2.4 - Enzymes Flashcards
Why are enzymes so remarkable?
- Low temperatures
- Normal pH and pressure
- More specific
How many amino acids is the active site made from?
About 6 to 10.
What happens in catabolic reactions?
Metabolites are broken down.
What happens in anabolic reactions?
Synthesis of larger molecules.
Where is catalase found in eukaryotic cells?
Small vesicles called peroxisomes.
In our digestive system, where are enzymes secreted from?
Cells lining the alimentary canal, into the gut lumen.
Which enzyme contains a zinc ion as a prosthetic group?
Carbonic anhydrase
What does carbonic anhydrase do?
Catalysed the inter conversion of carbon dioxide and carbonic acid which then breaks down to protons and hydrogencarbonate ions.
Which ion must be present from amylase to make maltose?
Chloride.
What are coenzymes?
Small, organic non-protein molecules that bind temporarily to the active site of the enzyme.
Where are many coenzymes derived from?
Water soluble vitamins.
Define enzyme substrate complex
enzyme model with substrate molecule in active site, joined temporarily by non-covalent forces
what is Q10?
temperature coefficient, calculated by dividing rate of reaction at (T+10) by the rate of reaction at T
How does pH affect enzymes?
Excess H+ ions interfere with hydrogen bonds and ionic forces, changing shape
Benefits of enzyme degradation
elimination of abnormal proteins
eliminating superfluous enzymes
What regulates an enzyme controlled reaction
End product inhibition
How do many toxins work?
By inhibiting or inactivating enzymes
What are two poisons/toxins that inhibit enzyme action?
- cyanide
- snake venom
- malonate (respiration)
- arsenic (respiration)
What does cyanide inhibit?
catalase
stop final stage of aerobic respiration
Which medicinal drugs act as enzymes inhibitors and how?
- some antiviral drugs (eg reverse transcriptase inhibit reverse transcriptase which catalyses the replication of viral DNA)
- some antibiotics (penicillin inhibits transpeptidase which catalyses the formation of proteins in bacterial cell walls. this weakens the cell wall and the bacterium cant regulate osmotic pressure and bursts)
What type of reactions do enzymes catalyse?
Cellular (eg respiration) and whole body (digestion)
Structural ( eg production of collagen) and function (eg respiration)
What enzyme catalyses intracellular reactions?
catalase
What enzyme catalyses extracellular reactions?
trypsin
Describe the role of catalase
Hydrogen peroxide to oxygen and water
Describe the role of trypsin
Catalyses the hydrolysis of peptide bonds
made in pancreas and secreted into small intestine
Describe the role of amylase
found in saliva
hydrolysis of starch to maltose
What about enzymes is responsible for lowering activation energy?
The formation of the enzyme-substrate complex
Why does the enzyme substrate complex lower the activation energy?
- if they need to be joined, they are held close together
- if they need to be separated, the active site puts strain on the bonds in the substrate
What does Q10 show?
How much the rat of a reaction changes when the temperature is raised by 10 degrees
What does a Q10 value of 2 demonstrate?
Rate doubles when temp is raised by 10 degrees
What are the factors affecting the rate on enzyme controlled reaction?
- temperature
- pH
- enzyme concentration
- substrate concentration
Describe two ways of measuring the rate of an enzyme controlled reaction
1) How fast the product appears, eg for catalase you could collect volume of oxygen
2) you could measure the disappearance of a substrate and compare with different conditions
Describe an experiment that investigates the effect of temperature of catalase activity
- boiling tubes with hydrogen peroxide
- add equal volumes of buffer solution for constant pH
- put each boiling tube in different water bath temp
- add catalase
- calculate volume of oxygen produced and repeat
Whats the difference between cofactors and coenzymes?
Coenzymes are cofactors that are organic molecules
- cofactors don’t get used up
- coenzymes are changed by reactions and recycled
Whats a source of coenzyme?
Vitamins
What an enzymes prosthetic group?
When a cofactor is tightly bound to the enzyme,
permanent part of active site
Cofactor of amylase
Cl-
Prosthetic group of carbonic anhydrase
Zn2+
Describe competitive inhibition
- similar shape to substrate
- compete for active site
Describe non-competitive inhibition
-binds at allosteric site which causes the active site to change shape
What happens when you increase the substrate concentration in competitive and non-competitive inhibition?
competitive - increase rate of reaction
non-competitive - wont make any difference an enzyme activity will still be inhibited
When is inhibition irreversible?
when there are strong, covalent bonds and the inhibitor cannot be removed
When is enzyme inhibition non-reversible?
when there are weaker hydrogen bonds or weak ionic bonds and the inhibitor can be removed
Why are enzymes sometimes synthesised as inactive precursors in metabolic pathways?
to prevent them causing damage to cells
Example of an enzyme acting as a inactive precursor
some proteases (which break down proteins) are inactive precursors so they don’t damage proteins in the cell that they are made
How do inactive precursor molecules work?
part of the precursor molecule inhibits its action as an enzyme and this part can be removed when the enzyme needs to be active
Why do we need small amounts of cofactors in our bodies?
- they can be reused
- enzyme mass is small
- some enzymes don’t need cofactors
What are models used for?
simple representations of processes
Define enzyme/biological catalyst.
proteins used in metabolism
that alter the rate of chemical reaction
lower activation energy
not used up in the process
