Enzymes (minus poisons and medicinal drugs) Flashcards
Turnover number
number of reactions an enzyme can catalyse per second
Why are enzymes better than chemical catalysts?
10¹² x faster at low temp, neutral pH, normal pressure
more specific
no unwanted by-products
rarely mistakes
metabolites
reactants, intermediates, products
catabolic
broken down to smaller molecules
release energy
anabolic
synthesis large molecules
Catalase
enzyme
pH7 optimum
protects cells from damage from reactive oxygen by breaking down hydrogen peroxide (by-product of metabolic reactions)
4 polypeptide chains
iron haem group
inside peroxisomes (vesicles)
when WBC ingest pathogens, kill with catalase
Amylase
in salivary gland to digest polysaccharide starch
made in pancreas to do same thing in lumen of small intestine
Trypsin
made in pancreas, acts in lumen of small intestine
digest proteins
pH 7.5, 8.5
Cofactors ensures…
enzyme-catalysed reaction takes place at appropriate rate
Prosthetic groups
a cofactor that is permanently bound by covalent bonds to an enzyme
Which enzyme has a zinc ion as a prosthetic group?
and explain it
carbonic anhydrase in RBC
catalyses CO₂ and H₂O to carbonic acid then to protons and hydrogencarbonate ions
it enables CO₂ to be carried in blood from respiring tissues to lungs
co-substrates
cofactor with substrate form correct shape for active site
some _________ change the ______ ____________ on substrates/enzymes so _________ _____ are easier to form in enzyme-substrate complex
cofactors
charge distributions
temporary bonds
Amylase turns ______ to _______ and the enzyme’s prosthetic group is a ________ ___.
starch
maltose
chloride ion
Coenzymes
organic, non-protein, bind temporarily to the active site and are chemically changed during reactions
The induced-fit hypothesis is how the ______-_________ complex is __________.
enzyme-substrate
stabilised
What causes the slight change in the active site in the induced-fit hypothesis?
What causes the product to leave the active site?
subtle changes of shape of side chains (R groups) of amino acids
product is slightly different shape so detaches from active site
Why do enzymes lower the activation energy?
they have a specific site shape so bring substrate molecules together without the need for heat
Why does temperature affect an enzyme’s active site but not it’s shape completely?
Weak hydrogen/ionic bonds hold the active site’s tertiary structure while stronger peptide bonds are between amino acids so the primary structure isn’t affected.
psychrophilic bacteria live in…
thermophilic can live at…because…
cold conditions
high temperatures…have more disulfide bonds which don’t break with heat
buffer
resists change in pH by accepting or donating H⁺ ions because H⁺ interferes with hydrogen bonds/ionic forces holding tertiary structure of active site.
if normal pH is restored…
H bonds re-form and active site is restored, except for if pH is extreme.
amylase function + pH
pepsin (protease enzyme) function + pH
trypsin/enterokinase function + pH
starch to maltose, pH 6.8
large protein to small peptide molecules, pH 1-2
peptides to amino acids, pH 7.8 (salts in bile neutralise food)
How does body change enzyme concentration?
depending on cell’s needs, genes for synthesising enzymes can be switched on or off
Enzyme degradation
elimination of abnormal proteins that might harm cell, metabolism is regulated by eliminating unnecessary enzymes is there is too much.
competitive enzyme inhibitor
similar shape to substrate so competes for active site, prevents ES complex. To reverse effects, add substrate. Inactivator is if the competitive inhibitor binds irreversibly to the enzyme.
non-competitive enzyme inhibitor
attaches to part of enzyme that’s not the active site (allosteric site) but changes the shape of the active site. Adding substrate doesn’t increase rate again. Some bind reversibly, some irreversibly.
End-product inhibition is when…
the product stays bound to the enzyme to stop it from forming more products then the cell needs. This is negative feedback.
Types of cofactors
Coenzymes
Prosthetic groups
