L3 - ENZYMES Flashcards
Enzyme DEF and structural features
PROTEINS
Biological catalyst - speed up a reaction
ACTIVE SITE - where substrate molecules bond to ACTIVATE the enzyme
Highly specific -produce particular product from certain substrate
NB; remain unchanged chemically after the reaction
E & S —-ES(C) —-E & P
Activation Energy
Energy needed to start a chemical reaction
enzymes affect on AE
- lowers it (even tho overall energy delta G remains unchanged)
- reaction can take place at lower temperature & less energy needed
- ROR increases
What forms when an enzyme & substrate molecule forms
ENZYME - SUBSTRATE COMPLEX
How ESC can catalyze a reaction (join or breakdown)
if 2 molecules need to be joined, the joining of the substrate molecule to the active site of the enzyme reduces FORce of repulsion and strengthens their bond (closer together)
breakdown reaction;
- joining of the substrate to the AS of the enzyme puts STRAIN on the substrate bonds & weakens them
- substrate molecule breaks down more easily
INDUCED FIT MODEL
- how E & S combine
- AS of E has a particular shape
- special substrate fits it
- 0 ES(C) forms (enzyme - substrate - complex forms)
- BUT protein & AS change shape to accomadate
How enzyme concentration affects ROR
- increase in EC means lots of enzymes to bind to substrate molecules - MORE ACTIVE SITES
- will happen more easily than usual AT START
- BUT, - SATURATION POINT - where there are loads of enzymes but no substrate molecules left - no more ES can be formed
- SUBSTRATE IS THE LIMITING FACTOR
How substrate concentration affects ROR
ES form at start lots of Substrate molecules
very high at start (ROR)
Then it ill decrease from the time we start to run out of enzymes
6 Main Classes of Enzymes (name)
Oxidoreductase Transferase Hydrolase Lyase Isomerase Ligase
Classes of enzymes - function/action, common names
OXIDOREDUCTASE
A; Oxi and Reduc reactions
N; oxidase, reductase.
PEROXIDASE, DEHYDROGENASE
TRANSFERASE
A- transfer of chemical groups like amino, carboxyl, methyl groups to dif. molecules
N; TRANSAMINASE, TRANSCARBOXYLASE
HYDROLASE
A; clevage/ separation of bonds by inerting water– HYDOLYSIS = separation of bonds by adding water
N; PEPSIN, AMYLASE. TRYPSIN
LYASE
A; SEPARATION OF C-C, C-S & C-N bonds but not peptide bonds = removal of atoms w/o hydrolysis
N; decarboxylase, aldolase
ISOMERASE
A; re-arrangement of bonds
N; epimerase, mutase
LIGASE
A; formation of bonds between C, 02, S, N. = rearrangement of atoms within a molecule
N; SYNTHETASE, carboxylase
Vmax
Max rate - occurs when all enzymes AS are full
Enzymes are saturated
Km
- Substrate concentration when the rate is HAlf Vmax
- Measure of Affinity of the substrate to bind to the enzyme
Low Km - means substrate binds to enzyme easily
Bonded tightly
High Km means affinity is low
A lot of energy would be needed for this substrate to bind to the enzyme
Competitive inhibitor
what is it
how does it affect Km and Vmax
- Inhibitor stops or slows down a chemical reaction
- Competitive means it’s competes with the substrate for the AS.
- Thus if u want to over come this the substrate Conc must be very very high
- Thus Km increases : as much higher conc of substrate is need to overcome the inhibitor
- Vmax is unchanged
Non compétitive inhibitor
- Does Not compete with substrate for AS of enzyme
- Instead it bonds to another site of the enzyme - Allosteric site ( can do this even if substrate molecule is in AS)
- thus Km remains the same
- Vmax decreases : as even if substrate molecule is perfectly binded the inhibitor will reduce the enzyme activity thus reducing Vmax
Reversible vs Ireversible Inhibitors
bond wise what’s different about them
Reversible- they bind to enzyme but can Release enzyme also
- NO COVALENT BONDS
- Once inhibitor is removed enzyme can be used again 100%
Irreversible - no going back
- Substrate and enzyme are permanently combined
- Enzyme is inactive and loses its function
- Cell will have to reccreate the protein in order to regain function
- COVALENT BONDS
How enzymes are regulated in cells - Short term
- Neg- Feedback loops
1) - Controlled variable, receptor, processor, set point, effector mechanism
Note: a product of a metabolic pathway often inhibits an enzyme early on
This prevents wasting energy &; wasteful overproduction of a metabolite = END POINT INHIBITION (I think)
2) - Allosteric regulation - means that the inhibitor binds to site other than AS ie the REGULATORY site
Can switch between activating & deactivating enzyme
3)- Post-translation regulation like Phosphorylation
Regulation of enzymes long term
NB enzymes are proteins
- Change in gene expression.
- Proteolysis: breakdown of proteins
Rate of reaction is affected by what?
Temperature
pH
Conc of enzyme & substrate
