enzymes Flashcards
what are enzyme features?
Globular
Tertiary or quaternary structure
specificity: many enzymes have evolved to act on a single substrate or catalyse one reaction.
catalytic power: do not make reactions occur that would not occur on their own, they make them quicker.
active site?
groove in enzyme that interacts with a specific substrate to produce a reaction.
enzyme-substrate complex?
when active site binds to the substrate.
what enzyme-substrate complex’s are there?
Lock an key model
Induced fit model means the enzyme active site changes in shape (conformational change) to fit the substrate.
can reactions be reversible? are enzymes used in reactions?
Some reactions are reversible, others are not.
Substrate to substance, substance to substrate
Usually different enzymes catalyse each direction.
Enzymes are not used in reactions
what does it mean that enzymes reduce activation energy and how do they do this?
Activation energy is the energy input needed at the start of a reaction.
Catalytic power of enzymes comes from their ability to reduce activation energy so less energy is needed in the reaction.
Enzymes do this by:
Proximity and orientation: bring parts of the molecule involved in the reaction closer together and position them so that they are more likely to react.
The microenvironment: active sites are hydrophobic so the non-polar environment allows stabilising interactions such as hydrogen bonds to occur.
Ion exchange: amino acids in the active site take H+ ions from or donate them to the substrate to facilitate reactions.
how do enzymes regulate biochemical pathways?
Many reactions occur in sequences
The product of one may becomes the substrate of the next
Sequences of biochemical reactions form biochemical pathways
Some are linear, other have branches and others are cycles
what is metabolism?
collection of all biochemical (metabolic) reactions in living cells.
catabolic?
substrates are broken down and energy is released (exergonic)
anabolic
require energy to produce larger molecules from smaller substrates by making bonds (endergonic)
how may reactions be paired?
A reaction that releases energy may be coupled with one that needs it.
why do enzymes need to be regulated?
Producing too much or too little substance can be bad
Uses excess energy
Have mechanisms to protect from this
how does temperature affect enzymes?
Increases as temp increases because particles increases kinetic energy and therefore there are more collisions
Too hot, enzyme is denature, hydrogen bonds break, shape changes, binding to substrate cannot occur
At lower temps, they slow down and the bonds are less flexible so conformational changes cannot occur
reheated, they will return to normal
how does pH affect enzymes?
Enzymes function best as specific pHs
May be denatured at extremes
If pH is not ideal, active site may provide a more ideal pH
how does enzyme and substrate concentration affect enzyme activity?
High enzymes, to small substrate, fast
If substrate concentration is high, it is faster than if there was less substrate as less distance between substrate
Too much substrate, rate levels off as the active sites are taken
cellular compartmentalisation and its affect on enzyme function?
Each organelle has optimum conditions for particular enzymes to function
how may enzymes be inhibited temporarily?
Reversible:
Bonds between inhibitor and enzyme are weak (hydrogen bonds)
Inhibitory can move in an out
Enzyme cannot bind with substrate if inhibitor is present
High concentration of substrate, higher chance or substrate connecting rather than inhibitor
how may enzymes be inhibited permanently?
Irreversible:
Strong bonds between inhibitors and enzymes (covalent)
Inhibitor blocks permanently
competitive inhibition?
Shape of inhibitor is similar to shape of substrate
Inhibitors are able to bind to active site
Blocks reactions
non-competitive inhibition
Allosteric inhibition
Inhibitor binds to allosteric site rather than active site
Changes shape of enzyme so binding cant occur
Sometimes binding to allosteric site means reactions can occur (allosteric activation)
Called allosteric regulation
feedback inhibition
Product produced late in pathway acts as a inhibitor to an enzyme earlier in the pathway
A lot of product, inhibition occurs, production slows
As product reduces, less will bind to enzymes so function increases
what is phosphorylation?
Binding of phosphate group to protein
Removal is dephosphorylation
Most common regulatory mechanism
Change the shape of of proteins so can regulate proteins
what are cofactors and coenzymes? organic/inorganic? what do they do? what are some examples?
Cofactors bind to enzymes and allow a catalytic reaction to occur
Can be organic: proteins, vitamins, ATP etc.
Inorganic: ions
small, non-protein organic cofactors are called coenzymes
Coenzymes allow some reactions to be catalysed
Often structurally altered during reactions but is reverted after to be reused
Some coenzymes: ATP, vitamins, NADH
what is the cycling of coenzymes? how does it work? examples with ATP and NAD+
Many reactions involve transfer of chemical groups such as phosphates
Coenzymes such as ATP move chemical groups between reactions
Constantly reused
Can move electrons and protons
Energy is transferred this way as the energy os stored in bonds between coenzymes and groups, proton or electron
Unloaded coenzyme can pick up group, proton, electron
Loaded when to has one
ADP/ATP
Involved in transfer of energy
Breakdown of ATP to ADP releases energy
NAD+/NADH and NADP+/NADPH
Involved in transfer of energy
what are examples of drugs?
Chemotherapy uses enzyme inhibition
For Alzheimer’s disease the enzyme acetylcholinesterase is inhibited (this enzyme breaks down acetylcholine which is important in memory). The inhibitor is competitive or non-competitive
inhibition of enzymes by rational drug design
Study of enzyme inhibitors
antibiotics, insecticides etc.
Uses information about the structure of the drug receptor to create drugs
designer drugs
The influenza virus
Drug agents Relenza and Tamiflu
Disrupt the viral proeteins involved with releasing the viral particles so they can infect other cells
These drugs block the action of an enzyme called neuraminidase that is on the surface of influenza viruses
Stored in case of an outbreak
