Module 2 Section 4 - Enzymes Flashcards
Pyper
intracellular
inside cells
extracellular
outside of cells
Why does increasing the substrate concentration initially increase the rate of reaction?
More substrate is available
this isn’t a full answer, but something else I can add to my explanation
Give two examples of extracellular enzymes.
trypsin and amylase
Give one examples of an intracellular enzyme.
catalase
How does catalase work?
It breaks down toxic hydrogen peroxide (H2O2 - produced from many cellular processes) into harmless oxygen and water.
How does trypsin work?
It catalyses the hydrolysis of peptide bonds to break down bigger polypeptides into smaller ones.
How does amylase work?
It catalyses the hydrolysis of starch into maltose in the mouth.
Where is trypsin produced?
Pancreatic cells
Where is trypsin secreted?
Into the small intestine
What organ system do amylase and trypsin work in?
The digestive system
According to the induced fit model, how does an enzyme catalyse a reaction?
An enzyme’s active site changes shape slightly to better facilitate the reaction, allowing the substrate(s) to bind more tightly
Describe two ways that the formation of enzyme-substrate complexes lowers the activation energy of chemical reactions.
- The enzyme’s active site holds two substrates closer together, reducing repulsion so they can bond more easily.
- The enzyme’s active site strains the bonds holding a substrate together, so the substrate molecules can be broken down more easily.
Explain why enzymes denature due to high temperatures.
Enzymes vibrate more at higher temperatures. This breaks bonds between the amino acids in the enzyme protein, disrupting the enzyme’s tertiary structure (changing the shape of the active site).
This is only part of an explanation
Explain why enzymes denature due to extreme pHs.
in terms of an exam question answer
As the pH changes from the optimum pH, there are fewer/more H+ and OH- ions surrounding the enzyme. These interact with the charges on the enzyme’s amino acids, breaking ionic and hydrogen bonds within the tertiary structure of the enzyme, including the active site.
Enzyme denaturation due to high temperature is ____.
irreversible
Enzyme denaturation due to changes in pH is ____.
reversible for small variations but irreversible for large variations
temperature coefficient
How much the rate of reaction changes when the temperature increases by 10°C.
temperature coefficient symbol
Q10
temperature coefficient formula
Q10 = rate at higher temperature / rate at lower temperature
Q10 of 3 = ?
rate of reaction triples (is multiplied by 3) for an increase in 10°C
How can you calculate the rate of reaction from a graph of e.g. volume of gas produced against time?
Find the gradient - you will likely have to draw a tangent
How can you calculate the initial rate of reaction?
Draw a tangent that passes through time = 0. Calculate the gradient of this line and include the units (y / x)
Vmax
The maximum velocity/rate of reaction with an enzyme - this is where the graph plateaus.
inorganic - in terms of cofactors
Carbon isn’t bound to hydrogen
cofactor
A non-protein inorganic substance that enables some enzymes to function
How do cofactors help enzymes to function properly?
They help the enzyme & substrate bind together without being directly involved in the reaction (e.g. not directly in the enzyme’s active site but does change the active site’s shape) so they aren’t used up/changed in the reaction
example of a cofactor
chloride ions for amylase
coenzyme
A non-protein organic substance that enables some enzymes to function.
How do coenzymes help enzymes to function properly?
They DO participate in the reactions so are changed by the reaction (e.g. they are carriers, moving chemical groups between different enzymes)
If coenzymes are changed in a reaction, how do we not run out of them?
They are constantly recycled (for example, the coenzyme bounces between enzyme A which changes it into one form and enzyme B which changes it back into its initial form)
prosthetic group
A cofactor that is tightly bound to the enzyme
Give an example of a prosthetic group and how it helps an enzyme.
Zinc is a permanent prosthetic group for carbon anhydrase (an enzyme in red blood cells) which catalyses the reaction
water + carbon dioxide -> carbonic acid
What does it mean if a molecule is a permanent prosthetic group? Give an example of one that you need to know.
They are a permanent part of the enzyme’s active site.
Zinc ions
Give a source of many coenzymes.
vitamins
competitive inhibitor
A molecule with a similar shape to the substrate molecule, that fills the enzyme’s active sites so the substrate is blocked from binding to them; they compete for the active sites
non-competitive inhibitor
A molecule that binds to any place on the enzyme apart from the active site, but that causes the active site to change shape so the substrate molecules can no longer bind to them
allosteric site
The place on an enzyme where a non-competitive inhibitor binds to (anywhere apart from the active site)
What do competitive inhibitor rate of reaction graphs look like, compared to the normal graph?
The gradient is less steep. The competitive inhibitor means that it takes longer to reach Vmax
What do non-competitive inhibitor rate of reaction graphs look like, compared to the normal graph?
The gradient is less steep and the graph doesn’t reach as high a Vmax
Competitive and non-competitive inhibitors can be ____ or ____.
reversible
irreversible
What makes an inhibitor reversible or irreversible?
Thre strength of the bonds between the enzyme and the inhibitor
What sort of bonds form between a reversible inhibitor and an enzyme?
Weak hydrogen or ionic bonds
What sort of bonds form between an irreversible inhibitor and an enzyme?
Strong covalent bonds
How can antiviral drugs use enzyme inhibitors?
Inhibitor of reverse transcriptase, so it can’t catalyse the replication of the viral DNA. This prevents the virus from replicating which keeps the virus level low
How can antibiotics use enzyme inhibitors?
Penicillin is an inhibitor of transpeptidase so bacteria can’t catalyse the formation of their cell walls. This weakens the cell wall and can lead to the cell bursting and the bacterium being killed
Give two examples of metabolic poisons.
Arsenic (chosen one to learn) and cyanide
Give an example of how one metabolic poison example works
Arsenic – non-competitive inhibitor of pyruvate dehydrogenase an enzyme that catalyses respiration reactions. Arsenic therefore reduces respiration - cells that can’t respire die
end-product inhibition
A metabolic pathway where the final product of the series of reactions inhibits one of the enzymes in the process
Give an example of end-product inhibition.
phosphofructokinase is one of the enzymes in the metabolic pathway that breaks down glucose to make ATP
ATP inhibits the action of phosphofructokinase, so if there’s a high level of ATP, the production of ATP is stopped temporarily
inactive precursor
An inactive form of an enzyme (one that cannot function properly)
Why are some enzymes synthesised as inactive precursors? Give examples of some enzymes which are produced this way.
To prevent them from causing damage to the cell e.g. proteases or lysosomal enzymes (found in lysosomes) contain digestive enzymes. These would start breaking down the enzymes which made them or other proteins inside the cell.
How do inactive precursors become active?
Part of the precursor molecule inhibits the enzyme’s action – this is removed via a chemical reaction when the enzyme is needed.
What does amylase break starch down into?
Maltose
What is the approximate temperature coefficient of an enzyme-controlled reaction?
2
Which one of the following conditions is least likely to denature an enzyme?
A a high temperature
B an extreme pH
C heavy metal ions
D a low temperature
It’s obviously C or D
Heavy metal ions can affect the pH? They can form strong bonds with the enzyme due to the charges, distorting its structure and leading to denaturation Therefore the answer is D (enzymes just work very slowly at low temperatures).
Order these bonds in order of least strong to most strong:
disulfide
ionic
peptide
hydrogen
hydrogen, ionic, disulfide, peptide
Do enzymes denature at low temperatures?
No - they tend to just work really really slowly without causing permanent structural damage
