cofactor example
They participate in the reaction and they are changed by it. They often act as carriers, moving chemical groups (between enzymes)
They are continually recycled during this process.
Eg. Vitamins are often sources of coenzymes
Prosthetic group
If cofactor is tightly bound to the enzyme
Eg. Zinc ions are prosthetic group for the carbonic anhydrase. They are a permanent part of the enzyme’s AS
Inhibitors can be…
irreversible or reversible
Irreversible inhibitors?
Strong, covalent bonds. Can’t be removed easily
Reversible inhibitors?
Weak H bonds/Weak ionic bonds. Can be removed
Inhibitors can protect the cell. (2 points why?)
- Sometimes enzymes are synthesised as inactive precursors in metabolic pathways to prevent them causing damage to cells.
- Part of the precursor molecule inhibits its action as an enzyme. Once removed the enzyme = active.
Examples of medicinal drugs being enzyme inhibitors? (1)
ANTIVIRAL
Antiviral drugs (drugs that stop viruses like HIV), eg. reverse transcriptase inhibitors inhibit the enzyme reverse transcriptase, this catalyses the replication for viral DNA.
This prevents the virus from replicating
Examples of medicinal drugs being enzyme inhibitors? (2)
ANTIBIOTICS
Antibiotics (penicillin) inhibits the enzyme transpeptidase, which catalyses the formation of proteins in bacterial cell walls. This weakens the cell wall, prevents bacterium pressure. As a result, the cell wall bursts and kills the bacterium
Cyanide
Irreversible inhibitor of cytochrome c oxidase. An enzyme that catalyses respiration. Cells that can’t respire die.
Malonate
Inhibits succinate dehydrogenase (catalyses respiration reactions)
Arsenic
Inhibits the action of pyruvate dehydrogenase. (catalyses respiration reaction)
Metabolic pathways are…
regulated by end product inhabitation
A metabolic pathway?
A series of connected metabolic reactions. The product of the first takes part in the second, so on. Each reaction is catalysed by a different enzyme
Product inhabitation?
Many enzymes are inhabitation by the product of the reaction they catalyse
End product inhabitation?
When the final product in the metabolic pathways inhibits an enzyme that acts earlier on in the pathway
- A way of controlling the amount of the end product that gets made.
An example of controlling the amount of end product made (EPH)
Phosphofructokinase is an enzyme involved in the metabolic pathway that breaks down glucose to make ATP
- ATP inhibits the action of phosphofructokinase - so a high level of ATP prevents more ATP being made
Are end product/product inhabitation reversible or irreversible?
Reversible
- So when a level of a product starts to drop the enzyme will start to function again.
