Biochemistry: Enzymes and Biological Catalysts Flashcards
what do enzymes effect and not affect
- speed of the reaction
- equilibrium
in what conditions do enzymes work
- body temp
- near neutral pH
- in aq solutions
how are enzymes specific
recognise a limited range of substrates
how are enzymes potent
convert many substrates to products quickly
what is the activation energy and why is it present
- energy required for enzymes to work
- stops reactions occurring in normal conditions
transition state
reaction intermediate substance that contains the most free energy
what do enzymes bind to and what do they do
- transition state
- lower activation energy
describe glycogen storage disease
enzyme deficiency resulting in failure of glycogen to enter its phosphorylated state
what are co-factors
metal ions
what are co-enzymes
organic molecules
what do co-factors form in the enzymes
a metallo protein - metal co-ordination centre
how do co-enzymes associate with enzymes and what happens when they bind
- transiently
- change or restructure themselves
prosthetic group
tightly bound co-enzymes
apoenzyme
enzyme without a co-factor
holoenzyme
enzyme with a co-factor
what type of reaction are co-enzymes involved in and what do they do
- redox reactions
- stabilise transition states
what are many co-enzymes derived from
vitamins
what do symptoms of vitamin deficiencies reflect and what are the classes of deficiencies
- the loss of enzyme activity
- functional or dietary
describe substrate binding to enzyme
- substrate binds to an active site
- this contains the amino acids essential for catalysis and specific interactions
what is the lock and key model
the substrate and active site are complementary shapes
what is the induced fit model
substrate binding induces a conformational change leading to complementary fit
what other factors can influence enzyme activity
temperature and pH
describe the active site of pancreatic serine proteases
contain reactive serine residues that catalyse the hydrolysis of peptides at specific sites
isoenzyme
isoforms of enzymes, enzymes that catalyse the same reaction but have different properties and structure
why can isoenzymes catalyse the same reaction but have a different make-up
- synthesised at different stages of development
- present in different tissues/cellular locations
what is the clinical use for isoezymes
diagnostic tests
how is lactate dehydrogenase used as a diagnostic test
it requires hypoxia sensitive transcription factors so a decreased presence in blood indicates tissue hypoxia
how is creatine kinase used as a diagnostic test
- dimeric protein that binds to muscle sarcomeres
- M form (muscles) and B form (brain)
- heart produces both
- M form in blood suggests MI, B form in blood suggests stroke
how does phosphorylation regulate enzyme activity
phosphorylation is a reversible covalent modification that converts enzymes to and in/active form
what carries out phosphorylation reactions
protein kinases
describe a phosphorylation reaction
fast, reversible
side groups form phosphate esters
how do irreversible covalent modification regulate enzyme activity
results in an active form of enzyme irreversibly
zymogen
inactive precursor of an enzyme
what do zymogens do
irreversible transform into active enzymes via covalent bond cleavage
give examples of zymogens
- tripsinogen to trypsin via enteropeptidase
- chymotrypsinogen to chymotrypsin via trypsin
- pancreatic enzymes, blood clotting factors, clot-dissolving enzymes
