Enzymes & catalysis Flashcards
Enzymes
- Biological catalysts speed up specific enzyme reactions
- In all organisms and regulates all chemical reactions
- Catalytic activity determined by the folding and conformation of protien
Properties of enzyme
- Specific to substrate
- Catalytic power which is fast
- Efficient can be reused and not used up in reactions (active at low concentrations)
- Can be regulated
Lock and key model
- Substrate binds to specifc region of the active site
- Forms enzyme substrate complex perfectly complementory
- Static model and ridgid
Induced fit model
- Substrate is not exactly complementory
- After binding there is a conformational change allows better fit between active site and substrate
- Dynamic model
Active site
Substrate binding site
- Maintain shape small 3D grove located in a small region of the enzyme
- Amino acid chaim interact withs substrate
- interaction orentates active site to the substrate
Active site
Catalytic site
- Few amino acid that performs a catalytic reaction
- Binding alters structure promotes formation of transition state
Catalytic power
- The ability to increase rate of chemical reaction
- Minimum amount of energy activtation energy
- Lower activation energy faster the reaction occours to go from transtion state to products
Temperatures effect on enzymes
- Archea are extreamophiles higher optimum temperature
- enzyme activity lower at lower temperature less kenetic energy less sucessful collision
- Higher temperature protein looses specific 3D structure of active site so no longer has a complementory fit
pH effect on enzymes
- About 7.5 pH in the small intestine
- About 1.5 pH for the stomach (Pepsin)
- 4-5 pH for digestive lysosomal enzymes
- Could effect charges of the R group activity decrease if not in optimal
- Tertiary structure temporaly altered so enzymes substrate cannot occour
Increase in substrate concentrations effect on enzyme
- Causes an increase in substrate concentration initially
- Enzyme becomes saturated with the substrate so the reaction rate decreases and this reaches Vmax
Enzyme kenetics (Km)
- Concentration of substrate where the rate of reaction is half maximal
- Inverse meaasure of how tightly bound the enzyme binds to its surface
- Higher Km lower affinity to substrate greated concentration of substrate to reach Vmax
- Lower Km stronger binding
Competitive inhibitor
- Competes with substrate to bind to the active site
- Effect is reversible or irreversible (covalent bonding)
Non competitive inhibitor
- Binding to the allosteric part of the enzyme causing a conformational change
- Blocks catalytic activity and the bindingis reversible
Enzyme cofactors
- Provide the active site with additional reactive groups
- Essential ions - activator ions (loosely bound) or metal ions (tightly bound)
- Coenzymes - Co-substrates (loosely bound) or prosthetic groups (tightly bound)
Essential ions
Activator ions
- Reversibly bind to enzymes and participate in substrate binding
Essential ions
Metal ions
- Cations that are tightly bound to an enzyme and participate in catalysis
Coenzymes
Cosubstrates
- Weak temporarily bound to enzyme
- Altered during course of reaction and dissociate from active site
- NAD and NADP+
Coenzymes
Prosthetic groups
- Tightly bound to enzyme via covalent bonding
- Must be regenerated each catalytic cycle e.g. heamoglobinand oxygen
Holoenzyme
- Catalytically active enzyme together with cofactor
Apoenzyme
Protein part of enzyme without its cofactor not activated
Oxidoreductases
Transfer electrons from one molecule (oxidant) to another one (reductant)
Hydrolases
Cleave/break specific types of covalent bonds, transferring groups to water
Transferases
Transfer of specific functional groups from one molecule (donor) to another one (acceptor)
Isomerase
Convert one isomer to another
Lyases
Break a chemical bond between two parts of a molecule (other than hydrolysis or oxidative bond breaking)
Translocases
Assisting in moving molecules, usually across a cell membrane
Ligases
Join two molecules by forming a new chemical bond
