Enzymes and Catalysis Flashcards
What are proteins?
- Polymers
- Linked together by peptide bonds
- Arranged in 3D structural hierarchy
Tertiary structure
single polypeptide chain
quaternary structure
multiple polypeptide chains
made up of monomers:
acid amino
= determines 3D structure - depends on sequence of a.a
Enzymes
Biological catalysts that speed up enzymatic/ chemical reactions
which organisms are enzymes present?
Present in EVERY chemical reaction in EVERY organism
What are proteins made out of?
Proteins
(except for catalytic RNA’s - ribozymes)
Single enzymes
single polypeptide chain
Allosteric and multifunctional enzymes
complex - more of subunits / multiple polypeptide chains
What determines on how good catalytic activity?
the native folding of protein
What are the properties of enzymes?
- specific for substrates
- catalytic power = fast
- Efficient. not altered after reaction (stays the same shape and size)
- can be regulated
What is substrate specificity?
- Ability of the enzyme to specifically recognise the proper substate (reactant)
- Molecular recognition mechanism - based on structural complementary
- substrate bind to specific region of enzyme - ACTIVE SITE
1st step of enzymatic catalysis
substrate-complex (E-S)
Lock and key model
Enzyme fits PERFECTLY into substrate
Induced fit
- Substrate is NOT exactly complementary to active site SFTR binding
- Conformational change occurs to allow better fit between active fit and substrate (hand in glove)
What is the active site? Where?
- 3D pocket where substrate binds to
- Small region of enzyme (10-20%)
What is the enzyme COMPOSED of?
- SUBSTRATE BINDING SITE
- CATALYTIC SITE
SUBSTRATE BINDING SITE
- A.a side chains interact with substrate
- Interactions that orientate the substate within the active site
CATALYTIC SITE
- A.a that performs or catalyses the reaction
- The correct folding of enzyme is required
S-E binding alters the structure of the substrate to promote the formation of the transition state
Catalytic power..
Increase the rate of chemical reaction
How many times can rate of reaction increase with the presence of enzyme?
range: 10^6»_space; 10^17
For start of reaction - energy is required. What’s this called?
Activation energy
Define activation energy
the minimum quantity of energy which the reacting species must possess in order to undergo a specified reaction
Lower the activation energy…
faster the rate of reaction
Does enzyme have an affect on the equilibrium of reactions?
No - no affect
Efficiency and reusability?
- unaffected by reaction which they catalyse
- can be reused
-active in LOW concentrations
Conditions that affect enzyme functions:
- Temp
- Ionic condition
- pH
- Substate concentration
- Presence of inhibitors
Temp and enzymatic activity
- ^ temp = higher the rate of reaction
- Usually 37C in humans (some archae - extremophiles its higher)
Denturation
Loss of native folding in protein - active side no longer matches the substrate = loss of catalytic activity
pH and enzymatic activity
- most active optimum pH
Optimum pH in the body
- Small intensine enzymes : 7.5
- Stomach enzymes : 1.5
- Digestive lysosomal enzymes : 4-5
when is structure disturbed by pH
in very low or very high pH as tertiary structure is disturbed
Constant concentration of enzyme + increase in substrate
Concentration will cause increase in enzyme activity up to the point where enzyme is SATURATED with the substrate
WILL NOT change rate of reaction!!!
Saturated meaning:
enzymes has reached their maximum activity (steady rate) and Maximum rate of reaction (Vmax)
Reaction rate
ONLY measures on how rapidly the enzyme can process the substrate
What is kinetics
the study of reaction rates
Km
concentration of substrate at which reaction rate is half-maximal
Higher Km
-weaker binding
Lower Km
-stronger binding
Competitive inhibitors
Competing with substrate by binding at active side and blocking it
(effect can be reversible or irreversible (covalent bonds)
Non-competitive inhibitors
Bind into allosteric site on enzyme (NOT active site)
-Cause conformational change in enzyme and block of the catalytic activity / active site changes in shape
-Effect is reversible (usually)
Enzyme cofactors
additional components - provide active site REACTIVE GROUPS
they are NOT substrates
Coenzymes
- Temporarily/ weakly bound to the enzyme
- Altered during course of reaction and dissociate from the active site
Examples of coenzymes:
- NAD+
- NADP+
Protheic groups
-Tightly bound to enzyme = covalent bond
- must be regenerated each catalytic cycle
examples of prothetic groups
- HAEM (in haemoglobin) for oxygen REDOX reactions
- FAD in REDOX reactions
- VITAMIN B7 or Biotin = carboxylse enzymes
HOLOENZYME
Complete catalytically-active enzyme together with its cofactor
APONZYME (not active)
Protein part of enzyme on its own without its cofactor
7 major groups of the international Union of Biochemistry
- Oxidoreductases
- Transferases
- Hydrolases
- Lyases
- Isomerase
- Ligases
- Translocases
ENZYME Class 1 Oxidoreductases
Catalyse REDOX reactions
ENZYME Class 2 Transferases
Catalyse functional group transfer reactions
ENZYME Class 3 Hydrolases
Catalyse hydrolasis reactions (transfer functional groups to water by breaking down of a bond)
ENZYME Class 4 Lyases
- Catalyse the cleavage of C-C, C-O, C-N or other bonds by elimination, leaving double bonds or rings, or addition of groups to double bonds
- They catalyse the breaking of a chemical bond between two parts of a molecule (other than hydrolytic or oxidative bond breaking)
ENZYME Class 5 Isomerases
Catalyse transfer of groups within molecules to yield isomeric forms
ENZYME Class 6 Ligases
- The joining ligation of two large molecules by forming a new chemical bond with the release energy
ENZYME Class 7 translocases
- Movement of molecules or ions across membranes or their separation within membranes
