Enzymes as Biological Catalysts Flashcards
what do enzymes do
catalyse reactions that make up metabolism
speeds up rate at which reaction reaches equilibrium
mostly proteins
do enzymes affect the position of equilibrium
NO
best conditions for enzymes to work at optimum
body temp
aqueous solution
neutral pH
describe enzyme action
enzyme specifically binds and stabilises transition state
transition state is reaction intermediate species which has greatest free energy
enzymes reduce activation
how do enzymes speed up reactions
lower activation energy
how do enzymes reduce activation energy
by providing alternative reaction pathway
what is glycogen storage disease
enzyme deficiency that results in failure of glycogen to enter transition ‘phosphorylated’ state
what is glycogen storage diseases caused by
defective glycogen synthesis/breakdown in muscle, liver and kidney
11 variants arising from defects in 12 glycogen/glucose metabolising enzymes
symptoms of Von Glerkes Disease
Hypoglycaemia Hepatomegaly (liver swelling) Skin/mouth ulcers Bacterial/fungal infection Bowel inflammation/irritability
treatment of glycogen storage diseases
slow release glucose mean
feed little and often
what are coenzymes/cofactors
small molecules upon which catalytic activity is dependant on
cofactors - inorganic metal ions
coenzymes - organic molecules
describe coenzymes
mostly associate with enzyme only transient
change charge/structure during reaction but are regenerated
what Is a prosthetic group
tightly bound coenzyme eg haem in haemoglobin
what is an enzyme without a cofactor called
apoenzyme
what is an enzyme with a cofactor called
holoenzyme
apoenzyme + cofactor = holoenzyme
what is a metalloprotein
metal cofactor forms metal co-ordination centre in enzyme
examples of cofactors
metal ions, involved in redox, stabilise transition
coenzymes - derived from vitamins, CoA, NAD/FAD, ATP
vitamins
why are vitamin deficiencies caused
loss of specific enzyme activity
what is NAD
coenzyme for redox reactions
may donate/receive electrons during enzyme catalysis
regenerated
where do substrates bind
active site
cleft/crevice
contains amino acid essential for catalytic activity/highly specific interactions
how do substrate bind to enzymes
lock and key
induced fit model - active site changes shape complementary fit
3 pancreatic serine proteases catalyse hydrolysis of what peptides at specific sites
chmotrypsin - hydrophobic
trypsin - negative
elastene - active site partly blocked
define isoenzymes
isoforms of enzymes
catalyse same reaction but have different properties/structure
where are different isozymes found in the body
synthesised during foetal/embryonic development
in tissues/cellular locations
give an example of of isoymes
lactate dehydrogenase
2 subunits - heart promotes aerobic metabolism, muscle promotes anaerobic metabolism
what is clinical use of isozymes
diagnostic in tissue/blood
what is creatine kinase
dimeric protein binds to muscle sarcomere
M in skeletal muscle
B in brain
heart produced both types - heterodimer (MB)
what does appearance of brain type CK in blood suggest
stroke/tumour
what does appearance of heart type CK suggest
heart attack
how are enzymes regulated - reversible
phosphorylation - reversible
makes enzyme active/inactive
carried out by kinases
how are enzymes modified - irreversible covalent
activation of enzymes
zymogens - inactive precursors of an enzyme - irreversibly transformed into active enzyme by cleavage of covalent bond
where do zymogens work
in pancreas - chymotrypsinogen/trypsinogen
small intestine - enteropepidase cleaves trypsinogen = active trypsin which cleaves chymotrypsinogen forming active chymotrypsin
what are irreversible proteolytic
enzymes regulated by partial proteolysis eg. digestive enzymes
5 general characteristics universal to all enzymes
active site induced fit model alternative route to products substrate specific stabilise transition state
