Enzymes Flashcards
what do enzymes do?
speed up the rate at which a reaction reaches equilibrium
what do enzymes bind to and what do they do to this molecule?
the transition state
they stabilize it
what is the transition state?
the reaction intermediate species with the greatest free energy
what do enzymes reduce and how?
the activation energy
by providing alternative reaction pathways
what is glycogen storage disease?
an enzyme deficiency that results in the failure of glycogen to enter its transition state
this results in defective synthesis and breakdown of glycogen
how many types of glycogen storage diseases are there and why?
11
due to defects in 12 glycogen/glucose metabolising enzymes
what is the most common glycogen storage disease and describe its symptoms?
von gierke’s disease
hypoglycaemia, ulcers, hepatomegaly, bowel inflammation
how are glycogen storage diseases treated?
slow release glucose meals
feed little and often to mimic glycogen conversion to glucose
what are cofactors?
inorganic metal ions that may be needed for enzyme function
what are coenzynes?
organic molecules that may be needed for enzyme function
what are tightly bound coenzymes called?
prosthetic groups
what is an enzyme without a cofactor called?
an apoenzyme
what is an enzyme with a cofactor called?
a holoenzyme
what do active sites contain that enzymes require?
amino acids for catalytic activity and for specific interactions
where does a substrate bind to an enzyme?
the active site
what two models are used to describe how an enzyme binds to a substrat?
lock and key
induced fit
describe the lock and key model
the active site of the unbound enzyme is complementary to the shape of the substrate
describe the induced fit model
binding of the substrate induces a conformational change in the enzyme, resulting in a complimentary fit
what are isozymes?
isoforms of enzymes
catalyse the same reaction but have different structure and properties
name a protein thats isozymes can be used for diagnostic purposes
creatinine kinase
what are the two isoforms of CK and where are they made?
M form in skeletal muscle (MM)
B form in the brain (BB)
what type of CK is made by the heart?
both, forms a heterodimer (MB)
what does appearance of BB CK in the blood suggest?
a stroke or brain tumour
what does the appearance of MB CK In the blood suggest?
MI
what carries out phosphorylation?
protein kinases
what are zymogens?
inactive enzyme precursors
how are zymogens activated?
cleavage of a covalent bond
what is Vmax?
the maximum velocity of a reaction
what is Km?
the concentration of a substrate which gives half Vmax
where is Vmax found when plotted on a straight line graph?
the Y intersection
where is Km found when plotted on a straight line graph?
the x intersection
what does a low Km suggest?
enzyme needs a little substrate to work at a half maximal velocity
what does a high Km suggest?
enzyme needs a lot of substrate to work at half-maximal velocity
what are the two classes of inhibition?
reversible
irreversible
