enzymes as Biological Catalysts Flashcards
does an enzyme affect the equilibrium of a reaction?
no, just speeds up the rate at which the reaction reaches equilibrium
enzymes are mostly proteins, what is the exception?
some types of RNA - eg. ribozymes
how potent and specific are enzymes, generally?
each enzyme only has a limited no. of substrates, therefore some can distinguish stereoisomers
V. potent - can convert many substrate molecules into product per second
how do enzymes speed up reactions, generally?
decrease activation energy by providing alternative pathways, stabilise transition state
what is the transition state?
reaction intermediate species which has the greatest free energy (basically the point at which the reaction tips over the edge)
what causes glycogen storage disease?
enzyme deficiency that results in failure of glycogen to enter transition “phosphorylated” state meaning glycogen cant be broken down resulting in low glucose
what is the most common glycogen storage disease and how does it present?
Von Gierke’s Disease
hypoglycaemia, hepatomegaly, ulcers, infections, bowel problems
how is von gierke’s disease treated?
slow release glucose meal
feed little and often
what are the 2 types of cofactor?
metal ions (cofactors) organic molecules (coenzymes)
what do cofactors (metal ions) do?
involved in redox reactions and stabilise transition states
form a metal co-ordination centre in the enzyme (metalloprotein
what do coenzymes (organic molecules) do?
many involved in redox reactions or group transfer processes (ATP, CoA)
most associate transiently with the enzyme, chaging charge or structure
what is a prosthetic group?
tightly bound coenzymes (eg. haem in haemoglobin)
give some examples of cofactors and coenzymes
cofactors - zinc, iron, copper
coenzymes - many derived from vitamins (i.e - vitamin deficiencies reflect loss of enzyme activity)
name a common coenzyme for redox reactions and describe its action
Nicotinamide adenine dinucleotide (NAD+)
may donate or receive electrons during enzyme catalysis
easily regenerated
give an example of an enzyme that works via induced fit
hexokinase
changes shape as glucose binds to active site
name the 3 pancreatic serine proteases and their reactive sites
chymotrypsin - hydrophobic pocket binds aromatic amino acids
trypsin - _ve Asp binds +ve Lys or Arg
elastase - active site partially blocked, only amino acids with small or no side chains can bind
give an example of different isozymes of an enzyme
lactate dehydrogenase
H (heart) form = promotes aerobic environment
M (Muscle) form promotes anaerobic environment
what is a clinical use of isozymes? give an example
relative amounts of an isozyme in a specific tissue are useful for diagnostic purposes
E.g - creatine kinase (CK)
- M type in skeletal muscle
- B form in Brain
Heart produces both types (MB)
appearance of brain type in blood = stroke or tumour
appearance of heart type = heart attack
how are enzymes regulated by phosphorylation?
reversible covalent modification
Via protein kinases
can convert enzyme to active or inactive form
what is a zymogen?
inactive precursor of an enzyme
how are zymogens activated, give examples
irreversible cleavage of a covalent bond
E.g - trypsinogen and chymotrypsinogen formed in pancreas and cleaved by enteropeptidase in small intestine to give active chymotrypsin
give some examples of enzymes that are regulated by partial proteolysis
digestive enzymes (trypsin etc)
Blood coagulation enzymes (VII, IX, X, XI, XIII, thrombin etc)
Blood clot dissolving enzymes (plasminogen etc)
Programmed development enzymes (chitin synthetase, cocoonase, collagenase)
