4- enzymes as biological catalysts Flashcards
what does enzyme do?
-speeds up rate at which reaction reaches equilibrium
-catalyse many chemical rfeactions which together make up process of metabolism
do enzymes affect equilibrium position?
NO
are all catalysts proteins?
mostly yes but some types of RNA are catalysts
are enzymes catalysts?
yes
what conditions are enzymes most efficient?
-at body temp
-in aqeous solutions
-near neutral pH
what does it mean by enzymes are potent?
each enzyme molecule can convert many substrate molecules into product per second= we mean they’re very efficient catalysts
what is the general concept of enzyme action to reactions?
-enzymes specifically bind and stabilise the transition state
-enzymes reduce activation energy by providing alternative reaction pathways
what is transition state?
the reaction intermediate species which has the greatest free energy
what does catalytic activity of many enzymes depend on?
presence of small molecules called cofactors and coenzymes (they help improve catalytic activity)
what are cofactors?
metal ions that are inorganic (non-protein chemical compound or metallic ion that is required for an enzyme’s role as a catalyst)
what are coenzymes?
organic molecules (an organic molecule that binds to the active sites of certain enzymes to assist in the catalysis of a reaction)
what has happened when enzyme referred to as metalloprotein?
metal cofactors have formed metal co-ordination centre in enzyme
what do you call tightly bound coenzymes?
prosthetic group e.g. haem in haemoglobin (non-protein unit necessary for function)
are coenzymes permanent part of enzyme?
no, they mostly associate with enzyme only transiently (temporarily)
what happens to coenzymes during a reaction?
they can change charge or structure during the course of reaction but are then regenerated
what do you call an enzyme without a cofactor?
apoenzyme (doesn’t have co-factor but needs one)
what do you call an enzyme with a cofactor?
haloenzyme (=apoenzyme + cofactor)
what are examples of cofactors?
- metal ions e.g. zinc, iron, copper
-> they’re involved in redox reactions and stabilise transition states - coenzymes
->many are derived from vitamins ->many involved in redox reactions
->many involved in group transfer processes like ATP transfer phosphate groups and coenzyme A transfer acetyl group
Are cofactors and coenzymes the same thing?
no, all coenzymes are cofactors, but not all cofactors are coenzymes
what do most vitamins function as?
coenzymes which means symptoms of vitamin deficiencies reflect the loss of specific enzyme activity
what is a common co-enzyme for redox reactions?
NAD+
-it acts as intermediate and may donate or recieve electrons during enzyme catalysis
-it’s easily regenerated and ahs to be recycled many times
what is free energy change?
change in free energy when one substance or a set of substances in their standard states is converted to one or more other substances, also in their standard states.
what is the activation energy?
the minimum energy required to cause a process (such as a chemical reaction) to occur.
what is transition state?
state of highest potential energy
what are the ways a substrate binds to an active site?
-by a cleft or crevice
-enzyme contains amino acid that essential for catalytic activity and for highly specific interactions
what are the 2 ways a substrate and enzyme are described as binding?
- lock and key model (active site of unbound enzyme is complementary to shape of substrate)
- induced fit model (binding of substrate induces a conformational change in enzyme that results in complementary fit)
what are proteases?
enzyme with active site which breaks down proteins
what are the characteristics of substrate binding active sites in chymotrypsin?
hydrophobic pocket bins aromatic amino acids (cleaves after as hydrophobic side chains fit very nicely)
=example of induced fit (hydrophobic pocket in active site means side chains fit nicely and tghen it adjusts again = cosy fit)
what are the characteristics of substrate binding active sites in trypsin?
negatively charged Asp interacts with positively charged Lys or Arg (since - charge it likes to cleave + charge)
what are the characteristics of substrate binding active sites in elastase?
active site partially blocked, only amino acids with small or no side chains can bind
what are 3 examples of pancreatic serine proteases?
chymotrypsin, trypsin and elastase
= they all contain reactive serine residue and catalyse hydrolysis of peptides at specific sites
what is relationship of enzyme activity and rate?
each enzyme will have optimum pH that will vary for each enzyme
what is optimum temp for
a) human enzymes
b) bacteria enzymes?
a)optimum temp of 37.5 degrees
b)optimum temp of about 70 degrees
what happens to active site if temp/pH exceeded optimum?
denatures and enzyme changes conformation so no longer functional
what are isozymes?
isoforms of enzymes, they catalyse the same reaction but have different properties and structure (and sequence)
when are isozymes synthesised?
during different stages of foetal & embryonic development
where are different isozymes present?
different enzymes are present in different tissues and in different cellular locations
how are relative amounts of isozymes in blood useful for diagnostic purposes?
-because different isozymes are produced in different places in the tissue and they’re not meant to leave that location so if you find for example brain form (BB) in blood then it suggests stroke or tumour
what is creatine kinase?
a dimeric protein which bind to muscle sarcomere (helps regenrate ATP)
what reaction can regulate enzyme activity?
phosphorylation, it’s very fast & reversible and found in all cells - especially involved in energy generating processes (quick way to switch activity on/off)
what is role of protein kinase?
catalyses transfer of phosphate from ATP to other protein (addition of phosphate to protein)
what is role of protein phosphatase?
catalyses transfer from other protein to form ATP (removal of phosphate from protein)
what are zymogens?
inactive precursors of an enzyme, they’re irreversibly transformed into active enzymes by cleavage of a covalent bond (cleaved to form fully active enzyme)
why don’t you want zymogens to be always activated?
because they form specific functions like blood clotting enzymes - you only want to be released when major bleed not always otherwise that leads to health problems like heart attack etc
what are examples of zymogens in pancreas?
trypsinogen and chymotrypsinogen, inactive precursors, are formed
what are examples of zymogens in small intestine?
enteropeptidase cleaves trypsinogen to form active trypsin which cleaves chymotrypsinogen to form active chymotrypsin
